Help With Threads

[robwilk]

I could do with a bit of advice please . I needed to thread a part M4 so I turned the part down to 4mm put a slight leading edge on the end then using the die holder in my tail stock and turning the chuck by hand I tried cutting the thread. This is the results.

As you may be able to see i don't have a lot of thread a m4 nut goes on OK but is very loose I had trouble starting the die which in turn started chewing the end of the part up then it just went from bad to worse. Can any body help me with my problem please as I have a few of these parts to make so I would like to get this correct now .
I have had trouble starting dies before but when they have started they have cut better than this. :shrug:

Rob........

 

[mklotz]

Are you sure that you're using the "starting side" of the die? Most dies have a lead-in chamfer on one side to assist them in starting. On some dies it is marked, on others you may have to inspect to find it. Try starting the thread on some scrap using each side of the die and see if one side works better than the other.

Are you using a split die? If so, open it to make it easier to start. Then, having gotten a thread started, close it down to bring the thread to size.

Put a goodly 45 degree chamfer on the end of the stud to help you get started. Apply pressure with the tailstock ram while starting the thread.

In extremis you can single point the thread to make a start, then finish with the die.

 

[maverick]

A method that I have used and that may amount to cheating is to drill and tap an M4 hole and loctite in an M4 set screw (grub screw?)

 

[Dave Sohlstrom]

Rob

According to G-Wizard the Major Diameter for a m4x.7 thread is 3.838 to 3.978 with a mean of 3.908 so if you are turning you part to 4mm then your major is to big and the threading die is having to take off the extra.

You can get G-Wizard at http://www.cnccookbook.com/CCGWizard.html It has a ton of info for the home machinist.

Dave

 

[MachineTom]

Are you using a hex type REthreading die, or a round split threading die. Is the dieholder sliding on an arbor in the tailstock, or fixed to the tailstock, which could also be the problem.

 

[robwilk]

Thank you for replying.

I am using a split die in a sliding arbor. Also i started the thread on the lead side of the die with a little pressure from the tail stock with plenty of lubrication. When putting the die in the holder i gently tighten the middle screw into the split not putting any pressure on then i gently tighten the outer two screws so the split die does not really change in diameter.

From the advice you have given i could try again with a bigger chamfer open the die a bit to assist the start and maybe turn the work piece down to slightly less than 4mm. How does this sound ?.

Thank you all.

Rob......

 

[mklotz]

From the advice you have given i could try again with a bigger chamfer open the die a bit to assist the start and maybe turn the work piece down to slightly less than 4mm. How does this sound ?.

That sounds good. Once you have a good start for the thread, you can reverse the die and use the "non-start" side to cut the threads closer to the shoulder.

Let us (and future readers) know whether your results improve.

 

[tel]

Also, leave the portion to be threaded over long, probably twice as long, until the threads are cut, then turn away the extra - you will get rid of any dodgy starting threads that way

 

[Maryak]

Looks to me like your die angled off centre, do everything tel said and keep a small amount of pressure on the die with the tailstock to stop it angling off. This happens in the lathe more often than you would think.

Hope this helps

Best Regards
Bob

 

[RManley]

Hi Rob. It does sound like your die is tilted in the holder, this is quite common as said and is done by the adjusting screws trying to rotate the die. So, make sure that the die is flat in the holder. Being only M4 you should be able to turn the diameter to 4mm without the die complaining - especially in brass. I tend to turn the diameters the thread size for all my threads - 10BA -> 5/8 whit. Occasionally for very small threads where I have enough material to waste, I turn down the end of the rod where I want my thread to its minor diameter for a 1/16-1/8". This guides the die onto the larger diameter section where you want your thread. Once done I just turn that bit off.

So, hold and rotate the die holder and not the chuck (even lock the spindle), this will give you greater feel and you should not need to use the barrel of the tailstock to apply pressure just use your hand. If you use the tailstock barrel you can sometimes force the die on the end of the job prematurely which can give funny results. Make sure the die is fully open and adjust to suit using a nut as a guide. Although once set to the right tolerance you should be able to do it in one hit. Oh, and you shouldn't need to use lubrication when cutting brass

Let us know how you get on.

Rob.

 

[robwilk]

Thank you all very much for your advise it takes a lot of the stress of learning a new skill when you know you have this kind of back up and support.
I tried cutting some threads tonight m4 on a piece of scrap brass I turned it down to 3.9 mm put a bit larger chamfer on the leading end then opened the die out and applied little pressure with the tailstock but I don't think I needed to as it started easily. After the first pass I released the die and ran it down the brass in its natural position and it turned out perfect.
;D Easy when you know how.
Thank again.

Rob........