Proportional Dividers

churchjw

churchjw

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Has anyone made a set of proportional dividers like the ones here?wp2610b341_06.jpg wpe27d95bf_05_06.jpg I would like to make a set to do golden mean sizing but I am not sure how the center slide works. I would love to find drawings or here opinions on the best way to make a set.

Thanks,
Jeff
 
If you only want to do golden ratio sizing you don't need a center slide: just a pivot at the 1.6180:1 point.
 
Yea that is primary usage but I love the look of the slide and I could use it for other ratios.
 
The primary use was originally was drafting and map making. They basically scale dimensions up or down. The nice ones also had a way to divide circles into even parts. Think like a bolt hole pattern.

If you have a mark on them for the golden mean ratio 1.6180 you can use it to design parts. I have a woodworker friend who builds everything by eye and fit. So for things like doors and such he likes using the golden mean when he can. These would give him a quick way to do that. Does that help? These are new to me as well.

Jeff
 
I've used them in the past for drafting but never heard of anybody making them.
 
mcostello said:
Could You explain their use for the great unwashed?
Click to expand...
OK - the basics ... Two bars with sharply pointed ends. The key to their usefulness is the fact that the pivot point can be repositioned. Let's say it's set exactly halfway along the length. Then as you spread one pair of points, the other will spread exactly as far ... a 1:1 ratio
Now consider moving the pivot to ¼ of the way along. One set of point will widen exactly three times as far as the other. (¾ vs ¼ = 3:1 ratio). Rinse and repeat. There's a scale on one of the arms, so you can set whatever proportion you need (up to some practical mechanical limit, maybe 1/10 or 1/12, I forget what). When the pivot is ¼ of the way along the length, the indicator is opposite the number 3.
Looking just opposite this scale, you'll see another one. On this one, the number 6 is aligned with the number 1 on the first scale. This scale is for dividing circles. If you set the pivot to 6 and the points at the center and radius of a given circle, you can tick off 6 equal chords with this setting. Other settings will let you divide the circumference of a circle to various even divisions.
I still have one, and even with CAD and DROs available, the proportional divider is useful when doing layouts.
 
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I just saw this set come up on the Phoenix Craigslist for $20. They look pretty good. If anybody's interested, PM me, and I'll buy them for you. Shipping should be pretty inexpensive for something this small.

phoenix.craigslist.org

proportional divider - tools - by owner - sale

Tacko proportional divider
phoenix.craigslist.org

Screen Shot 2021-08-21 at 10.32.33 PM.jpg
 
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