Measuring Thread with a single wire.

Scra99tch

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If all I care about is the normal pitch divided by 2. A single wire gives me a close result but my threads are almost four inches in diameter and I am basing the measurement off the O.D. and a solid works model showing me where my pin sits above the thread.

Anyone know of a setup that utiliizes a 4-5" micrometer and can easily hold wires into place. Some of the theread forms I make need <.02" wires.
 
You would be much better off with a thread micrometer; Chinese ones can be had fairly cheaply.
 
Thread mics are a real pain on fine, large-diameter threads. It's very difficult to get them properly lined up on opposing threads.

If you're using thread wires, you really need to use three, not one. I generally use two pieces of masking tape, one as a flag on the single wire so you can find it when it falls in the chip pan, and the other holding the two opposing wires from one end, making it a little bit easier to manipulate them (and to find them when they fall in the chip pan).

Another alternative are the small plastic holders from Flexbar that slip onto the anvils of your micrometer and keep the wires from flopping around. I would still put a piece of tape on the end of the wires just so that you can find them when, not if, they fall in the chip pan.

A third option is using thread triangles. These are machined triangular bars that attach to your micrometer anvils with little brackets. I haven't used them, but I think they would probably be ideal for your purposes.

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I have thread triangles, and they are no fun either; the cheap rubber things that are supposed to hold them on the anvils are not very effective.
Another possibility is a vee anvil micrometer, 'tho only good for comparative measurements, not pitch diameters.
 
I worked out a procedure to measure thread pitch diameter with a single wire. I basically involves measuring the O..D of the thread and measuring the diameter plus a wire.
 
I worked out a procedure to measure thread pitch diameter with a single wire. I basically involves measuring the O..D of the thread and measuring the diameter plus a wire.


Yeah this is about the best way I have found. Easier modeling it in solid works to find the amount the wire would be sticking above the diameter. It would be holy hell to use three wires on these dies I am making 4+ in diameter.
 
Yeah this is about the best way I have found. Easier modeling it in solid works to find the amount the wire would be sticking above the diameter. It would be holy hell to use three wires on these dies I am making 4+ in diameter.
I find that SolidWorks is the best machining math tool in my arsenal. It's really easy to whip up a sketch to solve a math problem that would otherwise be difficult or impossible to solve.
 
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Yeah this is about the best way I have found. Easier modeling it in solid works to find the amount the wire would be sticking above the diameter. It would be holy hell to use three wires on these dies I am making 4+ in diameter.
I did an error analysis of both methods and found that it was only slightly less accurate than the three wire method, largely because of making two measurements instead of one. It is important to remove any burrs from the o.d. when using the single wire method though. Burrs won't affect the three wire method.
 
I actually find it easier to use the 3-wire method on larger diameters as opposed to smaller ones. The micrometer seems to stay put a little better, there's a substantial enough diameter to rest a finger against, and the wires don't crowd each other as much.

I realize everybody has their own techniques and preferences, but for me anyway I was surprised that l had less frustration with larger diameters versus small. I haven't used any other of the alternate methods though, just the 3-wire.

-frank
 
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