[How do I?] Grind A Drill To Drill Smaller..?

EmilioG said:
I need to drill a 17/32" (.5313") through in 1/4" aluminum. The hole needs to be a few thou under 17/32".
Closer to .5300 or .5210"?
Is there a way to touch up the drill on a belt sander so it will drill a smaller hole?
I don't have time to bore the hole and there are no under size 17/32" reamers.
Can this be done? I was thinking that maybe the flutes on the sides of the drills cutting edges can be touched on the belt sander? I know most drills cut over size, so..?
Thanks
Click to expand...
Hold on one minute. Having been faced with this problem many a time I'll walk you through it. First, if you want to remove a little material from the side of a drill you'll get a tighter hole O.K., but your drill is shot. You can't get a cylindrical surface stoning the flutes of a drill. MSC has a large assortment of special size reamers if you want to go that route. Best way , in my opinion, use heat. What your cutting is 1/4" thick, that's 1/2 a diameter deep. First open the hole to 1/2"or 33/64" diam. Heat the piece up with a heat gun or good hair dryer as hot as you can get it or, put it in the oven @ 425-450 deg. f. for a 1/2 hour. Have everything set up so you don't loose heat when getting ready to drill it. Slowly feed the drill in @ 250 - 300 rpm USING A WAX LUBRICANT on the drill flutes. You'll have a smooth finish and when it cools down to room temp. it should be .0015-.003 smaller then the diameter of the drill. Do a test piece first to check it out. Happy drilling.
 
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BillVern said:
Hold on one minute. Having been faced with this problem many a time I'll walk you through it. First, if you want to remove a little material from the side of a drill you'll get a tighter hole O.K., but your drill is shot. You can't get a cylindrical surface stoning the flutes of a drill. MSC has a large assortment of special size reamers if you want to go that route. Best way , in my opinion, use heat. What your cutting is 1/4" thick, that's 1/2 a diameter deep. First open the hole to 1/2"or 33/64" diam. Heat the piece up with a heat gun or good hair dryer as hot as you can get it or, put it in the oven @ 425-450 deg. f. for a 1/2 hour. Have everything set up so you don't loose heat when getting ready to drill it. Slowly feed the drill in @ 250 - 300 rpm USING A WAX LUBRICANT on the drill flutes. You'll have a smooth finish and when it cools down to room temp. it should be .0015-.003 smaller then the diameter of the drill. Do a test piece first to check it out. Happy drilling.
Click to expand...

That sounds really good. I will try it. I like the idea. You say you've done this, so there is a scientific principle at work here. Expanding the metal, drill and let it cool/shrink down.
The reamers are too large, there is no 17/32" under size, that I can find. I don't want to invest too much $$$ anyway. The finish is not important.

A 33/64" drill with un even cutting edges may work, then I could sand down to size...???
I may try that too.
I'll report back. Thanks
 
Try an adjustable reamer. Drill the hole one size smaller than 17/32. Set the reamer to just touch the sides of the smaller hole. Open the reamer a few thou. each time. Repeat till you have the desired size.

"Billy G"
 
If I can find an adjustable reamer at work, I try that too.
I'm not buying one for this one hole. :)
Thanks
 
No offense meant, but why don't you have the time to bore the hole? Seems it would be the easiest and least time-consuming option, over regrinding a drill, heating the work up in the oven, etc.....
 
OK, Done. I was given a vintage set of Cleveland expanding reamers at my job.
They don't use them anymore and it looks like only one was ever even used if at all.
I'm going to clean them up and oil them. They're sharp and they really work.

I was able to slowly cut my hole to size after drilling it open with a 33/64" drill on the BP mill. The reamer that's missing is the one I'm using, it's on my Starrett tap wrench. Thank you all. And by the way, I didn't bore the hole because I was given this set and I wanted to try it out and it was something that I could do on my lunch break.
I work very long hours for a proto type development company in NY. They've been around for 42 years and they have a lot of great old USA tools and machines as well as all new modern cnc and 3d printing machines. They let use anything we want. Thanks

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You lucky dog! That set if bought new is over $400!

Glad it worked out for you.
 
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