Will turning a thread die around to thread to a shoulder break the teeth?

[basalt]

I tried to research this but could not find a good answer. Do solid thread dies have a relief behind the cutting edge? If so wouldn't turning the die around negate this relief and possibly break the teeth?

 

[atomarc]

Interesting, that's something I never considered. I have run small dies from the 'wrong' side on many occasions to thread to a shoulder and have never noticed a poor thread when using them properly at a later date. Maybe I should put on my magnifiers and take a closer look at the die.

Stuart

 

[Limy Sami]

Almost all HSS Ground Thread dies - both split and solid, are form relieved ground as per your pic, and yes running them backwards probably will damage them, and WILL produce poor ill fitting threads.

You don't say why you want to thread that close to a shoulder, but it's considered bad engineering practice, - it creates stress points etc etc,.......''good practice'' says 1 1/2 thread pitches minimum from a shoulder, with an under cut if the female has to abut the shoulder.

If you have to thread up to the shoulder either find a die with no lead in, or grind the face of a fie to remove the lead, .......if threading by hand etc you will need to go as far as you can with a die with lead, then do the last bit with a zero lead die.

Whereas Cut Thread dies have no form relief, so up to a point can be turned over, ....but Cut Thread dies are usually cheaper and considered inferior, for they are basically a tapped hole in high carbon steel that is then heat treated, with possible distortion etc etc from HT and having no thread relief can make threading on some material VERY hard work and often at best ''so so'' work.

 

[FredC]

I think this is done routinely to get threads close to the shoulder but most if not all dies do not have any clearance in the direction so eventually they will probably break down but if it does happen it probably will not affect the die much in the "forward" direction. You have to what you have to do.
Just to be clear this is done by running up to the shoulder in the forward direction then turning the die around trying to get a little more.

 

[gustafson]

I don't think I have particularly damaged any doing this. The problem is the leadin is too great on a standard die, if you are doing something short there is basically no correct thread, even with an undercut. It is a very small amount of material you are trying to remove.

Yeah its wrong but dies are cheap....

 

[thermite]

I tried to research this but could not find a good answer. Do solid thread dies have a relief behind the cutting edge? If so wouldn't turning the die around negate this relief and possibly break the teeth?

I've done rather a lot of that to finish up close to shoulders. There SHOULD be at least a modest undercut, radiused, and there FIRST. Even so, it surely can break one now and then.

One just has to take extra care.

And they do still make replacement dies, so nothing like the PITA busting a tap down-hole is.

JFDI

 

[projectnut]

You may be able to get away with it a couple times, but I wouldn't stretch your luck. I have half a dozen 1/2-13 dies setting in the cabinet with one missing tooth. It seems the swarf got caught between the shoulder and the last tooth and that was the end of them. The worst part is you don't even know it happened until you back off the die. When you clean out the swarf it's obvious what happened.

It's not so painful if you ruin a cheap $15.00 carbon steel die, but when it's a $50.00 HSS Greenfield it hurts a bit more.

 

[L Vanice]

In my experience, the answer to the question is maybe. The cheap carbon steel dies I got at the hardware store or Sears in the 1950's were usually flat on the back, with no chamfer on the teeth. That left one tooth razor thin and it would usually break off the first time I tried to get a half or one full thread closer to a shoulder after first using the die in the normal way.

Eventually, I started buying good quality HS dies and I found they often had one side relief chamfered normally and the back with a smaller chamfer. Those do not break a tooth when doing the final cut up to a shoulder. That type of die has chamfers sort of like the ones on plug and bottom taps and I use them for a similar purpose.

It is possible to use a miniature die grinder with a mounted point to add or resharpen the relief chamfer on a die.

Larry

 

[basalt]

Thanks guys, for all the answers and insights.

 

[EPAIII]

Perhaps they make them that way in the UK, but I have never seen one with any relief behind the cutting edge. It is, in fact a bad idea because this area provides guidance for the die and if it was relieved, then the die could easily cut a crooked thread. The same thing applies to taps.

As for breaking the teeth on the back side of a die, I have used them this way and yes, they can break. I doubt that there is any warranty that covers this. So you'll be careful now. And better brands often do have a shallow taper there, probably because they realize that they will be used this way.

Almost all HSS Ground Thread dies - both split and solid, are form relieved ground as per your pic, and yes running them backwards probably will damage them, and WILL produce poor ill fitting threads.

You don't say why you want to thread that close to a shoulder, but it's considered bad engineering practice, - it creates stress points etc etc,.......''good practice'' says 1 1/2 thread pitches minimum from a shoulder, with an under cut if the female has to abut the shoulder.

If you have to thread up to the shoulder either find a die with no lead in, or grind the face of a fie to remove the lead, .......if threading by hand etc you will need to go as far as you can with a die with lead, then do the last bit with a zero lead die.

Whereas Cut Thread dies have no form relief, so up to a point can be turned over, ....but Cut Thread dies are usually cheaper and considered inferior, for they are basically a tapped hole in high carbon steel that is then heat treated, with possible distortion etc etc from HT and having no thread relief can make threading on some material VERY hard work and often at best ''so so'' work.

 

[Peter from Holland]

When my dies are blunt I use them from the other side to get some extra time out of them
Or I put them in the holder the other way around by mistake
The ones I have (SKF Dormer A.O.) have a small chamfer on the back side too
No sharp thin sections
I don`t think they have a relieve Never noticed any in use
Peter