View Full Version : Dividing head question

Mike Amick
01-18-2013, 02:49 AM
I have an 8" RT .. not sure who made it (grizz I think)

Any ways .. thinking about getting dividing plates. Will an 8" dividing plate
fit any 8" RT ?

I have a sacrificial alum plate on mine .. making it almost 11" .. so would an
8" dividing plate still work on mine.

What happens when you try to put a 6" plate on an 8" RT ?

01-18-2013, 05:52 AM
I suppose, first of all, what I am about to say depends on whether you have an honest to God "Dividing Head" or a "RT" (rotary table). Most dividing heads are a 40:1 ratio (40 turns makes the chuck rotate 360 degrees) but a true Rotary Table has a ratio of 90:1.

If you have a true "dividing head" I would suggest making your own plate by drilling an accurate 18 hole pattern on a homemade disk making sure the pattern is concentric to the mounting hole in the center - the diameter of the plate doesn't matter. You'd have to trig out the positions of the holes and this might be tedious but you can do the whole thing yourself using the X and Y movements of your mill thereby allowing you to make the diameter of the plate whatever you wish. The 18 hole pattern is the one you would use the most (trust me) but as you find the need for other incremental movements you can just add a new circle to the disk. For instance, if you do a lot of 100 (and multiple) increments for graduated collars you might want to make a 25 hole circle as well.

I've never had a serious need to use a dividing plate on a "rotary table". I have them but I usually find that there is another way to get what I want without having to rely on them. For example if I want to make a rotary slot I trig out the beginning and ending of the slot and drill holes and then just mill till the end mill connects the two holes. I suppose what I am trying to say is that unless your need be very exacting you can usually get by without dividing plates on a rotary table. I will now brace myself for the beating I am about to receive from other machinists who disagree.

Edited to include - Of course you still need one hole to fix the exact position of the rotary arm on the turntable for hole patterns. A simple disk with one hole would suffice. Then you'd index by simply going off of the degree graduations on the circumference of the turntable.

01-18-2013, 06:44 AM
These days fitting a stepper motor and driving it from a Divisionmaster, or Arduinio/PC is probably a better bet.

01-18-2013, 10:56 AM
A little OT.

What I've observed is that a horizontal/vertical R/T with dividing plates is no substitute for a dividing head. It's a clumsy compromise at best. Making matters worse, an 8, 10" R/T used in the vertical mode eats up a lot of daylight.

01-18-2013, 11:29 AM
Are we talking about the same thing?

As I read the original post, he has a 8 inch table with an 11 inch plate fastened to the top. The assumption is that the other bits and pieces are there to attach dividing plates. This would be the sector arms, index pin and attaching system.

If there is a larger plate overhanging the top there has to be enough clearance for the index plates.

So a bit more information would be helpful.

I have a Bridgeport table with the full set of plates. They are all unused due to having a dividing head as well.

01-18-2013, 11:35 AM
These dividing plates: http://www.grizzly.com/products/Dividing-Plates/G9295 are said to fit multiple rotary tables. If you have this model: http://www.grizzly.com/products/Dividing-Plates/h7506 I bought plates through enco though I think you can get them through CDCO as well. If you can make 6" plates fit an 8" table there is no problem unless the handle-table turn ratios are different.

01-18-2013, 03:13 PM
Looking at the Grizzly web page it seems that their DT's are "Vertex" (look very similar) and if so they have the indexing plate assemblies for an ("Vertex"?) RT.

A "Phase 2" RT is very similar.

The name and size of the RT will be a big help.



01-18-2013, 05:56 PM
To determine if plates will mount on your RT you will have to measure the dividing plate center hole diameter and the location of the mounting screw holes. With your sacrificial table, you will have to place the edge of a ruler on the dividing plate mounting flange and see if the back of the plate will have clearance outside of your aluminum table.

I have an off brand 8 inch RT and needed dividing plates. The dividing plates I found mounted with either 3 or 4 screws. You will also find that the sets of plates will not have the same available hole circles.

I set up an Excel sheet to compare all the sets available and determine which set would support the maximum number of divisions with my 90:1 ratio RT. I ended up choosing the SOBA DP 2-3 set. They would allow me the divisions I needed for the project and the largest number of additional divisions. I figured if the mount was not correct, I would just modify them to fit. It turned out that they fit with no modification. When choosing a set of plates the thickness, center hole diameter and mounting screw hole locations will determine if they will fit on your RT.

The diameter of the dividing plate does not make any difference. I made an additional plate with a 127 hole circle to make a metric change gear for my lathe. I made the plate as large as possible and was only limited by the length of the sector arms that came with the plate set I purchased. The larger the plate, the larger the number of hole circles that it can support. With the larger plate I made, I figured it gave me more real estate to add additional hole circles as required.

Mike Amick
01-18-2013, 11:58 PM
The whole problem is .. I have no idea where these dividing plates mount. Believe it or not .. I can
NOT find any writing on my RT. And now that I know the difference .. it IS a 90 turn RT. My alum
plate is way back from the crank as you can see in the pics.

The only reason I want it .. is with my lack of experience ... if I needed to put some critically positioned
holes in something inportant .. I think I would feel more secure feeling it snap into a particular degree
whole ( if I am saying that right )


here is a side view if it helps anybody recognize it.


The Artful Bodger
01-19-2013, 01:34 AM
I believe that is a rotary table and I venture to suggest that fitting a dividing plate would be rather difficult. If you want to divide a circle using that you draw up a table of degrees and carefully wind the handle.

Dividing heads (or I should say the users of) need know nothing about degrees as their tool divides the circle into as many arcs as required, but you dont have a dividing head, you have a rotary table so you must use a calculator and a sheet of paper. Of course there is software out there to do that chore for you.

Mike Amick
01-19-2013, 03:06 AM
Thanks AB ..

good enough ...

I was just thinking that dividing "plates" could be added to RT's

01-19-2013, 09:48 AM
Unscrew the central allen head on the wheel handle. Pull off the wheel c/w graduations. This is mounted to either a 3 or 4 threaded hole boss. The dividing plates mount to this boss. As stated earlier, there are kits out there that will fit 6 or 8" R/T's.
I have a Vertex 6" horizontal/vertical R/T, which uses Soba dividing plates. As above, bolt straight on. If i had a choice and deeper pockets i'd have both a dividing head and my R/T. As i do'nt, the H/V R/T c/w dividing plates is a more versatile piece of kit. I've only used the plates on my shaper, rather than the mill, for cutting splines where the grads on the wheel and table were not accurate enough.

The Artful Bodger
01-19-2013, 01:29 PM
OK, thanks Mike, if kits are available I retract my comment that fitting dividing plates would be "rather difficult".:)