I'm making some parts with a .375-24 UNJF-3A threads. I have the proper insert for the "J" threads and have a .375-24 UNJF-3A "go" thread ring gage, but for the no-go gage I only have a .375-24 UNF-3A (not J). Can I use a UNJF go and a UNF no-go gages to check the threads, or do I need to have UNJF go and no-go gages.
Thanks for the help,
Originally Posted by Flash Gordon
Lets see if I can explain this correctly... it's been a very long time since I had anything to do with this sort of problem... but here goes.
Your making a part with a male thread and the J means it's a controled radius root thread..
For a low limit NUT to work, your male thread has to have a Pitch Dia near that low limit.
The controled radius has to be ground into the GO thread gage so it must go on. If the thread you make does not have the controled radius root, the GO gage may not go on because of interference with the crest of the GO gage and the root of your male thread..
Now for the NOT GO Ring gage, it should have a PD slightly smaller than the PD of the male parts smallest allowable thread your making so that IF it goes on, the PD of the part is deemed to small and not an accpetable part... if that condition exists then the root radius is not so much a problem, the part is undersize and scrap.
Therefore, I believe the same NOT GO Threaded Ring Gage for a standard thread is also used for a J threaded part...
If I'm wrong, I'm sure someone will be along shortly to explain why and how.
I found this by Googling when writing in another thread.
Unified National J Series vs. Unified National
Gary E is (almost) right but the link help explain things even more
The guy (Wayne aka gageguy) that gives his email at the bottom of the link is in my opinion an expert and I don't think there is much he doesn't know about gages.
I figgered it would be you to say "almost"
Originally Posted by Gordon B. Clarke
Now... just zactly where and why are you saying ALMOST ???
The Practical Machinist experts have come through again! That is exactly the info I was looking for. Thank you very much!
Depending on you customer they might not allow gauges to be used.
We are required to measure all J threads. This is done on a optical comparator with 100x lens. On a .375-24 UNJ the root radius requirement is R .0063-.0075. Ring gauges will not check that feature they are only made to clear the root radius. With go no-go gauges the flank angles can also be out of spec. but still gauge good.
If you have the equipment to measure the thread you can avoid using ring gauges for external threads.
You are correct about measuring the root radius. My QC dept measures the thread and root radius on the comparator, but it's nice to have the gages at the machine for set-up and in-process checks.
Well, since we're nitpicking, about the only thing Gary was "almost" 100% is that the go gage does not have the root R ground in, rather it's truncated to clear the root R.
This however brings up an issue Flash will have to take into consideration.
Since the Go-gage does not reach near the root of the thread, it is entirely possible that the gages ( even trirolls ) will show a perfect thread well within the tolerance, yet the shadowgraph shows a messed up rootform.
This typically happens on Inco, where the insert tip either breaks or wears off, yet the pitch is still perfect.
Just be sure to have some good procedure to take the extra step and look on the projector and not simply accept the results of the gages!!!
I can send a few pounds of Inco625 - 1/4-28 UNJF parts to set a bad example.