I made some rear axle shims, or...how to locate 5 evenly spaced holes on a circle.

[ratbailey]

Hey all.

 

While undoing some pretty sketchy repairs on the '48 DeSoto rear axle, I found myself in need of some shims. Someone tried to compensate for a spun bearing by getting rid of all but one shim on one side, and I was afraid I wouldn't have enough to do the job correctly. One single shim on the open market today is about $10. Being the cheap bastid that I am, I set about figuring out how to make my own, and probably spent 4x the amount that would have gotten me the few shims I needed on raw materials. But, I picked up some new skills, dusted off some geometry that was probably taught to me back in HS but I was too busy making eyes at Trish L_______, cut my finger only once, and now I'm swimming in shims and shim sheet stock. 

 

Anyhow, first step was to order some shim stock from McMasters-Carr. Got some packages of .007, .010, .012, and .015. A pack of 5 is around 20 bucks, I got two shims to a sheet, so that's about 2 bucks a shim. Or actually, even less than that, considering how much left over shim material there was on each sheet.

 

After cutting out my shim stock into squares, I sandwiched them between two pieces of pine, thusly: 

 

 

Next step was to figure out how to lay out 5 holes on a circle, evenly spaced. I was pretty sure I'd need some of that geometry stuff. This guy explains it well: 

 

Next, I traced the shim I had onto paper, and took a lot of measurements with a vernier caliper. 

 

At this point, you're probably thinking, "why not just trace it out on paper and use that as a template?" I've done that many times, and the results are never very good, or as good as I'd like. This time, I wanted to see if I could make something that fit pretty close to perfect right away. I also wanted to see if I could bang out 8 or 10 in one shot. 

 

So, as you can see in the drawing, I found the center of the big hole, which is pretty close to 3" diameter. Taking lots of other measurements and doing some simple calculations that I won't get into, I found the center of the topmost hole, and the diameter of the larger circle created by the smaller holes that runs through the center of all of them. I could've done all this in a cad program, too, but I don't know how to use one. Baby steps. 

 

Next, I had to figure out where exactly to put the other holes. As the guy in the video says, if you know the diameter of your circle, consult the table on pg. 75 of "Machinery's Handbook."  I happened to have a copy of "Machinery's Handbook", so I consulted page 75...

.

5 holes for a 1" diameter circle is approximately a .588 chord. Multiply that number by the diameter of my particular 5 hole circle, 3.75, and you get 2.205. Set your compass to 2.205, and you should be able to pace off 5 evenly spaced holes. 

 

 

I figured it'd be better to use a piece of shim stock on top of the wood for more accurate layout, so I went ahead and did that. Lacking layout fluid, I scribbled all over it with a sharpie.

It might be hard to see, but the Xs on the circle show the exact center of each hole to be drilled. I paced these off with a compass, then center punched each one. To the drill press...

 

Badaboom. 

 

Took apart the sandwich, traced the outline of the old shim onto each new shim, snipped with aviator snips. Mine is on the left, the old one on the right.

How do they fit? Well, I got sloppy with the drilling. But that said, it only took some minor tweaking of two holes with a round file for each one to fit perfectly. In the past, with the old trace and drill with a hand drill method, I would've made a mess out of everything. Hope this helps someone out. 

Edited September 29, 2022 by ratbailey

[keithb7]

Nice work! Great looking product. 
 

I keep scrounging up powertrain parts that people are scrapping. I seem to have amassed quite a collection of axle shims!  Pretty sure someome will throw them out after I’m long gone. Lol. 

[ratbailey]

50 minutes ago, keithb7 said:

Nice work! Great looking product. 
 

I keep scrounging up powertrain parts that people are scrapping. I seem to have amassed quite a collection of axle shims!  Pretty sure someome will throw them out after I’m long gone. Lol. 

Thanks for the kind words, Keith! I'm jealous that you're finding junker parts! If I could've harvested a bunch locally, I would've done that...it's pretty dry around here. Yeah, my kids are going to have a big dumpster party when I'm gone---"...what the hell is this thing? Dad was such a nut..."