Pictures of a dividing head

You may be able to adapt existing plates for less than what just the material will cost to make. see

some operating manuals

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

O.K. From my B&S one, which has somewhat smaller plates (largest number of holes is on the outside row):

Plate #1 #2 #4 Row == == == Outer 20 33 49 19 31 47 18 29 43 17 27 41 16 23 39 Inner 15 21 37

The apparently missing ones are multiples of smaller ones or divisions of larger ones.

1 Any disc and row 2 Any even row on disc 1 3 15, 18 on disk 1 21, 33 on disk 2 39 on disk 3

4) 16, 20 on disk 1

5) 16, 20 on disk 1

6) 18 on disk 1

7) 21 on disk 2

and so on.

My plates are 5" diameter, and about 1/4" thick. (0.243, 0.245, and 0.247")

If your existing plate is 1/2" thick, remove it and check the other side. It may have a different set of holes there, with the holes all going only half-way through (except where two line up by accident).

And what is the thickness of the plate on your index head? If

1/2", check whether they are doing the trick of flipping it over for a second set of holes. If not -- prepare to turn it thinner -- perhaps after drilling. Or -- get some 1/4" steel plate, lay out circles on it, bandsaw to approximate diameter, and turn on a faceplate with a live center clamping it (and something to spread the force to out near the edge). Obviously -- put a sacrificial spacer under the workpiece so you don't turn the faceplate.

Understood.

Most screw machine bits are also ground as split point. Split points wander a lot less than the standard chisel points found on most jobbers length drills. When drilling a flat plate, I think that you can do fairly well here.

Hmm ... you need really good fixturing with the carbide bits. Any slip to the side and "plink" -- a broken bit.

But -- this means that if it *does* wander, it will break instead of drilling a hole off location.

It has a split point, which is important. They are expensive, but I would suggest that you get several, since it will otherwise bring your project to a halt if the bit breaks. And carbide *does* break easily.

What spindle speed can you get?

How will you hold it? Collet, drill chuck, end mill holder? If a drill chuck, how much runout at 1/8". (BTW -- you did check the hole size in what you have I presume. IIRC, my B&S one is closer to 0.100" holes. But I've never had to drill a new plate, so I could be wrong.)

But if the holder has a short enough overhang and has minimal runout, if the spindle speed is high enough, and if the power feed is slow enough, then it could work quite well.

Are you planning to use your perl script to make a list of hole coordinates? You might consider using the index head itself to drill the circle of holes. Which set of holes do you have? Can you use them with the chart to make the other hole patterns you need? It will give you good practice using the dividing head and the sector arms. Just rotate it until the spindle faces up instead of horizontal. You can divide a temporary plate by hand or using your rotary table, and use that for drilling the hole circle you need. Note that the 40:1 ratio means that your placement errors in your temporary plate are reduced by a similar ratio.

Good Luck, DoN.

[ ... ]

I got the impression that his were 6" plates. What you have sounds like a match for my third plate -- except that I did not check the bore or the hole circles for the mounting screws.

Enjoy, DoN.

Looks good to me. Does your power quill feed work? I'd probably use the 0.003" per rev setting.

If you check out the PTD catalog, you can make an informed choice on speeds and feeds.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

======== Gingery covers how to make an index plate with minimal equipment in his book

#1153 @9.95$US {at bottom of page}

His methods will let you generate a 127 hole plate if you need to make a metric change gear, and other prime number > 50 gears that the standard plates don't cover.

I also developed an excel spread sheet that generates the angles in degrees/minutes and 10 second increments if you have a vernier for your dividing head. It also runs under the free scalc spreadsheet program you can download at

If you or the other readers want a copy send me an email. Good email address shown.

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

Someone else posted his plate counts on practicalmachinist, and it seems that it is the same set of numbers. Since I assume that these numbers have been carefully selected for best usefulness, I will try to replicate them.

Four screw holes.

I also found these plates on wttool.com, not sure whether they would fit.

Mine are the same diameter and thickness.

No, 1/2 is the thinnest circles at mcmaster carr. I wish I could get

1/4". I could make them, but it is more work.

I may do this also, it would be a good exercise. I would cut the approximate bigger circle with a plasma cutter. Also, my handle can work with bigger plates, easily up to 6" diameter, so I would make mine 6".

I think that I can adequately hold them with two vee blocks placed vertically.

up to 5k RPM at 100 Hz.

If

1/8" collet.

It was something like 0.1210 or some such, IIRC.

Because the head is already dividing everything by 1/40, there is not a big need for super tight tolerances on the sizes of the holes.

I thought that I could just feed manually.

Definitely.

This is much more error prone than using a perl script with DRO.

Also, I realized that if I make a plate with 540 equally spaced holes (they would be equally spaced in terms of angle, but not necessarily on the same radius from the center of the plate, so the holes would not overlap), then this permits me to set the dividing head to any minute of angle. I could write a script to give coordinates of these holes to ensure that they do not overlap.

i

My current plate is 5", but the handle can go up to 6 inches.

i

Those are the ones which are most useful for a 40:1 ratio gear.

You are saying that your plates have four?

The first question is the diameter of the hole vs the bearing boss on the dividing head.

The second is -- how useful will those hole patterns be with a

40:1 ratio head? The ad says that they are for a rotary table, so they are more likely a good choice for a 90:1 ratio (which is more common in rotary tables than in dividing heads).

Note that the smallest hole count on this is 26, so you miss all the patterns on the #1 plate, and the first two on the second plate.

You are totally missing any multiple of 20, 19 is covered by 38,

18 is missing, 17 you have as 24, 16 as 32, and 15 as 30. so you are missing from the first plate two of the initial circles. And your chart will be expecting the same number of holes.

Also -- assuming that you did mean that there were four screw holes in the plate you have, there are the questions of "what size screw", and "on what circle radius" -- even if the bore is right. (And it is probably metric on the plates in the ad, and almost certainly some reasonable fractional inch size in your dividing head.

For that matter -- does '12"' mean the diameter of the plates, or the diameter of the rotary table that they are to be used with?

[ ... ]

O.K. So other than the problems of the bore and the number of screw holes, they are similar to my B&S ones.

Better to go from 1/4" mild steel plate than from discs cutoff from round stock I think.

Check how high the crank bearing is from the table -- in all positions of the head -- to make sure that a larger plate will not hit the table.

[ ... ]

Hmm ... 164 SFM -- a bit slow for carbide in mild steel I think.

Good -- that should be short enough.

Agreed. The highest hole count in the standard plates is 49, which is 7.34 degrees direct, or 0 degrees 11 minutes 1 second error at the head's spindle. IIRC, the spacing between the holes is pretty close to the diameter of the holes, so an oversized hole just barely touching the next oversized hole would be about half that error. Real error probabilities are even smaller, of course.

That is more likely to break the carbide bit because you are feeding too fast for the drill to cut and clear the chips. The manual feed on a Bridgeport is a bit too stiff to get fine control over the feed of that small a drill bit. No feel. It looks like about 370 SFM in mild steel, which with a 1/8" bit turns out to be around 11,300 RPM.

If you are *very* careful about your feed, the 5000 RPM may do. Or feed using the knee crank. :-)

How slow can you set the downfeed? (My Bridgeport is CNC from birth so it does not have the manual downfeed.) Between setting a slow feed and an automatic depth stop release (which I seem to remember on older Bridgeports which I have used) you may be alright. Test it on some scraps first.

The index head? Assuming you have the right holes to start with, you can set it up to make it very difficult to make mistakes. Yes, you have to count full turns of the crank (assuming that you are making fewer than 40 holes in a circle) but you set the sector arms so one touches the indexing pin, crank the full turn(s) if needed) and then continue until you touch the second sector arm and drop the pin into the hole which is there. Then you move the two sector arms (which are locked together by a screw) until the first arm touches the pin, and then you are ready for the next step. If you want to be extra sure, you set the drill to just barely kiss the plate before the feed stops, and then go through everything for the required number of holes. Then go one more, and you should be right over the first "kiss" as a check. Once you are sure that works out right, you can reset the depth to drill the holes fully through into a sacrificial material behind the plate.

The chart should give you the number of full turns, then a choice of one of (typically) several hole circles, and either the number of holes from first sector arm to the second, or the degrees set between the sector arms (there should be a scale to tell you that. This way, you can set by hole count, and cross check it against the degrees, or vice versa.

Hmm ... 540 equally spaced holes -- six circles of holes per plate, That is 90 holes per circle, while the maximum on the standard plates is 49 holes in the outermost circle. 90 holes at 0.125" diameter, touching, will give a circumference of approximately 11.25", or a minimum diameter of 3.581" And if you have the holes actually touching, how weak will it be? Remember that you have to have the same number of holes in each circle. You can get the outer row fairly easily, but the inner is questionable. Let's allow 0.005" between holes so they don't actually touch -- That moves the smallest circle out to 3.7242"

You might be able to do this if you can fit larger plates -- and if you make longer sector arms and a longer indexing arm -- *if* the larger plates don't interfere with the table.

And -- remember with these plates, you will need to print up a new set of charts (fire up that perl interpreter and pray to Larry Walls. :-)

Enjoy, DoN.

But will the plate hit the table with the head at some angle between vertical and a bit below horizontal?

Enjoy, DoN.