11.5 TPI

[Just for fun]

I get the same as David when calculating it. How did you calculate it?

I didn't do any calculations .... I had a friend print me a 46 tooth gear and installed it, did a test cut just to see how it worked. See post #56 above.

 

[davidpbest]

This is very strange. The original formulas for all my calculations are from Mark ( @mksj ). The source data is attached. On the 4th tab ("Master Data . . . . "), note the red arrows/boxes. It clearly calculates the 11.503 TPI with 40-127 / 120-46 gearing and the Norton box position B8. My contribution here has largely been to reformat Mark's data into a format I find more useful when actually standing at the machine scratching my head - see the first three tabs in the attached. I've known Mark to question his calculations, but I've never known him to be wrong.

I'm wondering if you don't have a cockpit error at the lathe with your new gear. Have you inverted the positions of 40 and 46? Mark?????

 

[Ken226]

If I work out the ratios using the data and charts you guys have posted so far, position B8 is 14tpi according to PM, using the 40/127 x 127/40 gear arrangement (1:1 ratio). I used that to determine the ratio of position B8, which shows to be .57144. using the indicated 14tpi (the pitch as indicated in the pm chart) and (.125") 8tpi leadscrew.

To determine the ratio of position B8:
40/127 x 127/40 (.57144) x .125 = 1/14, where I solved for the parenthesis.

So if I use the same equation, except change the gear arrangement to 40/127 x 120/46, then solve for the pitch, I get:

40/127 x 120/46 (.57144) x .125 = 1/17.039

(17.039tpi).

Isn't that about what @Just for fun got when he tried it? 17tpi


So you can check my work:

 

[davidpbest]

 

[Just for fun]

Ok, So, I was mistaken on the Norton box I was using B3 not B2.

I tried it again. I had the gears correct. And I had the Norton gear box in B3.

Tim

 

[Ken226]

Ok, So, I was mistaken on the Norton box I was using B3 not B2.

I tried it again. I had the gears correct. And I had the Norton gear box in B3.

Tim

View attachment 421166
View attachment 421167

Using the equation and method above, for B3 I get 11.56229 TPI in position b3, using 40/127 x 120/46:



Close enough that your pitch gauge shows good.

 

[Ken226]

Ok, So, I was mistaken on the Norton box I was using B3 not B2.

I tried it again. I had the gears correct. And I had the Norton gear box in B3.

Tim

View attachment 421166
View attachment 421167

I forgot to ask,

Is the gear that fit the one I modeled with offsets to accommodate the 3d printers tendency to print oversize?

Or was it the one I modeled to exact dimensions?

 

[Just for fun]

I don't really know. He made three gears two out of PLA the gray ones, one was tight, and one was loose, and one out of ABS the black one and the one that fits the best.

 

[WobblyHand]

With 0.5% error, about how many threads can one engage before it binds on a true thread? Always wondered about that.

 

[Ken226]

With 0.5% error, about how many threads can one engage before it binds on a true thread? Always wondered about that.

A good question.

It would almost certainly depend on the fit and the length of the female part.

I imagine it wouldn't be an issue on a 1a/1b nut bolt assembly.

But would likely bind on a 3a/3b assembly, especially if the female part is long.