Shrink-fit Tooling

[jakemestre]

Hello everyone,
I just finished working on a 3" TTS face-mill (post to come) and I had a hell of a time cutting the small pockets for the APKT 1003 inserts. Because all barriers have been broken for making my own tools(really I'm a broke college student) I've heard about shrinkfit tooling and thought that would have been exceptionally handy. The problem is: I have little if no knowledge on the subject of shrink-fit tooling.
I'm not even sure if I'm asking the right questions but:
1) What sort of steel should be used for exact expansion and contraction?
2) Or is there some sort of trick to get steel to expand and contract exactly the same way.
3) Are there any other considerations I must make before diving into such a project?

I'd really love to have less than .0005 run-out but I'm not sure how to achieve it. Oh, and it will definitely be TTS compatible. Thanks for any insight.

Jake Mestre
University of Nevada Reno

[Freddy Bastard]

I've done many TTS shrink fit holders. I did them in stainless.

Here's how I did it:
1-start with a 1-1/2 stainless shaft.

2-on a lathe, make the 3/4" shank and the TTS shape (with the groove, ...) the fit in the spindle end, OR buy the TTS machinable blank.

3-on the lathe, make the shape of the other side of your holder. ie: for my 3/16" shrink fit holder, I started with 1" and taper it down to 1/2".

4-Put your holder in the spindle of your Tormach and do a reverse lathe(lathe on mill). If you make a search on this forum, you'll find some info on this. You'll drill a hole in your holder then finish it with a boring bar. I've done 1/8" shrink fit holder with a micro boring bar with no more than .0005" run out. That's the hardest part...

[danimal24]

How do you shrink fit the toolholders on your tools? Do you use a commercial tooling station or have you made some sort of fixture with an induction coil? Thanks

[307startup]

How do you shrink fit the toolholders on your tools? Do you use a commercial tooling station or have you made some sort of fixture with an induction coil? Thanks

I would imagine that a bearing heater would work quite satisfactorily for this...

[Magnum164]

ok, I have to ask as I am not understanding what a shrink-fit holder is. Is this just a different term for a standard tool type holder?

[jakemestre]

ok, I have to ask as I am not understanding what a shrink-fit holder is. Is this just a different term for a standard tool type holder?

From my understanding, and anybody please correct me if I'm wrong, shrink fit is basically a tool holder that grips the tool via friction. The hole for the tool is slightly smaller than the shank of the tool and when the holder is heated up the hole expands to allow the tool to be inserted; The holder then cools and shrinks to hold the tool quite securely. Do a quick web search for more info and photos. Shrink fit is usually used to get a tool into very tight locations where stick-out is a major problem.
Jake Mestre

[MichaelHenry]

How do you remove the tool, once it has been shrunk fit into position?

[Magnum164]

From my understanding, and anybody please correct me if I'm wrong, shrink fit is basically a tool holder that grips the tool via friction. The hole for the tool is slightly smaller than the shank of the tool and when the holder is heated up the hole expands to allow the tool to be inserted; The holder then cools and shrinks to hold the tool quite securely. Do a quick web search for more info and photos. Shrink fit is usually used to get a tool into very tight locations where stick-out is a major problem.
Jake Mestre

Yes, but I don't see how the process is cheaper. I found the same questions when searching. Once heated you would need to apply an even pressure around the tool to make sure alignment stays. Guess I just don't see the advantage if you don't have something to heat/seat the tool for a small home shop.

[Freddy Bastard]

To shrink fit, I just use a torch (propane probably work). I've not tryed it with a gun heater. If you want a "more uniform" heating, you can put your holder on the lathe and make it turn while you heat it.

Yes shrink fit is cheap to do , but it's a lot more accurate for a DIY holder since there's no bolt that push the tool offset. And yes, you can make it long and small to access difficult to deep features.

[pete from TN]

This is an interesting thread and I thought that this would be beyond the realm of the home shop machinist. Could you post some pics and maybe some build pics of your shrink fit toolholders. I like the idea of the shrink fit. What do you machine the holders to tolerance wise for the shrink fit to work correctly is it -.001" I would imagine this must be a very precise fit for it to properly grip the tool and function properly. Too small and you'll never get the tool in and too large and you will never get it to grip tight enough no? Peace

Pete

[Freddy Bastard]

I'll try to do something for your guys, somewhere in the next week.

[Magnum164]

Yes shrink fit is cheap to do , but it's a lot more accurate for a DIY holder since there's no bolt that push the tool offset. And yes, you can make it long and small to access difficult to deep features.

I saw thinking more or less for collets, like the TTS system. I have some holders with the bolt on the side but do not use them same with drill chucks on the CNC.. Hate them..

But interesting topic nonetheless.