Thread Rolling Blank Diameters

I think it is .1969 minus one thread depth. M5x.8

Diameter of Blank for thread Rolling:Machinist Handbook

The diameter of the screw blank or cylindrical part upon which a thread is to be rolled should be less than the outside screw diameter by an amount that will just compensate for the metal that is diplaced by the rolling process. The increase in diameter is approximately equal to the depth of one thread.

Beware:tolerances and allowances depend on material conditions.

also found this info from a Company who specializes in thread rolling .

The lack of CNC controls on most equipment means that the process is not as user-friendly as screw machining, turning, or milling. It is difficult to explain to customers that the major diameter actually increases in size when rolled. Some do not want to believe that they can turn their blanks below the major diameter and that their parts will not be scrap. For example a .250-28 UNF-3A thread has a pitch diameter of .2268-.2243 and a major diameter of .2500-.2435. The blank size prior to roll threading will be near the maximum pitch diameter and the material displaced by the dies will form up to fall within the major diameter tolerance.

Good Luck!

Old Bill

Are you using round dies or flat dies?

What material are you rolling?

Has it been cold formed prior to rolling?

What make of Machine is your roller?

and the speed of the machine PPM?

What class of thread are you expecting to acheive?

You are aware that you will be producing a production thred as aposed to a screw thread?

The Machininst hand book will help you out to some extent or you can get your thread rolling dies built by an experienced team that has solved all the issues that are going to present

Bill let us know how you get on

Bill we would love to help you out...... Anthony@alno

http://www.alnoproductservices.com.au

I think blnk turn diameter for external rolling thread should be equal to pitch diameter of the requried thread size.

Hey Vidyadhar,

Very Wise this is where we started possibly ten years ago but you need to consider forming clearances.

Anthony@Alno

www.alnoproductservices.com.au

Dear Anthony

Yes ofcorse have to consider forming clearances ,i think even it is depenp on class of thread you want is it not? ie.fine corse etc.

the minum diameter before rolling is 4.59mm and max. is 4.64mm

If you are pertaining to M profile threads it would depend on the class fit,metal being rolled,plate allowance if any and the hardness. that being said 80% of preroll blank dia's I use are between 60 and 80% of the pitch dia tolerance.If rolling say mild carbon steel lets say 4140 and there's no plate allowance and your pitch tolerance is .004 inch I would turn the blank at 70%threrefore add .0028(70%) to low limit of pitch dia