Dies

[redvan22]

Hi,
I was recently told that there are differences between hexagon shaped dies and round dies; hex dies are for repairing threads while round dies are for cutting new.
This doesn't make sense to me. I would think that the shape of the hex die would make cutting easier due to the fact that the die shape would prevent it turning in the die holder where as the round might turn with the work.
Also, I was told, that the hex dies are slightly tighter than the round because of their designed purpose - to fix bad threads.
Now from watching some youtube videos regarding machining small parts for kits, the machinist always uses round dies when cutting threads and, some have an adjustment screw that I guess, acts like a wedge to open the die a few thousands. Can't imagine more than that simply because there's no hinge on the opposite side.

Can someone clarify all this for me please. The internet was less than helpful.
Red.

 

[Bob Korves]

I was recently told that there are differences between hexagon shaped dies and round dies; hex dies are for repairing threads while round dies are for cutting new.

Not necessarily true. Round dies are designed for being used with a handle or other holder to drive them, and hex dies are designed for being used with a wrench or a socket to drive them. Often, trades like auto mechanics used hex dies for repairing existing threads in tight places, and that is where people got the mistaken idea that hex dies are only for repairing threads. Dies for repairing threads are easy to identify, they have negative rake geometry where the thread starts, and less or no relief for the rest of the threads.

What is important is not how the die is driven, it is how the tool makes or chases the threads. When straightening or otherwise cleaning up existing threads, the last thing you want to do is remove material. So re-threading dies are not made to cut threads, they are made to re-form threads. Threading dies have sharp cutting edges for removing metal. They remove metal to make the new threads.

If you look closely at the starts of die threads carefully, you can see what they are designed for. I have lots of dies, hex and square and round, and for all different holders sizes. Some are for cleaning up existing threads, others for cutting threads. I have two Craftsman "Kromedge" hexagon die sets, one imperial and one metric, that I bought new in the 1960's, which have cut hundreds of threads from new stock, some in pretty hard materials, and are still sharp and going strong. None have broken, and they still look like new, even close up. If they were specifically made for reforming existing threads, they would have failed at doing the work I have done with them.

So, again, you can only tell if a die (or tap) is for cutting threads or for cleaning up existing threads by looking at their geometry closely, regardless of how the die is being driven.

 

[Tom1948]

Thanks for the info. I had wondered about that myself.

 

[pacifica]

And good dies are expensive since you need one or more for each thread size.

 

[HoBBiePress!]

Not necessarily true. Round dies are designed for being used with a handle or other holder to drive them, and hex dies are designed for being used with a wrench or a socket to drive them. Often, trades like auto mechanics used hex dies for repairing existing threads in tight places, and that is where people got the mistaken idea that hex dies are only for repairing threads. Dies for repairing threads are easy to identify, they have negative rake geometry where the thread starts, and less or no relief for the rest of the threads.

What is important is not how the die is driven, it is how the tool makes or chases the threads. When straightening or otherwise cleaning up existing threads, the last thing you want to do is remove material. So re-threading dies are not made to cut threads, they are made to re-form threads. Threading dies have sharp cutting edges for removing metal. They remove metal to make the new threads.

If you look closely at the starts of die threads carefully, you can see what they are designed for. I have lots of dies, hex and square and round, and for all different holders sizes. Some are for cleaning up existing threads, others for cutting threads. I have two Craftsman "Kromedge" hexagon die sets, one imperial and one metric, that I bought new in the 1960's, which have cut hundreds of threads from new stock, some in pretty hard materials, and are still sharp and going strong. None have broken, and they still look like new, even close up. If they were specifically made for reforming existing threads, they would have failed at doing the work I have done with them.

So, again, you can only tell if a die (or tap) is for cutting threads or for cleaning up existing threads by looking at their geometry closely, regardless of how the die is being driven.

Hey Bob, that is great information, thank you. I have another conundrum... I have recently purchased the Irwin-Hanson 1766070 Die Stock handle. In the package there was what they called an "adapter" to be used with standard 1" hex dies. So I figured out what the adapter was for only by inserting it into the handle and then setting my hex die on top of it in the handle. I could not find any information explaining the use of this "adapter" either on their website or searching any videos or reviews. My conundrum now is, if they consider the die to be used with this "adapter" is called a "standard" die, what are the dies called that are the thickness of the std die and this adapter ? I have other dies that are 1/2" thick and these "standard" dies that are 25/64 of an inch... Is this just a manufacturers choice or is there an application reason ??? Thank you for reading my conundrum. I hope there is an interesting answer !!!
Scott