A newbie here could use some help attempting to understand threading.

On 12-13-08, regarding the thread "Threading Video", you posted the following: "I find most useful in the shop is a thread table that gives the distance of the compound needed for the various standards 60 for US and metric, 55 for British, etc. instead of having to work out depth x 0.880456378373552974653 [ approx ]."

If we are talking about 60 degree form V threads, I understand the depth of cut to be calculated as: depth of cut=(sin 60 degrees)(pitch) or = (sin 60 degrees)/#of threads per inch or =.8660/# threads per inch. No problem, simple trig.

Here's where I get lost. Assuming the compound would be set around 60.5 degrees, as referenced from the direction of the cut, which equates to 29.5 degrees, as referenced from a perpendicular extended from the round stock to be threaded, compound travel would have to exceed cross slide travel to provide the same depth of thread cut. My understanding is that when using the compound to cut, we would calculate the cross slide travel required =(depth of cut/(sin 60.5 degrees) or =(depth of cut)/.870 or =(depth of cut)(1.149).

Again, you stated, "depth x 0.880456378373552974653 [ approx ]". I do not understand how this was derived. I did find that the figure .880456378373552974653 [ approx ] is about the sin of 61.5 degrees. Do you use a greater relief angle? If 61.5 degrees was correct, should you not have expressed your formula for cross slide travel as =depth / 0.880456378373552974653 [ approx ]?? Typo??

What am I missing? Once I resolve this issue, I plan to create an Excel spreadsheet for compound threading travel, such as you mentioned. That could be a very handy item, as I just found out.

Many thanks.....

Fred

On 12-13-08, regarding the thread "Threading Video", you posted the following: "I find most useful in the shop is a thread table that gives the distance of the compound needed for the various standards 60 for US and metric, 55 for British, etc. instead of having to work out depth x 0.880456378373552974653 [ approx ]."

If we are talking about 60 degree form V threads, I understand the depth of cut to be calculated as: depth of cut=(sin 60 degrees)(pitch) or = (sin 60 degrees)/#of threads per inch or =.8660/# threads per inch. No problem, simple trig.

Here's where I get lost. Assuming the compound would be set around 60.5 degrees, as referenced from the direction of the cut, which equates to 29.5 degrees, as referenced from a perpendicular extended from the round stock to be threaded, compound travel would have to exceed cross slide travel to provide the same depth of thread cut. My understanding is that when using the compound to cut, we would calculate the cross slide travel required =(depth of cut/(sin 60.5 degrees) or =(depth of cut)/.870 or =(depth of cut)(1.149).

Again, you stated, "depth x 0.880456378373552974653 [ approx ]". I do not understand how this was derived. I did find that the figure .880456378373552974653 [ approx ] is about the sin of 61.5 degrees. Do you use a greater relief angle? If 61.5 degrees was correct, should you not have expressed your formula for cross slide travel as =depth / 0.880456378373552974653 [ approx ]?? Typo??

What am I missing? Once I resolve this issue, I plan to create an Excel spreadsheet for compound threading travel, such as you mentioned. That could be a very handy item, as I just found out.

Many thanks.....

Fred

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