Author Topic: Simplifying screw cutting.  (Read 2093 times)

Offline DavidA

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Simplifying screw cutting.
« on: March 22, 2015, 05:30:16 PM »
It is with some trepidation that I offer this.

Like many here I have followed Doubleboost's articles.  And for course threads he follows the procedure that many of us, including me,  use(d).

In a nutshell,  Set over the topslide to half angle.  Set the tool square to the job. Touch -on the tool and set both topslide and cross slide to zero.  Take a cut,  then (external thread), wind the cross slide out a turn, move saddle back to starting point for next cut and move cross slide back to zero.  Put on a few thou with the topslide and then start the next cut.

All pretty straight forward.  But DB does remind us that you need to get into the rhythm or disaster will come calling.

From here on I'm assuming that you leave the half nuts engaged with the leadscrew.

Now,  My Red lathe has no calibrated dials at all. So when I want to cut threads I have to attach dial guages to both top slide and cross slide. I also use a handle to turn the spindle,  but that is another story.

So,  my procedure is the same as above except I don't move the cross slide after the initial touch on of the tool. I set the cross slide clock to zero and forget about it until it is time for the final thread clean-up.

With the tool touching on I set the top slide clock to zero.

Carry out the first cut.

Wind the top slide out about half a turn. Not critical.

Return the saddle to the start point.(much turning of handle)

Wind the top slide in to zero,  add 5 thou',  and make the next cut.

From here on I just add 5 thou to the clock reading for each new cut.

This way I am only adjusting one slide instead of two.
My depth of cut is is being advanced in 5 thou' increments; well,  slightly less due to the angle.

When down to the required depth on the topslide I start to use the cross slide to clean up the thread and get the fit.

I find this easier than having to use two handles. Just need to remember the reading on the dial guage for my previous cut.

Why only 5 thou' cuts ?  Well,  cutting 8 tpi with a handle gets pretty hard if you cut deeper.

There is,  of course,  nothing wrong with the usual method. But I would recommend mine for anyone who is using a very old lathe with no dials.

Whether I'll still use this method when I get my Denford running is another matter.


Offline doubleboost

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Re: Simplifying screw cutting.
« Reply #1 on: March 22, 2015, 06:51:44 PM »
Just use whatever method works
Once you get in to a routine stick to it
I find thread cutting very "therapeutic"