Home |
Search |
Today's Posts |
|
Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
Folks,
I'm attempting to fit a 1.5 inch nylon cylinder into a 1 inch diameter metal sleeve. The nylon will act as a piston for my spring piston pellet gun. I've heard for years that auto engine pistons are lap fitted for each cylinder and would like to give it a try. Could someone give me the basic idea of how this might be done for nylon? Thanks Tut |
#2
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
wrote:
I'm attempting to fit a 1.5 inch nylon cylinder into a 1 inch diameter metal sleeve. [snipp] I've heard for years that auto engine pistons are lap fitted for each cylinder and would like to give it a try. Auto engine pistons lapped? No! And getting the 0.5" off with lapping is also not the right way. :-)) I'd take some PA with MoS2 in it (the black one) and simply turn it on a lathe. Just make it a nice gliding fit. I have done that with pistons (diam 12mm) for a compressed air engine to my satisfaction. Nick -- Motor Modelle // Engine Models http://www.motor-manufaktur.de DIY-DRO // Eigenbau-Digitalanzeige http://www.yadro.de |
#3
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
|
#4
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
Polymer Man wrote: A principal of lapping is the softer material (the lap) will pick up the abrasive and lap the other part. Nylon will pick up the lapping abrasive, and in turn wear the bore in your air gun. Things are lapped to get a very precise fit and a fine finish. Due to the extreme difference in coefficient of thermal expansion between nylon and your metal bore and the fact that nylon changes dimension with exposure to water (kinda like wood), you would not want an extremely close fit between your nylon piston and metal sleeve or you risk binding. You will need some clearance, probably around .005" plus or minus .001". It does not take lapping to get that kind of fit. A fine lapped finish would probably not be highly beneficial to the function. And I don't think nylon will lap well. My opinion is your best bet is to just turn your piston on a lathe. If you want a high performance plastic that does not absorb water, has good lubricity and high wear resistance and a low coefficient of thermal expansion and friction, look at polyimide (Nylon is polyamide and is very different) such as Dupont Vespel. Though some plastics polish well (Delrin for example) if you want an actualy lapped part, you should probably use metal. Polymer Man--Thanks! Calculations indicate that I'm looking at 2000-2500psi and thought lapping might result in less gas leakage. I'll give Vespel a look see. Tut |
#5
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
Nick
Thanks for your comments--I'm not sure what PA is but assume its polishing compound. I have four different grades--from rouge to black. Tut |
#6
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
Trevor Jones--
Thanks for your comments--my last auto engine rebuild was over 30 years ago--guess thing change.;-)) Tut |
#7
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
wrote:
I'm not sure what PA is but assume its polishing compound. PA is Polyamid. I would use it for the piston. Nick -- Motor Modelle // Engine Models http://www.motor-manufaktur.de DIY-DRO // Eigenbau-Digitalanzeige http://www.yadro.de |
#8
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
|
#9
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
Thanks again for your comments. The air rifle is a $135 Chinese one
imported by Compasseco--it shoots extremely well but needs some refinement. This is the only model the importer doesn't sell extra piston sets and springs for. The original machining on the piston assembly wasn't quite right and gouged the piston sleeve when fired. The sleeve then roughed up the plastic piston creating a sealing problem--(a plastic piston sits on a metal assembly.) It still shoots fine (dime sized groups at 35-40 yds) but the cronograph says the exit pellet velocity has fallen to around 815 fps--down from 1100 fps. My plan was to hone out the sleeve and then replace the plastic piston with a tight fitting nylon one. Tut |
#11
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
Jeff
Your car wheel piston cup may work. Thanks Tut |
#12
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
|
#13
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
Nick--Thanks for the PA info....
Trevor--some good ideas in your post. Jim Maccuri actually made the main spring for the rifle. What would your recommend for button material? Thanks again everyone Tut |
#14
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
|
#15
Posted to rec.crafts.metalworking
|
|||
|
|||
Lapping nylon
Trevor--
Thanks I'll check him out. Best Wishes Tut |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
softening nylon 6/6 | Metalworking | |||
Flat Lapping | Metalworking | |||
Nylon Carpets | UK diy | |||
Can I dye nylon? | UK diy | |||
simi off topic nylon gear with broken tooth in paper shredder | Metalworking |