How do I machine a ball nut for a 6.3mm X 1.25 screw?

[bigj2]

This ball nut will fit z 6.3mm X 1.25 screw that I will, turn and grind the form threads on the screw, I do not have any experiance in making a ball nut that is turned and heat treated only from 440 stainless.The finish on the thread form needs to be around 16 micro and all dimentions will be turned. I was curious as to how to machine (mill) the thread form in the nut and attain a good finish so I do not have to grind it. Any special tooling such as thread mills, or hones that I can use to finish the thread before H.T?
Please recommend the tooling and a process that will allow me to make these nuts. I have an opertunity to make a lot of them.

 

[juergenwt]

6.3 x 1.25 ??????
Pls. post a drawing.

 

[bigj2]

6.3 mm major diameter x 1.25mm pitch x what ever length does not matter, I am looking for a way to machine the ball nut profile to achieve the finish results. I attached a drawing

 

[TVP]

First, X30Cr13 is equivalent to Type 420 stainless steel, not 440. There will be a big difference in machinability between these two grades. I would clarify whether or not a free-machining version of this grade would be acceptable, since it would improve both the cycle time and the resulting surface finish. Second, have you investigated thread whirling as a possibility for machining the threads? This is becoming more popular, and may help to achieve the desired surface finish. Thread forming taps instead of cutting obviously can achieve excellent thread quality/surface roughness, but this grade of stainless steel would make that a difficult operation, with low tool life.

 

[tomwalz]

You might try Practical machinist as well

http://www.practicalmachinist.com/

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[juergenwt]

bigj2 - thanks for posting. Unless you are really into ball screws and nuts, I would stay away from this one.
The drawing seems to be a crazy mix of metric, imperial and all kinds of converted dim's.
You can spot those drawings by looking at dim,s like 12.7 and others. 6.3 x 1.25 looks like a bastardized 1/4-20.
Save yourself a big headache.

 

[bigj2]

Thank you for the advise juergenwt, but the question is, how do I achieving the finish on the ball nut, not do I want to save myself a headache. Unfortunately, I do not have the option of declining to quote this job. I need to find a way to make it and succeed at the process. This is a big project for an international company that manufactures and sells products throughout the world, today's world it is a mix of metric and english based on the location of the end user and the location of the factory manufacturing the products. If you look at ball bearings, the races are all metric but the ball diameters are in inch sizes. If anyone else has any feedback on my original request please respond. I thank you in advance.

 

[mfgenggear]

have special taps made that are coated.
consult with local tool company that specialize with taps & can make these for you.
that is the best bet.

grinding from solid, having an automatic internal thread grinder would absolutely would give you the finsh required.