MEW 260- Lantern Chuck

Despite owning an S7b with QC gearbox for 8 years I have never attempted to cut a screw thread. The Lantern Chuck project seemed like a good opportunity to start.

It calls for a metric ( M30) 1.5 mm pitch thread, internal and external. So at Warwick I purchased 8mm indexable internal and external cutting tools with metric and imperial tips.

However having got home and examined the tool bits it looks like the maximum thread depth I can obtain is about 1.4 mm with the metric tool.

So the question is what TPI should I select on my imperial Myford

M30 1,5 pitch has a minor of 28mm, 1mm thread depth.

If the insert marked ER1.5 ISO, (internal NR or IR) its the right one.

Jim

As you are cutting both threads it does not really matter what threads you use. As your lathe is imperial you may as well select 16tpi to keep things simple and then you can use either of the inserts metric or imperial as it is only the thread angle that differs, metric being 60deg will need slightly less depth.

Would need to know the size of tip to get a better idea of what pitches (depths) you can cut, assuming they are partial form which is most likely to be what has been supplied.

Edited By JasonB on 22/10/2017 10:14:19

the minor i refer too is the external, internal would be 28.5mm

jim

Jason and Jim

Thanks for the advice. That is exactly what I needed to know. I will use the metric tips at 16 tpi.

I will test first on some scrap ali bar.

For info here is a photo of the tools showing the sizes.

Peter

Those are probably size 11 inserts, if you extend the edges of the triangle to a point they would measure 11mm along one edge. usual sort of range for a partial profile in that insert size is 0.5 - 1.5mm pitch or 48-16tpi.

It is also possible to use the internal holder at the rear of the work with the lathe running in reverse, handy for threading upto a shoulder as you can start at the shoulder and cut away from it which allows a fast cutting speed.

I wouldn't do that with a Myford, the chuck could easily unscrew. It makes life a lot easier if you can have an undercut at the end of the thread, then the tool runs out into the undercut and you aren't frantically dropping out the half nuts and withdrawing the tool at the same time. This especially on internal threads wher you can't see what the tool is doing, when it stops making a noise drop out the half nut.

Could always do one of several mods I have seen that stop the chuck unscrewing itself.

Just cut my first matching internal and external threads which mated perfectly. Well pleased. Now for the threads on the lantern chuck.

Thanks for all your help.