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. That?s 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?