lathe trouble

Gadget,

Thanks a lot for that info, sheds a lot of light on the problem.

I’d always assumed that simply replacing the lead screw would totally fix the metric/imperial issue and that you could even cut metric threads albeit slightly off using the parts the lathe comes with, not that I had ever tried.

Hi Cygnus,

The problem you’ve run into with metric threading on an imperial lathe is common. Your method of not using the threading dial and instead keeping the half-nuts engaged is the only practical solution. I use a handwheel for most threading for better control of the stop point and this also makes winding back to the start point easy.

Metric threading is a bit of a hassle even on a lathe with a metric leadscrew – they need interchangeable gears on the threading dial. The difference is that imperial threads are specified as threads per inch while metric threads are specified the other way around e.g. mm per thread. That is: distance per thread instead of threads per distance — and this subtlety makes all the difference.

Best book I’ve seen on threading is “Screwcutting in the Lathe” by Martin Cleeve. He explains metric threading on an imperial lathe and lots more – one of my favorite machining books. This jig for sharpening threading tools is from the book: http://www.gadgetbuilder.com/ThreadingTools.html

John

For brass I use old king pin bushings out of big trucks–>http://www.talonownersgroup.com/modules.php?name=Forums&file=viewtopic&t=6879&highlight=&sid=e081077be131661f3f39355a54ebcdfc
I don’t have,want or need any hard ass stainless but I’m sure my local scrap yard would have plenty. They sell all that stuff (brass,aluminum,stainless,etc.) by the pound cheap but sometimes you have to dig for it.

Where did you get those tips? 😯 Have a link?

❓ Is that a chunk of hex bar stock your threading?

That’s cheating! 😛

Hey Cyg’
Does your lathe have a reverse ? I dont take my lathe out of gear once ive done the first pass. I put a clock on the toolpost go in 5 , do a pass, stop machine, then retract the toolpost to 5 past zero and reverse. Then start again +5 from the last pass.
I have a few spare 14tpi full form tips if you would like one.

For the bottle threads i just use a split die in my tail stock doodaa.

Thats a DIE, the one that cuts a female thread is the TAP.

I use them for small threads, but like Shadoh said, the large sizes are rather expensive to get one nevermind a whole set. Different materials require difference tolerances when cutting threads so the general purpose dies have a lot of leeway in them which means they wont be as good as a machine cut one that can be custom tailored to specific tolerances.