Press Fit Bushing Knurl Design for Nylon
Press Fit Bushing Knurl Design for Nylon
(OP)
I am designing a press fit bushing to fit into a nylon part. The bushing is actually a compression limiter so that a bolt can be torqued down over the part (and not compress the nylon). I have specified a medium diamond knurl pattern, based on seeing similar press-in inserts, but I don't really know what is the appropriate knurling detail (size, TPI, spec?) to use. We are going to make a prototype and try it, but I want to start with something reasonable.
Thanks,
Jeff
Thanks,
Jeff






RE: Press Fit Bushing Knurl Design for Nylon
imho I would suggest the best route would be to talk to suppliers of inserts. You will find that they will be the cheapest and have the capability to design exactly what you need, and indeed may have an "off the shelf" product for you!
Rgds
Harry
RE: Press Fit Bushing Knurl Design for Nylon
Jeff
RE: Press Fit Bushing Knurl Design for Nylon
In that case, I would suggest just a medium diamond knurl - if it's a compression limiter then I assume the insert will not fall out in use as it is retained and there is no force pushing/pulling it out. Keep the interference fit as small as possible to prevent stress raising around the insert (although unfilled nylon is pretty tough). If you can mould the insert in - then all you need is hex bar with a groove in the OD down to the across flats size.
btw, avoid zinc plating of inserts with nylon - especially if zinc can corrode - nylon does not like zinc salts, which can cause environmental stress cracking.
Rgds
Harry
RE: Press Fit Bushing Knurl Design for Nylon
I've been asked "which medium diamond knurl - give me a TPI" I don't know how many TPI to specify for a fit.
As for the zinc plating and nylon - we were planning on using a zinc/nickel plating to prevent corrosion. Is that a bad thing too?
Thanks,
Jeff
RE: Press Fit Bushing Knurl Design for Nylon
Under normal circumstances (ie no zinc or chlorine nor acids) nylon has exceptional stress crack resistance.
Unless there is something we don't know about your application, it sounds to easy and the knurling will not be at all critical.
Why not get a sample of an off the shelf insert that is the wrong size, but knurled, and copy the knurling.
Regards
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RE: Press Fit Bushing Knurl Design for Nylon
I'd use a straight knurl, or push the inserts in with a big 'ol soldering iron.
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
RE: Press Fit Bushing Knurl Design for Nylon
Do you know of any corrosion resistant coatings that can exist in contact with nylon parts? Everything I am aware of contains Zinc!
Thanks,
Jeff
RE: Press Fit Bushing Knurl Design for Nylon
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.