# Thread dies, question.



## Ttrees (21 Sep 2021)

Hello
Was attempting to thread a bit of round stock mild steel, and have a few simple questions on the matter.
My threads didn't come out sharp and I'm wondering what the cause was.

Had a very brief look on the tube as I was having trouble, and seems I need to bevel or roundover to start with.
It appears that the bevel I made wasn't large enough.
Checked that the die cutter was tapered correctly , and not upside down, getting tighter at the thread engages.

I think I ground too much off the stock, but tapered it slightly, so wondering why at least the bottom of the thread
wasn't sharp.
Didn't feel the resistance what was enough to back out and break the chip on this M10 screw.

Guessing the round stock wasn't thick enough, and I shouldn't have thinned it a bit more.

Would one expect to be frequently breaking the chip on a rod of this size, and what is best practice for 
bevels/roundovers i.e 45 degree chamfer progressively getting larger if the cutter is not engaging?

I didn't use any cutting fluid either, if that matters.


Couldn't find any links easily, sorry if it's been answered frequently.
Thanks for reading
Tom


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## Rorschach (21 Sep 2021)

Mild steel, pretty much says it all.


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## hunter27 (21 Sep 2021)

I would find the major diameter for the thread you want in the Zeus book or on the internet, 








ISO Metric Thread | Metric Thread Chart | Apollo International


ISO Metric Thread or Metric Thread is the worldwide most commonly used type of general purpose screw thread. M Series Thread




www.apollointernational.in




make the dia of the bar to fit within that tollerance and form a lead in. I have found if the bar is oversize I have a real problem getting started and end up with a mess, also plenty of lube and turning the die backwards and forwards helps a lot, also using good quality dies. Even then they usually need a light going over to remove any sharp bits.


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## jimmy_s (21 Sep 2021)

The stock should be 10mm diameter or slightly over for M10. You want a chamfer to start the thread and are best to use something like trefolex cutting compound or at least oil. Break the swarf off every half turn. You can open up the die slightly using grub screw in split and run the thread slightly oversize and adjust it using 2 other screws to fit female thread.


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## Ttrees (21 Sep 2021)

Hi again, checked the diameter of the round stock, and it's undersized for the thread,
but equal to the worn threads.
I'm making handles for the pillar drill.

I cut the stock slightly oversize, and thought I'd beveled enough, past a thread. (45 degrees?)
Couldn't get the cutter to engage, so tapered it a bit.
Surprised I didn't get a better result where the rod got a bit thicker, not so.
Maybe it's a case of having an inch extra each end for a gradual taper?

I don't think the dies I own, have a slot in them.
Seems the leading edge must be more important, compared to a cutter which can be started oversize.

Might have another go, should the dies I have cut a decent thread or not, it might make a good fit, or not at all.
I don't plan on removing them, only if necessary.

Thanks folks
Tom


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## Old.bodger (21 Sep 2021)

Several possible issues.
Is the stock the correct diameter?Have you actually measured it? Telling us the exact size would be useful.
What ACTUALLY is the mild steel you are using, there are different ‘blends’ , some will cut better than others.
What is the state of the die (old, new, worn, sharp?)
Are you starting the thread ‘square’ on the end of the rod. A guide would help. If it starts cutting ‘crooked’ it will soon ‘chew up’ as it digs into one side of the rod.
What lubricant are you using?
What is your cutting technique?
Post a picture of your thread, might give a clue
update us and we may be able to assist!


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## Ttrees (21 Sep 2021)

Hello thanks for your suggestions folks.

Can't say what the bar I'm using is, just some rough old stuff was lying around.
I had to bend and beat it flat so not much point in measuring it, but I'll try if I need to do it again.
Seems about the same hardness as any mild steel I've worked, cuts and files easily.

The tap and die set is from Lidl, so I'm guessing I need buy some fancy adjustable ones.
Might take a piccy should I need to remake the rod.


Tom


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## sploo (21 Sep 2021)

Even in mild steel, it strikes me as a little odd that it would be easy (little resistance) to cut an M10 thread with no cutting fluid. Sounds like the rod was way too small (diameter)?

I can't remember the source, but I was taught to reduce the diameter by 10% of the pitch - i.e. for an M10 1.5mm pitch, take the 10mm rod down by 0.15mm for the section you want to thread. Plenty of cutting fluid (even WD40 works well). Ideally use the lathe tailstock (with a die holder if you have one) to ensure the die goes on straight and doesn't "stake" on the end of the rod.

Oh, also, I understand EN3 steel can sometimes "tear", and doesn't cut as cleanly as EN1A.


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## Sandyn (21 Sep 2021)

Make sure you are using the correct diameter stock as already suggested. I start my threading in the pillar drill or the lathe to make sure it starts perpendicular to the die. I don't run the drill, just do it manually. When you get started, transfer to a vice, I do a quarter turn, then back (how I was taught in school) keep repeating this. An M10 takes quite an effort to cut. I use cutting fluid I get OK results using hot rolled mild steel, but I do turn the stock first to make it is round. I just use an old tap/die set I've had for years. Seems to work OK, but I'm sure a quality set would work better and using better quality steel would give a much cleaner thread.


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## Ttrees (21 Sep 2021)

Thanks folks, you are all spot on, measured it there and it's 9.22mm, seems I need some proper dies.
Might give it another shot with a nice tapered lead in, not too short for that this time,
and hopefully it might require oil.
Might just get away with using it, as I don't have any other rod apart from threaded, which wouldn't make a nice handle for the drill.
Cheers 
Tom


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## Bartfatboy (22 Sep 2021)

You might be shocked at the price of ‘proper dies’ as you call them. The ones you have will be fine if you only use them occasionally. I had a cheap set all the years I worked on my cars and they always did the job fine. It was only once I started using them much more frequently that I purchased Presto ones because, as mentioned in an earlier comment, you have some adjustment and you can starter and bottom taps whereas the sets only come with the middle one. As others have said, correct stock sizing, decent material and effective cutting agents would more than likely have resolved your issue rather than a named die.


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## Ttrees (22 Sep 2021)

I will take a piccy later today of these thread dies,
Pretty broke for the next while, so might just use some thread bar for the job.
No point in fixing drilling and tapping holes and wrecking them again.

I've rarely use dies but do use taps occasionally, and know they can be pricey.
My good'uns are at the folks though.
I can likely buy them singularly locally, if I find some suitable bar stock, but yes I will experiment 
with a good lead in using this undersized rod beforehand.
I don't think it's gonna work, but worth another go.

Thanks
Tom


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## John Brown (22 Sep 2021)

I wish the Sinclair thread would die.


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## jonn (22 Sep 2021)

jimmy_s said:


> The stock should be 10mm diameter or slightly over for M10. You want a chamfer to start the thread and are best to use something like trefolex cutting compound or at least oil. Break the swarf off every half turn. You can open up the die slightly using grub screw in split and run the thread slightly oversize and adjust it using 2 other screws to fit female thread.


"The stock should be 10mm diameter or slightly over for M10." 
Wrong!!! It should be slightly UNDER for a good finish. The threads are slightly rounded, so with an M10 thread you get an outer diameter of from 9.85 to 9.95 mm. If the stock is thicker it's harder to thread, and also, you're likely to get tearing. Looking at the image you can see why the threaded part is slightly under the nominal diameter. That's also why when cutting threads with a lathe, you square off the tips of the threads slightly.


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## clogs (22 Sep 2021)

T tree's
most everything has been covered.....
if u need to buy the odd tap n die I have used Tracy tools (they are on line)in the past....they sell shall we say re-sharpened good quailty taps n dies....
and even has the odd weired stuff/size.....
I use a lot of taps n dies so now buy new HSS items.....
or buy a job lot of used stuff and sell on what is not good enough.....
the items from the likes of Lidil etc are Carbon steel.....
they break a lot and tear the metal instead of cutting it...they also go off edge very quickly BUT ideal for the hobbyist when rethreading a damaged nut n bolt....I have a set with my breakdown kit......
A good qual 10mm split die could easily cost u £20 and more new.....
plus cheapo die hlders dont help...cast ally ones are total rubbish.....
if u do a lot get some all steel holders made in the US, UK or Germany.....
they hold the die better....no good having a wobbly die.....!!!!
as for ur taper.....aim for at least 2-3 threads over the taper....
the smallest end slightly under the bottom thread size and the bigger end at least 50-60% of the actual thread thickness...that way it'll start well.....
after u get experienced just a chamfer will do.....it just takes time to learn....
Not sure if I have posted this photo before....
the small tap holder is for upto 10mm....this will give u an idea on sizes....lol.....
the big'uns I got froma car boot as just the odd time I need em and for fun


...
when useing them, this gives u a real work out....hahaha....
ps ....they dont look like that now.....
good luck....


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## Ttrees (22 Sep 2021)

Thanks again for your replies.
I like shopping locally at my local engineering place, so will definitely be seeing what he has to offer, 
when it comes to needing a real good thread for more important applications.
Got a fancy tap wrench recently, so I suppose I'm as well to get kit for making threaded rod.
Think I will get by with some threadbar, and hopefully find some nice fitting plastic or rubber for the arms, likely have some at the folks.

Tom


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## J-G (22 Sep 2021)

I'd lost my normally permanently open link to this forum so have only just noticed this thread - I normally respond very quickly to any [Threading] thread  

There has been good and bad advice given above but no one has mentioned probably the most important method to obtain a good thread 'by hand' - that is to always use *two* dies. The first should be a split die adjusted as wide as the die-stock will allow and the second pass should be with a solid die.

Below M5 you can get good threads on steel such as En1a but En32, En8, Stainless etc. are more problematic.

Personally I tend to prepare my blank slightly high on the finished dia. but the final thread OD would be marginally low but the most important dimension is the 'Effective' or 'Pitch' dia. In the case of an M10 thread at 6g tolerance this is 8.994-8.862mm - the Major dia for 6g is 9.968-9.732mm. This can be achieved by using the solid die but naturally you should buy quality HSS dies which are manufactured to the specific tolerance (6g,4g etc.).

If you think about the opposite thread (internal) would you think of using a Plug or Nº3 Tap to start it? - I doubt it. That's why a 'set' of taps is Taper, Second & Plug. In the case of external threads a split die can be 'enlarged' by forcing the tapered screw in the die-stock into the 'split' thus reducing the amount of metal taken in the first pass. Above M10 I would tend to consider three dies. Of course you could use only a single split die and adjust the amount of expansion between each pass. I have a number of die-stocks so use a split die in one and a solid die in another - makes it easier if I'm making more than one component.

Avoidance of 'Drunken' threads is important and can be helped by the use of good quality Die-stocks and support from either the tail-stock if using a lathe or by a flat 'dolly' if using a pillar drill. I would never even think of cutting an M10 thread by just holding the stock in a bench vice, that way lies disaster!

Swarf clearance every ¼ to ½ turn is also the best way but experience will dictate that.


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## J-G (22 Sep 2021)

jonn said:


> "The stock should be 10mm diameter or slightly over for M10."
> Wrong!!! It should be slightly UNDER for a good finish. The threads are slightly rounded, so with an M10 thread you get an outer diameter of from 9.85 to 9.95 mm. If the stock is thicker it's harder to thread, and also, you're likely to get tearing. Looking at the image you can see why the threaded part is slightly under the nominal diameter. That's also why when cutting threads with a lathe, you square off the tips of the threads slightly.


I'm sorry John, Most of your advice is at best questionable.

First - whilst the OD is not critical (within tolerance) it is better to start with a minimally oversize bar so as to maintain the best crest available from a die.

Next - Metric thread form is not _*'rounded'*_ though a radiused Root is acceptable.

As far as being *'harder to thread'* that doesn't depend upon the OD being under-size - it is more to do with the amount of material being removed in any one 'pass' - ie. opening up a split die for the first (and maybe 2nd) pass will reduce the amount of metal being removed therefore making it easier. Though I should point out that threading is one of the most demanding machine operations as far as power is concerned.

_*'Tearing'*_ will have more to do with the quality of the steel but is also affected by the 'depth of cut'.

Regrettably you have either selected an already distorted image or have distorted it yourself when preparing it for attachment. The thread angle isn't 60° - it's close to 67° - I've already mentioned the 'Rounding' 

Here is a drawing of an M10 thread-form showing the different thread-forms that are acceptable within the 6g tolerance.




I'm sure you can see that there is a wide measure of acceptability but the 'Effective' or 'Pitch' Dia. is most closely controlled.


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## hawkeyefxr (22 Sep 2021)

I would say that the taps and dies most people buy have a lot to do with how the thread turns out. I have bought tap and dies sets off the internet but they are not a patch on what i used 50 years ago when i was in engineering.
You can buy good taps and dies but they cost.
Also use good cutting fluid, i use ROCOL (that quite expensive as well) back off regularly as well.
yly


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## Fergie 307 (23 Sep 2021)

hawkeyefxr said:


> I would say that the taps and dies most people buy have a lot to do with how the thread turns out. I have bought tap and dies sets off the internet but they are not a patch on what i used 50 years ago when i was in engineering.
> You can buy good taps and dies but they cost.
> Also use good cutting fluid, i use ROCOL (that quite expensive as well) back off regularly as well.
> yly


Tracey tools are a good source of good quality taps and dies at fair prices. And always buy HSS at least, the ones in most cheap kits are too soft to cut or last well, and tend not to be very accurate either.


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## J-G (23 Sep 2021)

Fergie 307 said:


> Tracey tools are a good source of good quality taps and dies at fair prices.
> And always buy HSS at least,


I'll second both of those statements!



Fergie 307 said:


> ...the ones in most cheap kits are too soft to cut or last well, and tend not to be very accurate either.


Cheap kits will pretty certainly be Carbon Steel rather than HSS. These will not necessarily be 'soft' but will lose their edge sooner depending upon the material that you are cutting. Used on Brass or Industrial plastics - or even to clean up existing threads - they should give reasonable service. I do have some Carbon Steel dies but only in the BA Thread series and use these to cut Brass rather than Steel.


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## Duncan A (23 Sep 2021)

If you do not have cutting fluid, use grease, not oil.
Best - cutting fluid
OK - grease
Poor - oil
Duncan


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## pe2dave (23 Sep 2021)

Another thumbs up for Tracy tools. Wide ranging stock and helpful.


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## Ttrees (23 Sep 2021)

Thanks for your suggestions again folks.
Had another shot for the craic, and the tap at least seemed to engage.
Had to press on the tap itself, as the wrench provided wasn't gripping the cutter flush.
This was why it wasn't engaging on the work, as my wee ball vice wasn't able to grip the rod.
No ability to rotate my new vice vertically, 
If I really needed I could have rigged up the vice to a leg of the bench.
That'll be necessary if needing to use these thread dies, should I have another shot.

I can't fault these yet, as the stock is definitely undersized 
9.2 mm at it's maximum, for a m10 thread isn't gonna cut the mustard.
I thought I'd be able to get some sort of thread all the same though,
as I've used these on old soft nails to make wee bolts, and they didn't appear to loose anything off the diameter,
It appeared to burnish the threads and possibly increase diameter, but admit I never checked.







Be interesting to see if a good tap would make more pronounced sharper threads,
as you can see there's no slit in the cutter, 
and made sure the tool was the right orientation, just incase I had it wrong.

Also got some grease, although likely not what one would use for tapping.
Might have improved things.

Although no backing out and breaking the chip was necessary, as there was little resistance.


Pretty lousy result, don't have any 10mm round stock to try, but I think I would expect better results
with that, from what you folks are saying.





Sorry can't give a review of these, nor an answer for those who might have been curious.
The only rods in the shed I have are already threaded.

Thanks again folks
Tom


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## J-G (24 Sep 2021)

That Die-Stock is suitable for use with 'Adjustable' -- ie. split -- dies and you could turn that M10 die into a split die as well. If you have access to a Dremel with a slitting disc you could cut through where the 'V' is.

Starting with 9.2mm dia stock though will always be a problem and of course you don't know what grade of steel it is. It could well be 'black bar' or En32 neither of which will yield a 'clean' thread.


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## jimmy_s (24 Sep 2021)

jonn said:


> "The stock should be 10mm diameter or slightly over for M10."
> Wrong!!! It should be slightly UNDER for a good finish. The threads are slightly rounded, so with an M10 thread you get an outer diameter of from 9.85 to 9.95 mm. If the stock is thicker it's harder to thread, and also, you're likely to get tearing. Looking at the image you can see why the threaded part is slightly under the nominal diameter. That's also why when cutting threads with a lathe, you square off the tips of the threads slightly.
> View attachment 118349


He's not cutting it on a lathe he's cutting it with a die stock. Personally I open the die up slightly and cut it oversize and then drop the die back on grubscrews and fit the other thread. Get a better finish IMO but I'm sure there's more than one way to do it.


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## cowtown_eric (26 Sep 2021)

hexagonal dies are intended for rethreading, or thread restoration. Round dies are for cutting new threads. Found that out about a year ago.

Eric in the colonies


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## Inspector (26 Sep 2021)

Ah Eric there are exceptions to those rules.  I have a HSS tap and die set I bought from the Mac tool truck 40 odd years ago that has hex dies and taps from #4 to 1/2" coarse and fine that were sold for cutting threads which they do nicely. Okay unknown stainless rod not so much. The dies are not split like the decent round dies usually are but they still cut. I see no reason a set would have taps for thread cutting, (marked with the tap drill size) and dies for thread chasing in the same box.

I also have thread restoration dies (thread chasers) that would have a hard time cutting a thread in liquorice, red or black. They are nut sized so you can run them down the bolt with the same wrenches you use for the nuts of that thread size. 

There is a definite difference in the two.

I see the OP problem as being the undersized mystery metal.

Pete


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