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JCD
03-16-2005, 04:21 PM
Help!

I have need to cut a 127 tooth gear using a mill and a 40:1 dividing head. As it turns out, this is not a simple index, and if I am reading Machinery’s Handbook correctly, it turns out to be a compound index. I haven’t done that, and after talking to five people in “the trade” I can’t find anyone who has.
If I am understanding the handbook correctly, for this number of divisions, I will make nine turns around the gear to finish, and each index movement will consist of 2 turns, and 23 holes on a 39 hole plate, + 12 holes on a 49 hole plate.
All sounds good, except how do I keep track of where I may be at each point? Do I move the pin to the 49 hole circle and back to the 39 hole circle, or do I move the index plate without loosing track of where I am?
Would someone who has done this before give me some advise as to what works so that I don’t have to re-invent the wheel and/or make this gear two or three times?

Thanks

JCD

Forrest Addy
03-16-2005, 04:50 PM
127 indexes per rev? 40 to 1 dividing head? 40/127 = 0.314961 revs per div. How many holes of what hole circle is that? If it doesn't come out how do I gear the index? I have no idea without digging out my books.

I bought a gadget that indexes for me. It's ruined me as an old timey, pencil chewing, gear swapping machinist.

I modded the dividing head to drive to take a NEMA 23 stepper motor. I work the ratios and run the stepper with a Division Master. Great gadget. Poke the button, it steps the motor to index one division of the total you selected, and then it stops. Clamp. Bzzz! Cut. Dial back to clear. Unclamp. Poke. Bzzz! Cut. Etc.

It's only a question of time before I start looking for drapes to match the cutting oil.

[This message has been edited by Forrest Addy (edited 03-16-2005).]

jburstein
03-16-2005, 04:57 PM
40/127 is very very close to 5/16. The difference between them is, in fact .00246 . I don't know if that amount of error is acceptable in making such a gear, but it's something to consider.

-Justin

Spin Doctor
03-16-2005, 08:28 PM
<font face="Verdana, Arial" size="2">Originally posted by jburstein:
40/127 is very very close to 5/16. The difference between them is, in fact .00246 . I don't know if that amount of error is acceptable in making such a gear, but it's something to consider.

-Justin</font>


To be honest the error may or may not that much to make a difference but when calculating out helical gear cutting ratios the standard we always used was +/-.0000X of the ratio as the gearing equations came out to. For threads (which in some ways can be thought of as a similiar machining operation) the question of error is just how long is the thread in the nut and how tight is the fit

John Foster
03-16-2005, 09:44 PM
Where are you in MO? I can cut 127 in Des Moines.

vmil3
03-16-2005, 09:56 PM
Hi JCD,
To cut a 127 T gear with a dividing head, it the dividing head must be a Universal Dividing head with the gears and quadrants and stub spindles, it looks like this when assembled to cut 127 Tooth gears

http://img.photobucket.com/albums/v727/vmil3/differentialindexing127tgear.jpg

The plate has to rotate a fractional amount, it does this by the bevel gear drive, driven from the dividing head spindle, throught the set of compound gears on the quadrent, then turning the bevel gear, which rotates the hole plate.
Pic of bevel gear drive

http://img.photobucket.com/albums/v727/vmil3/bevelgears.jpg

Pic of hole plate rotation after cutting 127 teeth, white mark on plate started at the top to cut the first tooth, then indexing to the next tooth the small gear in the spindle turns the set of gears on the quadrant, witch turn the bevel gears, on witch is mounted the hole plate. The plate has moved approximately 1/3 of a turn, see white mark on the plate.

http://img.photobucket.com/albums/v727/vmil3/platerotationred.jpg

------------------
Doug

[This message has been edited by vmil3 (edited 03-16-2005).]

drof34
03-17-2005, 12:07 AM
Without using a universal or cnc dividing head,you can make your own plate with 127 holes in it and then turn every 40 holes. The problem with this is it is almost as much work as making the gear.

This can be made on a mill with a dro and bolt hole feature. Another problem is that 127 holes are a lot of holes and the holes have to be the same size as the holes in your other plates. Also there needs to be a little meat between holes which may require a larger dia plate than your old ones which in turn may require a longer arm that holds the plunger/pin.Then you may find the larger plate will hit the table,unless you arrange the head so the plate hangs over the edge of the table. I had all of these problems with cutting several 89 tooth gears. http://bbs.homeshopmachinist.net//eek.gif

Maybe you should just buy a gear.

Jim W.

Spin Doctor
03-17-2005, 05:51 AM
There is an easier way. Just find a gear shop that has a Barber Colman 30-1 hob and have them set it up with a 30 driver and a 127 driven http://bbs.homeshopmachinist.net//rolleyes.gif Actually the hobbing ratio is 4.233333333 to 1 driver to driven for a 127 tooth gear. We have neat book at work with the absolutely catchy title of "14,000 Gear Ratios" Comes in very handy for coming up with gearing combos for helical work

hoffman
03-17-2005, 06:28 AM
Hey vmil, that head looks a lot like my old kempsmith although I'm missing the gear train parts. Thanks for posting the pics! Now I know what the rest of a universal looks like.

------------------
Hoffman in Warner Robins Ga

John Stevenson
03-17-2005, 07:05 AM
Spin,
If he had a 127 driven he wouldn't need a 127 http://bbs.homeshopmachinist.net//biggrin.gif

There are divison plates on ebay.co.uk with 127 hole circles.

John S.

SGW
03-17-2005, 08:20 AM
If you have a rotary table, you could make a 127-hole plate using that. 2.8346... degrees per hole...

CharlesM
03-17-2005, 09:55 AM
There is an article on the Jan-Feb 1998 "Home Shop Machinist" on compound dividing. I haven't pulled it out to reread yet, so I don't know if it will answer your question or not.

------------------
Charles McGough
Sterlington, LA

vmil3
03-17-2005, 01:24 PM
hoffman,
Not a kempsmith, it's a Vilh Pedersen from Denmark. Here are pic's of the complete Universal Dividing head with manual, there are 2 dividing plates.

http://img.photobucket.com/albums/v727/vmil3/UniversalDividingheadpartsa.jpg

http://img.photobucket.com/albums/v727/vmil3/UniversalDividingheadpartsb.jpg

http://img.photobucket.com/albums/v727/vmil3/VilhPedersenUniversalDividinghead.jpg

------------------
Doug

JCD
03-17-2005, 01:27 PM
<font face="Verdana, Arial" size="2">Originally posted by CharlesM:
There is an article on the Jan-Feb 1998 "Home Shop Machinist" on compound dividing. I haven't pulled it out to reread yet, so I don't know if it will answer your question or not.

</font>

Thanks Charles, It looks like my Numbers are correct. I am still looking for procedure.

JCD

JCD
03-17-2005, 01:32 PM
<font face="Verdana, Arial" size="2">Originally posted by vmil3:
Hi JCD,
To cut a 127 T gear with a dividing head, it the dividing head must be a Universal Dividing head with the gears and quadrants and stub spindles, it looks like this when assembled to cut 127 Tooth gears

http://img.photobucket.com/albums/v727/vmil3/differentialindexing127tgear.jpg

The plate has to rotate a fractional amount, it does this by the bevel gear drive, driven from the dividing head spindle, throught the set of compound gears on the quadrent, then turning the bevel gear, which rotates the hole plate.
Pic of bevel gear drive

http://img.photobucket.com/albums/v727/vmil3/bevelgears.jpg

Pic of hole plate rotation after cutting 127 teeth, white mark on plate started at the top to cut the first tooth, then indexing to the next tooth the small gear in the spindle turns the set of gears on the quadrant, witch turn the bevel gears, on witch is mounted the hole plate. The plate has moved approximately 1/3 of a turn, see white mark on the plate.

http://img.photobucket.com/albums/v727/vmil3/platerotationred.jpg

</font>

Thanks for your help,
I do not have the gears for diferental indexing, so I must do it with compound indexing.
I'm looking for that procedure.

JCD

eperkins
03-17-2005, 02:09 PM
Since the gear you are cutting is 127 tooth, I assume you are cooking up a metric transposing gear. If so, a much simpler solution is to use a 37/47 compound gear in the gear train. The ratio is so close to 100/127 that there are no pratical differences. It is also much more compact and will fit in the gear train nicely. This is how I made metric transposing gears for my 9" South Bend lathe. I made them out of aluminum plate and pressed them together on a bronze bushing to form a compound gear. The gears were cut on a small Benchmaster horizontal milling machine using a home built Gingery dividing head. It got the correct form cutter from MSC for about $25.00. No compound dividing is necessary. I also made a pair of these gears out of cast iron for a friend to use on his 1896 "American" 12" X 36" lathe. Information on this can be obtained from Scott Logan's website. Somewhere (I think in the Yahoo South Bend Group files) is a print out with all the necessary set ups to get the metric pitches you want. Good Luck!

Cheers

Perk in Cincinnati

hoffman
03-17-2005, 09:52 PM
http://images.andale.com/f2/129/111/8188590/1102854171519_ihead__2_.jpg
Wow, it looks real similar to mine which is a kempsmith. Same canted plate and they both have the bevel gear beneath the plate. All I have is what is pictured plus 2 more plates. Thanks again for posting the pics!

JCD
03-18-2005, 08:13 AM
<font face="Verdana, Arial" size="2">Originally posted by eperkins:
Since the gear you are cutting is 127 tooth, I assume you are cooking up a metric transposing gear. If so, a much simpler solution is to use a 37/47 compound gear in the gear train. The ratio is so close to 100/127 that there are no pratical differences. It is also much more compact and will fit in the gear train nicely. This is how I made metric transposing gears for my 9" South Bend lathe. I made them out of aluminum plate and pressed them together on a bronze bushing to form a compound gear. The gears were cut on a small Benchmaster horizontal milling machine using a home built Gingery dividing head. It got the correct form cutter from MSC for about $25.00. No compound dividing is necessary. I also made a pair of these gears out of cast iron for a friend to use on his 1896 "American" 12" X 36" lathe. Information on this can be obtained from Scott Logan's website. Somewhere (I think in the Yahoo South Bend Group files) is a print out with all the necessary set ups to get the metric pitches you want. Good Luck!

Cheers

Perk in Cincinnati</font>

O.K. I Give.

It sounds like compound dividing is a lost art.

What is the error in thread cutting lead with the 37/47 combination?

JCD

suomi
03-18-2005, 08:23 AM
hey hoffman I just bought a identical kempsmith unit they seem well built.

CharlesM
03-18-2005, 09:43 AM
JCD,
I found this site that shows a photo of a modification to a dividing head to do compound indexing. It is by the author if the HSM artical. Maybe this will give you a clue.
http://www.cams-club.org/meeting-history/27apr00/

------------------
Charles McGough
Sterlington, LA

CharlesM
03-18-2005, 10:00 AM
Jcd,
In doing a little more research, I found a series of 4 articals in HSM on compound indexing. They begin in the March/April 1997 and continue in the next three issues.
I hope this helps.

------------------
Charles McGough
Sterlington, LA

kap pullen
03-18-2005, 11:12 AM
Make up an index disc blank, and have a cnc shop drill the holes for you.

Than you would use 40/127 holes, or 60/127 holes depending on your head.

I can drill your blank and have it back to you in a day or so.

You may be able to fit another row of holes around the od of your existing disc.

I pulled that one off.

kap

Jpfalt
03-18-2005, 11:19 AM
I may have a solution. It may be tedious, but it should work.

With the dividing head, set up for the first tooth.

Then turn the crank 127 times. This should cut the 40th tooth

Turn the crank 127 times. This should cut the 80th tooth

Turn the crank 127 times. This should cut the 120th tooth.

Repeat and you get:

33,73, 113, 26, 66, 106, 19, 59, 99 and so on.

You will have to turn the crank 16,129 times, but the result will be right on as long as you can count to 127 in a repeatable manner.

I stumbled into this trying to make an 11 tooth gear when the only hole set I was missing on my divider plates was a multiple of 11.

SGW
03-18-2005, 11:42 AM
47/37 gives an error of a couple ten-thousandths of an inch per inch, more or less.

Jpfalt, I think there's a flaw in your logic somewhere. Assuming a 40:1 gear ratio, one complete turn will rotate the spindle 9 degrees. 127 turns will rotate the spindle 1143 degrees. Any number of rotations will result in a rotation of some whole number of degrees. The teeth in a 127-toot gear though, have to be 2.8346... degrees apart, and the only way to get that kind of fractional degree is to turn the crank a fractional amount...some fraction of 127.


[This message has been edited by SGW (edited 03-18-2005).]

eperkins
03-18-2005, 01:06 PM
JCD

The error in the 37/47 compound gear is as follows;

37/47=.7872
100/127=.7874

The difference is .0002 or .02%

The 100/127 compound gear gives you a perfect translation. Unless you are doing something like cutting leadscrews for machines or measuring insturments, or cutting very very long threads, this degree of error is completely insignificant.

Perk in Cincinnati

mklotz
03-18-2005, 01:35 PM
63/80 = 0.7875 is even closer.

Regards, Marv

Home Shop Freeware - Tools for People Who Build Things
http://www.geocities.com/mklotz.geo

John Stevenson
03-18-2005, 02:25 PM
<font face="Verdana, Arial" size="2">Originally posted by Jpfalt:

You will have to turn the crank 16,129 times, but the result will be right on as long as you can count to 127 in a repeatable manner.

</font>

JP, can you drop me an email when you are done ? http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

zl1byz
03-18-2005, 02:45 PM
<font face="Verdana, Arial" size="2">Originally posted by Jpfalt:


You will have to turn the crank 16,129 times, but the result will be right on as long as you can count to 127 in a repeatable manner.

</font>

Wow! Life is too short. http://bbs.homeshopmachinist.net//smile.gif

I can see a battery drill and counter comming up. http://bbs.homeshopmachinist.net//biggrin.gif

Does it work or not? http://bbs.homeshopmachinist.net//confused.gif

John.

zl1byz
03-18-2005, 03:01 PM
Umm! If using a 40/1 dividing head every 40 turns of the crank gives 1 turn of the work exactly. So we can do away with 120 of those turns as all that acheives is rotates the job 3 times. Am I missing something here? http://bbs.homeshopmachinist.net//confused.gif

John.

Jpfalt
03-18-2005, 05:13 PM
Never mind!!

zl1byz
03-18-2005, 05:20 PM
<font face="Verdana, Arial" size="2">Originally posted by Jpfalt:
Never mind!!</font>

Oh don't be like that. Put me out of my misery. Was I the victim of an old joke or what? http://bbs.homeshopmachinist.net//smile.gif

John.

Jpfalt
03-18-2005, 07:26 PM
It's one of those things that sounds really good til you try it.

Hey, watch this!!

JCD
03-18-2005, 08:53 PM
<font face="Verdana, Arial" size="2">Originally posted by eperkins:
JCD

The error in the 37/47 compound gear is as follows;

37/47=.7872
100/127=.7874

The difference is .0002 or .02%

The 100/127 compound gear gives you a perfect translation. Unless you are doing something like cutting leadscrews for machines or measuring insturments, or cutting very very long threads, this degree of error is completely insignificant.

Perk in Cincinnati</font>

Does that mean there is a .02% error in the screw lead?

JCD

Bill Cook
03-18-2005, 08:55 PM
Here's an explanation I put in the Dropbox.

http://metalworking.com/DropBox/_2003_retired_files/

Scroll down to:

Compound_Indexing.txt

Compound_Indexing_Error.gif - Shows how to use the table in the Machineries Handbook and how small the error is.

Compound_Indexing_Pin.jpg - Shows the second pin needed to be able to index in two hole circles at once.

In simple indexing, 5 holes in the 16 hole circle per index will generate 128 divisions. If 5 holes are "lost" evenly over the whole gear, it will have 127 divisions and be more accurate than it would seem. By the 25th index one hole should be lost, etc.

BC

JCD
03-18-2005, 09:00 PM
<font face="Verdana, Arial" size="2">Originally posted by mklotz:
63/80 = 0.7875 is even closer.

Regards, Marv

Home Shop Freeware - Tools for People Who Build Things
http://www.geocities.com/mklotz.geo</font>

Marv,

SOftware looks like nice stuff.

Thanks

JCD

speedy
03-18-2005, 11:57 PM
<font face="Verdana, Arial" size="2">Originally posted by Jpfalt:
I may have a solution. It may be tedious, but it should work.

With the dividing head, set up for the first tooth.

Then turn the crank 127 times. This should cut the 40th tooth

Turn the crank 127 times. This should cut the 80th tooth

Turn the crank 127 times. This should cut the 120th tooth.

Repeat and you get:

33,73, 113, 26, 66, 106, 19, 59, 99 and so on.

You will have to turn the crank 16,129 times, but the result will be right on as long as you can count to 127 in a repeatable manner.

I stumbled into this trying to make an 11 tooth gear when the only hole set I was missing on my divider plates was a multiple of 11.</font>

English ?? humour

My fable on tiresome execise..
I went out to the workshop, oops, forgot my glasses, back inside then out to the workshop, oops forgot to brush teeth, back inside then out to the workshop, oops, forgot my shed keys, back inside then out to the workshop....well this went on for ages but I finally got everything sorted.

You will always get there in the end...sometimes the journey just takes longer http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif



[This message has been edited by speedy (edited 03-19-2005).]

JCD
03-19-2005, 07:56 AM
<font face="Verdana, Arial" size="2">Originally posted by eperkins:
Since the gear you are cutting is 127 tooth, I assume you are cooking up a metric transposing gear. If so, a much simpler solution is to use a 37/47 compound gear in the gear train. The ratio is so close to 100/127 that there are no pratical differences. It is also much more compact and will fit in the gear train nicely. This is how I made metric transposing gears for my 9" South Bend lathe. I made them out of aluminum plate and pressed them together on a bronze bushing to form a compound gear. The gears were cut on a small Benchmaster horizontal milling machine using a home built Gingery dividing head. It got the correct form cutter from MSC for about $25.00. No compound dividing is necessary. I also made a pair of these gears out of cast iron for a friend to use on his 1896 "American" 12" X 36" lathe. Information on this can be obtained from Scott Logan's website. Somewhere (I think in the Yahoo South Bend Group files) is a print out with all the necessary set ups to get the metric pitches you want. Good Luck!

Cheers

Perk in Cincinnati</font>

Well, I'm confused again.

The South Bend people say I need a 120/127 combo. for english/metric transposing ratio, for my 10" SB Heavy. As I read some say 100/127.
What Gives?

JCD

mklotz
03-19-2005, 06:46 PM
I did a little research on compound indexing since the concept was new to me.
Apparently, one leaves the hole plate loose on the shaft so it can be rotated.
A separate indexing pin, NOT the one on the crank handle, is used to keep the
plate from rotating. With the hole plate secured by this extra pin, the crank
is rotated some number of holes as would be done in normal, non-compound
indexing. Then, the extra pin is released and the hole plate is rotated in the
designated direction for the required number of holes. When this is done, the
crank, which is fixed to the hole plate by its indexing pin, also rotates.
Thus the net rotation of the worm is the (algebraic) sum of the two separate
rotations (crank and hole plate) and the workpiece is rotated 1/40 of that
amount (assuming a standard B&S gear ratio).

It should be patently obvious that the hole plates can't be swapped while this
tedious process is being done so all the rotations must be accomplished via the
holes that are available on the single plate that is mounted. For example, we
can't mix 1/15 steps (15 hole circle on plate #1) with 1/49 steps (49 hole
circle on plate #3).

Now, you'll note that, in the MH (Machinery's Handbook) table, all the hole
plate movements are specified as holes on either the 20 (plate #1), 33 (plate
#2) or 49 (plate #3) hole circles. IOW, they confine themselves to solutions
that only use the outer hole circle on the plate. I'm not certain, but I
think this is because it's mechanically difficult to mount the separate
indexing pin (the one that indexes the plate) so it can reach the other hole
circles. I believe that Roy Kuzmack's work referenced elsewhere in this
thread (the three part article) addresses a means of indexing on all the
circles.

Some of the solutions in the MH table specify a negative (i.e. opposite to
crank rotation direction) indexing of the hole plate. For instance, it
indicates that, for 87 divisions, one moves the crank 23 holes on the 29 hole
circle and then rotate the hole plate 11 holes on the 33 hole plate IN THE
OPPOSITE DIRECTION. Considering the effects of backlash, solutions that
require negative rotations are not to be preferred. For both simplicity and
accuracy, we would like to always be moving everything in the same direction.
Roy has produced a table with all positive crank plate movements in his 1-2/88
article in HSM.

To test my understanding, I wrote a computer program to find all the compound
indexing solutions with error less than some input quantity. Running it for
this problem, I found that there were acceptable solutions using any of the
three plates. The MH solution is the most accurate if one requires indexing
on the outer circle of holes. If that condition is relaxed, there is a
slightly more accurate solution.

Partial listing of program output:

Number of divisions = 127
Approximation accuracy = 0.005000 %
Required increment = 40/127 = 0.31496063

PLATE #1 (15,16,17,18,19,20 holes)

0 & 1/16 +1 * (15/17) = 0.94485294 [ 3] (-3.0637E-003 %) **
1 & 1/16 -1 * ( 2/17) = 0.94485294 [ 3] (-3.0637E-003 %) **
0 & 15/17 +1 * ( 1/16) = 0.94485294 [ 3] (-3.0637E-003 %) **
0 & 5/16 +1 * (18/19) = 1.25986842 [ 4] (+2.0559E-003 %) **
0 & 18/19 +1 * ( 5/16) = 1.25986842 [ 4] (+2.0559E-003 %) **
1 & 17/19 +1 * (10/16) = 2.51973684 [ 8] (+2.0559E-003 %) **
3 & 8/18 +1 * (13/20) = 4.09444444 [13] (-1.0684E-003 %) **
3 & 17/18 +1 * ( 3/20) = 4.09444444 [13] (-1.0684E-003 %) **
4 & 8/18 -1 * ( 7/20) = 4.09444444 [13] (-1.0684E-003 %) **
4 & 17/18 -1 * (17/20) = 4.09444444 [13] (-1.0684E-003 %) **
4 & 3/20 -1 * ( 1/18) = 4.09444444 [13] (-1.0684E-003 %) **
4 & 13/20 -1 * (10/18) = 4.09444444 [13] (-1.0684E-003 %) **
3 & 15/17 +1 * (16/19) = 4.72445820 [15] (+1.0320E-003 %) **
3 & 16/19 +1 * (15/17) = 4.72445820 [15] (+1.0320E-003 %) **
4 & 14/15 +1 * ( 8/19) = 5.35438596 [17] (+1.0320E-003 %) **
5 & 14/15 -1 * (11/19) = 5.35438596 [17] (+1.0320E-003 %) **
5 & 13/15 +1 * ( 2/17) = 5.98431373 [19] (+1.0320E-003 %) **
5 & 13/19 +1 * ( 6/20) = 5.98421053 [19] (-6.9252E-004 %) **
6 & 13/19 -1 * (14/20) = 5.98421053 [19] (-6.9252E-004 %) **
5 & 6/20 +1 * (13/19) = 5.98421053 [19] (-6.9252E-004 %) **
6 & 6/20 -1 * ( 6/19) = 5.98421053 [19] (-6.9252E-004 %) **

PLATE #2 (21,23,27,29,31,33 holes)

2 & 10/21 +1 * ( 1/23) = 2.51966874 [ 8] (-6.4700E-004 %) **
3 & 10/21 -1 * (22/23) = 2.51966874 [ 8] (-6.4700E-004 %) **
2 & 27/29 +1 * (28/33) = 3.77951933 [12] (-2.1769E-004 %) **
3 & 27/29 -1 * ( 5/33) = 3.77951933 [12] (-2.1769E-004 %) **
2 & 28/33 +1 * (27/29) = 3.77951933 [12] (-2.1769E-004 %) **
3 & 28/33 -1 * ( 2/29) = 3.77951933 [12] (-2.1769E-004 %) **
5 & 14/23 +1 * ( 2/33) = 5.66930171 [18] (+1.8299E-004 %) **
6 & 14/23 -1 * (31/33) = 5.66930171 [18] (+1.8299E-004 %) **
5 & 2/33 +1 * (14/23) = 5.66930171 [18] (+1.8299E-004 %) **
6 & 2/33 -1 * ( 9/23) = 5.66930171 [18] (+1.8299E-004 %) **
6 & 4/29 +1 * ( 5/31) = 6.29922136 [20] (+1.3904E-004 %) **
7 & 4/29 -1 * (26/31) = 6.29922136 [20] (+1.3904E-004 %) **
6 & 5/31 +1 * ( 4/29) = 6.29922136 [20] (+1.3904E-004 %) **
7 & 5/31 -1 * (25/29) = 6.29922136 [20] (+1.3904E-004 %) **

PLATE #3 (37,39,41,43,47,49)

The Machinery's Handbook recommendation:
2 & 23/39 +1 * (12/49) = 2.83464155 [ 9] (-1.4536E-004 %)

3 & 29/41 +1 * (33/47) = 4.40944473 [14] (-9.2668E-005 %) **

MH's preoccupation with the outer row of holes leads to downright errors in
their table. For 51, divisions, MH shows:

8 & 41/47 -1 * (12/49) = 8.62744247 [11] (-9.8686E-005 %)

Roy converts this to a more usable positive hole plate rotation in his HSM
article:

7 & 41/47 +1 * (37/49) = 8.62744247 [11] (-9.8686E-005 %)

but there are numerous ZERO error solutions on plate #1, e.g.,

1 & 5/15 +1 * ( 4/17) = 1.56862745 [ 2] (+0.0000E+000 %) **
1 & 4/17 +1 * ( 6/18) = 1.56862745 [ 2] (+0.0000E+000 %) **
2 & 10/15 +1 * ( 8/17) = 3.13725490 [ 4] (+0.0000E+000 %) **

Sorry for the extra long post but I wanted to address the OP's questions, put
Roy's excellent work in context and make everyone aware that even MH has to be
used with forbearance.

Regards, Marv

Home Shop Freeware - Tools for People Who Build Things
http://www.geocities.com/mklotz.geo

zl1byz
03-19-2005, 08:11 PM
Wow! Thats a great post Marv. Thank you for posting that. I thought about the backlash thing and was thinking yes there would be an error by changing direction but if your procedure was the same every time the error would remain constant too where by it would not be a problem at all.

John.

aboard_epsilon
03-19-2005, 09:26 PM
ive only tried a few of the progs off your web site marv.
and they dont seem to work.
eg expand.zip
you fill in the the questions
comes to the last question.....you fill that in and press enter.....and the whole prog closes down and disapeers
happens on my friends computer also.
what gives..
all the best...mark

John Stevenson
03-20-2005, 05:35 AM
Mark,
It's the way your computer is setup to read DOS programs.
Right click on the program.exe that you are using, select properties, then program and unclick the check box at the bottom that says "close on Exit "

John S.

JCD
03-20-2005, 07:27 AM
Marv.

I believe that originally the dividing head manufactures, or at least the predominate manufacture BS, arranged there heads so that the outer hole circle is the only point the compound index pin would enter the plate.
That might explain using only the outer hole circle for compounding indexing.

Thanks for the reply; your information might make compound indexing easier, although still tedious.

JCD

JCHannum
03-20-2005, 07:42 AM
A very simple, quite accurate index wheel can be made by attaching a band saw blade with the requisite number of teeth to a round blank, and using that for direct indexing.

One could cobble up such a thing and have the gear cut and in service in less time than it takes to do all the calculations involved here.

John Stevenson
03-20-2005, 08:08 AM
All valid previous points, Marv's program really does help but this whole can of compound and differential indexing can get very fraught with problems and errors, mostly operator memory and boredom as the numbers increase.

Doing something like 127 even with direct indexing can be a problem IF you don't get into a routine.
Choose a time to do this when you can start and finish in one operation.
Disconnect the phone or leave it somewhere else.
Nothing worse than coming back off the phone and thinking, did I move the quadrants ?

There have been many ideas put forward over the years to make special plates. Using a rotary table with a printed spreadsheet of each division in degrees and corrected minutes as not many of us have rotary table that accurate to read minutes.
One note here thou, don't work out the first division then add that to get the second or you will get an acculamative error.
Use a formulae that divides 360 by each division in turn.

Another way is to use a length of band saw blade cut to the number of divisions and mounted on a plywood blank, turned until it just fits.

Rememebr most of these methods are good for the home shop and will give enough accuracy.
Remember if you are 5 thou out on one hole position this equates to an error of 0.000125" with a 40:1 table or head and 0.0000555" with a 90:1, far more than needed.

Making a blank plate to fit your dividing head for odd numbers is a good idea. Rememebr if you use compound indexing to make thet gear you have to do the same for subsequent gears.
Wheras a new hole ring in a plate is permanant and will stay to be used on other projects later.
Some people will say you can use the 127 gear as a master, true but what heppens if you sell that lathe. You have lost the gear and the master.

There are gaps in the standard B&S plates. 127 is one and 125 is another. some machines with 8tpi screws rely on 125 divisions for the dials.
The B&S is missing 25 holes that enables you to obtain these.
People do special plates to overcome these problems. One sells on Ebay.

John S.

John S.

John Stevenson
03-20-2005, 08:11 AM
Another way is to use a length of band saw blade cut to the number of divisions and mounted on a plywood blank, turned until it just fits.

[EDIT] JC's post just appeared whilst I was typing this, sorry JC. ]



[This message has been edited by John Stevenson (edited 03-20-2005).]

JCHannum
03-20-2005, 08:52 AM
No problem John, bet my fingers are not as tired as yours.

Another method that Terry Sexton had in HSM a couple of years ago was to run a soft metal band through the change gears to make a corrugated strip. This strip was mounted to a wood blank of appropriate diameter and the spaces filled with body filler. This produced a useable change gear good for occasional use.

Change gears do not need to be produced to the same level of accuracy as a gear that will be used in a high powered reducer of some sort. Minor inaccuracies are tolerable, and will work out. The main consideration is they have the proper number of teeth, and operate smoothly in the gear train.

bpsbtoolman
03-20-2005, 09:42 AM
I made a new 127 dividing plate using a plywood dia. to mark the spaces. I elected to use a large plywood dia. a little over 20". Since my lathes will not turn 20", I did it by turning it in my Sheldon horizontal mill with the use of my lathe compound. Instead of a band saw blade I used an inch scale and decided I wanted 127 half inch spaces. This made it easy to calculate the cut to get exactly 127 half inch spaces. Fastened my new dividing plate blank concentric to the plywood disc which I had marked off in half inch spaces. Center drilled the 127 holes. I did have to make the holes smaller because on the standard size plate dia. the holes were very close to each other. I had to make a new pin to fit the holes.
Another old idea I could have used was to use another 127 tooth gear of any pitch to index to make any other pitch gear. Later on in my regular run on two local recycle ( we used to call em junk yards) I found at $0.15 a pound a lot of larhe gears mostly stub tooth, but At that price I picked a bunch for stock includung one marked 127 tooth. It was about 10" dia. but could be used to index a smaller gear. I tried this once on a lower number of teeth gear and found one tooth space that looked a little narrow. I found the problem in that a small bur on one tooth misallined the index. So if you do use a gear to index another gear carefully inspect the gear for any irregularities.
Unfortunately both of my gold mine yards are closed. To give you an idea of sme goodies the had was a was a small size floor mounted Van Norman Mill ( vertical and horizontal) that had tipped over on soft ground and broke one hand wheel. Otherwise in very good condition. Unbeliveable $ 150 . If I did not already have a J head Bridgeport I would have bought it.
Walt

mklotz
03-20-2005, 10:39 AM
aboard-epsilon:

The fault lies not in the programs but in your ability to operate your
computer. Had you bothered to read the Introduction section on my page, you
would have seen that your problem, and its solution, is already addressed
there. RTFM.

JCD:

That was my guess too. Only the outer ring of holes can be easily reached.
However, none of the (very few) dividing heads I've seen have the extra pin
for compound indexing supplied with the unit. I guessed that the machinist
was supposed to cobble something up when this (probably infrequent) operation
was undertaken. Machinists being the ingenious folks they are, I would think
they could arrange something to use the pin on any hole circle. (Apparently
Kuzmack has done exactly that.) Obviously MH doesn't share that confidence
in machinists' abilities.

For the benefit of the lurkers, there are a number of programs on my page
which can help folks who are doing dividing work.

DIVHEAD calculates turns and holes for ANY conventional dividing head, even
homebrew units with non-standard gear ratios or hole plates.

DDH sorts out required gear ratios, etc. for differential dividing heads where
the hole plate is turned by a gear train driven off the crank handle.

VERNIER handles two hole plate vernier dividers which can often be used to
minimize the number of holes that must be drilled.

DPLATE does the calculations needed to construct highly accurate dividing
plates according to the technique described by Lautard in his MBR books.

ROTARY will print out an accurate table of rotary table settings (decimal
degrees and deg/min/sec) for making a dividing plate.

BOLTCIRC will print out a table of x-y coordinates for coordinate drilling a
dividing plate.

(As John points out, making a plate using the ROTARY or BOLTCIRC technique is
often more than adequate for the amateur since any minor inaccuracies are
reduced by a factor equal to the gear ratio of the DH when the plate is used
to make a part.)

Regards, Marv

Home Shop Freeware - Tools for People Who Build Things
http://www.geocities.com/mklotz.geo

JCD
03-20-2005, 12:52 PM
[QUOTE]Originally posted by John Stevenson:
[B]All valid previous points, Marv's program really does help but this whole can of compound and differential indexing can get very fraught with problems and errors, mostly operator memory and boredom as the numbers increase.

Doing something like 127 even with direct indexing can be a problem IF you don't get into a routine.
Choose a time to do this when you can start and finish in one operation.
Disconnect the phone or leave it somewhere else.
Nothing worse than coming back off the phone and thinking, did I move the quadrants ?

John,

You are right on. After scribing this thing three times in the dividing head, I have yet to get a good index using compound dividing.
I think I’ll make a 127 hole plate. That will create a whole raft of other clearance problems, but at least I think I can pay attention to what I’m doing long enough to accomplish these tasks.

Thanks for your input and insight.

JCD

aboard_epsilon
03-20-2005, 04:15 PM
OK Marv I'm without ability.
and I'm just used to progs working without fathing about.
Anyway.......all settled now..it works .
You are a Genius and thanks for sharing these progs with us lesser mortals http://bbs.homeshopmachinist.net//smile.gif,
but your going to get a lot more people doing the same as me first time round.
hope that you can put up with there complaints http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif
good luck .
all the best....mark

JS
03-21-2005, 09:29 PM
Why not make a plate with one hundred marks (lines) on its face and a venier plate with ten divisions equal to eleven ?

With a 40:1 ratio thats 4000 spaces divided by 127 = 31.496 marks of the plate