Generating division plates from scratch

I wonder if anybody has made division plates from scratch without using a master gear?

I have never seen this technique used but the principle is quite simple.

Suppose you needed a division plate which has, say, 12 holes, how would you make such a plate without a dividing head or a master gear?

Let's see what the Brains Trust comes up with!

12 holes on a PCD entered into the DRO and off you go

See my post about the divider wheel generator here

For greater accuracy, the best I have seen is to pack ball bearings into a groove ... But do you really need to go to those lengths ?

MichaelG.

P.S. For 12 holes, just do it with simple geometric construction ... A pair of dividers and a straight edge is all you need.

Edited By Michael Gilligan on 13/06/2016 10:27:13

OK - seems 12 holes is a bit too simple.

How would you generate a plate with 48 holes without a master gear, DRO and nothing more than a ruler?

What is this? 11+ for geriatrics? You need more than just a ruler, you need a centre punch, a scriber and a pair of dividers at least. Any number which is 6 times a power of 2 can be generated (6, 12, 24, 48, 96 etc), just keep dividing the last angle by 2. Similarly any number which is a power of 2 (2, 4, 8, 16, 32 etc) It gets increasingly innacurate.

One method that has been used to make rather precise divisions might surprise people. There are variation but just use a pair of dividers and adjust until it's correctly set. There is also a method that needs a straight edge and scriber as well. If a line is drawn through the centre of circle it gives a division of 2 that can be further divided. This sort of idea has been used to make very precise rather large protractors for measuring star positions. A microscopes can be used to help. This sort of thing might be why there are 360 degrees in a circle apart from the obvious one.

The only "engineering" method I am aware of makes use of steel tape and a jig. The jig has a drill guide correctly spaced from a location pin. One hole is drilled and then located via the pin and then the next drilled and so on. Last task is turn a disc so that they are correctly spaced when the tape is wound round it.

John

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John,

Is this a genuine request for information, or are you just showing-off?

Strictly: With nothing more than a ruler, it may be impossible

MichaelG.

Mark a piece of tape with the required number of divisions, turn a disc down until the tape just wraps around, then use the marks to make a master plate. If you are using a dividing head with a worm, the errors in the tape will be divided by the worm ratio. I did this once to make a 41 tooth belt drive wheel on a Unimat, which didn't have a worm, but I was able to get close enough for a tooth belt to run happily.

Since I now have a Vertex dividing head converted to do differential dividing, I can divide any number including all prime numbers, up to several thousand divisions.

John

Of course there are several time consuming methods available that do not need a master; but I'm with Jason, use the bolt circle function on a DRO. Here's one I made earlier with 63 and 69 holes:

The only oddity is that the three central screw holes are countersunk 60º rather than 90º.

Andrew

Hi, A lot of clockmakers use John Wildings way of using a bandsaw blade as a rim on a wooden wheel mounted on the outside of the head stock. with the right bandaw blade and wheel diameter all sorts of gears can be cut. the teeth on the blade are stopped every tooth and the gear in the chuck cut. until a got a division master set up on my rotary table I was about to cut a 290 tooth clock wheel like this.

Maybe obtain a large wooden disk, say MDF so it's stable. The larger the better for greater accuracy.

Cut the diameter such that a tape can be wrapped round it where the measurements overlap at a point exactly divisible my the number of holes which you wish to generate.

i.e. for a 48 hole plate, a disk with a circumference of exactly 48", or 96cm or whatever else seems applicable with the materials on hand. It would need to be slightly undersize to allow for the thickness of the tape.

The tape doesn't even need to be accurate, provided the marking is consistent along its length, and it doesn't stretch.

Glue/pin the tape to the edge of the disk and use the measurements on the tape to index your blank for drilling.

I'm sure that a few lengths of brown paper or similar, wrapped round the disc, would then allow a 49 division plate to be made, or some judicious sanding a 47 increment plate.

(Looks like I overlapped with several folk. Must learn to type faster)

Edited By peak4 on 13/06/2016 11:25:27

Neither Michael. Maybe I should have said in addition to the dividers in respect to the use of a straight edge and scriber. The method I was referring to that also involves microscopes is a guess and check. That may be in one of the ATM books but I can't remember details or where I saw it.

360 degrees as far as I am aware goes back to Arabic measuring systems. For angular measurement they used another simple idea - make the protractor even larger. Huge in fact. The reason for my comment about the number and subsequent divisions is a vague recollection that it helps with the guess and check method. Pass. The obvious answer is as it is with all 12 based numbering fractions.

I believe there was an attempt to decimalise degrees once but it died a swift death.

Huge rather a long time ago must relate to just the use of a rule of some sort. The wiki mentions that the technique they used to derive the divisions has been lost as european stuff that came much later was worse.

John

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Edited By Ajohnw on 13/06/2016 11:28:37

Edited By Ajohnw on 13/06/2016 11:35:48

But since we all have a computer of some sort (we are all reading this forum) why not use a PCD calculator as mentioned above or the one at Theoritical Machinist enter all of your requirements, then print off the resulting diagram that includes centre marks at 1:1 cut out and glue it to your disc, centre punch and drill away, most of your drilling inaccuracies will be taken up by the 60:1 or 90:1 worm as already mentioned.

For the tape method, you don't need to reduce the diameter of the disc - any size will do, you can transfer from say a tape measure (which will have accurate graduations) to a tape of disc circumference by having the shorter tape horizontal, then using the same origin for the second tape, move the second end until it is vertically below your maximum required mark, then simply transpose the markings vertically between the two tapes using a set square.

Wrap your new tape around your disc, draw a circle at the required diameter and then mark intersections between the outer edge marks and the centre of the circle on the circle itself, centre punch and drill.

Works for any number including primes

Edited By Timothy Moores on 13/06/2016 11:37:15

Anyone who stayed awake during geometry lessons should be able to fill a side of a4 with solutions.

Neil

**LINK**

It's still around and reputed to be in 'common usage' in certain circles

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Ajohnw,

Our posts seem to have crossed in the æther

My question was directed at John Fielding, not your good self.

MichaelG.

Edited By Michael Gilligan on 13/06/2016 11:50:11

I was curious about that aspect too.

To me the jig and metal tape makes sense and has definitely been used to add divisions to lathes. It can provide positive location too by having a groove under the holes in the disc it's mounted on.

However if I had nothing at all other than a lathe that can screw cut preferably in imperial I would buy a metric gear and cut a worm to go with it and make a dividing attachment.

The rest of this thread has been of some use - a division of 69 is a 20/23 of a turn with a 60T worm wheel. A standard division. A 63 is 20/21 of a turn. Another standard division. I wouldn't be using a DRO plus PCD. but I would do it that way with CNC.

That assumes the sums some one posted are correct which apart from a minor problem were.

John

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That's me out then!

Cheers,

Dave