dividing tuition

Hi

 

I live in Farnham, Surrey.

 

Is there anybody out there who is local and would like to teach me dividing -how to use dividing plates?

 

I am hoping to learn how to cut gears.

 

thanks

Toby

HI Toby,

pm me, I'm in Bordon hants, just started cuting gears for my 4inch Ruston Proctor, you are welcome to visit any time

 

regards

 

Graeme

Hi Toby,

 

I'm probably too far away in Cambridge, although you're welcome to visit if you are ever in this neck of the woods. To whet your appetite I've added a few photos showing some gear cutting in progress.

 

Regards,

 

Andrew

Hi Toby,

I have some exel spreadsheets that might help when using a rotary table or dividing head to help with the maths or just as confirmatation that you have done it right, email me if you want a copy, [email protected]

Regards

Tony Ashgrove

Hi Toby,

 

There are two main ways likely to be of interest to you. The first is direct dividing, where the dividing plate is mounted directly on the same shaft as the job. This means that  the dividing plate must be a multiple of the number of teeth you want on the gear. For example a 48 hole plate could be used to divide by any whole number divisor of 48, eg 24 teeth, 16 teeth, 12 teeth, and so on. You divide the number of teeth you want into the number of holes in the plate, and the answer is how many spaces between the holes you step over for each division.

 

The more versatile method is when you have a reduction between the dividing plate and the shaft with the job on it. This is usually a worm drive but may also be a gear train, simple or compound. In either case the effect is as if you have a division plate with many more holes in it. For instance, with a common 40 to 1 worm reduction, you have effectively multiplied the number of holes in the plate by 40. This mean you can do many more different divisions with a relatively small set of plates. Taking our 48 hole plate as an example, we now effectively have 48 times 40  (= 1920) divisions available for one full turn of the job, and can divide it into any whole number that divides into 1920.  Now we can easily see that ten is such a number, so what do we do if we want to put ten divisions around the job? Each division will require us to move the detent by 1920 divided by ten spaces round the plate. That is 192 spaces, which comes to a nice easy 4 turns of the detent shaft for each division. (192 = 48 times 4) So we would be using the same hole on the division plate each time, and just making sure we do turn four turns each time.

 

Not all numbers are so easy. Suppose it was 12 we wanted. 1920 divided by 12 gives us 160 spaces for each division. A full turn is 48 spaces, so each division will be three full turns, which comes to 144, plus 16 more to make the full 160. So we want to turn the detent around three full turns, then put it in the hole that is 16 spaces past where we started. To make this easier, many dividing heads have a pair of arms that can be set to help count the holes. In this case, when we are setting up, we would set the two arms to just straddle over the outside of two holes that have 16 spaces between them. Now each time we move, we start by holding one arm (the trailing one in terms of the direction we plan to go) up against the detent pin. Keeping the arm in that position, we move the detent around the three full turns, then take it a little more and drop it into the hole beside the other arm. So provided we have set the arms up correctly, we don't have to count each hole every time. It is of course possible for things to go wrong, so I tend to make marks on the plates as I go with a black permanent marker. A bit of meths will take these off afterwards. Another good idea is to go around the job once not actually cutting, but just scribe a line with a height gauge. Once you have gone around and marked all the way, you can check it it is showing the expected number of divisions and rethink it it is not.

 

Rather than do the arithmetic the hard way, you can probably find tables for the worm ratio you have. This saves some time.

 

Finally there is also a process called differential dividing, which at the expense of more complication and arithmetic lets you do divisions that the dividing plates and worm would not otherwise manage. I am not going to write that up here, but our learned editor does have an article sitting in his queue that gives a full explanation.

 

regards

John

 

 

John

 

Thanks for the above it has helped me somewhat. Currently I have a Vertex rotary table but without dividing plates. Your post has explained how to use the plates very clearly, I must get some when and if I get into gear cutting etc.

 

Thanks again

 

Martin

Hi Martin,

 

One thing to bear in mind is that with a rotary table you are quite well placed to  make your own plates. Whether it is worth you doing so will depend on the time to money relationship at your place. The idea is that you can set a plate out by using the Vernier scale and the degree divisions provided on the rotary table. Any angular error you make in setting out the holes will be divided by the worm ratio when you actually use the plate. Since the worm ration on the Vertex rotary tables is 90:1 this means the error would end up fairly small.

 

For example suppose you get one of the holes out by a tenth of a degree, or 6 minutes. When you use the plate to divide, this error will be divided by 90, so would end up being 4 seconds of arc. The most likely source of error would be the drill wandering, so you want to use a centre drill or a stub drill for this sort of work.

 

I have a set of plates and the related bits like the fingers under way for my Vertex rotary table, but this is not being treated as very urgent since I also have the Vertex BS0 dividing head. 

 

regards

 John

To expand slightly on the excellent introduction to dividing using index plates as described by John. To deal with numbers that are not possible using the standard index plates there are three possibilities:

 

1) Compound Indexing - In this method the crank is moved the appropriate amount and then the index plate itself is moved, forwards or backwards, by another amount. In essence this method consists of two simple indexing movements in sequence; hence the name

 

2) Differential Indexing - As described by John, gears are interposed between the main spindle and the index plate such that the index plate is moved as the spindle moves, to give a differential movement

 

3) Make a custom index plate - pretty straightforward these days with DROs with bolt pattern functions, or with CNC mills

 

As it happens I'm in the process of making 63 and 69 tooth gears, neither of which are possible on my 40:1 universal dividing head with the standard indexing plates. From a mathematical point of view this is because there are no common divisors of 40 and 63, or 40 and 69, ie, they are mutually prime. While I have the gears and quadrant arm for my dividing head I do not have the extension shaft that fits in the back of the main spindle. Therefore it is going to be much quicker to make a custom indexing plate using the DRO on the vertical mill. It's all designed, I just need to make it! I also need to make some riser blocks for the dividing head as well, but that's by the bye.

 

Regards,

 

Andrew

Gentlemen

 

Yet again a wealth of useful information and advice. Thank you.

 

Andrew unfortunately I only have a small vertical mill and it is without  X & Y DROs. Trying to drill a series of holes in a circle, even after the co-ordinates have been calculated, would be fairly difficult  plus remembering how many turns of each handle I had made and taking up the backlash in the same direction each time would, for me, be challenging .  Must think about fitting some DROs to the X & Y axes when finances and time permit as they will be useful for other jobs as well.

 

Again thanks to all.

 

Regards.

 

Martin

Hi Keith

 

I love the idea diminishing errors or improving accuracy, in my world of engineering that is really a plus point . As for 'Then there is this'  Yes I love some of the kit Niloch but at present one step at a time as they say, Oops there goes another unintentional pun .

 

Well Harold Hall here comes another investment and some late night reading providing that SWMBO, or the accountant as she is also known in my case, allows me to access her Amazon account and make said investment! Mind you I am very lucky as she is as interested in my workshop output as I am, she has even saved some practice bits from the scrap bin 'cause they look nice'. Just wait until the serious stuff starts!!!!

 

Regards

 

Martin

if you have access to a CAD program and a reasonable printer then you just draw the plate, print it out, attach to a blank using double sided tape, and then spot through all the holes. If you want better accuracy, use the first attempt to divide the final plate. This is much simpler than messing around with a DRO!

 

The reason to use double sided tape is that ordinary glue is liable to cause the paper to stretch. 

 

Another approach for dividing awkward numbers is to turn a diameter such that a suitable strip of tape will wrap around it. The tape can be thin metal with holes at regular intervals if you can find such a thing, or it can be graph paper, used against a pointer.

 

regards

John

I would agree that using a DRO to locate each X-Y position is fairly time consuming. However, if the DRO has a bolt circle facility then it is dead easy. Enter the data, press the button and zero the display for the first hole. Go to the next hole and zero the display for the second hole and so on. Must be quicker than making two index plates.

 

There are some interesting notes on making a precision index plate (without the use of a DRO or CNC!) in 'The Machinist's Second Bedside Reader' by Guy Lautard.

 

Regards,

 

Andrew

Hi all,

 

Alan Munday's very useful model engineers utilities program has a utility which will calculate and print out the coordinates for any given number of holes on a pitch circle.

 

It is free download and has many useful utilities especially thread data and gear calculations for screwcutting etc. here.

 

Regards

 

Terry

Hi

 

Thanks for all the tips. Last night I tried out the CAD way to produce a template. Initially I drew a polygon with 'n' sides, which when 'n' is large, looks more like a circle and the vertices are hard to determine. To overcome this I set the 'Snap' point to end of line and drew in, successively, links from opposing sides of the polygon until all were linked. This gave a multi-pointed star with a clear indication of the centre. I then removed the polygon leaving just the star with very sharply defined end points. This printed off very well and I can now produce templates for indexing plates with any number of points on the circumference. Not only that but changing the diameter of the polygon to fit is child's play.

 

I had the tools to hand but just needed a push in the correct direction, grey matter is not what it used to be  .

 

I will try again but this time plot small centre marks at the end of line points to see if this will produce a similarly clear diagram.

 

 

Thanks again and best regards to all

 

 

Martin

 

Just tried plotting the centre marker/cross hairs on the end points of the ploygon and it works a treat. MAGIC (yes I know thats shouting but its worth it )

Hi Martin,

 

Well, it will depend which CAD program you are using, but often there is a feature called something like "Copy entities", and under that there will be some choices like "linear" and "radial". (I'm looking at an older version of Turbocad as I type, these are under the edit menu there)

 

So what you do is put a cross at the centre, and another cross at a point that is the desired radial distance away. You select the second cross with the mouse, then go to "copy entities" and select "radial". You then go to the bottom of the screeen where it says "sets" and type in the number you want. With Turbocad you can get to this by hitting tab, and you can ignore the degree settings.  You then have to click on the point you want to be the centre. It will then magically draw in the circle of little crosses just like you want. Most other CAD programs will have similar facilities.

 

My Turbocad  is version 6, which came out last millenium, so any later versions should be similar.

 

regards

john