Re: turning hardened steel

Carl Bukowsky

I have to say you may not get results you are looking for by working the ER-40 collet chuck-to-spindle engagement last.  Ideal sequence is make the spindle threads first, then make the collet holder while mounted to the spindle.

Making a collet chuck in the reverse order, spindle threads last, you loose the concentricity relationship inherent in the single operation of creating the collet holder while it’s attached to the spindle.  

All your spindle-to-chuck concentricity you cut will be independent  to that of the collet block holder. Any small error in your chuck, and any error in centering the work piece in the chuck, will all be added into the spindle threads you cut. 

I just made an ER-40 collet chuck on my SB 9” from  2” piece of 4140 and it’s not that complicated.

You can make your own ER-40 nut if you don’t want to cut metric threads.  I went metric using some 3D printed change gears-my metric threads worked great with the ER-40 but I bought.  For the plans I bought a back issue Machinist’s Worshop (Feb/Mar 2015, Vol 28 No 1). Good Luck!  Carl

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On Oct 4, 2021, at 7:04 PM, William Nelson <wnnelson@...> wrote:

I'm thinking of making a ER40 chuck for my 10K. Because I don't want to set up to thread metric and bore the 8 degree internal taper (best ground, no grinder) I was thinking of using a ER40 hex block. I would have only one operation a internal 1.5"-8 thread of which I've done a bunch in aluminum and mild steel.. Now the problem is these blocks are hardened to 40-45 HRc. I'm not really sure how hard that is comparatively speaking. I have some 5C blocks which seem pretty hard. I'm sure I could use carbide to bore it out (not a lot of material as they are already bored) with no problem but I'm not sure how well the threading would go. I know I would need carbide for this too and besides the block itself would be my only expense. Has anyone had any experience doing a internal thread on hardened steel? I can not thread mill it. If nobody has tried this does it sound feasible to anyone? I'll be going over to my local machine tool shop (1/4 mile away) and ask them what they think too lots of knowledge with the guys who work there plus I can buy my carbide threader (Solid or insert?) there too. My only other "SMALL" problem would be getting it perfectly aligned which shouldn't take me much more than a day at most.  :(

Bill form Socal

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