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Air Gun Home Forum Index » Airgun Smithing » Mini Lathe Steady Rest Bearing Mod
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Mini Lathe Steady Rest Bearing Mod 
PostPosted: Tue Mar 13, 2012 4:05 pm Reply with quote
yourdaddyjoe
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I borrowed an idea from Littlemachineshop.com for adding bearings to the tips of my steady rest fingers and gave it a Joe twist... I did not care for the bearings hanging off the end.

Same mod can be done to the follow rest.

Parts & tools specific to this mod:
3x 4mmx8mm RC Hobby bearings (Local RC Shop or eBay)
3x 4mm-.70 x 9mm long Hex socket cap screws. (Heads must be smaller than 8mm) I used stainless that I picked up at ACE hardware.
#30 Drill bit
4mm-.70 tap

I milled out a pocket just a tad wider than the bearing.
Drilled and tapped all the way through both holes so that there would be no pinching the bearings with the cap screws when tightened.

The results:
Minimal marking that can be easily buffed out with a Scotch Pad.





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PostPosted: Wed Mar 14, 2012 8:31 am Reply with quote
SMP
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Nice mod Joe

I agree the brass wear buttons on older steady/follow rests can play havoc on aluminum. Not to mention constantly having to slop lube on the shaft. Which in inevitably picks up a chip that proceeds to cut a nice gouge in your shiny new part

I like it Thumb Up!

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PostPosted: Wed Mar 14, 2012 10:13 am Reply with quote
yourdaddyjoe
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This whole concept got me thinking on how to make it easy to choke barrels.

I'll wait for the new lathe to try it. the halo would have to be beefier and so would the bearings...

Same concept really, make some steel fingers and and replace the thumb screws with a bolt that you can get some leverage on. Just keep tightening while the lathe runs slow and pinch the end of the barrel to the desired choke.

Sorta like a tubing cut off tool.

Thoughts?

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PostPosted: Wed Mar 14, 2012 10:50 am Reply with quote
SMP
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Hahaha funny you mention that

A Rigid pipe cutter with the cutter replaced by a bearing is exactly what I use to choke barrels.

Works well and doesnt take much of a squeeze for that critical 0.001

Shhh...We're giving away all our voodoo Laughing

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PostPosted: Wed Mar 14, 2012 10:56 am Reply with quote
yourdaddyjoe
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Sweet!

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PostPosted: Wed Mar 14, 2012 11:13 am Reply with quote
rsterne
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I don't know how much force is required but it might work.... The only way to be sure would be to try it.... You can get a lot of leverage with threads, so make sure your bearing is beefy enough not to explode from the radial loading.... I don't know if I'm doing the math properly, but assuming the yield strength of steel is the same in compression as tension, I'll have a go....

OD of Crosman barrel 0.437".... ID 0.217" (.22 cal).... Wall thickness 0.110".... We'll assume mild steel with a yield strength of 44,000 psi.... Let's use a bearing width of 0.5".... The absolute minimum amount of metal that must be influenced by the pressure from the roller would be in a straight line from the roller to the center of the barrel.... ie the wall thickness 0.110" times the roller width of 0.5".... That is 0.055 sq.in. times 44,000 psi which works out to a minimum of 2420 lbs....

The way I see it, that is the MINIMUM force required to cause the molecules of steel to "slip" past each other and deform in a plastic manner.... It is assuming that all the force is transmitted in a perfectly straight line radially through the wall of the barrel.... That may or may not be the case, the force required could easily be many times that, I have no idea....

Just something to think about.... I'd make sure that the bearings you use have at least a 10,000 lb. radial load capability so that you have a 4:1 safety margin....

Bob

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PostPosted: Wed Mar 14, 2012 11:26 am Reply with quote
rsterne
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Just goes to show that a little math is a dangerous thing.... Rolling Eyes

How big are the three bearings in your modded pipe cutter, Sean?....

Bob

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PostPosted: Wed Mar 14, 2012 11:36 am Reply with quote
yourdaddyjoe
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rsterne wrote:
Just goes to show that a little math is a dangerous thing.... Rolling Eyes...Bob


That's our beloved Bob the builder! Mr. Green

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PostPosted: Wed Mar 14, 2012 1:30 pm Reply with quote
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The cutter I use is the Ridgid 202 wide roller. To be honest I can't remember exactly what size the bearing is that I replaced the cutter with...but the cutters are 1" OD on Pro Line cutters. So the bearing is similar.

Oh and I should mention it's not a race style bearing just an axial bushing type that I made myself and hardened out of a slice of tool steel

And of course I can't go look at it because it's at work with the lathe and all my other fun stuff

However when your considering the force required to squish you need to look at the clamping load of bolts. Using 1/2" NF Gr8 (which is what the tightening bolt is on the 202) you can achieve 14500 Flbs force. And trust me I've seen guys twisting on those cutters in shipyards for all they are worth....rather than go to the crib for a new cutter Laughing

It weighs 8lbs

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PostPosted: Wed Mar 14, 2012 9:15 pm Reply with quote
Gippeto
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Did some experimenting with barrel choking as well...have yet to verify results by shooting.

Took a piece of 1"dia 1045 ~1" long, and bored through to suit the barrel dia + .001".

Popped it in the vice and used a hacksaw to cut parallel to the bore until ~ 1/8" from being two pieces...deburr.

Put the barrel into this bushing, muzzle at the end where you started the cut. Put the assembly in an 8" vice...use a 24" snipe and put yer back into it.

Release, rotate barrel ~30degrees, repeat...keep going until you get back to the start.

Have managed a noticeable choke in crosman and qb barrels. Nice even marks on the pellet head where previously none appeared. Whether having two pressure points will matter has yet to be seen, but the pellets look good. Smile

Would like to try something like a collet at some point.


And actually on topic...

Nice idea with the bearings Joe. Cool

Al
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PostPosted: Thu Mar 15, 2012 12:06 am Reply with quote
yourdaddyjoe
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Thanks bros,

Last year I kept getting funky spirals = to the feed screw in my material and LMC determined that I tweaked my spindle. I got in a rush and just ordered a whole new gear head.

This head likes to chatter if work is not supported properly.

I just realized that I forgot I did the roller bearing upgrade on the old head. Not on this one...

Looks like after this batch is back from anodizing, Tear down time is in order. The lathe needs a good tune...

I bet I've made over 500 parts since the last tune.
Embarassed

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Mini Lathe Steady Rest Bearing Mod 
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