Cutting Airshaft

FrankV

FrankV

Active Member
Ok, so this is kinda specific. I have a new 2021 fox 36 factory at 160mm of travel. I want more travel but don’t want 170, I want 165. I’m super obsessive about getting the numbers right so it’s something I gotta try out.

I have seen one or two others online do this, but would it be possible to cut the airshaft and rethread it? I’ll put a diagram below, but I think I can take 5mm off of a 170 shaft and be all set. If anyone has tried it, lemme know!

 
jklett

jklett

Well-Known Member
Possible but might not cheap. The problem is that the thread is custom so you're looking at having a tap made if there's not enough threads left after cutting it. You may get lucky with only 5mm but it's a gamble. I don't mean to piss in your cheerios, just want to warn you of the possible pitfalls before you go spending money.
 
RobW

RobW

Well-Known Member
Sounds like a bad idea- but then again, there are people who juggle and swallow fireballs- up to you but I’m sure those jugglers didn’t perfect their tricks on the first try.
 
FrankV

FrankV

Active Member
jklett said:
Possible but might not cheap. The problem is that the thread is custom so you're looking at having a tap made if there's not enough threads left after cutting it. You may get lucky with only 5mm but it's a gamble. I don't mean to piss in your cheerios, just want to warn you of the possible pitfalls before you go spending money.
Click to expand...
Wow, didn’t even think about that. My schools shop has a vast range of taps but it didn’t even cross my mind that it might be custom. I’ll take it apart later and take a look at how far the threads are cut
 
jdog

jdog

Shop: Halter's Cycles
Shop Keep
I’m hoping that people saying you can’t pushes you to do it. I don’t however think the 5mm gain/loss is worth the trouble.

I’d guess you might feel 105mm vs 100mm but it’s less likely you’d feel 165mm vs 165mm.

some people can’t feel a 30psi change in their shock pressure while others can a feel 5psi variance.

let us know how it works out.

everyone also said the wright brothers were crazy.
 
FrankV

FrankV

Active Member
jdog said:
I’m hoping that people saying you can’t pushes you to do it. I don’t however think the 5mm gain/loss is worth the trouble.

I’d guess you might feel 105mm vs 100mm but it’s less likely you’d feel 165mm vs 165mm.

some people can’t feel a 30psi change in their shock pressure while others can a feel 5psi variance.

let us know how it works out.

everyone also said the wright brothers were crazy.
Click to expand...
Definitely going to be negligible, it tickles my brain a bit and allows me to learn more so why not
 
FrankV

FrankV

Active Member
I have a 150 air shaft for it in my basement, gonna attempt taking it apart tomorrow to see how long the threads are. If they are to short and need to be tapped I won’t go ahead with this and just run 170. I’ll update this thread with any progress
 
jklett

jklett

Well-Known Member
FrankV said:
I have a 150 air shaft for it in my basement, gonna attempt taking it apart tomorrow to see how long the threads are. If they are to short and need to be tapped I won’t go ahead with this and just run 170. I’ll update this thread with any progress
Click to expand...
If you're doing this for school and have access to a machine shop and a torch, why not use it as an exercise in how to make a tap? O1 and some scrap material to test it on(whatever the air shaft is made of) and you have a learning opportunity. They're not too difficult to make, just a little time consuming. I was never trying to discourage you from doing it, just wanted to let you know of any potential issues before you jumped into it.
 
w_b

w_b

Well-Known Member
jklett said:
.305"-48 according to the drawing. I know you can get 5/16"-48 UNS pretty easily but the major is .3125" and that may be too loose to work.
Click to expand...

If we are rethreading air shafts, the correct tool needed is a die, not a tap. External thread vs threaded hole. Most above-crappy ass level dies are split and somewhat adjustable with a set screw. If the specs quoted are correct you should have more than the 0.004” per side adjustment needed to get to 0.305” dia.

Or just start off threading the new section a few thou undersize, and you’ll prolly come out right on anyway.
Or you could just skim the major of the 5/16” thread a couple thou and file file file nice-a nice-a but that’s the hack way to do it.
This whole job is likely an exercise in futility anyway so hack at it...
 
You must log in or register to reply here.
Top Bottom