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+/-.0001 Dia Hole in Titanium giving me trouble

Cha0ticBliss

Plastic
Joined
Jan 18, 2019
Working on 1 piece order for a titanium piece that calls for a .1249 +/-.0001 x .600 deep thru hole. Material is 6AL-4V titanium hardened to 42RC. I have been going with .118 start hole. Tried a few different reamers but all of them have been cutting oversize. Started at 1400RPM 4.2IPM. Backed down to 700RPM hoping to shrink the hole size a bit. Also increased the feed to 10IPM without seeing it move more than .0001".

My next ideas are to try a some different reamers that I ordered and/or stone a reamer to bring hole down to size. Might have a go at pushing a ball bearing through the hole to smooth out the high spots if I get a hole that is a hair undersize. Also going to use MolyD/cutting oil instead of the coolant I was using previously.

Moving forward if the customer throws production qty my way, I will probably look into buying a roller burnisher but would prefer to avoid that for this 1pc if possible to get by without.

This is unfamiliar territory for me... anyone have any ideas on additional tips/tricks worth trying?
 
Is getting a boring head an option. We hold that tolerance with an $800 criterion bore head on a daily basis.
 
If the hole in question was, say .116 +-.0001 or somesuch I would be busily pondering how to get it done, but when a hole sounds so much like a light press fit for a 1/8 dowel pin, man I always ask the question

As a practical matter reamers react to conditions quite a bit. different oil or no lube will create slightly different sizes.

Try reaming x number of random holes with the reamer to get it not quite so sharp.

At the end of the day, get the one piece right and when quoting production qty give a price for as drawn and one for light press for 1/8 dowel pin.....
 
50 microinch TIR in a half inch deep 1/8 inch hole? What kind of boring bar is used there?

I suppose I am exaggerating a little.

Right now we are running a Ø.1877 ±.0001" bore thru (depth of about .563"), and we keep it inline to .001" with another same size bore a distance of 1.83" away.

We are doing this with a criterion bore head, and a custom made solid carbide bore bar.

I would have to look and see what the feed is, but rpm is somewhere around 375 if memory is correct.
 
Stone a reamer down to the size you need.

Roller burnisher finished hole size will be driven by the starting hole size, so you'll still have sizing issues based on reamer size. Burnishers provide a smooth and pretty surface.
 
You can screw around with reamers and finally get one to make the hole size you want but it won't do it consistently. If you're looking to do it on a production basis IMO honing is the only way. On your test part drilling .118 and finishing at .125 is way too much material for your reamer. Try drilling about .123.
How are you going to check +-.0001? It's not going to be with pins.
 
Designers are morons, there is nothing that needs a tenth tolerance. Just have 5 or six different guys measure it until you get the value you want. If that don't work, turn the heat up or down in the shop until it works.
 
Lapping for a new hand without bellmouthing? Thats only a little less dicy than a reamer unless you happen to be just .00005 small. I'd either bore it or ream it. I'd want a gage with more than 2 in-tolerances graduations no matter what the method.

Any other stupid requirements on the hole like errors of form limited to 1/2 size tolerance, or tenths true position to multiple features?
 








 
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