Ext threading inserts - I DONT GET IT!!!

[eskimo]

I need to cut a 1/2 BSW thread.

What has Pitch got to do with it, if the same size insert fits my tool holder. They take 16er

344390344390

so what do I order.

Do I have to order a insert whenver I need to cut a different thread size even though its BSW

[scottyd]

There are individual inserts for each size thread because the threadform changes with size. Although the included angle doesnt change, the radius at the root and tip of the thread gets bigger as the tpi increases. So each insert is individually formed for each tpi to get the complete form right.

Id be just using HSS myself, but if you turned a lot of one size thread, I spose you could jusitfy chasing down the right inserts. Too small a size will chop the top off of the thread profile and too large a size will have too large a radius on the inside of the thread, so you cant just "make it work".

edit: I dont think they make a cutter for 1/2in BSW (12 tpi) that fits your holder. They seem to only supply it in the U Miniature size.

[Stustoys]

Do I have to order a insert whenver I need to cut a different thread size even though its BSW
Yes. They are form tools, the crest and the root are the right shape......... but you need a different one for each pitch.
I assume you want to cut an external thread? I cant see an insert to suit....... but then I dont use inserts much, maybe I'm missing something.

Stuart

p.s. but I think you'll find them on page 17

[Techo1]

The inserts linked to in the Carmex catalogue pages are "Full Profile" and are designed to cut one pitch only, you could use a "Partial Profile" insert that covers 14 to 8 tpi. Depending on the type of toolholder you are using you may also need another anvil to suit the rather high helix angle on 1/2" whitworth.

[Michael G]

Another option is as Martin Cleeve did in the workshop series of books and truncate the thread so you miss out on the rounded tops of the thread. You could also single point a thread which was approximately right and then finish with a die to round the crests and profile the root.

Michael

[eskimo]

Ta for the help guys....bit I still dont get it
I have a diamond tool holder ...so lets assumeI grind a tool bit to 55 as scotty says ...so what is the difference between that and a 55 insert

[eskimo]

Maybe you all have made me think???
Is it that rounded bit at the top/bottom of the crest/ valley is different for each tpi?
If so then my thread on that dovetail knuler is crap?

[Michael G]

A Whitworth thread is meant to have a rounded crest and a rounded root. Just because they are not there does not make the thread crap - it's just not (strictly speaking) W/W.
In this post here, there is a W/W tool for a 16tpi thread
http://www.woodworkforums.com/showthread.php?t=171231&p=1856830#post1856830
Perhaps one of the reasons W/W is not used as much these days is because of the extra work to get the full form - much easier to do a UN/ Metric form with a sharp crest (the root can be any shape you make the tool). In reality the rounded crest and root don't do much for the holding power of the thread so the lack of them is not really detrimental in most cases.

Michael

[eskimo]

Ah...what a dumb ass I am
Does that explain why my dovetail knurler thread worked...considering ot included both internal and external lh and rh threads

[.RC.]

Maybe you all have made me think???
Is it that rounded bit at the top/bottom of the crest/ valley is different for each tpi?


Yes

But you do what I do and just use one of those 16ER inserts that does a range of pitches and guess the thread depth required...

If I have to do a critical thread or do work for someone else, I will grind up a threading tool either brazed on carbide or HSS...

99.9% of the time I do a non perfect thread, and probably run over it with a die.. or die nut.. or leave it as is, depends on application.

[eskimo]

Yes

But you do what I do and just use one of those 16ER inserts that does a range of pitches and guess the thread depth required...

If I have to do a critical thread or do work for someone else, I will grind up a threading tool either brazed on carbide or HSS...

99.9% of the time I do a non perfect thread, and probably run over it with a die.. or die nut.. or leave it as is, depends on application.



Now thats a answer i like....lol...after all...i am not perfect...at anything
ta RC

[Stustoys]

In reality the rounded crest and root don't do much for the holding power of the thread so the lack of them is not really detrimental in most cases.

As I understood it, the rounding was better for fatigue.... but then if you're worried about fatigue you aren't likely to be using cut threads anyway.

Stuart

[eskimo]

I hope to find time tomorrow do this BSW threading

using RC's method will it be okay to use a 60 degree insert on the lathe and clean it up with BSW button die

Material is 316 SS and the HSS button die doesnt like it...unless its two threads or less...certainly doesnt like three...

but will it be okay for the last 5 degrees for the thickness of the die?

[pipeclay]

It may work ok but I think you will still struggle and run the risk of tearing the thread,can't you use a piece of HSS ground to a thread profile garage rather than using a 60 degree tip.

[.RC.]

Stainless steel workhardens so if you let the tool rub then you create a hard spot in the tool...

I have been threading 12mm, 316 stainless with a standard chinese die in a die stock that has a proper guide made up... I get half a dozen threads of about 40mm long then time to throw the die away..

It is just not nice stuff to machine... You need sharp good quality cutters..

[Michael G]

Using something like Trefolex will help with threads on S/S enormously.
(May be able to grind up a reasonable facsimile of a radiused tool too if you like)

Michael

[rockettgpw]

An excellent guide for thread forms, tapping sizes etc etc is the engineers little black book available from places like Blackwoods,Coventry Fasteners and probably online. Has great diagrams of all threads with brief explanations of their uses and heaps of other useful info, well worth the $20-30. In the same series of books is the "fastener little black book" bit dearer but much more in depth info and history of fastener uses.

[eskimo]

can't you use a piece of HSS ground to a thread profile garage rather than using a 60 degree tip.

hahahahaha...what, you expect me to grind and shape a bit of hss to do that....



oh alright, it wasnt the answer I was hoping for ....but I will give it a try.....:(

[eskimo]

will let you all know how I get on after I do/try/attempt/giveup with the above