Chart for threading with compound set at 29 or 29.5 degrees

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737mechanic
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Chart for threading with compound set at 29 or 29.5 degrees

Post by 737mechanic » Wed Feb 24, 2016 12:30 pm

Was doing some threading the other day and thought I would try to follow the numbers on the threading fish tail and realize they did not work the way I figured they would.

So after doing some research found they are calibrated for feeding straight in using the cross slide not the compound set at 29 degrees.

I have tried to find a chart or something that shows how much depth of cut it takes using the cross slide set at 29 or 29.5 but have not found anything. So does anyone have a link that shows the proper depth of cut to get a proper thread using the crosslide set at 29 or 29.5.

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ctwo
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by ctwo » Wed Feb 24, 2016 12:41 pm

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warmstrong1955
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by warmstrong1955 » Wed Feb 24, 2016 12:52 pm

Compound Travel = Thread Depth (per side) / cosine of the compound angle

With the compound at 29.5 degrees, that equates to:

Compound Travel = Thread depth (per side) / .8704

Bill
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SteveM
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by SteveM » Wed Feb 24, 2016 2:20 pm

warmstrong1955 wrote:Compound Travel = Thread depth (per side) / .8704
Would that apply to measuring the thread pitch diameter, i.e. if I measure with my thread pitch mic that I have 25 thou to go that I need to advance the compound 29 thou (0.025/0.8704=0.0287)?

Steve

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ctwo
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by ctwo » Wed Feb 24, 2016 3:52 pm

The formula calculates the hypotenuse of a 29.5, 60.5, 90 degree triangle, and the compound follows the hypotenuse with the acute angle measured between the cross slide and compound.

That will take a radial amount, so it depends on if your compound is direct reading (which now that I think about it, aren't they all?) or diameter.

How do you know the thread depth per side without using another chart?

BTW, I was trying to see the difference between national form tool and V form tool. What is it?
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GlennW
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by GlennW » Wed Feb 24, 2016 4:16 pm

The truncated tip on National Form vs the sharp V.
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warmstrong1955
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by warmstrong1955 » Wed Feb 24, 2016 4:29 pm

SteveM wrote:
warmstrong1955 wrote:Compound Travel = Thread depth (per side) / .8704
Would that apply to measuring the thread pitch diameter, i.e. if I measure with my thread pitch mic that I have 25 thou to go that I need to advance the compound 29 thou (0.025/0.8704=0.0287)?

Steve
Divided by two....yes.
Calcs are per side.

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warmstrong1955
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by warmstrong1955 » Wed Feb 24, 2016 4:40 pm

ctwo wrote: How do you know the thread depth per side without using another chart?
Here....play with this.....

A simple thing I created to feed me numbers, without grabbin' a calculator.
Got seriously convoluted with 47 people askin' for me to "add this and add that".

I shoulda kept the original.....
But....here ya go....play....it's just math.....

FYI....I still use a chart...and a calculator.....it takes seconds....

:)
Thread-O-Matic 03.xls
(145 KiB) Downloaded 204 times
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ctwo
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by ctwo » Wed Feb 24, 2016 4:59 pm

Thanks Glenn and Bill. I had an inkling NF Tool meant with the tip ground. Who threads with a sharp point? I guess then that it will not be as easy as remembering .75/TPI

I like charts too, and the math. It's good to know where the charts came from, especially since I can never find them when I want them.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by Harold_V » Thu Feb 25, 2016 2:30 am

Unless the thread you hope to generate simply "doesn't matter", it would be my opinion that you should lose the notion of trusting a chart or formula. They work only in a perfect world, one in which your threading tool is precisely ground with the exact flat on the tip, and you have coordinated your dial setting with the major diameter of the part. All in all, too many possible places for error to occur when it's so easy to take measurements with wires.

The tolerance for pitch diameter is relatively close, and it gets narrower as the thread pitch decreases. It's way too easy to under or over cut by trusting dial settings and calculated depths.

Harold
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ctwo
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by ctwo » Thu Feb 25, 2016 3:28 am

Another "trick" that I've seen (and not to undermine anything Harold has said) is to place a clock to the tool holder to see the actual in-feed when working the compound.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

Harold_V
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Re: Chart for threading with compound set at 29 or 29.5 degr

Post by Harold_V » Thu Feb 25, 2016 3:55 am

That can serve to determine distance traveled, but it is totally reliant on identical setups. Theoretical travel may or may not be proper for a given pitch diameter, due in part to the variations in major diameter, as well as varying width of the flat of the tool in use. All in all, wires serve to provide a method of establishing where you are. Once you know that, calculations of travel can work, although for critical threads, one should always measure when approaching finish size.

I hope you understand that my position in this matter relates to having to satisfy specifications. For the guy trying to make one part fit another, there's certainly nothing wrong with using calculated travel. Hell, I've fitted more than my share of threads simply by ensuring a nut fits. Some times it just isn't critical. :-)

Harold
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