It's a thread Jim, but...

He is a diyer, we think? Cheap lightweight machines are not as rigid as a good heavyweight examples.

As a diyer, he does not need to finish every job inside a minute! HSS cutters will last more than 15 seconds (based on a minute per job and the suggestion of needing regrinding after only a 1/4 of the job is completed). But they do need to be used at lower cutting speeds and depths than carbide.

“Horses for courses”, I think?

So when does a lathe transition from a lightweight to a heavyweight?

I would not have said the OP's lathe was a lightweight at some 600kg which is the same sort of weight as a M300.

The poundland inserts don't help, go out and get a single one of decent parentage

Edited By JasonB on 20/11/2018 10:20:36

Not many people can screw cut a thread of 2mm pitch at more than 100 rpm or so . I don't think it matters if the threading tool is HSS, or a ground carbide insert. Some materials definitely tear and don't cut as well as others. I have a Myford S7 and my choice is a ground threading insert. It is sharp like hss but lasts longer. At the end of the threaded area, I make a thread relief, so am not trying to withdraw the tool at the end of the cut. on a M16, I make the relief diameter 13.75 to 13.8mm and normally I make the relief length about 5mm long. This gives about 1 second to stop at 150 rpm. Keeping the tool holder over hang to a minimum makes a huge difference , especially with a 0 Dickson holder on a deep thread like a 2mm pitch. If the material is difficult to cut, I will put on a cut with the compound, but take some of it off,by 0.05mm with the cross slide. Then retake the cut again, with the cross slide at the zero point. This makes then leading face cut not all in 1 pass. It reduces the total cutting volume and reduces the front length being cut by the tool. It is also called the zigzag screw cutting method. This is good when threads get deeper than 0.8mm deep , so like for M12 and courser pitch threads. It works for internal threads as well.

Neil

Thanks for further comments. For my experiment at 65 RPM I'd actually cut a 4mm relief to leave me plenty of room to stop. In the event I found that I I could stop within perhaps 0.5mm from the headstock end of the thread, so about half a second to snap the feed lever - the lathe has the luxury of a thread indicator, unlike my first one on which I had to leave space for the chuck to wind down before reversing. So I think I can go faster without danger.

I guess I need to experiment with feeds/speeds and see what's best, perhaps get nowhere, then buy some better inserts. Maybe I'll hit a 'sweet spot' :

These turnings came off EN1A, 2mm DOC, can't remember feed, but it was lovely watching them peel off. Some are 2m long! I may weld them to a brake disc and sell as industrial art. Got to be worth 400 quid.

Robin

As has been mentioned earlier if you want to run at speed and don't think you can stop in time work at the rear of the work with the lathe running in reverse and you have got until you hit the tailstock to stop the machine. Think I diod this at 4-500rpm

Please assist and advise what I'm doing wrong. 50mm long M42x4mm pitch thread using HSS tool ground once? Set over topslide, 4 way toolpost with shimmed tool and slide dials.

Do I need to change to CNC and carbides?

Regards Ian.

Depends what problems you are having. Can you give more detail?

Historically, people used to cut far larger threads than that with HSS, if your tools are blunting or failing just reduce the rpm and don't try and remove too much material in one go.

Carbide will work faster and with longer tool life if you have a lot of threads to cut, but if you only need a few threads you can get the results you need with HSS, if you take things steadily.

Neil

Is that a standard internal right hand threading tool, or a special for external right hand threading running in reverse ?

Standard Internal.

Neil, I think Circlips question was directed towards Jon who said HSS would not do the job.

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Please forgive my naivety on this matter, but how do you accommodate the difference in truncation?

P/4 vs P/8

https://en.m.wikipedia.org/wiki/ISO_metric_screw_thread#/media/File%3AISO_and_UTS_Thread_Dimensions.svg

MichaelG.

Edited By Michael Gilligan on 21/11/2018 19:28:34

It's a partial form insert so does not create the true crests and valleys, think of a HSS tool ground to a point. Needle file over the crests to ease them and make the other part to fit. This would apply to using a external partial form insert as well as the external.

Tip radius is a maximum not a minimum, and is actually the width - a flat is allowable..

To quote the article:

"In an external (male) thread (e.g., on a bolt), the major diameter D_maj and the minor diameter D_min define maximum dimensions of the thread. This means that the external thread must end flat at D_maj, but can be rounded out below the minor diameter D_min. Conversely, in an internal (female) thread (e.g., in a nut), the major and minor diameters are minimum dimensions; therefore the thread profile must end flat at D_min but may be rounded out beyond D_maj."

Neil

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That's O.K. then, Jason ... Sorry, I thought it was full-form

MichaelG.

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Quite so, Neil ... That's why [*] I was struggling.

MichaelG.

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[*] when I wrongly assumed that Jason was showing a full-form insert

Which means, when I came to cut a simillarly proportioned blind internal thread, I could have used my existing external tool, under power, in reverse, rather than buying an internal tool and turning the chuck by hand to avoid a crash. Every day is a school day.

As for inserts and high rpm, that was a hand turned chuck, with an insert threading tool, cutting (probably) EN1A. The thread came out fine. New sharp tool. Free machining material.

Might not be enough bottom rake on an external tool to do an internal thread.

Martin C

Don't know how you would get the usual external holder inside the hole as they tend to be at right angles to the lathes axis

Well, to report back on suggestions, I've now tried upping the speed (250 rpm instead of 65), using EN1A instead of EN3B and taking spring cuts. Still in badger's ar*e territory. I'm reluctantly forced to think that it must be the 'poundland' inserts - **LINK**

I don't understand the codes for inserts - can anyone point me to a source of decent inserts which would fit this holder?

Robin

Robin, measure the side of the insert, it will be 16, 11 or 8mm, the tip code will have that dimension included in the code number along with an E for external, an I for internal and R or L for right hand or left hand threads.

Emgee

Another weapon in your arsenal: sulfurized cutting oil. It is almost universally used by plumbers when threading pipe. I prevents tearing in really gummy steel.

I am not going to get in the debate of HSS vs carbide. I use both. HSS does give you the option of varying the top and side rake to suit the material.

Flank feed is preferred to plunge cutting. When plunging there adr chip impinging from two directions and tending to jam on top of the tool.