# Using dies



## jwmay (Jan 28, 2018)

Hello all, 

So here’s my issue: I must be doing something wrong because I can’t get any die to start. My dies are not expensive,but they are new. I had thought to blame the dies. Some of them won’t even thread onto a store bought screw. So today I was looking to thread a (unknown metal) shaft m8x1.25.  Turned it to   .315”, and fought it till the end of the rod was chewed up. Turned it it .307, and tried again. Same thing. Turned it to .302, and tried again. No go. So it’s technically too small I think, at this point. Anyhow, my final idea was to turn a 5 degree taper on the end of the shaft, to try that. Ofc, at this point the parts at .302, and hanging out of the chuck 2 inches. Turning at 220 rpm, the cutting tool grabbed the part and bent it. I’ve got three hours in this part.  So I laughed at myself. Having “known better” and then having the machine prove it to me, I can do nothing but laugh at myself, and start over. The  (12l14) part gets remade, this time with a taper on purpose over about a quarter inch. Anyhow the die (or my tactics) still doesn’t work. I have the idea to start the thread with an old adjustable 5/16-18 die I have. The size being very close. This works! After two threads , I switch to the metric die and it’s easy as pie. So I did get it done, but this is the only size I’m aware of that would actually work like that with. Long story I know. But the devil is usually in the details.  So what’s the problem? After I had a couple threads, the metric die worked great. Are my inexpensive dies just absolute junk? Or is there a possibility that I’m doing something wrong? I tried to use the tailstock to put pressure on the die to help it start. Put my success came when I took the part out, put it in a vise vertically, and used the big antique standard die. I will say the old dies I have,  start with almost no effort, but cut oversize. The new dies seem under size, and won’t start....like never. I can’t say I’ve had success with any of them. Usually I’d just single point the threads, to avoid using the dies. But this being a metric thread I was unable. I guess I could have single pointed 18tpi, for three threads, but I’m skeptical I’d have succeeded at that either. So again, bless you if you read this whole thing. Suggestions? Advice? Questions? What do ya got? Thanks in advance!


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## ELHEAD (Jan 28, 2018)

Had the same trouble with a tap and die set, tagged " HENCHO en CHINE". After rummaging thru my odd box of sies found an old Rusty American made die and finished the thread with no problems. Later tried more of the dies in the set on some thread chasing and found that they were worse than worthless for that too. Most buggered the thread they were supposed to be cleaning up. My thoughts lean toward getting better quality I don't think you will regret it.
DAVE


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## ezduzit (Jan 28, 2018)

This would not be a hex die, would it? They are intended only for cleaning up existing threads.


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## Aukai (Jan 28, 2018)

I just had a similar problem, and discussed it in another thread.

https://www.hobby-machinist.com/threads/ran-into-a-die-issue-today.65817/


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## RJSakowski (Jan 28, 2018)

A couple of points.  First, are you starting from the correct side of the die?  Dies have a taper entrance on one side to make cutting the thread easier.  The backl side has a chamfer but it would be difficult to start a thread from that side.  My dies have a "start this side" etched on the face but some dies don't.  Second, to make it easier to start a thread running correctly, I will turn a short lead to the minor diameter or slightly more.  When I've finished the thread, I cut of the lead.

Finally, some of the dies out there are crap.  I bought a set at a local farm supply store for a rediculously low price.  They were supposed to be HSS and weren't.  I took them back.


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## jwmay (Jan 29, 2018)

Ok. Well I’ll try to answer the questions. These are threading dies, and not rethreading dies. I started (tried to) with the internal taper of the die engaging the work first. They are “mid grade” dies. Meaning not the cheapest, but also not the most expensive. They were labeled as hss. 

So assuming I need to buy better dies, how much money buys a good set? It’s a shame we have to wait 50 years for a good set to be affordable. I paid 80 dollars for my standard set and 50 for the metric set.  Mibro is the brand name on the standards, but I can’t remember the name of the metrics. They DID come from a farm supply store. I don’t want to piecemeal the set due to compounding shipping costs. Will 200 dollars buy a good set?  300?  1000?


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## mikey (Jan 29, 2018)

I have some suggestions. 

I would turn a short 30 degree taper on the end of the work; this helps the die start easier.
Starting a die is much easier if the die is solidly held so the that the face of the die is perpendicular to the work piece. A tailstock die holder will probably make your life a lot easier.
A dull die will not cut. A sharp die will bite immediately. If your dies will not bite then they may either not be sharp or their thread form may be of poor quality. Check the die and make sure there are no defects in the threads inside. If you see burrs or inconsistent thread form then the die is probably not going to be useful.
Be sure your work piece is the correct diameter. An M8 x 1.25 thread requires a major diameter of 7.972 - 7.760mm OD; your work piece should be inside this range, then put a 30 degree taper on the end.
When starting a die, use the wider taper and make sure the die is square to the part. Then apply steady firm pressure and the die should bite immediately.
If all else fails, buy a good set of dies. Ideally, buy HSS dies - they will last much longer. There are many kinds of dies but the most common are the hexagonal ones; these are threading dies, not chasing dies. The dies commonly used on a lathe are the round button dies with a split on one side; they are the most expensive and require a round die holder with three screws to hold the die in place. One of the screws allow you to adjust the fit of the thread. HSS button dies can last for many years in a hobby shop and are worth their cost if you can afford them.

Every manufacturer of taps also make dies. As @Aukai noted, see his thread. If I wanted a decent set of taps and dies at a fair price, I would be looking for a Craftsman Kromedge metric or imperial set on ebay. Great HSS taps and dies but no longer made so the sets will either be used or NOS. Prices vary but if you're patient you will find them.

One more thing. Cutting theads with dies is a high pressure situation. Sulfur bearing cutting fluid works well for this.


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## savarin (Jan 29, 2018)

Do the dies have an adjusting screw to open them up a bit? If they have they may be adjusted too tight.
Just a thought.


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## rgray (Jan 29, 2018)

I have a set like this from snap on that is 35 years old. I have broken a few but most are still very good.
https://store.snapon.com/SAE-Metric-Combination-Set-117-pc-Master-Tap-and-Die-Set-P644918.aspx
I recently bought this set from snap on. https://store.snapon.com/SAE-Sets-41-pc-US-Tap-and-Die-Set-P630631.aspx
The quality is still good on the new ones surprisingly. They are worth the money as far as I'm concerned.

I bought new 1/4-5/8 japanese dies in hss about a year ago and they work but are not going to last long I can tell already.


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## ezduzit (Jan 29, 2018)

mikey said:


> ...There are many kinds of dies but the most common are the hexagonal ones; these are threading dies, not chasing dies...



Hex dies are chasing/re-threading dies. Round dies are threading dies.


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## RandyM (Jan 29, 2018)

ezduzit said:


> Hex dies are chasing/re-threading dies. Round dies are threading dies.



So, what makes them different other than the outer shape?


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## ezduzit (Jan 29, 2018)

RandyM said:


> So, what makes them different other than the outer shape?



One is designed to restore buggered threads; the other is designed to create new threads.


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## RandyM (Jan 29, 2018)

ezduzit said:


> One is designed to restore buggered threads; the other is designed to create new threads.



I know the definition of them, what is the science?


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## T Bredehoft (Jan 29, 2018)

mikey said:


> Cutting threads with dies is a high pressure situation. Sulfur bearing cutting fluid works well for this.



Uh, we're machinists and tool makers not scientists... 

It's probably in the geometry of the thread cutting surfaces.  Perhaps Mikey can help on this.


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## mikey (Jan 29, 2018)

ezduzit said:


> Hex dies are chasing/re-threading dies. Round dies are threading dies.



First time I've heard of this. I've been using hex dies to cut new threads for decades and have not had a problem. I have used thread chasing dies but they are labelled as such.


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## Silverbullet (Jan 29, 2018)

Some not all rethreading dies have staggered teeth in them so they do a better job of repairing buggered up threads on bolts and parts. Usually they never come with a wrench in the sets. I'd keep an eye on craigslist or eBay and some auction sites . Greenfield is a great old maker. Union, butterfield another , most any of the old USA sets are the best. 
Recently I saw a very big complete set in my area that if I remember was under $200 .


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## Silverbullet (Jan 29, 2018)

Greenfield ok junior set looks like both sae metric up to 1" with up to 3 sizes of dies its number 4700
Craigslist in NJ # 647-461-4220 
Marlton $260.


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## cg285 (Jan 29, 2018)

https://www.mcmaster.com/#tap-and-die-sets/=1bcbijf


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## magicniner (Jan 29, 2018)

RandyM said:


> I know the definition of them, what is the science?



Fixed size thread restoring dies cannot be opened up to take a first cut on an awkward material on which it may otherwise be very difficult to get a thread started, otherwise there is little difference, I have ground a slot in HSS Hex dies and used them like normal split dies, using my skill and judgement to expand them as required ;-)


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## jwmay (Jan 30, 2018)

Thanks to all for the help, advice, suggestions, and links. It was all very helpful!


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## GoceKU (Feb 5, 2018)

I'm little late on this thread, but wanted to add my own to sense to it, when i'm treading using a die in my lathe i often use the tailstock with a drill chuck to push against the die to start first 2-3 treads, some time back i build this holder to fit in my MT5 tailstock, i set my speed to 63rpm and push the tailstock by hand till it starts and the treads pulls the tailstock by it self, perfect threads every time and lastly don't expect to be treading hardened steel don't attempt anything harder then 1045 with inexpensive dies.


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## chips&more (Feb 5, 2018)

The only way to get “perfect” threads if perfect is possible? Is to roll the threads. Single point, geometric die heads and whatever dies all have limits to being perfect. And a flood of coolant...Dave


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## umahunter (Feb 9, 2018)

I would try buying one good American made die first to see if that fixes your problem before buying a whole set if it works great if not than you can try and figure out the problem  from there


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## Taborclock (Feb 16, 2018)

Or you could be like me yesterday and pick up a left hand die and try to make right hand threads with it.....LOL....


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## agfrvf (Feb 16, 2018)

Have you thought of cutting the start of the thread by hand. If you get close the die will catch and go the rest.


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