Good material choice for B52 collets

Gobo · Oct 26, 2021

Because of the crazy lead time and costs for the collets (B52) we use on our tube bender, the choice was made to make our own. What we now have are Rc33, so we would like to make the collets out of a material with comparable hardness. What would be a good choice of material for this project? I was thinking 4140. We will probably purchase them in the future, but lead time is critical.

sfriedberg · Oct 26, 2021

4140PHT or 4142PHT should be in that hardness range, and would probably be a fine material. Pacific Machinery and Tool Steel cuts from plate (well, bar in the case of 4142PHT) and probably has a table of small drops on the floor right now.

AlfaGTA · Oct 26, 2021

I would go with ETD 150 .
Stronger and better hardness right form the mill..No post heat treatment machine and in in service...
Easily available even from McMaster-Carr
Cheers Ross

Gobo · Oct 27, 2021

We machine ETD 150 but it is not Rc33. It machines quite nicely. We are somewhat concerned about the finished part "springing" when we EDM the slots in the collet. How much of a concern is that with ETD 150?

sfriedberg · Oct 27, 2021

I'd recommend that you leave a "ring" of extra material on the nose of the collet until it has been bored and slit. That prevents any motion and provides rigidity during those operations. Then grind or machine off the ring as the last operation. This was traditional for shop-made collets (and maybe OEM collets, but I don't know) which had to go through heat treatment, and would probably provide some value even when you use pre-hard material.

jonathan.bougie-lauzon@st · Mar 21, 2023

sfriedberg said:
I'd recommend that you leave a "ring" of extra material on the nose of the collet until it has been bored and slit. That prevents any motion and provides rigidity during those operations. Then grind or machine off the ring as the last operation. This was traditional for shop-made collets (and maybe OEM collets, but I don't know) which had to go through heat treatment, and would probably provide some value even when you use pre-hard material.

Nice tip about that extra "ring" of material. Thanks. We will make a special collet for a "Tug Gun" tool used to remove valve seats in engine heads.
I will try 4340 HT for this application. 4140 HT would be a good choice also, very similar, though a bit less tough when I check on this nice comparison site: https://www.makeitfrom.com/compare/Normalized-4140-Cr-Mo-Steel/Normalized-4340-Ni-Cr-Mo-Steel

Here is an image of the collet in question:

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Good material choice for B52 collets

Gobo

Titanium

sfriedberg

Diamond

AlfaGTA

Diamond

Gobo

Titanium

sfriedberg

Diamond

jonathan.bougie-lauzon@st

Plastic

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