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ER Collet Holder- Material? Hardening?

UptownSport

Cast Iron
Joined
Jul 25, 2012
Location
Cable WI
I want an ER collet holder. I watched a few vids and read this man's helpful post.

I'm planning to use 4140 annealed unless you think better. I'm scared of turning 'Prehard'

Hardening- Is it necessary? I've got no clue here.

Any other advice appreciated.

Thanks in advance

also, a question on the bore.

The diagram shows a backspace (left most part of 'E")- what is this used for? I was leaning towards putting collet next to spindle with only a small space.
Is it for allowing collet with an undersized piece to retreat further?
My calculation is that the space is .35" 9.1mm. seems a little deep for that

How deep does this space actually need to be?
 

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I would think you want something as hard as the collet itself, or you will score up the taper when you tighten the collet nut. Pre hard 4140 will only be 28 -32. My bet is the collets ares mid 50 R/C, probably S-7. I would use A-2 and hard turn or grind the taper and shank after heat treat so the run true.
 
I've made them out of our EN24T (hardened and tempered) which I think is your 4340 HT .........on a run of the mill small engine lathe one of which - ER20 has run intermittently in a 1 man job shop for 25 plus years - with no damage or loss of concentricity (that particular spindle's taper being machined in it's own bearings.)
 
OP, If your concern that it may be difficult for you to machine the prehard because of its hardness, I would comment that it is quite common practice to mill, turn, and thread 4140 Prehard. I have made may parts from it and find it not at all difficult to machine using sharp carbide or HSS tools. Two days ago I made 10 5/8-11 heavy flange nuts from it for use as setup hardware on a large Lucas horizontal. It machines very nicely.

Here is a photo of the PH nut on the left and the commercial Rc10 nut on the right. I made the nuts as the commercial ones don’t hold up over time to the heavy use they get in the commercial shop I do some maintenance work in.

4B90E0C8-FB46-4793-A63D-C7F5774EE5DA.jpg

Here is a brief vid of me power tapping it
Tapping 4140 Rc32. 5/8-11 - YouTube

So, go ahead and make up your collet. It will hold up a long time and the PH is easy to machine and naturally is inclined to take a nice finish. If you wear it out, then you can go the hardening and grinding route.

Denis
 
Add another to the list. I made a small 5C collet chuck almost 15 years ago from 4140 Q&T (same as pre-hard). It was used pretty frequently though not every day and the only indication of wear is a little shinier finish where the angled part of the collet bears. I would not make one out of 4140 annealed (usually about 10Rc). Pre-hard is good, hardened to 50Rc is even better. For home shop use pre-hard will probably be more than adequate.
 








 
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