how to use a rotary table and dividing plates free sample

If your table has a ratio of 90:1 then you will have to turn the dial 90 turn to make the table go around once. That means that you divide 360 degrees by 90 turns and you get 4 degrees per turn. Simple enough.

Now lets say that you want to cut something that has 4 slots in it. Divide 360 by 4 cuts. That gives you 90 degrees per cut. So haw many turns to make 90 degrees? Divide 90 by 4 degrees and you get 22 1/2 turns. (90 turns divided by 4 will give you the same results) You could do this one by sight but it gits harder when you are cutting gears or something with odd numbers and lots of teeth.

So here is what you do. This is where the plates come in! This example is easy but the theroy is the same. You only need a plate with two holes but since there is no such thing you will use any plate that the row of holes you want to use will divide by 2 since you need half turns. Set your index arms so that the pin on your arm falls inside the dividing arms. Set them so that you can find the next hole of the same count. IE: If you used a 24 hole plate then you will have 12 holes between the arms thus giving you half turns each time you index.

So count off the 22 turns then the 12 holes on the index plate. Move the arms once you establish this hole. Do this four times and you have the four slots at 90 degrees.

All you have to remember is that you need a plate that the number of holes will divided by the fraction of a turn that you have left after turning the full turns. IE: 3 1/3 turns needs a plate that the holes will divide by thee. 5 1/5 turns needs a plate that will divide by 5. 2 1/8 turns needs a plate that will devide by 8.

The number of full turns has nothing to do with the plate hole count. Only the remaining partial turn needs to be indexed. You have to count the full turns youself. Using the RT degree scale helps make sure you counted correctly if you get interputed. It happens!

One of the programs included with the DIVHEAD archive on my webpage allows you to calculate the hole plates required for any number of divisions up to an input maximum. Below are the results of that program for rotary table gear ratios of 40, 80 and 90 assuming one wants the ability to make all divisions up to 50.

These solutions are minimum hole drilling solutions so it"s possible that some of the lower number divisions could be accomplished with a single circle of holes at the expense of drilling more holes. For example, the 4 and 6 hole circles in the 40:1 solution could be accomplished with a single hole circle of 12 holes or some integer multiple of 12 holes.

Dividing heads allow you to divide a circle into equal fractions conveniently. Anything that involves regular action around a circle is a candidate for a dividing head.

A rotary table has no stops so it is not convenient to do large numbers of things at equal intervals because you would have to painstakingly determine the interval. Also, the rotary table does not divide the circle. For example, if you were making 13 equally spaced operations using a rotary table you would have to calculate some wierd angle for each operation and dial it in--a tedious process. For example, here are the 13 angles for a circle division:

Do you want to manually set each of these values? Have fun doing that. Now, imagine doing it for 53 divisions. You will be there all night. Not only that, the error will be a lot more than a dividing head.

This plate can be used either directly, or through a geared dividing mechanism. In direct indexing the workpiece and plate rotate in a 1-to-1 ratio, and holes are used directly. That is, a plate with 12 holes can divide the workpiece into 2, 3, 4, 6, or 12 equal segments. A dividing head incorporates an internal gear ratio (usually 40:1, 60:1, or 90:1) with the same plates. In doing so, the dividing head enables many more combinations than just direct indexing.

For example, imagine a plate with 15 equally-spaced holes and a dividing head with a 40:1 gear reduction. In direct indexing, a workpiece could be divided into 3, 5, or 15 equal segments. Using the dividing head, the same workpiece could be divided into 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 25, 30, 40, 50, 60, 75, 100, 120, 150, 200, 300, or 600 segments. Essentially, the dividing head acts as if it’s a direct indexer with 600 holes; 15 holes in the actual plate * 40:1 gear ratio. Let’s look at how some of these combinations are possible.

Rotary tables are mounted horizontally, and most can also be mounted vertically. In both cases only at 90° to the mill table. A Dividing Head is always vertical, but can be tilted through 90°.

Dividing heads are always fitted with "indexing plates" (holed wheels and clock hands), allowing a wide range of angles to be turned. The indexing mechanism can do intermediate angles. Rotary tables can be fitted with indexing plates as an accessory, but usually the number of angles supported is limited compared to a dividing head. (A generalisation. And, because rotary tables do all common angles, the limitation may not matter.)

Rotary tables are more convenient for general work because most jobs are mounted at 90° or 180° relative to the milling table. Possibly more robust than a dividing head for rough work. When close accuracy isn"t needed, jobs can be spun rapidly by the rotary table without cranking the handle - a time saver. When accuracy is needed the handle and worm are engaged. Usually there"s a vernier scale sufficiently accurate for most work. The handle is also relatively fast because most simple angles can be produced with it. For example, easy to crank from 0, 60, 120, 180, 240, 300, 0 to cut a hexagon head. Unfortunately not all angles are "simple"!

Indexing plates are useful for awkward angles. Cutting a 19 toothed gear requires 19 steps of 18.9474°, which is the hard to remember sequence 37.89, 56.84, 75.78, 94.74, 113.68, 132.63° etc. The Index plate and clock hand mechanism remove the need for the operator to track the sequence but they are still a pain to use in my opinion!

Indexing plates are so awkward that driving a Rotary Table with a stepper motor and microcontroller is popular. You simply tell the controller how many divisions are needed, press "Go", and the computer does the rest. Apart from reducing brain strain and automating a tedious task, the computer eliminates most mistakes. Computers don"t get sums wrong, have excellent memories, and are hard to distract! Also, a computer and stepper motor will do a good job of angles too complicated for the Indexing plates.

Generalising again, I suggest most people, most of the time, only need a rotary table. I see Dividing Heads as specialist tools and have never felt the need for one. For the same reason I drive an ordinary small car rather than a Land Rover. The closest I get to off-road driving is a supermarket car park! You might live on a farm...

Unless there"s a specific reason for needing a Dividing Head, I wouldn"t spend money on one. My rotary table is used a lot, in contrast a Dividing Head is only "nice to have".

You remove the nut holding the hand wheel on and pull the handwheel off. They are usually on a keyed shaft that also has two flats on it. Behind this are three tapped holes to take one of the three plates you should have with the table.

Fit one plate { more on this later } then fit the spacing arms over the shaft. Some have a bush that fits the keyed shaft, some require you to remove the key.

Most popular dividing heads use a 40:1 ratio and the tables published reflect this. Rotary tables are usually 90:1 or 60:1 so you will need a set of tables to cover this ratio. This is why you need to choose which plate you use carefully as you need a plate with a row of holes to match your divisions at the required 60 or 90:1 ratio.

The handle can be removed easily by releasing the caphead bolt. The handle being located with a keyway. This then allows the dividing plates and crank to be fitted in place of the free-rotating handle.

The crank handle is held in place with a grub screw – ensure this is tight and that the handle and pin are at 90° to the crank plate before trying to fit the crank to the table.

12 divisions is achieved with 7.5 turns – so 7 complete turns of the handle and then with a 20 division plate the dividers are set at 10 + 1 holes apart.

his takes a bit of concentration to use as you count off the rotations and then add the part rotation needed for the division – just be consistent and all will be fine.

A very small 12 tooth gear made with a cutter designed for a larger number of teeth and hence the undercut on the teeth – the wall is rather thin at the centre, but this was a trial to see how the rotary table works when being used as a divider – aim is to make more gears for my Wood and Metal Clock.

A pair of gears cut together out of mild steel – 60 teeth and 43mm diameter. One of these is for the camshaft side of a four-stroke engine in construction.

I created a quick google spreadsheet (below) that gives me divisions up to 200 and for completeness the first row gives 360 divisions. I have added a link to a downloadable pdf version if that helps. Note: number of hole intervals means you need to count the hole that the pin is in as 0 and then count out the number of intervals/steps from there (next step being 1).

A freely available spreadsheet that has the full dividing plate and rotary table calculations. You can set it up for your specific table and print off the sheets. You just need to know the worm drive ratio.

As you can see from the output, the hole plates are chosen to provide all the divisions through fifty; beyond that some are possible but many require higher number hole plates which the program specifies.

A rotary table can be divided automatically, according to the size of the table. Secondly, a kitchens can benefit from longevity and convenience. It is easy to use, a spice rack can help to organize items andlyize accordingly.

A server rotary plate can be used as an alternative to a standard rotary plate. It is easy to operate as a server rotary plate, it can be easily moved to the objects by rotating on them. The kitchenware can benefit from the different benefit of a rotary table dividing plate as it is easier to operate. It is environmentally friendly, dishwasher safe and drying, and can benefit from the advantage of a rotary table dividing.

As one might expect from the name, the dividing head is all about dividing. Dividing is not about moving through a certain angle but is more about dividing a whole circle into a specific number of parts. The most obvious use of this is when gear cutting. The circle has to be divided by the number of teeth needed on the gear to be cut. (Of course, in reality, teeth are not cut – it is the space between them that is cut.) One tooth is cut then the workpiece is rotated by the required amount and then the next tooth is cut and so on till all of the teeth have been cut.

Most dividing heads have a built in indexing ring. This is fixed to the spindle. It has holes spaced round it and a pin mechanism to lock the spindle on any one of these holes. This form of indexing does not have to use the worm and worm wheel. These can be disengaged. The workpiece is free to rotate except where the indexing pin locks with the indexing plate. Of course the only numbers that can be divided by are numbers that divide into the number of holes on the indexing plate. But there are many times when this is useful.

The advantage of this is that it is much quicker than having to rotate the spindle using the worm and worm wheel. It is also possible to have the worm and wormwheel engaged and to turn it using the handle and then to lock the spindle using the indexing plate.

Dividing plates can either have rings of holes on one side only. In this case the holes are drilled all the way through. Alternatively they can have rings of holes on both sides. In this can the holes are drilled just less than halfway through. Only the rings of holes on one side can be used at any one time. If one of the rings on the other side is needed the dividing plate has to be taken off, turn round and screwed back on.

On a small dividing head there might two or three dividing plates. Together these will cover rings of holes up to about 50 holes. The numbers selected in the rings of holes will be arranged so the division by any number up to 50 is possible. Of course, it is possible to divide by numbers way beyond fifty but not numbers whose factors include one or more primes larger than the ring with the largest number of holes that are prime. For example, on a small dividing head it might be 51. This is the largest number of holes that can be fitted in one circle on the plate – given its size.

The dividing plate fits onto the body of the dividing head and is concentric with the crank handle. On more complex heads this plate can rotate but on plain dividing heads it is fixed.

On a simple crank handle there is just one handle that contains a retractable pin. This handle can be moved so the pin can engage the holes in any one of the rings of holes. On more complicated , and therefore, larger, dividing heads there are two handles. One contains the pin and can be moved as before. The other is fixed and does not contain a pin. It is as far out as possible so is easier to use for turning the worm that turns the spindle.

The other feature that goes with this are the sector arms. These arms can be adjusted to encompass any number of holes in any ring of holes. This can be set so the space between the two arms goes from one hole through any number of spaces between the holes ending up at another hole. Between one arm and the other there will be n+1 holes but only n spaces. We are only really interested in the number of spaces between the sector arms. In practice the arms are used so that the handle can be moved through so many spaces between the holes in one ring of holes.

The number of holes on a dividing plate depends on the manufacturer of the plate. For example a Browne and Sharp dividing head uses a set of three dividing plates. These plates contain rings with the following numbers of holes:

We have to remember that one turn of the handle turns the worm by 1/40 of a circle. To go through a whole circle, therefore, requires 40 turns. Using just whole turns of the handle we can divide by any permutation of the factors of 40, for example, 2, 4, 5, 8, 10, 20.

If we can turn the handle by a fraction of a turn then the choices are much greater. Suppose we pick the ring of holes with 15 holes in it. It will also have 15 spaces in it. To turn the spindle through a whole circle involves the handle going past the number of spaces in the currently selected circle, say, 15 times 40 turns. That is 600 holes.

Suppose we want to divide a circle by 30. In this case the number of spaces will be 600/30 which is 20. Since this is greater than 15 this means each step will be one complete turn, that is, 15 spaces, plus another 5 to make 20 spaces altogether. The sector arms would be set to cover 5 spaces between holes. Between the sector arms would be 5 spaces but it would start with a hole and end with a hole so 5 spaces would have the arms encompassing 6 holes.

As we have just seen, dividing by any number less than 40 will need one or more complete turns of the handle plus a certain number of spaces. Dividing by 40 will require one whole turn of the handle. Dividing by any number greater than 40 will involve less than one rotation of the handle, i.e., just so many spaces.

If we look at the numbers of holes in the rings on the Brown and Sharpe dividing plate above we can see that the rings of holes give us the following factors:

It can be seen that with this dividing plate we can divide by any number up to 49. What we often cannot do is divide a circle where 40 times the number of spaces in a circle does not contain the factors required for the division we want to do. For example we cannot divide a circle by 51, whose factors are 3 and 17, because we cannot get a ring with both 3 and 17 at the same time and these numbers are not factor of 40. Similarly we cannot divide by 81 because it has 4 three’s as factors and we can only get a ring with 3 three’s. Apart from these sorts of problems we can divide by most numbers up to 49 x 40, nearly 2000.

The reader might have noticed that dividing heads seldom use degrees. But if it is necessary it can be done. Since there are 360º in a circle, one degree is simply a whole circle divided by 360.

Find the factors of 360. They are 5, 3, 3, 2, 2, 2. All of these factors have to be in the product (multiplication) of 40 and the number of spaces in the ring.

With a small dividing head with only one handle, if there is more than one ring that contains the required factors it is best to choose the larger ring. It is easier to turn the handle.

In the above example the 18 ring was chosen for having the factors required. But the 27 ring also has the required factors and would, therefore, be easier to use.

A more complex type of dividing head, which is sometimes referred to as being universal, has an auxiliary input at the back. This input can be used to rotate the dividing plate. The dividing plate is on a shaft that contains the shaft with the worm on it. This worm rotates the wormwheel etc.

In differential indexing the dividing plate is not locked. If the auxiliary shaft rotates it rotates. In differential indexing the main shaft of the dividing head is connected via a gear train to the auxiliary input.

If we turn the handle from one hole on the dividing plate to another the workpiece turns. But doing that feeds through to the auxiliary input which, in turn, rotates the dividing plate.

This enables us to divide by numbers we could not do using just the dividing plates. In this method of indexing we cannot rotate the workpiece from the leadscrew – we cannot do helical milling but then that is not why we are using this set-up. Also it is not possible to have the dividing head tilted at an angle.

The merit of this is that it makes it easy to divide a circle by unpleasant numbers. Suppose we want to make a gear with 127 teeth. The number 127 is of great interest because it is the factor that converts from imperial to metric but it also happens to be a prime number.

This number is a number that is easy to handle. In the case of wanting 127 teeth a good number would be 120. The closer this number is to the required number the smaller the gear ratio needed to correct it.

Since the ratio built into the dividing head is 40 this means each tooth will need only one third of a turn of the handle. Therefore we have to use a ring on the dividing plate that contains a factor of 3. If we use a ring with 27 holes then each tooth will be 9 spaces.

This arrangement is called differential because the ratio is determined by a difference, i.e., two numbers added or subtracted. It is easy to see that this technique is a very powerful way of dealing with ratios with intractable factors.

If the number chosen is too big then the ratio will be negative. If it is too small the ratio will be positive. This means that the dividing plate will have to turn one way rather than the other. This can be changed by adding an idler gear in the gear train to change the direction of rotation.

For the sake of completeness some mention will be made here of compound indexing. This can be used to divide by odd numbers. The trick here is to rotate the main shaft by a certain number of holes on one ring of holes on a dividing plate and to add or subtract from this a different number of holes from another ring. It is necessary that both of the rings being used are on the same plate. In “Practical Treatise on Milling and the Milling Machine” published by Brown and Sharpe in 1927 refers to this as being of “little practical accuracy”.

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