Anyone know how to check an external (due to old rule number 3) thread for pitch also so i can use it as a Datum ? Any simple step-by step direction would be awesome!!!
Checking the pitch diameter is not possible, but you have options.
You can check the pitch diameter outside of the program, use a key-in dimension and input the measured value into a generic circle.
You can also forgo the pitch, and just measure the major diameter using auto-circle/cylinder and utilizing the pitch option.
Also, you can combine the two to get a relatively accurate center from the auto-feature, combined with the pitch measurement obtained outside the program in a generic circle.
If it is RFS, I would skip measuring the pitch diameter altogether. If it is MMC, I would still advise against using the pitch diameter. The way threads mate leaves practically no usable positional shift to make use of anyways.
Anyone know how to check an external (due to old rule number 3) thread for pitch also so i can use it as a Datum ? Any simple step-by step direction would be awesome!!!
You can buy a datum simulator, they are like ground sleeves that fit over the thread with a plane diameter on the outside. That is as close as you can get to actually picking the pitch diameter up as a datum feature. They are also available for inside threaded holes and used to check the position of them.
You can buy a datum simulator, they are like ground sleeves that fit over the thread with a plane diameter on the outside. That is as close as you can get to actually picking the pitch diameter up as a datum feature. They are also available for inside threaded holes and used to check the position of them.
I've seen the plugs for ID threads, but I have never seen one for an external thread. Are they priced similar to their internal counterparts? Do you have a link for a company that manufactures these? The internal Jo-Plug's worked great, but it doesn't look like they manufacture for external threads.
Anyone know how to check an external (due to old rule number 3) thread for pitch also so i can use it as a Datum ? Any simple step-by step direction would be awesome!!!
Old rule number 3? I do not know rule number 3, or I have forgotten it. Please explain.
Can't be done.
Shane,
Checking the pitch diameter is not possible, but you have options.
You can check the pitch diameter outside of the program, use a key-in dimension and input the measured value into a generic circle.
You can also forgo the pitch, and just measure the major diameter using auto-circle/cylinder and utilizing the pitch option.
Also, you can combine the two to get a relatively accurate center from the auto-feature, combined with the pitch measurement obtained outside the program in a generic circle.
If it is RFS, I would skip measuring the pitch diameter altogether. If it is MMC, I would still advise against using the pitch diameter. The way threads mate leaves practically no usable positional shift to make use of anyways.
I used to think it was not possible too, until I saw them doing it on a API taper thread at NIST!
You need a probe as close to the ideal wire size as possible.
You need one of the newer versions of pc-dmis that allows you to take a self-centered hit, or else you will need a lot of variable code to take a hit on each flank and then generate a midpoint between them.
Wes can you describe the self centering aspect of a hit? Have not a clue of what you speak.
Not certain which version it rolled out with, but now in autocylinder there is a measurment strategy option to do this.
Using the Cylinder Centering Thread Scan Strategy
The Cylinder Centering Thread Scan measurement strategy performs a thread scan by maintaining the probe centered within the thread. When you use this strategy, the diameter of the probe tip must exceed the size of the valleys in-between the threads in order to prevent probe shanking.
At NIST they were running Quindos. The probe was oriented perpendicular to the thread axis. The probe touched the part 3 times to record one P.D. hit. I asked and was told it was "self centering".
Then BKulpa told me the newest version of pc-dmis has this ability. Perhaps he can weigh in on that. I am not sure the centering thread scan strategy I found is what he was referring to, and it is not the same as what I saw happening at NIST.
At NIST they said they were using a probe the size of a thread wire for that thread, the ruby went into the valley of the thread, hit each side, then collected a P.D. hit. I suspect the first two were "up" the flank from the P.D and that final hit was the ruby contacting both flanks simultaneously, (just like a thread wire does). They were collecting 4 hits, (at the cardinal points, the tip rotated 90 degrees for each location), for each level to check the P.D., the pitch, and the taper. Then with a much smaller probe they scanned the flanks for thread form checks.
I now think the only way to do this is in pc-dmis is with logic and variables. Might turn ones brain to gelatin, but it should be do-able.
What we use is a center scan. We're finding the pitch diamter of a sprocket using a stylus with the same diameter as the pin called out on the drawing.
The center scan probes down one side of the tooth until it touches the adjacent tooth flank. Then it pauses for a second to equalize the pressure in the probing system to register a point.
But you MUST have a scanning system for this to work with.
What we use is a center scan. We're finding the pitch diamter of a sprocket using a stylus with the same diameter as the pin called out on the drawing. The center scan probes down one side of the tooth until it touches the adjacent tooth flank. Then it pauses for a second to equalize the pressure in the probing system to register a point. But you MUST have a scanning system for this to work with.
Thanks! I found it. It is a "basic scan".
So for the OP, you would need a scanning system, a probe that is the wire size, then you would have to decide a way to "clock" the thread and calculate the location of 4 points on the pitch diameter, at least two levels, then center scan each point, from those scans you should be able to construct the pitch diameter cylinder.
