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

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[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.

[sburck]

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

I was wondering the same thing...

[Andre' B]

Normally you heat up the holder.
Pull the old tool out.
And put the new tool in.

Heat shrink works best with carbide tools because of the difference in expansion rates.
With high speed tooling it can still work but you are depending more on being able to heat the holder up faster then the tool heats up.

[Upnorth4]

Normally you heat up the holder.
Pull the old tool out.
And put the new tool in.

Heat shrink works best with carbide tools because of the difference in expansion rates.
With high speed tooling it can still work but you are depending more on being able to heat the holder up faster then the tool heats up.

This hits the nail on the head. The trick to removal is fast heat.
I’m a millwright and often deal with shrink fit hubs and shafts. If the part with the hole can be heated fast enough then the shaft comes out no problem, heat it slowly and you end up with the same amount of “interference” just hotter. A rose bud on an oxy acetalyne torch would be good, but I don’t want to spend the $$ and don’t want that in a home shop.
I saw some small induction heaters on Amazon, I think these would be perfect. I doubt a bearing heater would work because the bearing has to have a bar slid through it and then becomes part of the induction circuit.
A small hole drilled through the “seat and shaft” of the holder might help to drive the tool out, to though anything smaller than 1/4” and that may be hard.
I agree that with carbide you get a leg up on the heating, slower expansion of the tool.
The hard part of this would be cutting the hole in the holder. As the size decreases the accuracy become more important and much harder to hit.

My plan is to use and “undersize” reamer from Shars and do up a couple of holder for 1/8”, 3/16”, 1/4” and 1/2”

I found great support for using my G0704 as a lathe on this forum. The holder are not hard to make, fingers crossed that shrinking the tools in works.

[kstrauss]

I've wondered if one of the low cost induction heaters (https://www.banggood.com/ZVS-1800W-1...p-1235621.html or https://www.banggood.com/Low-ZVS-12-...p-1038472.html) would work for heating the holder. They are cheap but you need a husky power supply or perhaps a couple of car batteries.

I'm about 100km east of Toronto; where are you?

[Upnorth4]

I've wondered if one of the low cost induction heaters (https://www.banggood.com/ZVS-1800W-1...p-1235621.html or https://www.banggood.com/Low-ZVS-12-...p-1038472.html) would work for heating the holder. They are cheap but you need a husky power supply or perhaps a couple of car batteries.

I'm about 100km east of Toronto; where are you?

Car batteries would be a great solution, I think.
Heads up to anyone using a power supply for induction heaters:
A switching power supply ramps up slowly, this will blow up the mosfets on the heater. I have read that if you do use a power supply put a switch in the circuit directly before the heater and check that the voltage is there before turning on the switch.
Two car batteries in series should do it, the heater wouldn’t be on for long to heat a small holder.

BTW I am in Nanaimo, I created the user name “Upnorth” when I was living in Ft. McMurray

[AUSTINMACHINING]

The commercial shrink fit machines ive seen are induction heaters ~5k. They are used for several reasons.
Low runout. Prevent tool pullout under heavy roughing, and the holders are smooth (no wrench flats etc) to throw coolant when spinning 24k rpms. And obviously well balanced for high rpm.