It’s the little things …

that annoy me. One of those has been the many different screws on my lathe tool holders. Three manufactures cloning an Aloris part (they even copy each others part number) but the screws are different on each brand (also the SHARS set screws are really cheesy). What up with that? Other than that, all three holders work fine for me.
So, I decided to do something about the SHARS screws and try to make socket head cap screws. Two new things for me are cutting metric threads and broaching a hex socket.

new screws

My screw, off the self ¼x20 cap screw, SHARS set screws

My lathe is imperial; to cut metric threads, you have to switch out a couple of gears, and important! don’t disengage the lead screw while cutting a thread. This means take a cut, reverse, repeat vs the more “normal” method of engage lead screw, take a cut, disengage, wind the carriage back, repeat. In the normal method, things happen pretty fast, as fast as driving a screw with a drill wide open. You get used to it: engage when the dial hits “1”, disengage in that 1/8″ gap where the thread ends, back the bit out, back up, repeat. With the lead screw always engaged and no brake or 3 phase reverse, it’s a yawner (it may take up to ten passes to cut the thread). Worse, all that mass doesn’t just stop when you switch off the power and I rammed the bit into screw shoulder a couple of times. Lucky me the insert has/had three edges. Way worse was the time I hit reverse too soon and the motor stayed in forward (single phase motors do that), and plowed the bit into the collect. Not a happy camper.

Now you might be wondering “why not just run down the hardware store and buy something?”. Because a M8 cap screw takes a 6mm key, the holders I have take 4mm, 5mm and 3/16″. M8 set screws take a 4mm hex (as on SHARS) but the no-name holders have M10 set screws (5mm hex) and the PhaseII have M10 set screws with a 3/16″ hex. So, just to add to the weirdness, I’m going to make M8 screws with a 3/16″ hex (I like the wrench I have).

broachedThe broach. I’ve seen them but really don’t have a clue. So I took a piece of 1/4″ O-1 drill rod and milled some flats and hardened it. I didn’t temper, wanted to see what would happen (it broke, then I tempered and reground the face). I drilled a 3/16″ hole and pressed in the broach (both on the lathe). Attempted to anyway; even though pretty much only the corners are cutting, had lots of oil, it takes some force. And, since I didn’t add back relief, the broach broachingdidn’t want to back out either. What I wound up doing was starting the broach on the lathe, then putting the screw in the vise, tapping the broach home and back to the lathe to back it out (using the drill chuck in the tail stock with everything as tight as I could make them).
I thought about use the mill as a press but I was having problems with the broach cocking as it went in, didn’t want to make an alignment jig and using a hammer was pretty controllable.

To finish up, I heat treated them (they are made from O-1). Just because. The video shows that. After fishing them out of the veggie oil, I baked them at 500°F still soaked in oil to both temper and leave a black finish.

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