Friday, October 10, 2014

Making the Rotor Turner

Mounting the old fashioned way
When you go to the shop to have brake work done they will sometimes come out, wipe their hands on a rag, look you in the eye and say, "Well, your rotors are looking a little worn.  We need to turn them or replace them."  At that point, get ready to hand over $100+ per rotor to get them to do it, not counting remove and replace.

We have several vehicles needing brake work. We are doing it on the cheap, so we didn't want to buy rotors if we didn't need them and we didn't want to pay to have them turned.  Instead, I decided to turn the rotors myself.

This means that I have to mount the rotors on the lathe, center the rotors and then make the runout as close to zero as possible.  I'm sure Adam Booth could do this with a four jaw chuck in 3 minutes but I'm not Adam, so this is going to take a bit longer.

It took more like 5 minutes to get it centered, then a few more to get the run out to zero. Then, just as I was ready to go, the surface that I was using to register against crumbled and the run out was off so much it all had to be done again. With two rotors still to do on the car and at least two more cars to go, 14 rotors total, it was time to re-think my methods.

Question: How can I quickly and efficiently mount the rotors on my lathe such that the runout is acceptable, and then turn them?

Answer: Build a mounting plate for the rotors.

After a little thought, I decided on a two piece mounting system.  The first was a mandrel that could be quickly mounted in the lathe chuck, 3 or 4 jaw.   If in the 4 jaw, it could be quickly dialed in to have near zero run out.  The second part would be a mounting plate.

The mounting plate would have a threaded center with registration lip to allow for it to be removed and replaced and always go back to the same alignment.  In addition, the mounting plate would have a registration hub to register the rotor against for rotational alignment and the surface outside the hub would faced to bring the surface perpendicular to the axis of rotation.

When the tool is dismounted and remounted, a very light surfacing will bring that face back into perfect alignment again.

1.5" 1018 bar stock - the big pole.

Thus we start with 1.5" 1018 bar stock, or as my lady called it, "The big pole which will become the holder thingie."

0.375 A36 plate, 18.48

 And a piece of 0.375 A36 plate, 18x48.  We'll cut a strip off this and then turn that into our mounting plate.  And to use my lady's words "The plate that becomes the flat part of the holder thingie."

Here is Liri hard at work cutting a 6" wide strip from the plate.

Using a cheap Sawsall we cut a strip off the plate.  While I have a horizontal bandsaw, I do not have a vertical one so no way to cut this except with hand tools.  It cut very easily and I was able to do the first seven inches in about three to five minutes.

Of course it took Liri another 15-20 minutes to cut the remaining 11 inches.

The A36 cut very quickly and easily.

The four jaw was the right tool for the job.
While Liri was working on the plate, I cut a five inch slug off the bar stock, mounted it up in the four jaw, and got ready to spin it up.  Fortunately, the horizontal bandsaw did a quick job of cutting the mandrel blank. While I could have done this with a three jaw chuck, I knew that the next step would be to chuck up a squarish chunk of plate.  That would require a four jaw.  As such, it was faster and easier to just leave in the four jaw and work with that.

With the new Noga mag base, it only took a few moments to get the mandrel centered up and ready to turn.  I do need to make a new chuck key for the four jaw.  The key I have is a little small.  If I do make a chuck key, I'm likely going to make two:  a small and a normal.

When centering using the two key method, you take a measurement on both sides of the chuck.  You figure out where the center should be and then turn both keys without rotating the chuck until the piece is in the middle. 

People using this method report that they can center the work in just about the same amount of time as using a scroll chuck.  Of course, a better option for me would be a nice 6 jaw adjust true chuck.  Yeah, at about $1000-$2000 without a backing plate.

The mandrel is faced.

Here I've faced the mandrel, turned a surface to indicate against, turned a registration ledge.  After that, the end was turned down to the outside diameter for a 1.25-12tpi.  An exit groove was created for the single point threading tool and everything was set up for cutting the threads.

The 6" x 6" plate with center marked.

Having spent 20+ minutes cutting a 6" by 18" strip of 0.375 plate, we dropped it in the horizontal bandsaw, turned on the saw and just a few minutes later a 6" by 6" plate was delivered to us.  This plate was then marked so we had an idea of where the center was.

Plate mounted in the four jaw.

Here the plate has been mounted in the four jaw chuck, centered and we've started by drilling out the center to 3/4 of an inch.  We'll further bore out the center until it is the right size for a 1.25-12tpi internal thread.

Our photographer was sick so we missed all those fun steps.  Part of the process was grinding a threading tool to mount in my 5/8 boring bar.  First time for that, first time using the boring bar.

During the threading process I managed to knock the boring bar out of the tool holder.  At that point it took a few minutes to get everything set back up but I did manage to get everything aligned and was able to finish cutting the threads.

(Please note the doubleboost light there in the foreground.)

I had machined the mandrel first so I was able to test fit the plate to the mandrel to check the threads.  Once the threads were correct, I cut the registration ledge.  At this point, I know that I should have made a test plug for the registration ledge and cut the registration ledge first, before threading.  Doing it in the opposite order allowed me to avoid cutting the test plug but did cause damage to the threads that had to be repaired for each test fitting.

Once the mounting hole was completed in the plate, the plate was removed from the four jaw chuck and the mandrel mounted.  I could have switched to a three jaw chuck but I decided to continue with my four jaw learning curve.

With the plate mounted and spinning I started the process of rounding the square.  This is an interrupted cut.  I'm still not sure what the best way of doing such a cut is but that A-36 (machinability of 72%) cut easily even if it was throwing very hot chips everywhere. Each chip left the cutting tool at around 600°.  I had them landing on my head, bouncing off my safety glasses, landing on my arms, and more than a few going down my shirt collar.

Finishing the plate.
Once the plate was rounded, it was time to finish it.  First step was a light facing to bring the face true.  After that the inner hub was created to register the rotor when mounted.  Then a relief groove was cut just outside the hub to hold a raised ridge on the rotor.

With all of those operations completed, the plate was dismounted and layout dye applied.  The rotor was put in place and a transfer punch used to mark the center of the lug bolt hole in the rotor.  With that mark in place, it was a simple mater of drilling that hole on the drill press.  I could have used the milling machine but it was faster/easier to just use the drill press.  Once the first hole was drilled the rotor was fastened to the mounting plate and center punched for the remaining holes.  It turned out that the layout dye wasn't needed as the transfer punch left a very clear mark.

After all five holes had been drilled, the mounting plate was screwed back on the mandrel.  Because the mandrel had not been moved there was no need to reface the mounting plate.

A mounted rotor, ready for turning.
Now we have the first rotor mounted up and ready to be "turned".   You can see how the registration hub is holding the rotor centered while the back of the rotor is firm against the mounting plate.  There is no wiggle or wobble in the system and after starting up the lathe, while standing well out of the way in case it all came apart, it was time to turn the rotor.

Rotor, turning at speed.

Here is the rotor turning at speed.  There is cast iron dust going everywhere.  I did place a rag over the cross feed screw to help protect it a little bit but clean up is a pain.

This is one of the first faces cut.  Later faces looked much better as I changed out my tooling. 

Here we can see the huge piles of iron dust generated by the facing operations.

This was both a useful project but also a great learning project.  I've been spoiled by using 12L14 (machinability of 170%).  The 1018 of the bar stock and the A-36 plate do not machine as nicely.  This shows in the quality of the surfaces.  In addition the chips on the A-36 were ugly, nasty, stringy, evil things.  They remind me of the time I got to play with razor wire.  They feel like a sliced finger waiting to happen.

Grinding tools shouldn't scare me but I do need to get a wheel dresser.  This is a tool that takes the gunk out of a grinding wheel, it makes it square and exposes new grains of the wheel to cut faster and cleaner.  At this point I'm not going to "fear" making my own cutting tools.  I've made the threading tool, a round faced forming tool, a boring bar and a few other tools.  My big need is to get out my stones and hone my tools to clean up the cutting edge.  Not that big of an issue with this project, but one that I have to address.

Cutting threads is fun but I've got to be more careful in my prep work and in measuring.  I'm pretty sure that any real machinist would have thrown the work out as "ruined" for the slop in my measurements.  My only saving grace is that these are matched parts.  As long as all the rest of the parts are made to fit, it doesn't matter.

The Machinery's Handbook has everything you will ever need.  Finding what you need in that 2800 page work is a different story.  I had actually spent the time using the formulas to figure out the specifications for the 1.25-20TPI threads.  Later I was looking through tables and found that for 1.25, "fine" was defined as 12TPI and that was in the book.  There was also a row for 1.25-20TPI for "Ultra fine" but in looking at the book and a bit more investigation in the book I found that 12TPI was a better choice.

While the total amount of time spent on the project exceeds 6 hours, I feel that it was worth it.  The first two rotors I turned were "ok enough to pass inspection" but they did not turn true.  With my mounting tool, it is possible to take the rotor off the car, mount it up, turn both sides and have it back on the car in under 30 minutes.  Without the mounting tool it takes closer to an hour.  With 12 more rotors to turn, the tool will save me time in the long run.

While a two part tool with threads is a bit complex, the ability to make other plates is a great thing.  In all likelihood, I'll turn two more plates to have the mounting hole in the center and then rounded ready to use in the future.  With that work done, it really is only a matter of a few minutes to make a custom mounting plate for any set of rotors.

Sunday, April 6, 2014

When all you have is a hammer . . .

. . . a screw looks an awful lot like a nail.

My 8 year old son is in Cub Scouts as a Wolf this year, and we just experienced our first Pinewood Derby.  I wanted this to be Mike's car and not daddy's car, which meant that I had to take a step back and let him succeed (and fail, if necessary).

The official kit.
Image by Grika.
At the pack meeting, Mom picked up the official box with number decals, a block of wood, four wheels and four axles, and the "official rules". To help in Mike's success, I made sure that I read the rules, that we followed all the rules, and that everything we used was "BSA" approved.  This included a trip to Michael's (where I hate to shop) to pick up some BSA approved and stamped weights, paints, decals and a "speed" kit, in addition to the original stuff we received from our local BSA troop.

The first thing that I noticed was that the package didn't have details as to what was actually included nor how to use what was in the package.  There was a lot of French language on the outside, but nothing to help the purchaser make an informed decision on whether the contents were useful, how to use the contents, or even really what the contents were at all.

When I got home, I opened things up and found that the speed kit consisted of sandpaper (which I already had), a mandril, graphite lubricant, some polishing paste, and four extra axles.  So I paid $12.00 for a mandril and some polishing paste.  What I was expecting to find was four polished and prepared axles. I wasn't real happy with the kit, but it is what it is.

I've had a scroll saw on my "low priority buy" list for a year or so, but this project required either a band saw (which I want but is expensive), or a low cost scroll saw.  The scroll saw, available at the local hardware store for $99.00, was a win over a $700.00+ band saw which wouldn't be delivered until sometime next week (past the weigh in date).

In the meantime, Mike started learning how to draw patterns.  I had him freehand the design of his car, which he did a good job of.  He was very clear that there was going to be a spoiler in the rear, and that there were going to be doors as well. He even drew an extra view just to label the doors as "not opening".

Next, his Mom and I taught him how to draw at a 1-to-1 scale on graph paper.  That took longer than expected, but his mother has the patience of an angel.  She figured out that Michael needed to learn about symmetry.  Once he got the idea of symmetry he did a great job laying out his pattern.  We also watched a video by Oxtools on YouTube where Tom shows how he printed out a pattern, glued it to a piece of stock aluminum, and then used a bandsaw to cut it out.

Practicing with the scroll saw.
This was exactly the method I had intended to use.  Cut the pattern out, glue it to the block of wood, then use the scroll saw to cut it out according to the pattern.  From other examples, I knew that I could make a series of cuts on the work, then hold the pieces together and turn the work, allowing me to cut from the other direction. Watch this two minute video all the way to the end for an amazing example of the magic this can create.

After Mike had his finished pattern created on the graph paper, Mom cut it out. Unfortunately, the first time she cut it out, she followed his pattern instead of just cutting out the rectangle to paste onto the wood. This led to Mike having to re-do the pattern. I think the two of them redrew that pattern three or four times before we finally got it glued correctly onto the wood block. Of course, they wanted to glue it on with regular Elmer's glue, and I had to send them out for glue sticks, but it got done.

Unfortunately the block of wood had a bump, almost a reverse groove, going right down the center.  I didn't want to run the block through the jointer for fear of it breaking out the axle groove.  This was a mistake on my part as we would later find out.

The 'line' going down the top of the center line was left behind when the block
was cut out. It should not have been there, and it caused us problems.
Mike and I then started the process of learning how to use the scroll saw.  We cut straight lines and we cut curve lines.  Mike laid out a pattern of curves on a block of wood and then cut those out to make a puzzle.  We printed a jigsaw puzzle pattern, glued it to the back of a piece of wood, Mike drew a picture on the front, and then the two of us took turns cutting out pieces of of the puzzle.

When Mike (and I) had gained as much experience as we were able in the time available, we did the cuts on the car itself. I was happy with the finished product, which was pretty amazing considering the design was made by an 8 year old!

The completed car.
With the cutting finished, Mike was put on sanding duty.  Mike sanded for hours.  He kept bringing it back to me for guidance on where to sand next.  In the meantime, I had set up a paint box.  Basically, this was just the box the scroll saw came in, plus a turntable and a stand for the car body.  Once Mike was done with the sanding, it was time for me to spray paint the body.  After two hours, there were a dozen or more coats of yellow paint on the car, and the wood pattern was no longer showing.  I need to remember to tell Mom to buy primer if there is a next time, as it would have made the painting much easier and more professional. I also need to remember to wear my respirator/filter mask when spray painting.  There is nothing quite so instructive of "the spray goes everywhere" as sneezing bright yellow paint colored snot.

The next day after school Mike and mom are back at it, as dad is still at work.  Mike is given paint brushes and the paint he selected and he goes to work painting the car.  After the car had been cut out he decided the car look a little bit like a rattlesnake so that's what he went for.  That included eyes and some snake decals.

Once the car was painted and drying, we went off to the shop to work on the wheels.  The limited instructions said, ". . . wrap a drill in a rag and then hold the drill in a vise, put the nail/axle in the chuck, then use . . ."  Well, when all you have is a hammer, a screw looks an awful lot like a nail.  LATHE TIME!

Except that my three jaw chuck has a minimum size of about 0.125 - 0.250in.  Okay, you might start to see the problem there.  We were working on a wood item and I was thinking in terms of thousands of an inch when being concerned about 1/32nd was overkill.  I spent a little bit of time thinking, and figured out how to mount one of my drill chucks in the three jaw and we were off to the races (I could have removed the three jaw and used a MT3 to MT4 adapter to turn the drill chuck directly, but did not).

Stock axle.
Image by K. Murray.
Having devised a way of holding the axle and spinning it, we started cleaning up the axles.  I used a file to take the flashing off, and then used some of my sandpaper to clean it up just a little.  It was cold that night, and Mike and I were not real interested in spending time in the frigid shop (think 10°F, warming almost all the way up to a "balmy" 30°F by the time we were ready to leave).

Mike did a great job making sure the parts were moved from the holding area to the work area and back as needed. Next year I'll grind a left hand tool to be able to reach in and turn the axles, which will do a much, much better job. It might also help to have a better set of files, maybe some second cut and smooth files. I'll also cone the axles a little.  If legal, I might even groove the axles.

With the axles complete, it was time for the wheels.  The wheels went on the mandrel and we started sanding them.  This just wasn't right, so I set up a good turning tool and turned them.  Amazingly enough, the wheels were not true to begin with.  In the end, we wound up with some very nice looking wheels and some better-than-stock axles.  Next year, I plan to fill the axle holes with something, drill and ream them to size, then put them on the mandrel and turn them.

Then we went back inside for assembly.  Out came my triple beam scale to get the weight just right: 141.74g  (you can see that OCD coming out again).  I set the weight to 142.25g just to make sure that if the official scale was a little off it would still work out.  And with the car, wheels, axles, and all the extra weight on the platform, I couldn't reach 141g.  Oh bugger. So back to the shop, this time to the reloading station.  Ah, there it is, a 170 grain .308. That plus the other stuff put the car up over 141.7g.  This meant that we could do it with what we had on hand.

The next day, Mike and I got back in the shop, this time at the drill press.  After a quick setup we had a hole right where he wanted the bullet to be.  I'm thinking, "I'm such a cool dad.  A bullet for a weight.  And it's sticking out looking cool!  No other kid will have a bullet for a weight."  Well, when we got to check in on Thursday night what did I find but a half dozen cars with bullet weights.  I guess we live in part of the country where hunting and reloading is a normal thing.

Weighing the finished car.
Regardless, finally the car was done!  The weight was adjusted to within a half a gram, the painting was done, the axles and wheels had graphite (everywhere) and the car was ready to run.  Off we went to the Cub Scout meeting and the pre-flight check.  The car went into the test box but it didn't pass.  The wheels were too close together.  Well, maybe we got the wheels a little close, but if the wheels were spinning freely then there should have been enough space.  But noooooo.

The car weighed in at 5.0oz so I knew their scale was not as accurate as mine.  I spent a few minutes and adjusted the wheels, then tried again.  This time the wheels fit, but the weights on the bottom of the car were not clearing.  The weights were not giving the car enough clearance! (It turns out that the reason the weights would not clear the track without risers was because of that aforementioned bump, which pushed the carefully sized weights out of kilter just enough to drag.)

The weights wouldn't clear the track until we added risers.
I had an internal meltdown.  How the heck was I going to get the clearance I needed?  If I removed wood, the car would be too light, as I didn't have any extra weight.  I would still need to add some more.  Maybe another bullet?  Okay.  How was I going to hold the car? There was exactly one flat surface left and that was the bottom where I now needed to hog out some wood.

Close-up of axle and groove.
Image by K. Murray.
And then Allyson came up with the idea of putting on some risers.  I re-read the official rules.  Nothing in the rules prohibited risers.  It looked like the rules even allowed moving the axles if needed.  Nothing in the rules said that all four wheels had to touch the track, either.  I did a bit more reading and found that there were extra rules that some packs use that included things like the axles had to go into the original axle grooves cut in the car body.  Not us though; our pack's rules said nothing of the sort.  The risers were a go!

In regards to the axle groove rule, there were some interesting points to note. One pinewood derby site talked about how to cut the body into different chunks and then glue the pieces back together to move the axle grooves but still retain the "original grooves" and to be able to place the axles in the original grooves.  Following the letter of the rule while totally breaking the spirit.

There is a great deal of controversy in the Pinewood derby world regarding this "father and son" project. There are those who believe that the spirit of the rules should be followed and that the son should do most of the building. There are others that push the rules to the absolute limits, and still others that outright break the rules.

We know that a car will run faster with good axles and wheels. We know it will run faster if the wheels are lighter and we know a bunch of other things that will make a pinewood derby car "faster". And there are always fathers (and mothers) that want their little boy to *WIN*.

Sure it's disappointing when a child spends hours working on a car and it doesn't come in first. But somebody has to lose and somebody has to win. How far can you push and still be legal? My goal was to make this as much my son's project as it was possible to do safely. When I was in the shop he was in the shop. When I was turning cranks he was there to turn them too. He was an intimate part of building this car.

All that said, if he could (and he can) turn a set of accurate and correctly size stainless steel axles, should he be allowed to use them? If we take those "nails" used as axles and apply thousands of dollars worth of equipment and knowledge in order to make the car faster while still "following the rules," is that violating the spirit of the rules?

I know that I am a "rules monger". I am very good at staying just this side of shattering the rules. And I'm willing to do that in order to help my son perform well in these sorts of events.

So it was time to design.  If we were going to build the risers then we had to figure out exactly what was needed. Research on the net showed that the lane guide is 1.750.  The hub offset is 0.050.  That meant the risers should be 1.650 wide.  (OOPS, my second error.  I didn't leave any clearance.)  We only needed the risers to be as wide as required, that is 0.500.  The height would be 0.250, just stock size.  The first piece of stock I pulled up was 1.750, but I didn't notice.
Dang, I'm starting to talk like a machinist without even thinking about it.  My editor says "You should put units on all these numbers, or leave them off as you prefer."  In the machinist world, numbers that are given as are acknowledged to mean that the units are inches and we are specifying to the 1000th of an inch.  In the same way if a machinist says "It is three tenths over size." he means that the piece is 0.0003 inches over size.
Mike and I put the bar stock in the horizontal band saw and cut off a chunk 0.625 wide.  I am new to machining so I left a machining allowance of 0.125.  I had watched Tom of Tom's Techniques and he talked about leaving 0.075 for a machining allowance. That Lazy Machinist had talked about 0.4mm for a machining allowance from stock material. (He was making a 25m, 50mm, 75mm block from 1in stock.)

I started the process.  Following directions from Tom's Techniques I put the piece on a parallel and took the least amount off the first secondary surface.  Since the primary surface was against the vise face this meant that the secondary surface was now square to the primary surface. If I had been really worried I could have surfaced the primary first but that level of precision was not required.

The next step was to flip the part and surface the second secondary surface.  Because the down surface was machined, it was banged down firmly.  Once we had the second surface machined the part was removed and measured.  The total amount of material to be removed was calculated and the dial set so that it would be zero when at size.  THANK YOU, Tom and Marc (That Lazy Machinist),  for showing me how to square material and set my dials.

A few passes later, the part was squared and parallel for the primary and secondary surfaces.  In the past, I'd had trouble with the tertiary surfaces and I could see I was having problems again.  In order to square the first tertiary surface the piece has to be set square in the vise.  To do this the primary surface is placed against the vise face making the piece square in one dimension.  A reference square is then placed against the top of the vise jaw (or bottom) and against the secondary surface.  Doing this squares the piece in two dimensions so that when the first tertiary surface is machined it will be square to the primary and secondary surfaces.

Diagram of risers.
My machinist squares were all too big to use as a reference square.  Well I think they were, but I only had one out.  I used an adjustable square and got it set right.  (Okay, a Starrett 6in combination square with the satin blade just went on the wish list.)

With the piece squared and parallel on four surfaces, and with the part square in the vise, I surfaced the fifth surface (first tertiary) and so had five square surfaces. The work was flipped over and the final surface was machined.  I measured it and machined it to size.  YEAH!  My first piece squared correctly!

One of the things my teachers have taught me is that burrs and dirt are the enemy of good work.  I de-burred and de-burred again every time I pulled the work piece from the vise.  This led to very good results in the squaring process.  I was happy with the results.

The next step was to drill the axle holes. This was a more difficult operation.  The main reason is edge finding.  Until now there had been no need to know the X,Y location of anything.  The closest we came was in moving the Z axis to machine the work to size.  Since I was using a 1/2in end mill in a 1/2in collet, I changed in a 1/2in edge finder and quickly found the right most X edge.  Using a bit of math I moved to the center and then off the edge in the Y direction.  Then I locked the X axis and found the edge in the Y direction.

Illustration of off-center axle.
Image by K. Murray.
I got the piece into place with the axle hole centered in X but not in Y. I wasn't precise in where it went in the Y axis as I was just trying to make sure there was enough material.  I drilled the first hole and it went well.  The #45 bit cut well and I was happy with the result.  I flipped the piece and got ready to drill.  As I did, I could see that the piece was not positioned properly.  I was very unhappy.  I had the stop in place, I had the parallels in place, so it should have been good.

Removing the work, I flipped it over and used the drill bit to guide it into place. I reset and flipped the work again.  Still off.  A bit more work and more and more and I could NOT get the work to line up as expected.  Finally I opened the vise up and what did I find?  A chip sitting on the parallel.

With the chip cleaned off and things in place again, I was able to get things lined up using the drill bit as a guide.  I kept flipping the work piece and checking, and it looked good.  I started drilling using a pecking method.  I was almost to depth when the bit snapped off in the hole. I had just totally ruined the work.  I couldn't even figure out how to get the bit out.

Mike was with me this whole time.  He'd been raising and lowering the tables, supplying "kid power feed" to the cross feed, moving parts as needed, and holding the flashlight when I needed extra light to read the dials.  We were done for the night.  Plus it was cold as sin in my shop, and we were out of propane for the heater.

Thus ended Friday. The race was at 1300hrs on Saturday and I still didn't have the risers and the car still wouldn't pass inspection.

One of the risers, ridge up for sliding into the original axle groove.
Saturday morning I finished breakfast and headed out to the shop.  I started by cutting a piece off a sheet of 1/4 aluminum about 2in wide.  I used this instead of the bar stock I started with on Friday because I knew it had to be wider. Of course I forgot this when it was time to size the work.  Everything was the same for squaring the work but it went much faster.

Next up was drilling the axle holes.  Following Marc's rules I was meticulous in keeping the work area clean.  This time when I flipped the work to put in the axle hole it lined up perfectly. I know this because when I drilled down, the two holes met somewhere in the work piece and when I probed the hole, I really couldn't feel the joint.  Once the axle holes were in place I repositioned the work so the primary surface was up. I found the edge and centered the work, and drilled a hole for a #8 wood screw.

The work then went over to the drill press.  I thought it would be fast and easy to put the counter sink in the drill press and change to the slowest speed. That was true.  Unfortunately that was still too fast.  I got chatter.  It wasn't until much later that I remembered that the mill had back gears and could have gone slower than the drill press.

Finally the work went back to the mill.  I found the edge on the Y axis.  Once there I adjusted the work to leave a 0.065 wide ridge to use for registration with the axle groove in the car.  I adjusted the height of the table and cut the width of the piece.  Flipping the work end for end I cut the other side of the work.  When I looked I saw that the registration ridge was too wide.  I was about to go back to math when I remembered Tom's instruction on cutting a square headed bolt.

A riser, ridge down.
In his video he took a first cut on the bolt head then rotated the work 180 and cut the other side.   He then measured the width and found the difference between the current size and the intended size.  Since the piece is rotated we don't have to reposition the cutter on both sides.  Therefore the amount to remove is 1/2 of difference.  I did the math, moved the cutter, re-cut and the registration ridge was to size!

Oh, the fact that I left the cutter in place and removed and put the work back is also from Tom's example.  The swap was MUCH faster than re-positioning the tool on both sides. At that point the only things left to do were more deburring and cleaning the hole for the holding screw. From there it was clean up and time to put everything together.

While the order of operations given above is correct for machining a single piece, it is not what I did for this project because I was creating two risers. When creating more than one piece, it is easier and more accurate to square all of one class of surfaces on all parts, before moving on to the next set of surfaces.  So you machine all the primary surfaces first on all parts, then all the secondary surfaces on all parts, and then all the tertiary surfaces. This saves a lot of time resetting the dials, and allows multiple pieces to be machined rapidly. It also ensures that all the pieces are the same size.

There is a great deal of thought that goes into "order of operations" When the order of operations is correct then there are reference surfaces and good ways to hold things at every step of the process. Do the operations in the wrong order and you can find yourself stuck.

For example, I choose to drill and chamber the hole for the hold-down screw before I milled the ridge but after I had drilled the axle holes. I considered drilling the axle holes the most difficult part of the project. It was where I expected to make mistakes and I was right. If I had drilled the holes first then I would have wasted more work time when I made my mistake and "ruined the work."

If I had milled the ridge before drilling the hold-down hole then I would not have had a flat surface to rest the part on while drilling. The part would have had to be supported in some way while drilling and we would have had to worry about drilling into those supports.

As expected the axle holes were a little large. The cure was blue Loctite.  The risers went on and the wheels went on.  While the Loctite was setting, the axles were sliding.  Unfortunately with too many people moving the car around, what I had expected to happen did happen.  One wheel was pushed in far enough to rub against the car body and also against the lane guide. When the Loctite set up the axle could not be moved. As I stated earlier, if I had machined the risers 1.850 instead of 1.650 there would have been enough space and the wheels would have had the smooth surface of the machined riser to ride against.

What I learned

First, it always takes longer than expected to do anything.  Machining the risers took 5 hours of shop time.  I learned that I need to allow myself a lot more time than I generally estimate. The wife suggests multiplying by a factor of 2.5 or more . . .

The second thing is always always draw your pictures and write down your dimensions.  Because I was measuring and working on the fly, I made a couple of mistakes.  Most of those mistakes could have been avoided if I had drawn up a dimensional object.

My goal of putting the work back on the lathe to turn a hub around the axle holes was a correct one and I should have done it.  This would have given the wheel something to ride against as well looking nicer than having a big chunk of riser sticking out.

Last, don't be afraid to start over if you make a mistake.  What I just realized is that I should have made three pieces instead of just two.  The amount of time it takes to do three pieces is hardly more than making two.  Most of the time was spent on set up. Taking a piece out of the vise and getting it back into the vise in the same place is not difficult.    All it takes is a vise stop and taking the time to do the set up.

In closing, I want to go back to the shop and remake both risers "right".  That would start with a detailed drawing in a CAD package.

What Mike learned

I'd like to think that the most important thing that my son learned is that he can count on me. We put a lot of work on this, and he held my hand and I held his hand, and we "got her done." I'm very proud of the effort and patience that he showed.

He learned some practical things, like how to use a scroll saw and how to use a triple beam scale. He also learned another practical lesson: that doing something like this is Hard Work. It wasn't easy, and there were times when it wasn't all that fun (especially in the cold workshop), but he walked into that race knowing that it was HIS car. So he learned that there is a pride that comes along with a job well done.

Me and my son.
One of his hardest lessons was to learn that he couldn't complain about working. We were both cold, working out in the shop, but the work had to be done and we didn't have a lot of choices at that point. Complaining didn't change anything, and didn't solve anything. He had to learn that persevering also means not whining and being upset. It was a difficult lesson, but he did great.

His final commentary on the whole experience was this: "It was 25% boring, 50% okay, and 25% with my Daddy!" And when he told us this, he was grinning madly. Basically, it was hard work, kind of boring, maybe a bit interesting, but all of it was something he got to do with daddy, and that made the whole thing worth it. Yeah, I'm grinning, too.

Saturday, February 15, 2014

The Z-setter

Along with all of the fun metal working toys I have I also have a CNC Router that I built from scratch.  Last fall (15 months or so ago) I managed to make a stupid mistake and broke it.  I destroyed part of the Z axis, burned out the router and managed to do something to the electronics.  In the end it turned out that the issue was a broken wire in one of the motor connections.

I fixed the physically broken parts and then realized that the electronics weren't working.  Two weeks ago the electronics on the CNC made it back to the top of my list and I purchases a G540 4 axis controller and break out box.  I bought it from  A damn good company.

As I was going through their website I saw a Z axis position setter for only $90.

So what does a Z axis setter do?  Well when you are using CNC you need to know where your material is.  Normally X and Y axis aren't critical because you just want to make sure you are cutting inside the material.  If it is critical then you can do standard edge finding but it doesn't happen very often. 

The more critical position is the Z axis.  If you miss the surface by a few 1/1000s you could end up cutting to deeply or you could cut to high and miss features.  Worse, it is often the case that you will change tools in the middle of working a complete CNC program.  If the tool you put in is not have exactly the same stick out as the last tool or you don't know exactly how much it sticks out your 2nd (or third passes) could cause problems.

If you are doing CNC work you often do a roughing pass.  As long as you don't turn off the machine your X and Y axis will stay exactly the same.  When you change tools for the finishing pass unless you get the tip of the tool exactly right then the roughing and finishing passes might not match up.  Leaving a poor result.

There are lots of ways to set the Z axis.  You can use the paper squeeze where you put a paper under the bit, lower it till it is "stuck" then slowly raise it till it is barely free.  You know know your bit is exactly the thickness of the paper above the surface.  You can use a dowel pin that is exactly 0.500 thick.  You lower the tool until you can no longer roll the pin under the tool, then you raise the bit until you can just barely roll the pin under the tool.  Then you know the tool is exactly 0.500 inches above the surface.

There are other methods but they all are slow and have the potential of error.

In the best of all worlds you would want to change the tool then just press "figure it out" and have it "work."

That's where a Z setter comes into play.  A Z setter acts like a Normally Open (NO) switch.  There is a sensor plate which is on one side of the circuit.  The tool is attached to the other side of the circuit.  When the tool touches the sensor plate the circuit closes and the computer senses that the tool is exactly sensor plate away from the surface of the work.

You could just use a flat plate but that plate has no give to it, so when the tool touches down it puts lots of stress on the CNC system unless the tool is moving very slowly.  I originally tried a piece of printed circuit board but it was too light and flexed upwards causing still other problems.

This Z setter is designed to protect the tool as well as be heavy enough so that it doesn't flex or move when placed under the tool.

The design is a 2in diameter cup with a spring loaded plunger.  The entire cup is one side of the circuit.  When it is time to set the Z axis the setter is placed under the tool and then a CNC program is run.  The program does a rapid lower.  It doesn't matter if the tool bit hits "hard" as the AL is softer then the tool bit and the plunger will give.  Once the program detects that it has touched the plunger is backs out rapidly until the tool is no longer in contact with the plunger.  At that point the program lowers the tool at a much lower rate of speed but it only has to go a short distance so this doesn't take long.  When the tool touches down we know exactly where the tool is relative to some surface.  (top of the work or the bottom board or something else.

I plan to make a second z-setter.  This one will be placed in a fixed position on the router table.  This will give us an absolute Z location.

To start using the program we would use the movable Z setter to determine a point above work surface.  (We don't have to use the movable Z setter for the bottom of the work because that can be determined from the absolute location from the fixed Z setter)

With two Z locations, one absolute and one relative we can calculate an offset and remember that offset.  When we change tools we can recalculate the offset from the absolute Z and not have to measure to the work surface again.

Enough about what a Z setter is, let's get into making it.

I started with a 2.250 round of AL that was 12 inches long
I set this up in the 3 jaw chuck and then added a steady rest way out at the end.  My son Michael then faced it off and turned a section about 0.375 down to 1.500 +0.000 -0.005.  This was parted off to create the plunger/plug.  When parted off the part ended up about 0.250 thick with a very smooth top space.  I was pretty happy as we hit 1.499 for the diameter.

Next the work piece was faced and a section a little longer than 1.000 was turned down to 2.000 +/- 0.005.  I hit this at 2.000 which was very nice.  Now that I had the diameter of the cup and retaining ring established it was time to start boring.  I started with a center drill  then I drilled with my largest drill 0.500.  I drilled 0.750+ a little more deep.  I do have a 5/8 and 3/4 in drills but they are MT2 and the tail stock is an MT3.  I've not yet gotten the adapter sleeve.

After drilling I then set the micrometer stop and started boring.  The goal was 1.375 +/- 0.20 diameter.    This is the interior diameter of the retaining ring.  Once the bore reached diameter a slice 0.063 was parted off.  Since one side was faced it was "perfectly" smooth. This face will be against the top of the cup and plunger which will bring the plunger into alignment with the top of the cup.
Next the cup was again faced and the boring was continued.  The goal was 1.500 +0.005 -0.000.  When I hit the 1.500 mark I test fitted the plunger and decided it was a little to tight so I took another 0.001 off the diameter.  The final size of the bore was 1.504 which gave a loose slide fit to the plunger.

At this point it was time to part off the cup.  The cup was parted off at 0.800 to leave some room for facing and finishing to 0.750.  I had to make some soft jaws, actually brass shim stock to cover the jaws of the chuck.  I seated the piece against a pair of parallels then faced of the base.  Once the base was faced off I flipped the piece over, touched off, measured and cut to 0.750 +/- 0.000  I was able to hit this to the limits of my ability to measure (0.0001 on my micrometer)
Now that the major pieces are shaped it is time to drill and tap some holes. I wanted four screws in a standard bolt hole pattern 0.125 from the edge.  After doing a little research I decided on #6-32 as my screw size.  A #6-32 hole is produced by a #36 drill bit.

The fun comes from the fact that I don't have a fully functional DRO.  I only have Y axis capabilities on my DRO.  This of course complicates just about everything. 

To place my 4 holes in the bolt circle the right way to do it is to locate the center of the circle by sweeping the outside edge.  When this is done you keep track of which way the table was being moved when you found center.

From that point on you can move to the correct X,Y coordinates based on your dial settings as long as you are moving in the same direction as when you found center.

I was able to cheat a little bit.  Because I have one axis working with my DRO I'm able to locate the center value of Y.  At that point I move to just outside the cup in the X axis, move towards the cup until my edge finder twitches.  From there it is only a mater of turning the dials .225 in the same direction to end up where I need to go.  The extra 0.100 is to adjust for the size of my edge finder.

This gets me the "left" and "right" holes.  From there I just need to move in to 1.100 to be at the exact center of the cup.  A quick down stroke with the spindle and I can see that it is lined up exactly with the center of the cup as indicated by the drilled hole.

Using my Y axis DRO I'm quickly able to move to the correct locations for each hole and drill them.

In order to start tapping each hole vertically I'm actually doing three tool changes for each hole.  I start with the edge finder, touch off, move to final location, change to the drill bit, touch the top of the cup, set the stop to 5/8", drill to depth.  Switch to plug tap, take the mill out of gear, twist the drill chuck by hand to slowly tap the hole part of the way. 

I didn't go as deep as I could have because I was afraid I would not be able to feel when the tap hit bottom.  I'll have to test sometime when I'm not worried about destroying 4+ hours of love labor.

Once the four holes were drilled and the tapping started I took the cup out of the vise and started to hand tap the holes the rest of the way.   At which point I started cussing Grizzly.  The tap set I bought from them has taps that start at #4 and go up, but the tap wrench doesn't actually HOLD a #6 tap!

I ended up using the larger wrench and driving the square at the end of the tap.  This worked fine and I was very careful to feel when I hit bottom.  I had picked up a taper tap and a bottom tap as well so I finished out with the bottom tap.

Next I put the cup back in the vise on its side.  I used the edge finder to locate one side of the cup and then move to the center of the cup.   A quick edge find off the bottom and I moved 0.250 up from the bottom to drill and tap the edge hole.

This all seemed to work exactly as expected.

Now it was time to drill the clearance holes in the retaining ring/disk.  I carefully placed the ring in the vise, found the right place to drill, used the 9/64th drill with parallels holding up the sides.  The drill started cutting in with no problems.  A little tap magic did wonders.

Then as I went a little further the drill seemed to "stick" and the disk suddenly flexed and bent.  I repositioned the parallels for better support and finished drilling my holes.  Boy were they ugly.  The forth hole was the worse.  I barely started to drill when suddenly the ring popped out of the vise. 

I checked and there was a good mark so I went over to the drill press.  There I saw the drill cutting just fine and then again it seemed to stick.  I finished the hole with a little more pressure then cleaned up the ugliest holes I've drilled.

When I went back to get the drill bit I finally looked at the bit.  The cutting edges fine, but about 1/4 inch back from the cutting edge the bit suddenly got "larger" as if there was a second very bad cutting edge.  The bit is no in the garbage.

The end result was one hole that was misplaced so that I can't get a screw into it.  I'll go back and open all four holes up a little bit more (and clean them up).  This will allow all the holes to align.

Here is the Z-setter being put together:
The spring under the plunger might be a little two strong and a little to small but both can be easily adjusted later.

The retaining ring is then placed on top:

And here is the letherman screw driver acting like the cutting tool pressing down the plunger(sorry for the bad focus):
The South Bend 13"x5' that I used to turn the parts.  I'm hoping that someday it will be warm enough to enjoy cleaning it a bit more.  These chips are almost all from this project.:
Thats a DoubleBoost light pointing down at the three jaw and my Walmart special off to the back.

Here is the Bridgeport used for drilling the bolt hole circle:
Any rust you see on any of these machines came with the machines.  I've been cleaning and fixing as fast and as much as I can.  This vise was frozen when I got it.  I've cleaned it and it is now mostly in good shape.  The fixed face and bottom of the vise are in very good condition with the exception of a couple of nicks on the fixed face.

A special thanks to Marc L'Ecuyer for his rapid response to tell me how to do x,y bolt hole circles right and for some great teaching videos.

Doubleboost for his fun videos and methods.

Tom's Techniques for more great learning videos.

Oxtool, Abom79 and Kieth Fiener for production machinist videos.

And of course, Mr Pete (tubalcain) for the videos that got me started