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Thread: Using a dividing head to make gears

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    Founder Nels's Avatar
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    Using a dividing head to make gears

    Dividing Heads pretty much all work the same. If the main gear is 40:1 as most are. The Ellis & L&W manuals are available in our downloads area at http://hobby-machinist.com/index.php...wnloads;cat=36. The plates often fit just one brand machine, But are easy to make or search ebay, the dimensions to fit are the bolt pattern, center hole diameter, pin hole dia.

    Plates are numbered 1,2,3 called low number plates will do most any common dividing, the 4,5,6 plate high number plates are for the higher dividing. There are still high prime numbers that need a different machine to accomplish.

    For example you need to make a 250 division dial, to do that you need a 25 hole plate, you don't have one, but you have a 15 hole plate, with a 15 plate you make the 25 plate, then use it to make a 250 division dial.


    Heres the plate hole counts for a 40:1 head.

    #
    1) 15, 16, 17, 18, 19, 20

    2) 21, 23, 27, 29, 31, 33

    3) 37, 39, 41, 43, 47, 49
    ***************

    The 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 first plate is 20, 19, 18, 17, 16, 15.
    The second plate is 29, 28, 26, 21, 20, 16.
    The third plate is 61, 59, 49, 44, 39, 33.

    [attach=1]

    The key to making accurate gears is the dividing head. This can be a commercial unit or a shop built device using various gears and plates as a reference. You can mount the dividing head on a sturdy aluminum rail. This allows you to pull the unit out of the cabinet and put it in the milling vise very quickly. The headstock and tailstock are always in alignment. You can also mounted a small chuck on the head and this comes in very handy. The dividing head uses a worm gear arrangement that produces a 40:1 ratio. It requires forty turns on the handle to rotate the head through 360 degrees. There are 24 holes in the plate mounted on the main spindle for use in dividing 2, 3, 4, 6, 8, and 12 places. The plates on the side of the head are also used to divide the rotation of the handle into various amounts. Three plates are provided with hole counts of 15, 16, 17, 18, 19, 20, 21, 23, 27, 29, 31, 33, 37, 39, 41, 43, 47, and 49. Sector arms make it easy to move a set number of holes and not lose count. All numbers from 1 to 50 can be done, and many more beyond. To cut a gear of say 29 teeth, do the following: Divide 40 by 29, this gives 1and 11/29's. Use the 29 hole plate, set the sector arms so that when one arm is placed against the pin of the handle, the other arm just uncovers the hole, 11 holes away. For each space, make sure the sector arm is placed against the pin, rotate the handle one turn and 11 holes, to the other sector arm. Make sure you advance the sector arms each time or you will loose your place.

    For example, to make a pair of gears that may be used for the valve train of a four cycle engine: One gear is a 30 tooth aluminum spur gear, and the other is a 15 tooth pinion made of steel. The 30 tooth gear has a .375" bore and a standard keyway. The 15 tooth gear has a bore of .250" and two 6-32 setscrews to fasten it to it's shaft.

    First we need to do some calculations. We will be using the 24dp system. This is the system based on diametric pitch. It is very simple, a 24 tooth gear would have a 1.000" pitch circle. The pitch circle is the imaginary circle that passes approximately through the center of the teeth. A 12 tooth gear would have a pitch circle of .500". For these to mesh properly they would have their centers 1.000/2 + .500/2 inches apart, or .750". The distance is the sum of the two pitch circle radii. The outside diameter is the number of teeth +2 divided by the dp. For our 30 tooth gear, this would be 32/24 or 1.333". The 15 tooth gear would be 17/24 or 0.708". The depth of the tooth is 2.157 / dp or in our case 0.090". The tooth depth is essentially the same for all gears of the same dp. For 30 divisions 40/30 = 1 and 1/3. I had the plate with 18 holes on the head, so 1/3 of 18 is 6. Great, so I will use 1 turn and 6 holes on the 18 for my spacing. Since the 15 tooth gear would require half as many steps, I just double the setting for 30 teeth and use 2 turns plus 12 teeth on the 18 tooth disk.

    To make the 30 tooth gear, we drill and ream the end of a piece of 1.5" aluminum bar stock. Then a slab .250" thick is parted off. This is the rough blank. It is then pressed onto a 3/8" tapered mandrel. This mandrel has a center cut at each end, and a slight taper along it's length. The + sign at one end of the mandrel signifies the larger end. Placing the mandrel in the lathe, with the large end toward the headstock, the blank is turned to the proper diameter. Also, profiling of the sides of the gear can be done at this time. I use an Adjust-Tru chuck to hold the mandrel, but turning between centers is the best way for most lathes. The next step is to carefully set the gear cutter to the proper cutting height. I generally do this using the eyeball method and the tail stock ( or better yet, the drive center ) of the dividing head. This is very important to get right, because the gears will not run smoothly if the teeth are off-center ( been there, done that ).

    Set the dividing head to zero. Turn the handle until it drops in a hole on the 18 hole circle. It is a good idea to mark this hole since it is "HOME" position. Set the sector arms for six holes as calculated above. Practice cranking the head through several cycles and make sure the degree wheel reads as you would expect. I always operate my dividing head handle clockwise. This helps to prevent confusion. Bring the head back to zero and HOME. Mount the mandrel in the head and tailstock. Make sure the thrust from the cutting operation will be toward the + end of the mandrel. Bring the cutter up to the workpiece until it just touches. Zero out the cross feed. Advance the cross feed for the first cut, be sure not to run the mill too fast, those cutters are expensive. Cut all teeth at a setting, then move the cross feed. The final depth will be 0.090" as calculated above. Just be careful not to lose count on the dividing head. At the end of each pass, you should find yourself back to the HOME position. If not, well that's why they call it scrap. Lastly, the gear is removed from the mandrel and the keyway is broached.

    The pinion gear blank was machined and left on the bar stock. This piece can be center-drilled and put on the dividing head between centers, or held in the chuck. In this way, the dividing head can be used to drill and tap the setscrew holes.

    Other good links:

    Gears & Gear Cutting [Paperback]
    Ivan Law

    http://www.amazon.com/Gears-Gear-Cut...ref=pd_sim_b_1

    Making Gears the Easy Way
    ...with Jose Rodriguez

    http://smartflix.com/store/video/77/...s-the-Easy-Way

    Machining a Spur Gear on Youtube:





    Please give your thoughts on the use of Dividing Heads!


    Thanks!

    Nelson
    Attached Images Attached Images
    Last edited by Starlight Tools; 11-30-11 at 01:38 AM.
    My toys: South Bend Heavy 10L Lathe (1978), Burke #4 Milling Machine (1946), Van Norman #12 Milling Machine (1942), South Bend 14" Drill Press.

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  3. #2
    Conrad Hoffman
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    Re: Using a dividing head to make gears

    There are lots of spreadsheets and such out there for dividing heads- mine is in my threads and changegears spreadsheet located here.

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    Cast Iron pjf134's Avatar
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    Re: Using a dividing head to make gears

    Back in the 60's while I was taking a machine course at night I used a automatic gear maker. It had a lot of holes, like a QCGB has, you would put a blank in the holder and set the machine to the right pegs then turn on and walk away, then come back to a finished gear. Has anyone seen one of these? I can't remember too much about it being so long ago. I have never seen another one like it since. I do remember that you had to pick the right blank, O.D., I.D. maybe. I would like to see one like it, if they still make them. I guess a gear manufacture would have something like it.
    Paul
    To error is human, but doing it a second time takes a better excuse!

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    Re: Using a dividing head to make gears

    David Thanks thats another thing on the wish list Number 964 I think.
    Until then I will have to keep twidleing the thing.

    Walter has a ace program for dividing in in his metal shop calc download.

    Regards Brian
    If all else fails, read the instructions.

    http://briansworkshop.weebly.com

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    Surrender Re: Using a dividing head to make gears

    Thanks for all the info, I do have a good question, I have a PTO shaft that fits an old Gravely I need to make another one and I have never made one before, the shaft has 15 splines, dia. .985 o.d. aprox. and 6 1/2" long would a spin indexer do this job? and how do I find out what cutter to get?

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    Administrator Tony Wells's Avatar
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    Re: Using a dividing head to make gears

    Spin indexers are not all that heavy duty, and lack a positive indexing means that you could use to establish the exact spline spacing, but there are ways to get around that. As far as a cutter goes, probably simplest to do this job with a 90° fly cutter and hand ground tool that matches the original profile. Use thread wires to measure the old one and the same wires to make the new one.
    "A man who works with his hands is a laborer. A man who works with his hands and his brain is a craftsman. A man who works with his hands, his brain and his heart is an artist."

    -Louis Nizer

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    Really Re: Using a dividing head to make gears

    That's kinda what I was thinking Tony, those things don't look all that great, so I should get a 4" rotary table divider combo with a 3 jaw chuck. Fly cutters work good for cutting splines? what kinda cutting tool should I use? any particular name brand? Thanks! Vernon

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    Administrator Tony Wells's Avatar
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    Re: Using a dividing head to make gears

    Well Vernon, tell us a little about what kind of machinery you have to work with, first off. Second, and certainly no insult intended, how experienced are you? I ask that simply so we don't detail out too much information that you already know and makes you feel insulted. If you are a real beginner, on the other hand, we can give you every step as needed. Along the way, just ask for clarification if you feel that you need it.
    "A man who works with his hands is a laborer. A man who works with his hands and his brain is a craftsman. A man who works with his hands, his brain and his heart is an artist."

    -Louis Nizer

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    Re: Using a dividing head to make gears

    3yrs in high school 30 yrs ago and a little simple stuff along the way cutting keys, bushings that sort of stuff.

    - - - Updated - - -

    Oh I have a smithy 1324 max combo

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