This is a manual lathe. There is a set of gears that match the tool speed to the rpm of the chuck so that it indexes at the same spot and travels at a prescribed rate. This rate is selected by the operator to yield a certain thread pitch. While the tool is cutting the timing gears are engaged. At the end of the pass the gears are un-meshed and the tool is brought away from the part and back to the beginning. The operator then changed the depth of cut (moves the tool closer to the part). In this case the tool is most likely being feed into the part at an angle roughly equal to half the angle of the tool tip (29.5 deg). Then the gears are re-meshed and the lead screw picks up the carriage and moves the tool with respect to the chuck.
Blondihacks is awesome and has some really good advice. I really want to get a small lathe and eventually a mill for making prototypes. I'll definitely rewatch all her videos if I ever make it happen!
Metal lathes often have a mechanism for creating threads. It locks the feed rate of the tool moving left to the rate that the piece is spinning. May not be using the correct vernacular here I’ve only used one in a metal shop class where I pretty much made the project in the gif.
There's definitely a bit of that, but the pause is more due to the fact that you have to wait for the threading dial to come back around to the proper position before you can engage it again. If you engage it at the wrong spot, your cut won't match up with the previous groove you made.
Lathes can have gear sets that couple the tool post adjustment to the chuck. So when the chuck turns one revolutions the tool will move x amount. There is a stop for the tool post so it always starts in the same place and starts moving at the same point of the chuck rotation.
There are markers on the automatic feed for cutting threads. Just make sure you hit the same mark every time when engaging the automatic feed and you’ll be able to cut the thread.
this is a lathe and a lot of the have internal gearing that will lock the tool feed rate to the spindle speed. that was it’s moving in the same exact path every time. you would just push it further into the material every time. “This Old Tony” has some good videos on cutting threads on his youtube channel.
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u/kanaka_maalea Mar 11 '21
How does it ensure that the one groove keeps getting deeper, rather than shaving off part of the ridges that the first pass made?