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  1. #1
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    Default Hand wheel dial thread matching?

    Hi guys and girls,

    i have a couple of knurled dials that have division markings on them 1 has 200 div and the other has 100.

    i want to match the dials for some projects and i want to learn how to match them to a certain leadscrew or drive so that i can use the divisions as a measurement. ive tried Dividing it into 360 and i get 0.55555 or 1.8 for the 200 div and 0.27777 or 3.6 for the 100 im assuming that 1.8 and 3.6 are the degrees between divisions?

    so how do i match that to a leadscrew? metric or imperial?

    thanks for any help you have, im hopeless with maths so ill learn what i can

    Troy

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    You need to keep track of your units just like the numbers and that will help you find what you’re looking for. In science the units are even more important than the numbers. If the units don’t work out right through a problem you don’t have the right answer.

    (360 deg / 1 rev) x (1 rev / 200 divisions) = (360/200) x (deg/division) = 1.8 deg/division The revolutions cancel.

    If you do it the other way around you get .555 divisions per degree. They’re the same though. If you do a problem out and the units are upside down of what you want just divide 1 by the number and the units and the units flip (1/1.8 = .555).

    Leadscrew math is similar. Take 10 TPI or 10 threads/inch. Flip that upside down so that’s also 0.1”/thread or also 0.1”/rev.

    So (0.1”/rev) x (1 rev/360 deg) x (1.8 deg/div) = (0.1x1.8/360) (in/div) or 0.0005” per division

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    The best thing is to choose a screw that works with the dials. As an example, micrometers typically have 50 divisions. They use a 20 tpi screw (pitch=0.050"/turn.) 20 tpi would work well with both your dials. So would 10 or 100 or a few others, but those are less common.

    edit- actually I think 40 tpi (.025"/turn) is more common.

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    The divisions relate to the lead of the thread, that is, how far the slide moves in one rotation of the dial. So, assuming the graduations are marking thousandths of an inch, the 200 dial will move .200" per revolution and the 100 dial, .100". So what does .200" represent? That's 1/5th of an inch or 5 threads per inch. And even more obviously .100" is 1/10 inch or 10 threads per inch.

    Metric works the same way of you thing about thread lead and it's how metric threads are specified. If a leadscrew is a 5mm pitch, it would take 500 graduations for each one to represent .01 mm. That's maybe a little too finegrained and too crowded for markings on a dial, but 250 graduations would be .02 mm or .0008" or just less than a thousandth of an inch if your mind is calibrated in imperial.

    To actually graduate a dial you don't need to even think about degrees unless you want to make things complicated. For 100 graduations on a dial you need something that divides a circle into 100. This could be a gear, if you have one or a one hundred tooth saw blade if you're making a lash up. If you have a dividing head you need to know the ratio of the worm, often a 40:1 or 72:1 ratio. Then sort out the hole plate options to find what proportion will provide the divisions you need. There are tables and formulas and helper programs on the internet but I usually just use simple factoring. With my 40:1 divider, 40 turns is one whole rotation and I need to divide that by 100 divisions. The ratio 40:100 (one turn divided by 100 divs) is equal to 4/10. I look for a 10 hole plate but there isn't one. However there is a 20 hole plate so a rotation of 8 holes in the 20 hole plate will give me exactly 1/100th of a full turn. There's my graduation setup.

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  7. #5
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    Of course if you're contemplating graduating a dial for metric dimension moves with an imperial pitch screw or vice versa that's a whole different calculation.

    Tell us if that's your problem and we'll try to work you through that too.

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    Europen lathes tend to measure diameter removed while North American lathe measure radius with the cross slide.
    Bill D


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