Drilling Accurate Holes In Acetal

So maybe get an adjustable reamer? I bought a 1/2" ream and tried it without success. Of course, I am very new to this and could have been doing something wrong, it did seem to chatter quite a bit when I was reaming.

In case anyone is curious, I have attached a pic of what I'm making. I need to run 500 of these, so the fewer steps in the process the better, not sacrificing quality though.

Roller pic (337 x 600).gif
 
Could you not bore a length of Delrin, press the bushing in and then part off pieces? Seems like it would be faster.
 
That's worth trying. I will give that a shot.

Another idea I just came up with, the issue being the hole is only a little too big. I'm going to try a 12.5 mm drill bit, that measures .4921" maybe that will be enough of a difference to make the bearing hold better. The acetal should stretch that much I think.
 
If you are making 500 parts, ream them small, press in the bearing, buy a pin gauge for measurement, if any come up small toss them in the scrap and carry on.

Go-No go gauges are available from many sources including McMaster-Carr, just specify the go and no go dimensions http://www.mcmaster.com/#go/no-go-gauges/=14ddo6s

If you are buying the bearings there is no reason to think that the bearing manufacturer is any better at controlling diameters then you are, if the gauge will not pass through the free bearing before installation then toss it.
 
I would buy a 0.498 reamer for that job. If the reamer is chattering, slow the spindle speed down. The chatter will cause the reamer to cut oversize.
 
With the healthy wall thickness you have there on the Delrin. I would put about .015" interference between it and the sintered bushing. Ream it with a 31/64" reamer and call it good. Resultant hole size will probably leave a .008/.010" interference. Will not hurt a thing. The Delrin will give somewhat to the bushing. If it shrinks the ID of the bushing a little, run a adjustable guide bearing reamer thru the bore to size it. Ken
 
Uncle D, looks like you got lots of advice, but these two quotes are spot on for your issue. Make sure your tool is seated corrected to minimize run-out and a Reamer a couple thou short of final size should do the trick. As JimDawson quoted, a reamer likes to be feed and act as a "sliding" blade instead of boring type of operation. Helps hold your hole concentricity, if you are worried about that. Anyways, good luck with the application.
 
Just a quick addon:
I've done a handful of uhmw, acetel and delrin, holes like this tend to end up different sizes if the bit is warmed up, I've consigned to drilling holes small and then reaming or pressing the bushing/bearing in after freezing it
 
a trick to make the drill bit cut on size is to touch the outside of the cutting edge with a stone to round it over and make the outside of the drill cut to size instead of the cutting lips this will let the of the drill sixe the hole. sometimes the lips are uneven and the drill will offset from center and drill an oversize hole. use lots of coolant to avoid the overheating of the plastic. the plastic I have worked with did change the size greatly. bill another thing that you can use is a hougan bit. these drill accurate holes usually less than .001" oversize. bill
 
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