Originally posted by rcaffin
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And TG Tool wrote "My QCTP parting tool holder also has a slight angle at the bottom. It's there to help hold the tool inward against the vertical face. Since it's such a narrow ledge it's possible to have downward pressure from cutting force the blade to slide off."
My tool holders are 16mm "square", and I milled the grooves in the two new tool-posts 15mm deep. So there's just one millimetre of tool holder standing proud of the groove for me to sight on to line up parallel to the cross-slide's edge.
Since the insert's tip and the tool-post hold-down bolt(s) are not in line, the reaction to the advance of the cutter into the work will cause a rotational moment which has to be resisted by the friction caused by the clamping forces of the set screws holding the tool-holder in the groove, and by the friction of the bottom face of the tool-post on the compound or cross-slide. The former are three M8 set-screws, which will strongly resist any slippage. The latter is just one M10 stud holding down the smaller tool-post to the compound, or two M6(!) bolts holding the compound or the big tool-post to the cross-slide. The cross-slide does not, alas, have any tee-slots in it, just two crappy M6 captive bolts which I have now replaced with stronger ones, though the circular groove those bolts slide around in on the cross-slide (to enable the compound's angle to be varied) mean I can't make them any fatter. The lathe is an otherwise nice 10 x 20, but the cross-slide is definitely a sub-optimal design. (See https://www.machineryhouse.co.nz/L149).
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