RequiredOutside Diameter to Cut 5/16 BSF Thread

[Danni Burns]

On Danni Burns Said:

In conclusion, a 1″ dia Die for cutting a fresh 1/2″ thread is way too small. Lesson learned.

As illustrated by this manufacturer:

https://www.avontapdie.co.uk/bsw-1-2×12-split-circular-die-hss

There is a saying for tools: buy quality, buy once.

Julie

[Clive Brown 1Participant @clivebrown1]

I’d be very reluctant to cut a 1/2″ Whit. thread dirctly with a die if I could possibly avoid it, especially a fairly long thread and in steel. Screwcutting in the lathe would be my choice and maybe using the die to take a final fine cut to size. Apart from being easier, the thread should be more accurate, particularly wrt concentricity.

[JasonBModerator @jasonb]

On 25 March 2025 at 20:57 Danni Burns Said:

In conclusion, a 1″ dia Die for cutting a fresh 1/2″ thread is way too small. Lesson learned.

 

I agree with Clive 1/2″ Whit is quite a coarse thread and needs a lot of effort to cut with a die. Even if you had a larger diestock chances are the work would spin in the chuck. Screwcut fully or at least do 75% and then finish with the die.

I’ve cut finer 1/2″ or 12mm threads with 1″ dies without problem so it is more the pitch and therefore amount of metal to come off that determines how much force is needed to cut the thread rather than it’s diameter which in turn determines the size of diestock you need to get the leverage

[Danni Burns]

On Danni Burns Said:

 

Nick, maybe those kits are OK for little taps/dies that don’t need any real torque. You could easily make your own tap wrenches using square bar and some cap-head allen screws. Maybe even rubber/nylon pipe on the handles. They’ll last your lifetime.

Hi Danni, I probably could have made my own tap wrench, but it would’ve cost more in material and electricity, than the price I paid for the No. 0 one, plus cap-head screws standing out, would be most uncomfortable to use, as I only hold the body of the wrench using such small taps, and I very much doubt that I will ever have enough time to wear this one out.

Regards Nick.

[Julie Ann]

On Julie Ann Said:

On Danni Burns Said:

In conclusion, a 1″ dia Die for cutting a fresh 1/2″ thread is way too small. Lesson learned.

As illustrated by this manufacturer:

https://www.avontapdie.co.uk/bsw-1-2×12-split-circular-die-hss

There is a saying for tools: buy quality, buy once.

Julie

Julie

Is ATP a manufacturer or reseller of the same I can find elsewhere online?

If UK manufacturer, I would happily support them, but I’m guessing they’re a reseller and charging for this Die at least £5 more than others I’ve found (11 and 15) online.

 

 

[Danni BurnsParticipant @danniburns84841]

Clive, I also agree 100%.

Screwcutting should be a painless choice for me. It’s too painful even to talk about it.

cheers all

 

[noel shelleyParticipant @noelshelley55608]

I would always use a split die, it gives some control of the thread OD. NEVER buy a really cheap set, I was given one, some of the threads were so far out of true there was plainly NO QC. The WPS “Metal Workers Data Book” No42 DOES give the OD for threads and I hope all of us have a copy ? It is a mine of all you need to know on many subjects. Whilst the OD of a thread MAY be it’s size, there are plenty where this is not so, BA, some small American threads, Hydraulic and pipe threads are some. BIG threads, 7/16″ up are to big for a 1″OD Die and if a coarse thread the more so. 1 5/16″ OD is the next size, then 1 1/2″, there is a 2″ but that is Not a model engineering size ? Tool steel may not be cheap but a split die that is in 2 pieces is not much use to most of us. In my case a 12mm die 1″ OD broke ! Most small BA and ME threading dies are only 13/16″ OD, this size is good to 1/4″. Remember that a bigger die and stock will have longer handles and give more leverage in use. Noel.

[bernard towersParticipant @bernardtowers37738]

Danni, a few hours of practice with ref to (screwcuting in the lathe) will pay dividends for years to come and when you have mastered it you will wonder what all the fuss was about. It opens the possibilities of any dia with any thread( and if you repair old stuff you won’t need hard to find taps and dies)

[BazyleParticipant @bazyle]

First make a mandrel handle for your lathe – it makes screwcutting much easier as it incorporates autostop and quick reverse. After learning you can move to power for a number of years then as your reactions slow in old age return to the manual process. It really should be a standard issue item with lathes like a set of chucks.

[Danni BurnsParticipant @danniburns84841]

Hi Bernard and Bazyle

Thank you both for your confidence. I’ve done screwcutting >30years ago, so I know what I should be doing. That was on a Colchester Student 1800 – with minimum play and backlash and a clutch brake. I’ve never done it on the Clarke 500, but I have the gears and belts, so I agree that it should be possible (or rather, I should be capable).

I intend on having a bash. I can get a mandrel handle together quickly enough. That was another side-project I had designed and bought the materials for (1″ Rawl bolt and a winch handle). It just needs a bit of fettling.

cheers

[Danni Burns]

On Danni Burns Said:

Is ATP a manufacturer or reseller of the same I can find elsewhere online?

The simple answer is that I don’t know. Avon taps and dies are laser etched with their logo as well as the usual size information. So I very much doubt they are generic items sold by all and sundry.

For metric, and other current thread standards, I buy from industrial suppliers. For obsolete threads I buy from Avon. What I can say is that their taps are very well made, are sharp and are easily the equal, or better, of taps supplied by the large industrial suppliers.

I can’t comment on their dies as I haven’t bought any. While I have a large number of split dies I don’t use them much. They are PITA to adjust to size and even with tailstock holders tend to cut wonky. I much prefer to use Coventry dieheads or screwcut.

Julie

[Nigel Graham 2Participant @nigelgraham2]

I tend to use both, for larger diameters: screw-cut then use a die to trim the profile.

Note that a plain screw-cutting tool with a sharp tip, intended for a range of sizes, needs be fed in slightly deeper than the “book” thread depth. Or widen the cut by a few thou?

Another difficulty with using just a die and conventional die-holder without a guide-bush is creating a straight, concentric thread. I imagine it’s possible but with steadier hands than mine and far more practice than me!

I do have one of those commercially-made die-holder sets based on a cylindrical holder sliding on an arbor with a Morse-taper shank but find it a right pain to use. It is very bulky for a small lathe like a Myford 7, and the shank slips in the tailstock. I may be wrong but it seems fractionally over-long for the barrel so is gripped on only a small area.

[Danni BurnsParticipant @danniburns84841]

Thanks for the update Julie.

Nigel, I use the tailstock with an extension MT and maybe also a drill chuck. I constantly have slight pressure on the die wrench to keep it square while turning the wrench by hand. It gets congested though and knuckle rash is unavoidable.

Do you mean that the MT tang seems to be too long? This is also a problem on my lathe. The measure/guage on the tailstock starts at approx. 20mm because, less than that, the MT pops loose. I think this can be fixed (yet another side project).

I will try screw cutting. I have metric (60 degree) tip tool and handmade HSS, but no 55 degree. I’ll grind one tomorrow.

cheers

[Danni BurnsParticipant @danniburns84841]

Another question, please – can anyone advise on the Angle carbide tip tools?

I have a SER1212H16-12mm Lathe CNC Cutting Tool Holder+10Pcs 16ER AG60 Threading Insert

Can a 55-degree tip be used in this (I assume it would be ref: 16ER AG55)?

[Julie AnnParticipant @julieann]

The toolholder will take all inserts of size 16 irrespective of thread profile.

The AG refers to a partial profile insert which will cut a range of thread pitches of a given included angle. The problem is that the calculated thread depths are wrong as the insert will have a nose radius for the smallest pitch. For larger pitches the thread depth will need to be greater than the theory says. Also the thread crest is not machined.

Personally I find partial profile inserts a pain and use full form inserts instead. With full form inserts the thread depth to be cut is as per theory and the root and crest are properly formed. That is important for Whitworth where the crest is rounded.

I screwcut large numbers of Whitworth threads and always use full profile threading inserts. The one needed for 1/2″ BSW external is:

16ER 12 W T350

where the T350 is just the carbide/coating grade and will vary according to the manufacturer.

Julie

[Danni BurnsParticipant @danniburns84841]

Hi Julie.

I’ll do a search; see if I can buy just 1 or 2 tips, as I may never need it again.

Thanks again

[JasonBModerator @jasonb]

Sounds like me, I don’t have the need to do much screwcutting so the slight inconvenience of a partial form does not matter for me.

As it is a Whit thread if you have a DCMT holder and insert they can also be use dto cut the 55deg thread needed, like the partial inserts depth will need to be adjusted and crests eased but as you have that die might as well screwcut 75% and then finish with your die which will be a lot easier to turn as most of themetal has been removed.

Dare I say it – you could rough it with the 60deg inserts that you have or any freehand ground tool then finish with your die.

[Julie AnnParticipant @julieann]

I normally buy inserts from Cutwel, but they are relatively expensive. You could try APT:

https://www.shop-apt.co.uk/whitworth-w-external-threading-inserts/16er-12-w-t350-external-threading-insert-for-general-use.html

They will sell one insert, but I don’t know what their postage rates are like, or if there is a minimum charge.

All the external threads shown below were screwcut, 32tpi and 40tpi, both Whitworth form:

Julie

[Danni BurnsParticipant @danniburns84841]

Hi Jason

I will use that die down whatever way I cut it. It would be no hassle to grind a 55-degree tool, but I’d also like to get some good use out of that Tool.

I need to do some M15x1 external threads for a couple of indexing Plunger’s (designed by Mr. Bernard Towers). I have a die for that also, so it will be interesting to see how that goes.

Julie – Thanks again. I saw the APT site  – It’s around £10 for 1 tip (£4 each + P&P + VAT). I bought one for the heck of it and also got a 16ER AG55 Tip (also £4 + vat) for any other Imp threads.

Those are some lovely looking parts there. Clearly, you’re making a Gin Still.

Thanks all

[noel shelleyParticipant @noelshelley55608]

When it comes to taps and dies Etc, a copy of Tracy tools catalogue is worth a browse. I have found there service to be always good and prices fair. Noel.

[Danni BurnsParticipant @danniburns84841]

Thanks Noel

Looks like a great site.

They don’t stock the Die 1/2″x12 (1.5/16) HSS, so I can’t compare the price with the earlier recomended Avon. But they do stock the 1″ dia HSS, and that would be (12+3p&p+vat), so a lot more expensive than my initial purchase.

I would love to support more UK vendors and manufacturers, but I think you need to be buying a few things to make it worthwhile for the buyer and the seller; if only buying low-value or low-qty items, they’re not competitive.

AND – with Royal Mail being so crap these days (I waited 11 days for 12″ of 12mm dia bronze bar to be delivered [1st class] a total of 23 miles), waiting for a China delivery is no inconvenience and probably quicker. Is it the exact same product anyway?

I digress …

[Danni Burns]

On Danni Burns Said:

But they do stock the 1″ dia HSS, and that would be (12+3p&p+vat), so a lot more expensive than my initial purchase.

Are you comparing like with like? Tracy Tools price for a 1/2″whit. carbon steel die is £4 (+ extras). Is your £6 die HSS? the earlier picture suggests not.

[noel shelleyParticipant @noelshelley55608]

Like Clive I question if you have looked up the right one. Unless you are running the die very fast in a machine then for hand tapping carbon steel will be fine.  Noel.

[Danni BurnsParticipant @danniburns84841]

Hi Clive.

Yes you’re right. Applologies for the incoreect comparison.

It says Tungsten as opposed to CS or HSS.

 

[old martParticipant @oldmart]

I cut a 1/2W thread with a split die the other day about 3 inches long simply because I couldn’t be bothered to singlepoint it on the lathe. I did make sure the die was open as far as possible an used the lathe with tailstock to start the thread square. Then it was finished in a vise by hand and a second pass used to get the nice fit on the nut. The die was a Galtona, so top quality.

Not all threads are quite so simple to size, take pipe threads, both parallel and tapered go by the bore size which has no relation to the actual threads that are cut.

[Author]

Posts