thread start position

[pedrof]

This may be a ridiculous question, but if you have an M66x1 thread on 2 mating parts, is it possible to specify the start position of the threads on each and hence guarantee the orientation of the screwed together parts?
Please be gentle.

 

[LECmeasurement]

First of all, I don't think this is a very accurate way to locate a part. When you tighten the part, there will be at least 1/4 rotation between tight and very tight. Using some sort of torque wrench might make that situation better, however I doubt you are going to get a very accurate alignment.

If you still want to do it, there are two ways..

If you were running production on this part, you would simply need to establish a constant setup. Common for all parts. (i.e. a hard stops to locate the part, automatic feed in from a set distance). Once you have it setup right, it should produce a constant result.

If this is a case of it being a one off part, I would cut the threads like normal. Then adjust it by grinding the contact surface between the 2 parts. This will of course alter the length of the part, but hopefully you have enough tolerance or the overall length doesn’t matter... If the length of the mated part does matter, I would make the thread 1st, see how the parts align at the required torque, and use that for a reference to fabricate the remainder of the part.

I have to admit I have never done this. I would personally not design something this way, because I don’t believe it would be accurate at all. But that doesn’t mean it hasn’t been done, and I could well be wrong about its accuracy.

Regards,
Ross Evans

http://www.lecmeasurement.com

 

[EngJW]

You could try a cotter pin joint where you tighten the nut to a certain torque and then continue to tighten it until the holes line up. If you postion the holes and slots correctly you would not have to over-tighten the joint.

 

[ornerynorsk]

Yes, you can specify thread start orientation (timing) on manufactured parts. Expect the cost to reflect your timing tolerances. This is actually common practice on many parts.

 

[RRBD]

I would not recommend it, but if you must,here's my two cents. 66 x 1 is very big diameter with a really fine pitch. Considering you will be cutting an internal thread,I would mill the threads,which will make it easy to orientate the starts of each. Next,I would try to use the minimum an maximum pitch diameters to my advantage and cut the piece closest to the head of the "fastener" to the higher end of PD tolerance and the piece furthest away in the normal to tight end of the PD tolerance.This will allow you some "forgiveness". Most Machinists will cry about syncronizing the ends/starts of threads.

Scott

 

[aamoroso]

I agree with the rest, it is possible, usually not practicle for the cost of getting it done and controlling it. If it is the only way to achieve the goal and you must use timing then you have no choice. If it is convenient then I would look for a better solution such as pinning the hardware.

Fill what's empty. Empty what's full. And scratch where it itches.

 

[CMfgE1]

The start position is irrelevant when concerned with where the part ends up. What is relevant is the distance from the start of the thread to the shoulder. Now each turn of the thread will be a specific distance. Using the shoulder as a stop you will achieve the same distance by cutting the same amount of threads needed to orientate your part by the time it gets to the shoulder. The Machinery's Handbook has formulas for the distance per TPI and diameter.
The torque at which you achieve the desired 'tightness' is subjective and will have to be controlled as stated above.


Good Luck

Quote: "Its not what you know, its who you know" - anybody trying to find a decent job

 

[icrman]

Leave extra material and lap or grind to fit.

 

[RRBD]

The lead/pitch of a metric thread is noted in its description, M66 x 1, "66" being the diameter and "1" being the lead or pitch,of, 1mm per rev. No handbook required.