View Full Version : Index Holes on Back Plate

Paul Alciatore
02-19-2005, 03:51 AM
So I'm making a backplate for my new Bison 3 Jaw and I want to put holes in it for indexing in the lathe. I figure 60 will provide for a lot of different divisions.

My question is, should they be on the back side or on the OD of the backplate. I have room for them in both places and I am just wondering about the advantages and disadvantages of each location. The only thing that comes to mind so far is an arangement for clamping the pin/arm in place while indexing.

Since my backplate is about 1/2" larger diameter than the chuck, I think I could devise a clamp to hold the pin/arm in a rear hole by clamping on the front, around the edge. If the holes are on the OD, some external device would be needed.

Has anyone done this before? Any thoughts?

Paul A.

Allan Waterfall
02-19-2005, 04:51 AM
I would have thought put them wherever it's easiest to fix the index pin.

Personally if I did it I'd put them on the outside,they are easier to see,they tend to be self cleaning as the lathe spins and they look pretty.


Herb Helbig
02-19-2005, 07:35 AM
Paul - I put mine parallel with the axis, near the rim, and all the way through. My choice was on the basis that you can use them like a sine plate that way to interpolate between the 6 degree increments by using space blocks resting on a horizontal platform that's level with the lathe spindle axis to support a pin in one of the holes.


02-19-2005, 07:52 AM
Paul...a timely post! I'm just doing the same thing! I had planned to put mine on the back side and use a spring loaded pin in a slotted arm the same as my index pin on my R/T. I figured the back side because there is more room for different combinations of holes. I'm only going to set it up for a few common bolt patterns at first but was sort of looking to the future for the "who knows" factor. One example is making spacers for supercharger pulleys. they have an even bolt pattern but one hole is slightly off set. On the back there would be more room for oddball things like this. I was thinking that once the slotted arm is set you would also be less likely to make a counting mistake as all the holes in a given pattern would be the only ones that the pin would fit into. If the holes where on the OD you would have to be a lot more careful with pin placement. Having the holes on the OD might also make certain combinations difficult to achieve...no?

Spin Doctor
02-19-2005, 09:46 AM
The central question as stated was the positioning of the index pin. One thing I would consider is the unit holding the index pin having holes that space on a 7D increment to allow for 1D spacing. a btter option might even be to simply purcase one of the imported Spin Indexes and gut it for parts especially if you can get a cheap used one some place.


This is a mew one (and I am not the seller). The nice thing is it saves you a lot of the work in doing the division of the index plate. Because to do it really accurately you almost have to have or have access to a dividing head anyways. Trying to lay one out by hand raises too many potential errors creeping in. And to do one a milling machine you are looking at either using digital readouts for positioning or better yet standards, gage blocks and indicators

02-19-2005, 10:13 AM
I have seen somewhere here, I think Evan did it?, instead of useing the backplate, use the other end of the spindle.

I think he used a gear or gears to get the divisions. A plate with holes could of course be used.

I like the gear thing, I have access to a motorcycle salvage yard. Usually this guy just scaps a lot of the trany, timing, spockets, etc.

I have also seen a mechanism that attached to the top of the headstock and uses the bull gear and some kind of vernier. It was on a Myford. Very clever.

Torker, I used 'other end of spindle' is that what you meant by backside?


02-19-2005, 01:09 PM
Gene...I meant the backside between the chuck and the spindle. I have a jury rigged index that I used a few times to drill bolt patterns in axles...it bolted throught the spindle and was positioned at the very rear of the spindle. I want something a little more flexible and easier to lock in position. When I'm done I'll post pics of it. This will stay on the back of the chuck and the index pin and locking "brake" will remove with two setscrews.

Mike Burdick
02-19-2005, 01:28 PM

Apparently South Bend offered this as an attachment at one time.


Paul Alciatore
02-19-2005, 02:19 PM
Great ideas. Thanks to all.

I hadn't thought about the "self cleaning" thing. But then, holes on the OD are more likely to collect chips than ones on the back. Is this a 50/50 thing?

Some of the comments have me thinking a bit more about the possible uses. I was doing this just as a general, nice to have, feature. I didn't have any particular use in mind. But it seems to me that one of the first to spring to mind is marking divisions on handwheels. Now I am thinking about a ring with 100 or perhaps 50 divisions. I wonder if I could get two rings in.

Spin, if I were to do the 1 degree thing, I would change to a 36 hole circle and do holes on the arm at 9 or 11 degrees. That would make the math easier for less chances of error. The smoke just started, I'm thinking. How about 36 holes on the OD, 10 degree spacing, Vernier holes on the arm for 1 degree increments, ... but that wouldn't allow for 100 divisions for scales? Seems to me that is the real reason why I have resisted the idea of buying one of the inexpensive spin indexes, no way to get 100 divisions. Need another trick.

Still thinking.....

Paul A.

02-19-2005, 03:11 PM
Mike, yes, that's what I had in mind to do.

I figure I could use gears, sprockets, what ever to make standard size plates that would attach basicaly like the picture.

Thanks for the photo.


02-19-2005, 04:03 PM
I don't know how the South Bend attachment attaches, but Myford makea one with an expanding plug to fit the spindle bore. It uses change gears for indexing.

Watchmaker's lathes use similar setups with multiple index plates. I would think something like that would be more useful than a drilled backplate, as many more combinations are possible.

Spin Doctor
02-19-2005, 06:29 PM
Yah Paul, the 36 and 60 hole plates do make a mess of trying to get 100 divisions. Perhaps an extra set of plates for the 11D vernier that have 50 and 100 holes might be a nice idea. The way the cheap spin indexes are made this should be possible. If you are really interested in building one of your own index devices or even machines these are good groups at yahoo


Paul Alciatore
02-20-2005, 10:42 AM
Again, thanks to all for the ideas. Here's what I'm coming up with.

I want as much versatility as possible - as many different divisions. But, I doubt that this will be used very often so I'm not going to drill hundreds of holes. By using the same Vernier style technique that the spin indexes use, a single row of holes can be made to perform multiple divisions.

I'm going to use a single circle and put it on the OD (self cleaning). Then I will make two or more "sector plates" with a number of holes in them to provide Vernier action to provide finer divisions. Each hole will be drilled and reamed to 3/16" diameter (I have that size reamer) and also drilled a bit deeper with a 1/8" bit and tapped 5-40 to provide a positive locking mechanism for the index pin. I may delay the tapping and just see how it works w/o first.

I have experimented with different numbers of holes and found that the most important thing for my Vernire scheme is that the number be a divisor of the number of divisions you really want. I checked for total divisions of 100 and 360 as these two will provide a total of 25 hole patterns including all numbers from 2 to 12 except 7 and 11. This will take two "sector plates", one with five holes to divide the 60 into 100 and the other with six holes to divide it into 360. The "sector plates" will be mounted on an arm clamped to the ways and will be fixed, not swinging.

The beauty of this idea is that it is at least theoretically possible to make additional "sector plates" for any number of divisions like the missing 7 or ll. Some may possibly be a bit too large to be practical but that remains to be seen. They certainly would not require any more holes than the number of divisions they are intended to produce so small numbers like 7 or 11 would certainly work. Although I would try to do a multiple of such numbers like 28 or 35. Larger primes like 53 might be problematic. But how many times do you ever need such a number of divisions???

I'll post pixs.

Paul A.

Spin Doctor
02-20-2005, 10:47 AM
Short of actually springing for a dividing head it seems a very practical approach. I am curious on just how you plan to do the main plates and the sector plates and still maintain the degree of accuracy needed for them to be reliable.

Paul Alciatore
02-20-2005, 10:51 AM
One more question on this.

This is likely the most accurate drilling job I have ever attempted. Up there with jig boring, IMO anyway. I am thinking about the best way to drill the holes for the best positional and size accuracy. It seems that reaming is the best way to insure an accurate size and I have an assortment of reamers so this is possible. The 3/16" size seems to be the best choice when looking at the backplate and my reamer collection.

But what about the locational accuracy. I have both center drills and spotting drills. Which would be better for the first cut? How deep should I go? Would the simple cone shapped of a shallow spotting drill be the best guidance for the larger sizes? Or would it be better to go in a ways with it, perhaps 1/16" or 1/8"? Or would a small center drill provide a smaller (web sized) pilot hole for the larger drill to follow?

Will the reamer really track accurately in the drilled holes? Any tricks here?

Paul A.

02-20-2005, 10:54 AM
I would go with Mike's idea - the nice thing with this method is once you have th disk, you can divide it up as you please just as with a normal indexing plate - this will give are more options and is easier to set up on the ass-end of the spindle anyway.

This has been done this way in England for a hundred or more years by Model Engineers - it works. You can use many of your lathes change gears for this, but I think a nice bronze or cast iron indexing plate is far classier. (although...stainless steel is shiney!)

Don't hack up your tools - improve them.

When I make indexing plates I use a sharp 1/8" carbide endmill to drill the indexing holes. Once this is finished you can slightly countersink the frontside for easier pin insertion, but I prefer my holes crisp and clean - taper the pin for easy insertion, but make sure it is long enough to engage the holes with the parallel sides of the pin (full diameter and depth), much easier.

Also, remember if you make the indexing plate to line up all the #1 holes. If you use a Horizontial table to index the plate, you can move the milling machine table back the approriate distance and drill the next hole series. One other tip, when you mill the holes with the endmill and come back around to the start - it better enter the hole without shaving any metal off - or you screwed up the indexing! At least you know then you never made a mistake indexing...

This plate should include the entire B&S indexing series and I would include 100, 127, and possibly 200. Idealy, if you use a worm drive (Myford GB owners have used these back from when G.Thomas invented it and posted in in ME) and the indexing plate on the worm you will require less holes as you can index exactly like thor dividing head or H/V tabler, direct indexing, however requires holes - lots of holes, Your choice.

[This message has been edited by Thrud (edited 02-20-2005).]

Spin Doctor
02-20-2005, 11:08 AM
With out a dividing head the only way to really get the positional accuracy needed would be to rely on using the gear train on the lathe to supply tour divisions. But then you would be half way there already. Now that I think about it there was an article in HSM maybe 12 years back on a dividing plate system that mounted on the back side of the headstock. But in this csae I think I would make the sector plate first and then mount the spacing plates on the machine and use the sector plate holes as a bushing plate for the reamer to maintain alignment. If you have a small drill press it might be a good idea to try and figure out a way to mount it on the cross slide for the drilling operation. I have no isea just what kind of equipment you have available but here's another option. Pick up a worm gear set and find a place to mount it to the lathe spindle. Install the worm in either some sort of swing arm or other arangement that eliminates the backlash entirely. Now if you can control the rotation of the worm shaft you can get any amount of index that you need. That's the problem with this idea. The longer I think about it the more ways I can come with to skin this particular cat. But no matter what you do Paul keep the pictures coming.

PS Reading this later today I really should be more careful in what I post. The spelling and grammer is horrid

Our motto "should be waste not want not" otherwise our childern will want

[This message has been edited by Spin Doctor (edited 02-20-2005).]

Alistair Hosie
02-20-2005, 06:44 PM
If you are looking for indexing plates etc or info ask John Stevenson he makes beauties .Alistair