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Davidhcnc
04-23-2009, 08:35 AM
Any exteriences of Press fit for very small diameter..5mm or 3/16" approximately as an alternative to screw threads?

Think of a cap nut and bolt or a tube rivet with a blind hole.

I know the thou per inch thing but does this hold sure for the small stuff?

And the follow on question...can a cnc lathe churn them out easily enough at the required fit...this is something I would have to outsource

And the follow on question to that...How would you know the pull out load so as to validate the alternative.


Thanks:)

airsmith282
04-23-2009, 08:47 AM
this may not answer your question but you need to make a proto type first that works then get the cnc chop to make the mesurments on there equipment, i made a few of them my self for some projects the fit was so tight that i needed a block of wood and let her have with the hammer untill it was at its proper debth that i wanted,, i was working on small stuff using stainless steel was really interesting. i wanted to thred it but fiquired what the hell i dont want it to come apart, so a tiny bit at a time will i was with in about 1 thou and hammered it in place there is likey nothing that is going to take it apart at least not with damage happening to something..

once you have one made then when they are cnc'd they should be all the same fit.. how many thou you leave for the press fitting will deterem how strong it is going to be, what that level is will have to be mesured some how to find out what it will take to take it apart..

if the press end of the shaft is to thin in OD then its not going to be strong enough for your peice to press fit onto, on the other side of the caps thick ness is to thin you will split it in half trying to press it in place as well..

i dont know if this info helps at all but hopefully gives you and idea if anything at all..

oldtiffie
04-23-2009, 09:12 AM
These are from worked examples in a previous thread but should provide your answers. Ignore the colours in your instance as the colours were for the previous example:


Use a H7/s6 (press) fit:
http://i200.photobucket.com/albums/aa294/oldtiffie/Tolerancing/Caliper_accuracy2.jpg


for 5 mm hole (H7): = 5.000 +0.012/-0.000 = 5.012/5.000mm

for 5mm shaft (s6): = 5.000 +0.027/+0.019 = 5.027/5.029mm

http://i200.photobucket.com/albums/aa294/oldtiffie/Tolerancing/Caliper_accuracy3.jpg


This was a worked example:
http://i200.photobucket.com/albums/aa294/oldtiffie/Tolerancing/Caliper_accuracy1.jpg

Davidhcnc
04-23-2009, 06:06 PM
Great and thanks men. That is a bit of digesting for me to do.


I'm afraid, smith , that the old fellow blew you right out of the water that time:D