The Shop > Tools

Rear parting toolpost

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awemawson:
I fitted a rear tool post on my Colchester Master 2500 for parting off many years ago. The lathe is rigid and pretty solid, but I confess that since I acquired an inserted tip carbide Sandvik parting tool set up I never use the rear tool post  :palm:

PekkaNF:
For a light weight chinese lathe parting off was never that great. I have heard about the tool flex.

1. I replaced the top slide with a foot for oversized QCTP

2. I made a parting off tool with a jack screw support. bit like crank shaft turning tool.

These helped a lot, but I noticed that the head stock mounting to bed casting is not too rigid. Maybe I should access that next....and tailstock could have a longer stroke as well...

appletree:
Good thinking out of the box

PekkaNF:
Yeah, started thinking how much support I need to resist bending and turning. Actually pretty much on cantilever beam. Why not to put support under the tip, a little doodling on the paper, then 1:1 scale drawing on paper and see how to clear the rotating part in most of the use cases. Last step was the height control. I realized that I don't need stop on QC tool holder in the usual manner, because there must be adjustment on the jack screw: Threaded the holder body and put there nut and standard hex socket screw.

Then I needed to figure how to hold the insert blade securely in the holder. The blade had rounded edges, one dove tail curret had just the perfect rounding (and bevel) to mach. Hold down is simple, Just a cross bar and set screw top of it to press it down. I considered a key or pin to draw it inside, but all fits were hard push fits, I haven't detected there flex.

After the initial idea it was one evening of drawing and another in making. I didn't finish it at all, because I was convinced that it was a prototype, but to my surprise it worked! I also reasoned that the blade could be deeper to allow cutting of larger diameter, but the lathe does not seem to rigid enough for any larger on steel and that was the blade I had in hand.

jackary:
I made this vertical parting tool to try to avoid the lack of rigidity and flex of either a front or rear parting tool due to the cantilevered projection of the cutting tool. It works well. A front mounted version could be made similar to your supported tool.



Alan

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