Dave K
Diamond
- Joined
- Mar 21, 2004
- Location
- Waukesha, WI
If yes, how is it done?
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Crap. Gonna need some thread wires then.
The "how" isn't difficult. Extend the lines so you have a sharp pointed thread, both crest and root. The pitch diameter is measured from the 50% points. You should be able to make an overlay on clear plastic that's good enough to get the job done.
Depends how you use it. Precision leadscrew moves part in relation to crosshairs. As good as the leadscrew if the feature is clear. Micrometer- compares to a precision leadscrew. No Aero-Defense allows comparator inspection? How about video inspection? Somebody's still in the 1940s.
Holy mother of micro stuff, how do they make those? That's right about the size I use.
Now, just to rant a bit, why can't we get anything like that made in the US? Almost everything I do, if you can get it here the costs make it a non-starter. The affordable specialty items all come from overseas.
Or a Thread measuring micrometer. Stop by if you need me to measure something.
Yes you can measure pitch diameter this way.
Simple thought, make an overlay with your thread wires on it.
BUT measuring pitch dia is not the same as all the things a go/no set checks.
The same goes for thread wires. Most experienced people have seen a wire mic check ok but it fails the go/no gauge.
Hence the deal for not accepting just an optical and the requirement for the go/no check on fussy stuff.
Simple optical methods do give you a number to adjust from that a go/no won't but they don't check for overall form fit so may pass threads that a go/no will not.
A vision system correctly set up for thread checking makes lots more measurements than just PD and gives numbers on true to form.
Such systems are normally custom builds for high volume production in a family of parts. Read that as expensive. I have built some for very picky people making many wheelbarrows worth of parts every hour.
Yes you can measure pitch diameter on your optical comparator if you have the right mag and do the table offset twist angle thing, but there is ton more things to get right when making threads. You can check those too but it becomes very time consuming on a manual compartor.
Threads are a form fit, worse yet you can violate the PD and pass a go/no set so everybody becomes fat,dumb, and happy with a bad thread.
So common that you would think it easy but screw threads are in fact a nightmare to inspect and qualify.
I learned that it is a rabbit hole that once you go deep into.............
What sucks to no end about go/no gauges is that they tell you nothing about what to move or how much so the guess and check model becomes the way out. I'm not a fan of the go/no alone technique but I know it's SOP.
One should trust your inserts/dies etc. to be right. Nail the PD and length spacing and all is good, What could go wrong?
Bob
wow old thread but since you brought it upunderstand a little late to the party but how do you account for the helix angle of the thread? on the comparitor?
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