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David George 124/07/2022 12:06:48
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1871 forum posts
505 photos

Having just started using carbide tips for screw cutting ( I always used to make my own tools grind by hand. ) what tips do I need to buy ie do I need to buy a tip specific to thread dimensions or just get round it. I have only bought some 18 Whit tips so far but do I actually have to buy a tip for each thread size.

David

DC31k24/07/2022 12:31:16
725 forum posts
2 photos

Please have a read of this to see the possibilities:

https://www.sandvik.coromant.com/en-gb/knowledge/threading/thread-turning/pages/how-to-choose-thread-turning-insert-and-shim.aspx

If you search for 'Seco threading guide', the pdf they give you is very good as it includes number of passes and infeed for each pass.

Every major insert manufacturer produces a similar guide, so pick any of them (Seco, Sandvik, Iscar. Pozithread).

Emgee24/07/2022 12:32:14
2444 forum posts
291 photos

David

I think you may have to with imperial sizes or at least they are listed for sale as thread TPI.

I use metric full form inserts which also are pitch related although a 60 deg insert will cut all threads but not provide the finished crest shape.

Emgee

JasonB24/07/2022 13:09:25
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Moderator
23022 forum posts
2763 photos
1 articles

A partial form will do for most jobs, just requiring a file running down the crests of the male thread a few times as the work rotates.

So a 60deg metric and UN AG60 will do 0.5-3.0mm pitch and for imperial AG55 will do 8 - 48tpi

Andrew Johnston24/07/2022 13:09:45
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6668 forum posts
701 photos

For each thread form there are two types of insert, partial profile and full profile. A partial profile insert will cut a range of tpi/pitches. The root profile will be set for the largest tpi (smallest pitch) and will be too sharp for lower tpi (larger pitch). So some tweaking of DOC may be needed. In addition the crest will not be formed properly. In contrast a full profile insert will cut a full profile thread, including root and crest, thread but is limited to a single tpi/pitch value. Of course there are also variants for internal/external and LH/RH.

I screwcut a lot of the threads on the lathe, mostly imperial but also some metric. I prefer to buy full profile inserts. It makes life easier and forms a better thread profile. I buy inserts as needed. In practice I cut a fairly limited range of tpi/pitch values. For instance the majority of Whitworth threads I cut are 40, 32 and 19tpi.

For reference, a partial profile insert for metric threads:

16er-ag60_me.jpg

A full profile insert for metric thread, 2mm pitch:

16er-2.0iso_me.jpg

Internal and external inserts for Whitworth 19tpi:

inserts_bspt_19w.jpg

Andrew

JohnF24/07/2022 15:44:43
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1172 forum posts
193 photos

David, as has been said there are full form and partial form but think about what you did/do when you grind your own tools ? they are partial form and good enough for most jobs in the home workshop, one advantage you do have with home ground tools is you can add the correct root rad to the tool. As far as the crest goes the best way is to truncate the thread thus removing the need for a crest radii . This was standard practice in the 1960's and beyond and I was working in the Aero industry all cut threads were truncated.

I still use home ground tools but also tipped tools for these I purchase full form tips for each thread size/pitch

John

David George 124/07/2022 16:38:59
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1871 forum posts
505 photos

Thanks for information it gives me more thoughts like I can use UN inserts for meteric and visa versa and as long as the root diamiter of a tip is not too big I can use that for other size and pitch.

David

old mart24/07/2022 22:37:54
3886 forum posts
264 photos

APT are a good source of single threading inserts and they also sell a range of turning inserts in singles fot hobbyists who like to try different grades, but don't want to buy a box of ten.

**LINK**

Mike Hurley25/07/2022 09:04:52
325 forum posts
87 photos

To be honest, I have given up using them and reverted to hand ground HSS. Whilst I initially thought they would make thread cutting a breeze, it was not so.

I just suffered so many breakages/chipping of the tips. Admittedly this was not the fault of the tooling but more my cack-handedness probably, I ended up spending more time trying to get the jobs done than before. I say not the fault of the tooling, but in at least one case I did suspect an 'economy' set from a large weel known supplier of tools.

Horses for courses as they say, and I'm sure most people find them a great boon, Personally, as I'm lucky enough to be able to grind toolbits quite well, I sticking with what I know (and saving a few bob in the bargain).

All the best. Mike

Andrew Johnston25/07/2022 09:39:00
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6668 forum posts
701 photos
Posted by Mike Hurley on 25/07/2022 09:04:52:
...suffered so many breakages/chipping of the tips...

Must be something wrong with the tips or the technique? Touch wood I've never broken or chipped a threadking insert. I normally buy inserts from Cutwel. This is a 3/4" BSF thread screwcut with an insert:

press tool spigot.jpg

Andrew

JasonB25/07/2022 10:26:00
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Moderator
23022 forum posts
2763 photos
1 articles

Probably not got a fancy attachment to stop the carriage travel, that is where you are most likely to damage an insertsmile p

Andrew Johnston25/07/2022 11:04:27
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6668 forum posts
701 photos
Posted by JasonB on 25/07/2022 10:26:00:

...not got a fancy attachment...

This is what Jason is referring to, an Ainjest high speed threading unit:

ainjest_unit.jpg

It has it's own half nuts and also has a repeatable trip mechanism. When threading to a shoulder, or internal threading, I leave 5 thou clearance. My lathe is imperial, and the Ainjest unit only works on imperial threads.

This is a M16x2 thread screwcut in the normal manner, using an insert, leaving the normal saddle half nuts engaged:

m16 thread.jpg

Andrew

David Noble25/07/2022 11:04:35
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328 forum posts
18 photos
Posted by DC31k on 24/07/2022 12:31:16:

Please have a read of this to see the possibilities:

https://www.sandvik.coromant.com/en-gb/knowledge/threading/thread-turning/pages/how-to-choose-thread-turning-insert-and-shim.aspx

Thank you for this, I have never heard of 'thread whirling' before. Interesting stuff.

David

JohnF25/07/2022 11:42:26
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1172 forum posts
193 photos

In the absence of any sophisticated threading equipment and undercut at the shoulder is the best way forward, as a rule of thumb the U/cut dia should be the thread root dia -- .002" to -- 0.005" and the width approx 1.5 x pitch. A small rad on the LH corner of the U/cut tool and the RH should be the thread flank angle.

You can also start in the undercut and run in reverse with the tool inverted [beware screw on chucks] also a useful technique when thread cutting into a blind hole.

John

Neil Lickfold25/07/2022 12:20:14
890 forum posts
195 photos

Find some PeeDee thread wires or buy their thread wire kit. Works great if you want to make thread of a known pitch effective diameter. The full form external inserts are great and I use them to size the OD of the thread form. So on a M16X2 thread, I cut the thread until the OD is Ø15.95mm. I use 0.05mm in diameter on all the out side thread sizes down to 5mm. Then I reduce it to 0.02 for below M5.

Using the tread wires you can use a full form or a partial form to create the thread. Often I will make a short section and use that as the gauge for cutting the ID of the other thread, like a M20X1.5 for a nut or something. If making a thread gauge, I then make it +0.02mm to +0.04mm larger than the nominal diameter. So a M20x1.5 gauge would be 20.02mm to 20.04mm on the outside of a full form thread insert. Then when you cut the M20x1.5 and make it Ø19.95mm , it will definitely fit.

At the end of most threads I have a run out thread relief area. That makes it a lot easier to stop at the end of the threaded part.

Neil

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