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Collets to hold drill bits

Modelman

Titanium
Joined
Sep 12, 2007
Location
Northern Illinois
One of the things missing from this discussion is the style of the collet. The collets that people are saying don't have much range, R-8, 5-C, etc. are only split from one end. If you think about it, as the collet collapses, it has to bend, and the sides of the internal hole become non-parallel. This isn't good for gripping the tool, and excessive bending will "spring" the collet and it won't work well thereafter.

There are other families of collets, DA, ER, TG, that are split alternately from both ends. This keeps the sides of the internal hole parallel as they close, and these have greater range. I have a set of ER-40 collets that go from 3mm to 26mm in 1mm increments. We are an inch measurement shop, but this set has the ability to grip any tool between 1/8" and 1" diameter, which is handy for tools with odd size shanks like drills and reamers.

Dennis
 

dsergison

Diamond
Joined
Oct 23, 2003
Location
East Peoria, IL, USA
come on people. we are talking about holding a drill in a bridgeport collet, hand fed.

stop arguing about the ideal/theoretical capabilities of collets, cnc equipemnt, automatic collet closers, reliable clamp up, etc....

you can darn well abuse an r8 or a 5c collet far outside it's intended range, enough to drill a little hole a few times.
 

moregrip1

Plastic
Joined
Apr 15, 2022
Thank you for the info posted. I'm in a similar situation and would like to run 21/64 drill bit in a 11/32 R8 collet. I have some .005 shim stock I can wrap around the drill but it would still be a bit smaller....by my calculations about .0057. thoughts on this working? thanks!
 

guythatbrews

Hot Rolled
Joined
Dec 14, 2017
Location
MO, USA
Thank you for the info posted. I'm in a similar situation and would like to run 21/64 drill bit in a 11/32 R8 collet. I have some .005 shim stock I can wrap around the drill but it would still be a bit smaller....by my calculations about .0057. thoughts on this working? thanks!

I would not do it but if needs must try it. If you just have to get by it might work but IMO never a good idea.

Maybe an ER collet chuck with 3/4 shank in an R8 collet. Not much overhang. Or you can turn the shank of the drill down to 11/32. Both better options.
 

CITIZEN F16

Titanium
Joined
May 2, 2021
It all depends on what you are trying to do. It will probably be hard to keep the runout down, but you might get lucky.
If you are just drilling a wide open tolerance shallow hole you should have no issues.
 

moregrip1

Plastic
Joined
Apr 15, 2022
I'm drilling a pilot hole through aluminum. Also, very new to milling in general and have only done a few very easy projects thus far. Running a G0704 with import tooling (R8 collets) for now. I went ahead and ordered some reduced shank 21/64 drill bits and appropriate collet.
 

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
If you have a lathe, you can make a reducing sleeve to adapt a drill bit to fit a larger collet. Start with a piece of bar stock the size of the collet and drill the needed hole through it. Then put a lengthwise slit in it.

Larry[/QUOTE]

And that sleeve does not have to be fiddly narrow wall. I would make it say 1/2" outer diameter.
Bill D.
 

TeachMePlease

Diamond
Joined
Feb 11, 2014
Location
FL
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Mcgyver

Diamond
Joined
Aug 5, 2005
Location
Toronto
If I had to hold an undersized drill in a collet, I'd try a bit of brass shim of the right thickness as a sleeve around the drill

TeachMe, I thought the issue was not enough daylight so no room for a chuck?
 

mhajicek

Titanium
Joined
May 11, 2017
Location
Minneapolis, MN, USA
Collets have a range. Just use the next size up collet, within the range, and you're good. I do this all the time with ER collets, and they hold securely, on center, and don't slip. No amateurish dinking around with shimstock.
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
What you can do is put the collet in place, then stick the drill bit in the hole. Tighten the collet until it seems pretty much tight. Then, let go of the drill bit. If it falls out, you can't use that collet for that drill bit. If it stays in there, and especially if you try to wiggle it a little and it doesn't wiggle at all, you are ready to start a-drillin'.
 

projectnut

Stainless
Joined
Mar 4, 2006
Location
Wisconsin
According to Hardinge the gripping range of their standard 5C collets is +.015" to -.001". I have an older set in 1/64 increments, and that seems to be the normal working range. I'm sure you can force them to hold something slightly larger, but not very much smaller. Personally, I wouldn't take the chance of ruining a $50.00 collet when you could easily modify a $3.00 drill or spend a couple bucks on a screw machine drill.

As an FYI I also have a set of Shars 5C collets. They have the same clamping range as the Hardinge. However, they're less than $10.00 a copy. Still a modified jobber length drill or a screw machine drill would be my choice rather than abusing a collet.
 








 
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