Thread: Tight Tolerance 0.0629-0.0630" hole in Titanium

Originally Posted by vettepicking

What machine shop doesnt have a lathe??? i have 3 (two at my house) c'mon now. how do you make fixtures? Your holding .0001" in a shop with no manual machines. do you have a sign that says "NO SHAFT WORK DONE HERE" ..

LOL. I should put one up. I do everything on my sloppy Fadal VMC. Usually my prints are +/-0.005" or +/-0.010". When I took this job on, I was told I could do 0.0628-0.0629" w/a reamer. Apparently, I can't.

I just got word from my friend that he'll take care of the hole diameter, I just need to drill an 0.0625" hole. .... I wish I would've known sooner!

Matt

Next time just ask the Engineer if he would like it on the high or the low off the Tol. !

Originally Posted by oceanpout

Next time just ask the Engineer if he would like it on the high or the low off the Tol. !

Better yet,explain to the engineers boss that for every tenth of tolerance they open up the price goes down by a factor of 10

Originally Posted by dksoba

I just got word from my friend that he'll take care of the hole diameter, I just need to drill an 0.0625" hole. .... I wish I would've known sooner!

Matt

Out of curiosity, what does the print state for tolerance on the hole position?

Originally Posted by Radar987

Out of curiosity, what does the print state for tolerance on the hole position?

Print states 0.005" regardless of feature size, total tolerance. The hole is referenced to the side of the part (where the datum is).

Update:

The shop that subcontracted the work to me said it's my responsibility to get the hole size correct (probably since they weren't able to hold the tolerance on that hole on their sister parts). I did what Steve said to do in post 14 (Tight Tolerance 0.0629-0.0630" hole in Titanium). Steve: I owe you a beer, lunch, or something!

My exact procedure:

1. Learn to use my CNC mill (Fadal 4020) as a lathe. This worked out great, but it did take some getting used to.
2. Turn down aluminum rod (1/2"), since I wasn't having any luck with 1/8" brass and I didn't have any other barstock around, to 0.045".
3. Pinch end of the rod in the vise, until just over 0.0630".
4. Using a micrometer, measure the end, and use 1000 grit sandpaper to get the aluminum rod down to .0627-0.0629". (Now it's called a lap).
5. Use my mill to push/pull the lap down/up for 10 cycles, at 1000 rpm, and a feedrate of 10 ipm. I just guessed at those numbers. Before this operation, the hole was coated with a mixture of Dico premium buffing compound and Rapid Tap cutting fluid. I put it in a syringe and filled the hole.
6. Clean the hole using isopropyl alcohol injected from a syringe.
7. Evaporate/blow out any left over isopropyl alcohol using compressed air.
8. Inspect hole using gage pin. If still too small, go back to step 3. Repeat 3-8 until hole is in tolerance. It took about 6-8 cycles to get it in tolerance. The material is expensive and takes a long time to get, I don't have any spares, so I don't mind that it takes 6-8 cycles. It takes about 30-45 mins to get the hole to the right diameter.

I noticed that my lap kept getting smaller after each cycle. I'm wondering if a brass lap would work better?

Steve: where do you get diamond lapping compound (#10)?

Thanks for everyone's help!

Matt

I'm glad it worked out for you Matt. The last time I got it was at McMaster Carr. However, I've had syringes for a few different grits for years. Yaaa...blind hole laps do wear fast, even brass ones. Next time I'm in San Diego I'll get that lunch and beer from you!

Steve