60 degree thread insert

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As nobody else has replied here goes

A lot here will offset the topslide but there are also a good number like myself who plunge straight in and as you have a reasonably hefty machine I see no real reason not to unless it's a very coarse thread in which case you can still go straight in but move the tool slightly sideways for each pass with the topslide (set parallel to lathe axis).

BTW for a 60deg thread form the topslide would be set to about 29deg ie just under half the angle, 26deg is used for 55deg form threads

Also be aware that a partial form insert will need to be fed in further than a full form one.

I do as Jason, even on an Emco 5 lathe which is very much lighter than your Harrison L5, I normally use full form inserts for external metric threads from 0.50mm to 1.50mm pitch but for imperial sizes just a 55 deg tool with a minimum nose radius.

Emgee

A lot of people with smaller lathes do angle the topslide to lower the forces when cutting threads. I would advise that you do not until you have more experiance. If you cut fine pitch threads, say 1.75mm or less, then the added force will not be too big. Each thread should be cut in multiple passes, with the increase in cutting depth getting less at each subsequent pass until you are creeping up on the finished size. I personally never offset the topslide, even for 5tpi threads, but I have the luxury of a Smart & Brown model A which is heavier built than most.

Why 27 degrees. Tad under 30 I would have thought.

regards Martin

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I do the same as "Old Mart" and I have a Myford never had a problem cutting threads, last cut i always repeat 2 or 3 times to allow for tool "spring"

For coarse threads it s best to flank feed the tool. On medium pitches ether flank feed or plunge feed is acceptable. On fine threads plunge feed is preferred.

Definitions:

Plunge feed is feeding with the cross slide.

Flank feed is done with the compound. The compound is set 1/2* or so steeper than the trailing flank of the thread. The idea is to do the major amount of metal with the leading flank of the tool. Th trailing flank takes a very fine cut to prevent steps in the thread form.

Is it possible you are cutting a 1.25mm pitch? 1.25 tpi is an extremely coarse thread, not one I would expect in model engineering?

For coarse threads …

And this thread IS a coarse one!!!🙂

dw dw 2 wrote: Its an external thread 1.25tpi,

A typo, maybe?🙂

A 1.25 tpi would have a lead of 0.8 inches. My 16" lathe will not cut that coarse a thread. I figure it was a typo

He also said in the post above that it is 1.25 metric in response to the comment about pitch

Recently I had to cut numerous various sized threads in steel & brass, Metric and imperial using both HSS and Inserts. My lathe is only a moderate sized bench job. I ended up using a variety of methods both straight plunge in and angled compound slide ( the angle isn't that critical - it's only there to ensure the cut only takes place on one side of the tool so reducing the loading )

Overall, I couldn't really see much difference between any of them! Maybe my standards aren't as high as some guys on here, but essentially as long as the thread is the right size and fits the job as I want, I'm happy.

My only advice, echoing old mart's comment, is to carefully reduce the in feed the deeper you get - may seem tedious but try to keep the feed to quite small amounts ( as long at it still cuts as opposed to rubbing ) that way you should get a good finish and accurate thread form. Like most things, the more you practice the better your results will be.

p.s because I can't get a slow enough speed on my machine, all threads were hand-cranked.

regards

From the annals of things which aren't quite right, but do work ...

If you don't want to offset your crossslide, you can fudge it by feeding in at 90 degrees in combination with advancing 1/2 of that amount in the direction of travel. This has the effect of approximating a 30 degree feed, but still keeping your "depth" on the crossslide and at 100% of actual depth of the thread. Plus you retain the advantage of keeping the load on the advancing edge of your threading tool.

It's not kosher, but it works!

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