On Tuesday, October 30, 2018 at 11:42:39 AM UTC-4, Bob La Londe wrote:
I've been wondering if shrink fit tool holders are single use.

You heat up the tool holder drop the tool in and let it cool. How do you
get the tool out when its worn out?

The reason I have been thinking about this is because I did a shrink fit a
while back on a large ring on a tool (not a machine tool) for a friend a
couple months ago. It worked fine, and I didn't care if it was permanent
because the tool was beyond its intended life anyway. He's been using the
tool everyday in his business. Its on its second life.

Now my success with that lead me to think about a toy I picked up a while
back and the poor success I've had with tool holding with drill bits in a
regular jacobs style chuck on the lathe. Particular 1/2 shank stuff. The
toy is a turret for the tail stock. I'd have to go look, but I think the
sockets on the turret are 5/8. The pieces are just held in with a set
screw. Seems that anything you put in it would have to have a flat machined
on it to have any chance of not spinning.

Now here is where the shrink fit comes. I have a part I make periodically
that is quite simple and it makes a few dollars. I make up to a dozen at a
time. Ideally if I was making hundred at a time I'd send it out to be CNC
turned. Best practice is spot drill, pilot drill, drill, turn, part off,
flip, drill, and then bore. Thats a lot of drill changing One drill bit
is 1/2 inch, and one is 5/8. The part is aluminum, though so a sharp bit
isn't too likely to spin. Aluminum isn't all I turn though.

My thought at first was to make set screw holders for a variety of bits to
go in the turret. Then I'd have to grind flats on all the drills. Yuck.
Then I thought about shrink fit. Then I'd only have to grind flats on the
tool holders. Might be a bit dicey for a 1/2" shank drill in a 5/8 diameter
holder though. LOL.

Of course I wondered if I could easily get a good enough fit that way to
prevent a dull tool spinning in the shrink fit holder. I can soak the
holders at close to 600F on the BBQ grill pretty easy. That would provide
about .0025 expansion for a 0.500 hole in steel (apx), but for say a 1/4
hole 0.00125 (apx). I don't have a practical way to cool the tool much
lower than 0F, so that's not going to gain much. I guess 100 under ambient
most of the year is something, but on a small tool only about .00025. I'm
using the rough approximation of .001 /1"/100F. I know not all steels
shrink or grow the same.

Anyway, even if the whole shrink fit tool holder thing works. How do you
get a broke tool out of the holder? Its not really material cost. A short
piece of steel isn't all that expensive. Its the time to make it all. I
suppose for a drill, unless I break it, its not all that big of a deal.
When it gets dull I walk it over to the grinder, resharpen it, and pick up
the rotary tool to touch up the split point. Probably not a big deal on the
lathe since I'd mostly be using drills.

They do this for mills and drills and other things in relatively expensive
shank tool holders for milling as well. Are those tool holders considered
disposable?

I'm not sure I follow all of your question, but tools are easily removed from heat-shrink holders. I've even seen them *drop* out in demonstrations.

The better heat-shrink systems work quickly enough that the holder is expanded before the tool shank has much chance to expand. So, unless you wait too long, you have plenty of clearance to remove the tool before the shank heats up and expands.

--
Ed Huntress