Help Measuring External Buttress Thread

# Thread: Help Measuring External Buttress Thread

1. Plastic
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## Help Measuring External Buttress Thread

Need some help measuring an external buttress thread. First time cutting a buttress thread, so bare with me. The print calls for a 5.800 - 12 BUTT - 3A. Luckily, the customer does give some more information on the thread. It is called out as follows:
Major Diameter 5.7885 - 5.7911
Pitch Diameter 5.7385 - 5.7441
Minor Diameter 5.6712 - 5.6836
Thread is a 45 & 7 degree

I have read several posts about measuring buttress threads and was planning to use the traditional 3 wire method. However, I have not been able to find anything online about a suitable wire size and constant. One post in particular I found said that measuring external buttress threads is "Otherwise Basically the same" as measuring standard threads. I was unsure if that meant that using a wire size and constant for a 12tpi 60 Deg thread would give me an accurate measurement on an asymmetric thread like this. Does anyone have a way to calculate what size wire I should be using and a constant for that wire size?

2. The best wire diameter is 0.04512". I use ThreadPal - dimensions and tolerances for inch and metric screw threads
and that gives me everything I need.

I've been making measuring equipment for, among other things, Buttress threads for years. See the following for how I do it. After zeroing no calculation necessary. What you see is the pitch diameter.

3. Plastic
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Is it possible to use .055" wires? I have a set of .055's in a thread measuring set I have. And if possible, what would the constant be?

4. Originally Posted by MR2Stewart
Is it possible to use .055" wires? I have a set of .055's in a thread measuring set I have. And if possible, what would the constant be?
I think the largest wires you can use are 0.051.

Find/buy wires at perhaps 0.05 or slightly less and either use CAD or do the trig. calculations.

If I seem slightly "unhelpful" then I'm acting on "Give a man food and he'll soon be hungry again. Teach him to fish and he'll live much longer".

Your "constant" will depend on the wire diameter you choose to use so you can't be helped before you or anyone else knows what that is.
Last edited by Gordon B. Clarke; 05-03-2019 at 04:31 AM.

5. Plastic
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I have a set of .045" wires. What would the constant be for those wires, or how would I go about calculating it? From what I am seeing it looks like with a .045 wire I would use a constant of .0681. Can anyone confirm this?

6. Originally Posted by MR2Stewart
I have a set of .045" wires. What would the constant be for those wires, or how would I go about calculating it? From what I am seeing it looks like with a .045 wire I would use a constant of .0681. Can anyone confirm this?
Looks about right but I'm wondering how you arrived at it.

Make sure the top of the wires are above the thread OD.

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