Any success with "composite filled" axle bores?

[Vitamin K]

So in musings on how to improve my build process, I'm wondering if I might be able to tighten tolerances for axle holes by eschewing the fickleness of wood grains and pre-drilling and pre-filling the axle area with some kind of composite.

The basic procedure would be: Drill bore larger than axle hole. Fill with composite. Allow composite to fully cure. Drill #44 axle holes.

Has anybody tried this with any measure of success or failure? Also, does anybody have thoughts on what the best composite to use would be? Obviously, I could do good old epoxy (either 5 minute or 24-hour), but I also wondered if something like mixing epoxy with sawdust (or the finer leavings from sandpaper) might also be worthy.

What do you guys think?

[LightninBoy]

So in musings on how to improve my build process, I'm wondering if I might be able to tighten tolerances for axle holes by eschewing the fickleness of wood grains and pre-drilling and pre-filling the axle area with some kind of composite.

The basic procedure would be: Drill bore larger than axle hole. Fill with composite. Allow composite to fully cure. Drill #44 axle holes.

Has anybody tried this with any measure of success or failure? Also, does anybody have thoughts on what the best composite to use would be? Obviously, I could do good old epoxy (either 5 minute or 24-hour), but I also wondered if something like mixing epoxy with sawdust (or the finer leavings from sandpaper) might also be worthy.

What do you guys think?

I've read somewhere of people filling the slots with JB Weld and redrilling when the rules stipulate the slots must be used. I never used the slots so I don't have any direct experience.

I've drilled lots of axle holes though. I haven't had any trouble with wood grains impacting the bit. In my opinion, you'd be better off investing in a really good carbide drill bit.

[FatSebastian]

The basic procedure would be: Drill bore larger than axle hole. Fill with composite. Allow composite to fully cure. Drill #44 axle holes.

Interesting concept. How big of a hole? A large hole would come out the bottom. A small hole would be difficult to fill.

I've read somewhere of people filling the slots with JB Weld and redrilling...

For example, here. Of course, JBWeld also has a bit of a reputation for being difficult to drill.

[Vitamin K]

Good question. Maybe double the diameter of the desired axle hole, and drilled straight all the way through? Could cover the other end with some tape or something while filling and sand flush before drilling.

I'm not sure about the JB Weld (doesn't it contain metal?), which is why I was curious as to how an epoxy/wood-particle mixture would do.

The basic procedure would be: Drill bore larger than axle hole. Fill with composite. Allow composite to fully cure. Drill #44 axle holes.

Interesting concept. How big of a hole? A large hole would come out the bottom. A small hole would be difficult to fill.

I've read somewhere of people filling the slots with JB Weld and redrilling...

For example, here. Of course, JBWeld also has a bit of a reputation for being difficult to drill.

[FatSebastian]

Good question. Maybe double the diameter of the desired axle hole, and drilled straight all the way through?

If we were to dry this, I would also consider opening a channel along the bottom - like an "oversized" slot - to avoid the difficulties of trying to drill a small, 1.75" deep hole. Then fill and drill as if it were a slot. Such a channel might be carved with router, table saw, or mill, for example.
Some require the axles go directly in wood.

[Vitamin K]

Good question. Maybe double the diameter of the desired axle hole, and drilled straight all the way through?

If we were to dry this, I would also consider opening a channel along the bottom - like an "oversized" slot - to avoid the difficulties of trying to drill a small, 1.75" deep hole. Then fill and drill as if it were a slot. Such a channel might be carved with router, table saw, or mill, for example.

Yes, I like your thinking here...definitely easier to fill too, I think. And it might dry faster.

Some require the axles go directly in wood.

All the more reason to try my Epoxy/Sawdust blend, perhaps?

[Stan Pope]

Some require the axles go directly in wood.

All the more reason to try my Epoxy/Sawdust blend, perhaps?

I'd better check our rules ... some "improvements" might be in order.

I wonder about the concern with drilling perfect holes when alignment with (even slightly) bent axles is so easy.

[glider90]

I was wondering the same Stan. I milled my slots on the Bridgeport and installed 3/32 ID brass tubes to put the axles in, then filled the slots with an epoxy/micro balloon mix. This ensured the slots were true. However, I really questioned my reasoning when I bent the axles and then aligned them by testing anyway. I did not intend to bend the axles since we turned a point on the wheels, but I ended up doing it to ensure they stayed out on the axle heads rather than against the body. I also figured it would give me a way to tune the car to compensate for any issues...

[FatSebastian]

All the more reason to try my Epoxy/Sawdust blend, perhaps?

Another option to explore might be lead (Pb). It can be drilled and shaped, or cast directly into the body. Or, if one had a reproducible method of cutting a channel, one might first cast lead ingots in channeled scrap and then transfer the ingots to the car to avoid scorching the body. (Just speculating here; we have no direct experiencing casting lead.) It certainly adds mass in an area where one would generally want it.

[Vitamin K]

Another option to explore might be lead (Pb). It can be drilled and shaped, or cast directly into the body. Or, if one had a reproducible method of cutting a channel, one might first cast lead ingots in channeled scrap and then transfer the ingots to the car to avoid scorching the body. (Just speculating here; we have no direct experiencing casting lead.) It certainly adds mass in an area where one would generally want it.

This is an interesting approach, though I'm not certain how I feel about mounting the axles directly into lead. My philosophy with lead is that it should be completely covered from external contact once installed in the car. If you were mounting your axles into it, your wheels would be rubbing up against the lead, right?

As for casting ingots, that is similar to what I did for this years' builds with my kids. I cut wood strips that were the same thickness as our car bodies and nailed them to a board in rectangles the size of the lead sections that we wanted. As it turned out, I still ended up having to drill out lead to adjust weight because I discovered that A) depth is hard to get exact when pouring lead into a small mold and B) you get bubbles underneath the lead that change your volume.

BTW, who is the "we" that you always refer to your work in, FS?

[FatSebastian]

If you were mounting your axles into it, your wheels would be rubbing up against the lead, right?

Unless the lead was painted over, or recessed a bit and covered with a wood veneer, or...

BTW, who is the "we" that you always refer to your work in, FS?

My children. (Who else?) DT is a forum about kid's racing.

[Vitamin K]

If you were mounting your axles into it, your wheels would be rubbing up against the lead, right?

Unless the lead was painted over, or recessed a bit and covered with a wood veneer, or...

I don't think I'd want the hubs rubbing on paint, since that tends to get 'gummy'. But if you installed the lead so that maybe 1/16" of wood sat between the hub and the lead layer...well that might be something. And you might even be able to pass the 'axle must be in wood' requirement too...

BTW, who is the "we" that you always refer to your work in, FS?

My children. (Who else?) DT is a forum about kid's racing.

I more or less assumed that this was the case, but I thought I'd ask to be sure. After all, you could be using the Royal "We". But then, we'd have to change your moniker to King Sebastian...

[knotthed]

I have used JB weld mixed with bell graphite from menards for a similar purpose. It is not hard to work with and I would not think twice about drilling it. I have cut it with a utility knife before.

You are definately on the right track about getting a consistent material to drill into - this will eliminate the variance the wood grain gives you.

You will still need to have a great drilling setup to accomplish the desired results, without Stan's bent axle tuning procedure.

Since it doesn't look like I will be getting to this anytime soon - I have hypothesized for over a year that taking this one step further would be the ultimate.

I wanted to make a fixture to hold gauge pins at the desired locations for my axle holes and then drill bigger holes into the body and then fill the holes with epoxy to set the given location of the axle holes into the body in a free state in the bodies completed condition. If you are clamping the wood to drill it, it could still be moving from the clamping force and then also you might be removing residual internal stresses from the wood.

Using the fixture and gage pins, you should achieve repeatable axle locations from block to block with no trouble at all.


I also have a block laying around from 3 years ago that I drilled a hole in the axle location and poured lead into it with the intention of drilling the axle holes directly into the lead. I stopped when I didn't know how well the surface would be for the wheels rubbing..........LOL Fast forward to today - the wheels should never touch that area if drilled correctly so maybe I should circle back on that idea. We also started using tungsten and that abruptly stopped our use of lead.

Good topic guys!

[FatSebastian]

I don't think I'd want the hubs rubbing on paint, since that tends to get 'gummy'.

When you surmised that "wheels would be rubbing up against the lead" I read this in an academic sense (such as a rule which forbids the wheel from having contact something that is not wood). As knotthed suggests, a well-designed rail rider should have the wheel migrating away from the body.

Note that Doc Jobe designed many cars where the entire rear-end was molded of lead separately and the axles were inserted into the lead. There is a picture of some staged cars, made with this construction technique, in this lecture. So it seems possible.

After all, you could be using the Royal "We".

Ah yes. That could especially make sense in the context of the earlier post.

[Scrollsawer]

This seems like a design approach better suited for the Professional Boards. I doubt many 9 year olds are going to be exploring composite inserts when building their cars. Not to say that the science around this isn't worth investigating with the Scouts (e.g., the nature of materials, densities, etc.), but other than looking for vertical grain vs. horizontal grain blocks, and lighter vs. heavier density blocks, we figure everyone's starting with a level playing field, more or less. I'm also not a proponent of Teflon inserts next to the wheels in either Pack or District races.

Scrollsawer