Cincinnati Dividing head tail stock pinion gear dimensions?
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  1. #1
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    Default Cincinnati Dividing head tail stock pinion gear dimensions?

    I bought a Tailstock for a 12” Cincinnati dividing head and the pinion gear that raises and lowers the dead center is missing all but one tooth. I have been to a couple of gear shops in my area with no luck and figured someone may have the information I am looking for.

    If anyone has one of these tailstocks I would be interested in getting dimensions/specs for that gear so I could either cut a new one or find one online and modify to work with the original shaft possibly.

    Thank you for your help.

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    8239 is Cincinnati number for the 12" "pinion"

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    I think I have had to make that shaft for 3 10” tailstocks as well as my 12”. My recollection is the pinion is the same, but some different measurements on the length of the shaft between the 2 sizes.
    A quick check of my bad parts bucket and measuring one for the 10” is as follows:
    16 DP, 9 teeth, 14.5 pressure angle. OD calculated at .6875”. That is basically shaft diameter.
    I make my replacements from a grade 8 bolt.
    Hope this helps. If your shaft diameter is different, let me know. My junk 12” shaft should be here somewhere.

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    Good luck on the right profile for only 9 teeth. Sounds like a hob job since no milling cutters ("gear cutters") do that few teeth

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    You are correct John. I cut my last one on my gear hobber. Gear tooth profile is undercut at the root.
    Before I had a hobber, I cut on a mill and dividing head with an involute cutter.
    Considering use of part, and rpm’s it is used at, I believe I offset final cuts slightly. May have cut a little deep instead. I have slept since then. In my opinion that pinion does not have to be finished to ISO standards to work. As long as there is no interference, and a modicum of common sense used, it will work fine.
    A stub tooth might have been a better design. I am just duplicating Cincinnati’s design to my best ability on my replacement parts for my tail stocks.
    A pox upon the ham handed that beat them into submission to begin with.
    I have not had any issues with my replacements, but I don’t move center heights very often. I also try to use the hobber since it is there. Dividing head gets a little less use now.

    A helpful hint if someone has to make a replacement bearing for the screw to move the center in and out, I made one for a tail stock and it was not on centerline. Frustrating because I had to make another with the the offset, whatever it was.

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    Here is a 6 tooth 12 DP I had hobbed for the Lockheed project long ago - had a box full done. They are getting on down there for being "pointy"

    20210317_152156.jpg

    LAC part number 32033A from 90 years back

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    Oh man I didn’t even look at the number of teeth before I posted. And I don’t have access to a gear hobber so looks like I’m up a creek without a paddle on this one sadly

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    Quote Originally Posted by ISEN AG View Post
    Oh man I didn’t even look at the number of teeth before I posted. And I don’t have access to a gear hobber so looks like I’m up a creek without a paddle on this one sadly
    Not true. This part can be made with a dividing head and involute cutter, it will work fine for what it needs to do. You just need to cheat a little so don’t have interference between pinion and rack.
    Will last you a lifetime. I have made 3 in this manner. Have not had a problem yet.

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    ISEN AG, Sir
    You are not screwed.. You have one tooth and know the major diameter and the number of teeth. So grind a single point tool, use a fly cutter and your dividing head and make one. Not a tough job at all if you think about it. The tail stock is worth the effort..
    Stay safe
    Calvin B

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    Quote Originally Posted by ISEN AG View Post
    I bought a Tailstock for a 12” Cincinnati dividing head and the pinion gear that raises and lowers the dead center is missing all but one tooth. I have been to a couple of gear shops in my area with no luck and figured someone may have the information I am looking for.

    If anyone has one of these tailstocks I would be interested in getting dimensions/specs for that gear so I could either cut a new one or find one online and modify to work with the original shaft possibly.

    Thank you for your help.
    I am dealing with the same issue on tailstock that has just come into my possession. I had NO TEETH. I am working on making a replacement as soon as I get some stock delivered. I had access to the larger tailstock from a friend (not sure the size but it is double the size I have)and used that gear in my smaller tailstock and it worked like butter if I kept the gear centered in the rack. So, that pitch and diameter will work. There is not cutter (a round cutter that you would mount in a mill) that is specific for a 9 tooth gear, as was stated previously. What appears to me to be the case is that they used the same cutter profile (14.5 degree, #8, 16DP) to cut the rack on the centers for the tailstock as they did to cut the gear. Again, as was stated, you are only trying to use the gear to vertically adjust the height, you are not spinning it under speed or force, so close is good enough. The OD on the gear I could measure (from the larger model) was close to 0.670. The points of the gear were worn a bit. The shaft OD was 0.6870 and this was ground. So you can see the gear is a little less...call it 0.015. (Note: The 0.015" reduction in the diameter of the gear makes sense in my head if they used the same profile cutter of that cut the rack (#8) as it would have been wider than say using a #1 cutter to cut 12-13 tooth gears. My long winded point here is that this would have shaved off some of the tip of the tooth if you started from a 0.6870 OD. And, when I smooshed platicine clay into the rack, it matched in the teeth of the gear perfectly.) The gear is 0.330" wide with 9 teeth. I have hand ground a 1/4" piece of tool steel to the profile that fits between two of the teeth and I am going to try the fly cutter approach. Labor of love. I am still looking for a nice 2"-8 backing plate to mount a chuck for my Cincinnati dividing head. That size seems hard to find..... I may have to break down an buy a slice of cast iron and make my own. Let me know if this info helps or if you need more information. When I get it made (hopefully in the next week or so) I will post to let you know how it went.

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    For what its worth department

    I revised George B. Grant's numbers for 10 teeth to suit nine teeth in his book A Treatise On Gear Wheels on page 29

    I made no effort to state minor dia (which is less than .438") nor the corner radii where flanks come down to minor since this is common gear making info

    Base dia comes from P.D. times Cosine of 14.5 degrees - the radii are swung from Base dia
    nine-tooth.jpg

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    Success. Old pinion with no teeth, new pinion and the cutter/tool holder.tailstock-pinion.jpg

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    I do appreciate all the information you have all provided. I will need to look into how to grind my own cutter and if anyone can point me to a thread, video, etc that would provide information in that area it would be appreciated. Simple lathe tools are one thing but a gear cutter would be new for me.

    Also seems that if I had a #8 cutter in the correct PA & DP that might work as well?

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    Isen AG, Sir
    Grinding a single point form tool is the same as grinding a lathe tool. Maybe if Porter 2019 is feeling generous he can show his tool and holder a little better. Biggest thing is your part is stepping off into the unknown. Just get a high speed steel blank and grind one side to fit the profile of the tooth that you have. Grind the other side to match the opposite side of the tooth. Cut the gear, check it in the tail stock. If it works, GREAT ! If not chuck it up ( assuming it's to small, narrow what ever) and index it over two holes or what ever your think you need to remove and cut away.. This is one of the many jobs your dividing head is designed to do. USE IT. AND don't rule out hand fitting/filing your part. Really, I just encourage you to jump in and try it. Great learning experience and confidence builder. Plus a really cool skill to have.
    Stay safe
    Calvin B

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    I am sure if you use the #8 16DP cutter on a mill it would work, but you may still have to do some hand fitting. The rack that the pinion fits in was chipped in spots and deformed in places from the destruction of the teeth. I got in there with a Dremel to clean things up.

    Couple thoughts from my lesson:
    See the attached photos: grind the relieve angles on the top and sides first and then work on the profile. I did't pay attention and when I ground the agile on the top (to scoop out the materia)I did it after my profile. In doing so, I made the profile a little smaller since I went down in the relief taper. This turned into more material I had to remove after the first pass. Point being is that the more time you spend making the profile closer, the less tuning you will have to do (on potentially 18 spots!). Again, none of this is critical and there is a lot of room. Functional is the goal. I would second the use of the dividing head and adding an extra pin hole(s) after your first pass if you need to remove more material. I didn't do that and just tuned each tooth as I needed by hand. If I do it over again.....I am now just a little smarter.....
    It really is as simple as turning the OD to 0.687 (shaft od as well as the gear. Turn the relief on both sides of the teeth to 0.400 ( Noted by Mr. Oder above, the smaller diameter is simply a "less than" number. For a neophyte like me, there is a LOT of stuff in his reply. It takes me a few days to digest and even then I only get a percentage....hahaha).
    Hope the pics help. The hardest part was grinding the cutter. It is relatively small and getting it as even as I could was a 40 minutes with 3 "start overs".

    img_20210730_074150.jpg

    img_20210730_074224.jpg
    img_20210730_074103.jpg

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    For what you are doing with it, it doesn't even have to be that good of a gear... Go use one of the online gear DXF "generators". Even WITH the errors that many of them have, it won't matter one whit for your purposes. All you need is a cogged wheel to affect motion. Doesn't even to need really be good, smooth, nor even accurate motion. Just "motion". Make a space cutting fly tool and off you go.

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