Clock Wheel Question 2 + Indexing+Depthing

Hi,

I'm making the Weight Driven Brass Alarm Clock and am starting to cut the wheels. I made my own Modular Dividing Head from a series in either Home Shop Machinist or Machinist's Workshop. It's like the Universal Dividing Head ? that uses a worm wheel and change gears plus an index plate for indirect dividing. After trying to cut the 48t wheel and discovering that my 36 hole circle only has 35 holes( homemade plate) I decided to check the hole spacing with digital calipers. My hole spaces on the other two circles(22 and 25 )are'nt very consistent.Up to about 10 thou variation.

So here are my questions. I thought I've read that even if the hole spacing on the index plate is'nt perfect the mechanism of transmitting the division request, so to speak, through the worm gear somehow produces a much lesser error in the in the finished tooth or gear ?

And even if your clock wheels are'nt perfect does'nt the act of depthing the wheels compensate for any imperfections? How does an imperfect wheel affect the operation of the clock? Two hundred years ago the equiptment available to clockmakers was much cruder than it is now yet they were still able to produce workable clocks.

Thanks ,

Mark

Mark a lot depends on the type of pinion you are using if its a lantern you shouldn't have much of a problem

HI Mark,

Any error in the dividing plate is reduced by the ratio of the worm and wheel (e.g at 60:1 a 10 thou error in the hole becomes an undetectable 0.00017" error.

But if you have a 35 hole plate instead of a 36 you will start to accumulate errors, although if you allow for them by dtropping a hole half way through each turn of the plate you will limit these to half a hole or 5 degrees. Divide 5 degrees by the worm ratio (again assume 60:1) and it becomes a worst case of 0.08 of a degree. This is probably near the limit of the error you could see, and also probably as good as in an old hand made clock.

Neil

The imperfections in wheel divisions have direct influence on the angle accuracy of your transmission, but if you make a full turn with the driver the error you make is back to zero.

Any error in wheel divisions will cause extra wear to the teeth, to minimise wear it is advisable to use teeth numbers that when divided not give a round number. For example not a 10 tooth pinion driven by a 100 tooth wheel, the error in division stays than in one place on the wheels but if you use 10 on 99 you spread the error and wear over 99 teeth. The faster wheels turn the more noise a division error will give.

Niko