turning hardened steel

William Nelson

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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