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Thread: Dividing video
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3rd Jul 2020, 12:13 AM #1Senior Member
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Dividing video
Here's an interesting video on what appears to be compound dividing using a semi universal dividing head.
https://www.youtube.com/watch?v=aSIcY4wjtEQ
I got lost in the explanation. Can you understand it ?
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3rd Jul 2020, 08:30 AM #2Philomath in training
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I could not stand watching the whole video, but what he is saying is that you index with one ring on the index plate and then using another ring, add or subtract from that initial indexing to get the movement required. It is possible to do and has been documented before, but is a very fiddly way of doing things. (Imagine - you index on one ring, then without losing your place, change to another indexing ring (perhaps plate) to index some more. It requires that the holes line up if nothing else. If "taking away", it also requires no backlash)
Michael
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3rd Jul 2020, 09:18 AM #3Senior Member
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Also found this
https://www.youtube.com/watch?v=5fXo27mJIkU
looks like it's only using the one plate.
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3rd Jul 2020, 10:13 AM #4Most Valued Member
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Given that excel can give you a table of the deg/min/sec you need for division I'm not convinced this is any more accurate or faster. Maybe less chance of an error?
Still its's an interesting idea even if I cant see myself using it anytime soon.
Pretty sure you can take the backlash out, but just something else remember to do.
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3rd Jul 2020, 11:15 AM #5Golden Member
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If you have a dividing head with an incomplete set of plates or even a homemade dividing setup and a limited set of dividing plates then this video shows a possible way of dividing using only what you've got, however if you have a dividing head with a full set of plates then no need to complicate things by using the method in the video, which is quite ingenious - I wouldn't have thought of it myself.
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3rd Jul 2020, 11:54 AM #6Senior Member
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3rd Jul 2020, 06:21 PM #7Golden Member
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phaser I think you are right there, I don't have "proper" dividing head but a rotary table supplied with indexing plates, I went through the user manual and checked on the range of available divisions - listed from 1 to 100 and I did not notice before but realised there were some missing like 67 and 71 plus a few others, the last part of the manual is a page on "approximate" indexing, there is an example and the manual states that trial and error is involved in picking the hole set, they do however conveniently pick a hole set at "random" that works out very very close, in practice very time consuming doing a series of calculations that involves converting a decimal to a fraction on each hole set for a result that is not spot on.
Maybe the idea has some merit but one would have to be on the ball fully so as not make an error, I haven't done a lot of gear cutting/index milling but do know it is easy to lose your place as the work is very repetitive - your mind wanders and next thing you are thinking did I just go 5 turns or 4.
I have in the last few weeks been playing with my new 3d printer, it seems to me it would be easier to 3d print an index plate with the required number of holes - something for me to explore.
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4th Jul 2020, 11:22 AM #8Golden Member
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The missing numbers from your 1 to 100 list are the prime numbers. The only prime numbers that can be obtained with a semi-universal are the ones that are actually on your dividing plates. A commonly desired prime number is for a 127-tooth gear for an imperial lathe to be able to cut metric threads.
There was a video floating around a few years ago of a lecture to some US metalwork club by an American guy who invented the method shown in those hinglish videos, he wrote a chapter on it in Machinery's Handbook. He used either a second pair of fingers or a second crank arm on the DH, can't remember which.
Another method is to get someone with a mill and DRO to drill you a plate using the hole-circle function. Or get a universal dividing head.
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4th Jul 2020, 07:33 PM #9Golden Member
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Yes you are right - once I went through and wrote down the missing numbers I realised that were all prime numbers with the exception 65, not surprising as 65 is the example used in the manual to work out which hole set to use.
I have a mill and DRO and have used the circle hole function a few times - it works very well, but the 3D printer thing also looks good if the job is for a one off, no need to aquire a 130mm diam or bit of 6mm plate, I may even go have a go and see how it turns out.
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4th Jul 2020, 08:24 PM #10Most Valued Member
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Both options but so is making a plate on the dividing head itself. The gearing means being "pretty close" gives a "damn good" result. With a 90:1 ratio even if the hole in the plate was 90degrees from where it should be the work piece will only a 1 deg out. Given to get a 90 deg error you would have to be 22.5 turns out, hopefully the error will be some what less than 90deg . Assuming my maths is correct, if while making a plate you limited yourself to "the closest full turn" your greatest error on a work piece while using that plate would be 13 minutes 29 seconds. Of course however you made the first plate, you could then use that plate to make another plate..........
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