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Yup, I used the segment arms (spiders). I’ll have to do the crank thing and see if it is a 40 and not a 60.
Just checked and it has the standard 40-1 ratio. Made by Skinner, New Britain CT. Vintage style letters seems to be of same vintage as the mill.
Yup, I see that now after 2 failed attempts, but honestly I figured I would have success the first time because I researched this so much ahead of time. But from the responses so far, I have everyone stumped. The gear blank diameter appears to be correct and using the #39 index correctly, I still am having failures. Divider head gear ratio is 40-1. And I’m positive the other change gears on my lathe are 12DP..... stupefying.......You know, when you're a beginner, you can just lightly mark the blank with 52 nicks as you practice your first round of indexing. Dealing with hard facts in hard metal is humbling at first.
The difference between theory and practice is that in theory, there is no difference, but in practice, there is
I completely understand what you are saying about overshooting the hole and having to back up a ways and approach the hole again, I did that several times and did exactly what you said to do. Not sure what you mean by clamping the spindle. The piece is secured very well in the 8-1/2” chuck. And the plate with the holes has the number in a perfect vertical line up and down from start to finish.It bears mentioning that you must be aware of backlash when using a dividing head. THOU SHALT NOT OVERSHOOT THY POSITION.
I do not drop the indexing pin onto the angle bevel of the sector arms. For one thing, using the sector arms this way does not work for some index numbers because you cannot get the sector arms close enough together. So bearing that in mind, you carefully turn the crank and drop the pin ONTO THE HOLE PLATE, and then bump it forward til it falls in the hole. THOU SHALT NOT OVERSHOOT THY POSITION. If you do overshoot, you must turn the crank about a quarter turn back and then approach the proper hole in the plate again.
Clamp the spindle of the dividing head before the cutting begins. For straight cut gears in steel, there can be a bit of bumpiness as the cutter gets started in the cut and this could rattle the blank out of position by whatever backlash exists.
A rough diagram of what I am doing. Start with the divider point in the 39 hole. Advance the guide stops so I have 30 holes showing and insert the point in the 30th hole. I then advance the guide again to where I have 30 holes showing. With a gear of 52 teeth my crank should and does end up in the #39 hole at the 90, 270 and 360 degree spot which means I’m advancing correctly but somewhere I’m screwing up with either the size of blank or something else none of us are catching. I did the blank diameter computing with 3 other gears in the set and they all come up correct to a 12 DP gear so I’m sure the DP is correct.....
The bottom sketch shows where I’m ending up on the last tooth. Seems to me that my blank should have been larger than 4.500. But doing the math of 52+2 divided by 12DP equals 4.500....Argh!!!!!
First off my comment on diameter was in reference to where the last groove cut was made. If my piece was too large, the 52nd cut would have a larger space between it and the first cut, and if the piece was too small, you wouldn’t get 52 cuts in. And yes, I have a high school education and learned simple math at an early age..... my reference to holes is the same thing you reference spaces as, same thing cause it is a circular “ hole”.... My diagram shows clearly how I indexed it, even has numbers added to aid in the visual.
