Screwcutting on the Denham Junior mk11 lathe

[Roger ClarkParticipant @rogerclark]

I need to make a couple of chuck backplates but really not sure how to approach this as the leadscrew has no counter connected to it.

What the lathe does have though is a forward and reverse on the leadscrew so would this keep the thread in sinc? Otherwise how can I do this?

Thanks

Roger

[Roger ClarkParticipant @rogerclark]

Need to cut 6tpi internal thread

[JasonBModerator @jasonb]

Just leave the half nuts engaged.

If the forward/reverse is by gears then don't use as you will probably not mesh the same when you change back to moving forwards, just wind the spindle back the few turns by hand

Edited By JasonB on 03/01/2022 16:45:21

[Howard LewisParticipant @howardlewis46836]

As Jason says, do not, under any circumstances disengage the drive ANYWHERE between the Mandrel and the Leadscrew.

And when you withdraw the tool after each cut, and then reverse the lathe (Motor ) to take the Saddle back beyond the start of the cut, take it back far enough, that when you start to run Forwards again, all the backlash between the gears, half nuts and Leadscrew is taken out.

(If it needs saying, when resetting the Cross Slide for the next cut, take out the backlash in that as well. )

Failure to take out backlash means that any hope of accuracy disappears.

Rightly, or wrongly, whether screwcutting Imperial or Metric threads, I always leave the half nuts engaged and back off the tool. As an aid, the tool is carried in a retractable tool holder (Martin Cleeve type in my case, for external threads  ) which avoids disturbing the Cross Slide setting, except to increase the depth of cut ,

Howard

Edited By Howard Lewis on 03/01/2022 18:14:26

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