Which Mothers?

Secrets, tips, tools, design considerations, materials, the "science" behind it all, and other topics related to building the cars and semi-trucks.
Speedster
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Re: Which Mothers?

Post by Speedster »

This is getting Off Topic but I would say finishing wood is a lot different than finishing metal if we are talking about a pinewood derby car and we're going to finish it with paint. The main difference is with wood you can abuse the product, mainly the Primer/Surfacer. The wood need not be Super Smooth nor is it even recommended. The Surfacer needs something to grab onto. It is designed to fill and it is designed to be sanded. Surfacer sands a lot easier than wood. Walmart, Rust-Oleum Automobile Primer, Fast drying & wet sandable. Comes in a rattle can.

Does anyone simply polish their shiny zinc coated axles with Brasso and go racing?
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Stan Pope
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Re: Which Mothers?

Post by Stan Pope »

Speedster wrote:This is getting Off Topic but I would say finishing wood is a lot different than finishing metal if we are talking about a pinewood derby car and we're going to finish it with paint. The main difference is with wood you can abuse the product, mainly the Primer/Surfacer. The wood need not be Super Smooth nor is it even recommended. The Surfacer needs something to grab onto. It is designed to fill and it is designed to be sanded. Surfacer sands a lot easier than wood. Walmart, Rust-Oleum Automobile Primer, Fast drying & wet sandable. Comes in a rattle can.
...
The context of my wood finishing reference was, "In the world of stain and finish", where the color and grain of the wood is expected to be a significant part of the end product.
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Speedster
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Re: Which Mothers?

Post by Speedster »

OK, Everybody disregard what I said. I misunderstood the question. Thank you.
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Stan Pope
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Re: Which Mothers?

Post by Stan Pope »

Speedster wrote:OK, Everybody disregard what I said. I misunderstood the question. Thank you.
No problem, Bill!

The key issue is whether getting metal to a required smoothness has the same parameters as getting wood to a required smoothness. The 2:1 particle size guideline for wood made sense to me, but I don't know if it translates well to metal.

Ideally, each grit reduces the prior texture to grooves no deeper than those created by the new grit. It could eliminate the old grooves entirely, but that would seem to create new grooves deeper than the prior grooves and waste both material and abrasive. If carried to that extreme, the 2:1 progression would remove material thickness totaling twice the depth of the original grooves.

So, to preserve the diameter of the axles, each grit should remove 1/2 of the remaining groove depth, ending finally with a surface near the level of the original groove depth. Anybody have easy (cheap) ways to measure when that state has been achieved?
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Re: Which Mothers?

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Stan Pope wrote:
So, to preserve the diameter of the axles, each grit should remove 1/2 of the remaining groove depth, ending finally with a surface near the level of the original groove depth. Anybody have easy (cheap) ways to measure when that state has been achieved?
Image
Micrometer.. Calipers.
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Stan Pope
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Re: Which Mothers?

Post by Stan Pope »

Right! We could measure the amount of groove removed instead of the amount of groove remaining.

But the starting groove depth is _____??? And which of those can measure +/-8 microns? Not to mention +/- 0 .25 micron?
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whodathunkit
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Re: Which Mothers?

Post by whodathunkit »

Stan, I may be way off on this..
Is one micrometer = to one micron.

like you say the starting groove depth is ___???

Could one use the formula for determing metal removal rates.. if the starting depth was known.
By multipy the depth of the cut by the width of cut and feed rate to find cubic inches per minute of material removed.
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Stan Pope
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Re: Which Mothers?

Post by Stan Pope »

whodathunkit wrote:Stan, I may be way off on this..
Is one micrometer = to one micron.

like you say the starting groove depth is ___???

Could one use the formula for determing metal removal rates.. if the starting depth was known.
By multipy the depth of the cut by the width of cut and feed rate to find cubic inches per minute of material removed.
Yes, one micron = 1 meter * 10^-6 = 0.0000394 inches
For sake of discussion, if I start with 30 micron paper, I should be able to smooth out a surface starting with 60 micron (0.0024") deep gouges. Yes, some of those gages could measure reduction by 1/2. The next level (0.001), then 0.0005", 0.00025", 0.00013", 0.00006", ... 0.00001" (0.25 micron). Where is the measurement limit?

No idea what the cutting rate is for any of these papers!
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Re: Which Mothers?

Post by Nate »

Stan,
Is there a measurable effect in spin time or track speed as you polish down the microns? I'd think that it wouldn't make a difference as long as there's no irregularities across the axle, even if you had regular 80 grit paper grooves WITH the direction of wheel rotation. It might even retain a lubricant better.
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Stan Pope
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Re: Which Mothers?

Post by Stan Pope »

Nate wrote:Stan,
Is there a measurable effect in spin time or track speed as you polish down the microns? I'd think that it wouldn't make a difference as long as there's no irregularities across the axle, even if you had regular 80 grit paper grooves WITH the direction of wheel rotation. It might even retain a lubricant better.
Good question, Nate.

I've considered it before but never reached a firm conclusion. Nor have I put it to a test. My intuition is that those 80-grit paper grooves aren't "clean enough" to perform well.

How might you go about testing the hypothesis?
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Re: Which Mothers?

Post by TXDerbyDad »

I had read somewhere, I believe from one of the wheel/axle vendors that polishing beyond 8,000 grit was pointless in their testing. But they didn't post their testing protocol or their reasoning. Has anyone done any testing to determine what the sweet spot is for polishing and graphite lubrication? I'd really like to know more about the science behind all of this and not just the scuttlebutt. :D
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Re: Which Mothers?

Post by sporty »

TXDerbyDad wrote:I had read somewhere, I believe from one of the wheel/axle vendors that polishing beyond 8,000 grit was pointless in their testing. But they didn't post their testing protocol or their reasoning. Has anyone done any testing to determine what the sweet spot is for polishing and graphite lubrication? I'd really like to know more about the science behind all of this and not just the scuttlebutt. :D
You are asking for about a 30 page report.

Many of us have done many hours of testing and tinkering. To find more speed.
Do keep in mind. That this was also confined to the rules we raced under. Which very.

8,000 grit.. u mentioned.

Sadly the upm. Is more important to know. Most know as pm. Parts per million.

Example.

Different types of sand paper or products. Seem to skimp a bit on the real rating. Or universal rating scale method.
the parts per million.

I have found. 1 micron to do just fine. When going to that fine. With axlepolishing. (Graphite racing).

Sub micron polishing. Yielded no faster times. However. The drop off times for how many runs. Where another run or two more before the times dropped off. Helped win. When the times lasted a bit longer during the race.
naturally races are held differently everywhere.
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