[How do I?] Cutting threads

[Michael Wassenaar]

I have A King 1440ml lathe and I am trying to cut threads but cant seem to get the feed speed right using the charts on the machine, any suggestions?

 

[Tom Griffin]

What size threads are you cutting and what do you mean by "can't get the feed speed right"?

You do realize that you use the half nut/lead screw to cut threads, not the feed, right?

Tom

 

[British Steel]

I took a look at the handbook on the "maker's" site, it's very similar to the one I use at work as far as the gearing's concerned!

The gearbox isn't a proper quick-change Norton 'box, so you're going to have to swap change-gears whether you stick with inch threads or not... All the knobs do is halve /quarter etc the leadscrew speed, which is why the tpi in the columns on the (inch) chart double as you go down - and why the metric pitches halve!

Taking as an example cutting 24 tpi whe it's alredy set up for 22 tpi: you'll need to swap *both* a and b gears in the gear cover at the headstock end, 56 tooth in the a position and 54 in the b position. That's just step 1...

Once you're good and greasy from swapping change-gears, on to setting the gearbox controls!

you need the top right knob on position 2, lower right on V, other two on B and D, and the left/right-hand feeds/threads lever (lever number 3 up by the speed selection levers) over to the left for normal right-hand threads (daft how they do that - left for right, right for left!) - Despite the words in the book, lever 3 is NOT the spindle direction selector - that's number 15!

Once you have 'em all in position, make sure the feed lever's in its middle (neutral) position, then see if engaging the half-nuts will get the carriage moving (it should!)

Now... chuck a piece of scrap, turn it to a reasonable finish, take the spindle speed down to something sensible (e.g. 70 or 115 RPM, threading's a bit of a timewarp and everything speeds up around you) and engage the half-nuts at one specific number on the thread indicator - remember which number, you'll need it again in a minute!

Take a really light pass just scratching the surface, disengage halfnuts, back the tool out and stop, check the thread against a thread-pitch gauge (there will probably be some in a tap + die set if you dig a bit!) - if all's good, wind the carriage back with the handwheel, set lathe in motion and re-engage the half-nuts when the same number comes around on the indicator, the tool should follow the "scratch" you've already cut.

If this doesn't get you out of the crud, post up some more detail of what you're doing - thread you want to cut, knob positions, what changegears are fitted to the machine etc, and what thread it's actually cutting!

Dave H. (the other one)

 

[Michael Wassenaar]

What size threads are you cutting and what do you mean by "can't get the feed speed right"?

You do realize that you use the half nut/lead screw to cut threads, not the feed, right?

Tom

Hi Tom, I guess I missed a step with setting things, I had one setting wrong, cutting 5/8-11 TPI managed to get it done and even cut some left hand as well thanks for the reply though

 

[Michael Wassenaar]

It is quite satisfying to see it work, it has been about 35 years since I worked a lathe( back in high school)

 

[Tom Griffin]

Threads are fun. Glad you got it worked out.

Tom

 

[Hawkeye]

The toughest part of cutting threads is to stop when you've cut deep enough. Time flies when you're having fun. :biggrin:

 

[Michael Wassenaar]

The toughest part of cutting threads is to stop when you've cut deep enough. Time flies when you're having fun. :biggrin:

That's for sure, I just used the nut that goes on and kept turning till it fit right , I suppose you could measure the inside of the nut to get the depth of cut as well...