M14 die cutting major diameter to 13.5mm

[perky416]

Hi guys,

Im trying to put an m14 x 0.5mm thread on an aluminium bar. I originally purchased a dye from china, used it and i found that it cut the major dameter of the thread to 13.5mm instead of 14mm.

Thinking it was a faulty dye i got my money back and ordered another, this time from germany. However yesterday evenining i tried to cut the thread and exactly the same thing happened it cut the major diameter to 13.5mm.

This time i cut a slot in the dye to open ip up a bit however the thread now cuts really rough and uneven.

I am using the dyes on my lathe...holding the bar in the chuck and using the tail stock to push dye holder.

Does anybody have any ideas as to what could be going wrong? Now it has happened with 2 different dyes i am starting to think it may be my technique.

Many thanks.

 

[3DDave]

According to this the OD should be smaller, but very close to 14mm

http://www.engineersedge.com/hardware/metric-external-thread-sizes1.htm

I would guess that the aluminum is galling in the die. Either it is feeding too fast or not able to eject the chips fast enough. Using tapping fluid can help; also it is important that the OD of the bar be the OD of the finished thread; I think 14 mm diameter material won't work well in a 14mm thread die.

You might also try single pointing the thread to remove most of the material and finish with the thread die.

Other than that I'm a bit stumped as the operation is normally successful, so there is less information on what causes the process to fail.

Check this thread to see if anything looks like it will help.

http://www.practicalmachinist.com/vb/general/how-do-you-pick-correct-rod-dia-threading-175196/

 

[Compositepro]

It is likely that the die is tearing the tip off of the thread profile. Having a sharp tip on an aluminum thread is not necessarily desirable. Check the thread using a micrometer over wires.