Thread notation drawing
Thread notation drawing
(OP)
Design - shaft partialy threaded with external thread 1/2-20 UNJ.
I want to minimize fatigue failure by having the thread taper off at the point where the thread terminates on the interior portion of the shaft, versus having the single point cut a full rotation at the end of the thread.
Is there a standard callout for this operation?
I want to minimize fatigue failure by having the thread taper off at the point where the thread terminates on the interior portion of the shaft, versus having the single point cut a full rotation at the end of the thread.
Is there a standard callout for this operation?





RE: Thread notation drawing
that should be sufficient. You would have to be specific so as not to confuse the machinist into thinking it was some sort of tapered thread. I would highlight the detail on a drawing and use notes on the side to explain. Or a cross section with dimensional callouts would work to.
Maybe you just started something new!
Good Luck
Quote: "Its not what you know, its who you know" - anybody trying to find a decent job
RE: Thread notation drawing
If you are using a thread cutting die you should not have a circumferential cut at the end. The die starts as a taper and will end as a taper. Look at any pipe or screw tread.
BTW, having a circumferential groove at the end of the thread can profide some stress relief if a small radius is allowed in the bottom corners.
If you are machining threads on a lathe you should have a bit of run out to exicute the thread ending. Run out is a small gap where the thread ends to where the maiting component seats. Again provide ample radius there at the bottom of the runout groove and you should be fine.
If I have miss interpreted your meaning forgive me.
Best Regards
pennpoint
RE: Thread notation drawing
On a side note.
These are wheelchair axles. Our marketing guy is a wheelchair user and of course managed to break one. Here is the funny part. A local University’s test lab built a fatigue test fixture which failed before the axle. Maybe I will have marketing do all the testing from now on....NOT! :)
RE: Thread notation drawing
In the oilfield, the typical convention is to call out a quick start, which is simply grinding or cutting the minor to major diameter for about 1/8 rotation on the box. In this regard, there is no standard but a practice developed out of design concerns.
I'm not overly surprised with the lab results. Your marketing guy could of had a faulty shaft, perhaps a minor crack at the root of the thread, material issue, perhaps the shaft was somehow overloaded, etc. If you statistically monitor the population of failure and their mode, you would probably find the shaft to be of acceptable design given the loading.
Good luck with it.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Thread notation drawing
If that is not an option, I would specify that the thread root must runout over a length of not less than three thread pitches.
RE: Thread notation drawing
RE: Thread notation drawing
What model wheelchair were you talking about in your side note?
RE: Thread notation drawing
I'm not sure any of the CAM systems can automaticly generate the proper CNC codes to do it. This will probably have to be manually programmed and not with a canned cycle thread process but with individual threading passes.
Over the years I have cut face thread/groove and removed the first thread on an OD threaded part with a grooving tool used in a threading cycle with a threading cycle to withdraw the grooving tool from the part.
RE: Thread notation drawing
The callout is "Threads Full to Taper" both books show exactly that in a pullout with the arrow pointing to the position where the taper is to start.
Doing some checking I found the same notation in a reference to creep and fatigue testing coupons from US Steel Research labs.
RE: Thread notation drawing
Does it give an angle or the rate of pullout(in/ft)?
RE: Thread notation drawing
Just talked to an old machinist and he stated he usually used 1/4"/ft based on the diameter of the part being threaded. He also stated this was not always possible and the norm was to taper out in 1 1/2 to 2 revolutions of the part being threaded if possible.
None of my books have good indexes so I’ll keep looking. I will try to get some information from some people who do single point threading for living.