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Off center arbor for making a multi-tooth gear cutter

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Saturday, December 27, 2014 - 22:37

Just recently i made a gear cutter and ground the relief for the trailing lands of the cutters with a dermal. While searching the net before making the cutter i seen a couple different ways to create the relief along with having a couple ways suggested to me, but none of them seamed like an easy (set up for later use) and long term solution. Well... now an idea popped into my head and heres the start...

An arbor with a straight shank which will be held in a three jaw chuck or a collet. The end of the arbor which the gear cutter blank will be locked to for turning and shaping will be offset. The face of the arbor will have a pin sticking out of it (green in drawing) and a cap (the cap will lock the gear blank to the arbor) that will have 'x' number of holes in it (for this i picked ten) which will correspond with the number of cutting edges the gear cutter will have. The cap will also have a square broached hole in it which a key (blue in drawing) will set it (fastened to the cap some how) which will lock/align the cutter blank.

On the shank end of the arbor mill a small flat then make a sleeve with an off center bore (same off-set as the arbor) so you can use the same arbor in a dividing head to cut the cutting edges. Instead of using the dividing head to rotate the cutter blank, you would use the cap to rotate the blank just as done in the lathe.

On paper im pretty sure this set-up could be used over and over again and there will be no need in using a four jaw chuck or drilling the cutter blank with holes or any other method except for making new caps for the different number of cutting edges you want. Just need to broach the cutter blank first and you could use this for any gear cutter blank you want.

Making the arbor ( updated 6/15/2013 ):

Played around with a few test cuts with an off-center piece of stock in a four-jaw chuck, jumped on CAD and tried to draw something up looking for an off-set which will work, got a rough idea and now trying to make something with is. As i get something done ill add/update this page so you will see the work in progress and if it works.

  • Turned a .687 shank on a piece of stock
  • Put on the four-jaw and turned the off-set hub/seat (which the gear cutter blank will mount to)
  • Drilled and bored the sleeve
  • Pinned the sleeve to the arbor by drilling and tapping it to the .687 shank
  • Turned the sleeve off-enter to it will be concentric with the hub

Turning the .687 shank, pop on the four jaw chuck, clamp on the shank indicated jaw 1 and 3 with a .325 off-set to one an other, indicated jaws 2 and 4 with a .355 off-set, then turned a 1" dia x .625 deep hub (for the cutter blank) and then turned the rest of the stock back to 1.5" for clearance.



After the gear cutter blank is formed on the lathe it will need to be moved to the mill to notch the cutting edges and then later on if you need to resharpen it you will need a way to hold it in a dividing hear or something. Being the arbor is off-set this will cause a problem while trying to hold it in a dividing head and index the blank to the next tooth to be cut or resharpened so im hoping this offset sleeve will give a surface to chuck on that will be concentric with the off-center hub. Chuck a piece of 2" stock (1-9/16 would have worked) drilled/bored to .687 and test fitted the arbors shank in it. Chucked on the off-center hub of the arbor at the "mill", slide the 1/2 finished sleeve on it and put a clamp on the two to keep them from moving, drilled and tapped a 1/4-20 thread through the both of them. This 1/4-20 thread will be used to pin the two together for later use.


Pinned the two together and chucked on the off-center hub in the lathe and turned the sleeve- Now the sleeve and off-center hub are concentric:


Here they are just about complete. Only thing left for to do it drill/ream a .187 hole in the face of the hub to be used as an indexing pin.


And heres the cap... please excuse the very crud job done here... struggled alittle trying to find a way to attach the 'key'.
Drilled six .187 holes (this will be for a six tooth cutter) at 5/8 dia.
Drilled a single .062 hole at a 1" dia all the way through the cap.
Opened up the front of the .062 hole till i could just get a broach into it, then ran a /125 broach down through it.
Attached a piece of key stock by welding it on both ends of the cap.
Put the cap in the lathe and re-bored it out removing the inner/bottom half of the key so it could fit on the 1" dia hub of the arbor.
Grabbed the dremel and cleaned up the weld and squared the key back up so the gear cutter blank would fit.
* The hole directly opposite of the 'key' is a screw up, was the first attempt at making the key hole.
One nice thing about this way of making a gear-cutter is just make a new cap for the different number of cutting teeth you want (or re-make it because you messed-up :-) ).


Cutting a blank ( updated 6/22/2013 ):

 OK, made two blanks before what im showing here which did not pan out too well... i lost track of the numbers on the DRO (was using multi-tool off-sets and ended up making things more complicated then need be). Also, the HSS bit i ground is not perfect (i didnt try too hard for this test run). When the time comes to make a real cutter, i will use a HSS drill blank to make the cutter, cut it off 1/8 thick and mount it to a home made tool holder (will post something when that time comes). These cutter blanks where made from  2" dia x .187 thick 1018 steel slugs.

First chucked the arbor then mounted a cutter blank.
Next (which will be better with an accurately ground/round HSS bit) i moved the tool in so the left side of the tool touched the right side of the cutter blank and zeroed out the Z axis, moved the HSS cutter to the left of the cutter blank, touched off again with the right side of the HSS bit, split the difference and zeroed the Z axis again. Now if i was using a perfectly round HSS bit it will be easy to form the sides of the gear cutter.
Then i turned the OD of gear cutter blank till i got 1.970" (from cut to un-cut).
Moved the HSS bit .195 off zero and then plunged in about .450 deep on one side of the blank and did the same on the other side of the blank.
Indexed the cap and repeated the above five more times.
Removed the arbor, slid on the arbors sleeve, moved it over to the "mill", aligned it, took a light test cut in all six indexing points and then milled out the teeth.
All in all, it took 1 hour to make the gear cutter blank from start to finish (aside from hardening which i didnt do).

Lathe work, touching off and finding center...


Just off the lathe and you an see the oblong shape...


And one off the mill...


Next will be a test with a piece of O-1 tool steel blank and afterwards make a gear with it :-)
When measuring from the OD of the cutting tip to the ID of the cutters bore it reads .499 and if measured from the end of the trailing land of the same cutters tooth it reads .477, dont know if that is enough relief, but there is relief there.

So far im pretty happy with this. Will make up a couple more caps;  one with 4 indexing holes another with 8 and possibly a 10 (probably need a 3" blank for that one).
One thing which might cause a problem and limit the number of indexing holes is the size of the indexing hole/pin and amount of material in the cap. Six holes at .187 seam to be the most currently, but the pin which is in the end of the arbor is screwed into it, so a smaller pin can be made and hopefully more holes will fit in the cap.

As you can see, using a 2" round piece of stock - six cutting edges did not come out too bad, don't think eight will work, probably will need 2.5" stock for that.

Will update this article after the next test is complete.


Reference links of ideas and help - thanks.



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Great job and well documented but could you describe how this device would be indexed in its normal use?

Joe's picture

Humm... not sure i understand your question.

The intended (normal) use of indexing is done by the cap on the end.

For different indexing intervals, a new cap needs to be made. The cap hear has six indexing postions. If only 4 teeth are needed on the cutter, a new cap would be made with only four holes.

The gear cutter blank is broached for a 1/8 key.
The cap has a 1/8 key tack welded on the inside.
So when the cap is indexed the gear cutter blank keeps its orination to the cap, while the cap is indexed around.

Not sure that answers your question, feel free to post back if it does not.
When time permits, ill try and shoot a small video of the arbor in use, both on the lathe and on the mill.

When you loosen the cap (how much) and do you have to feel when the pin detents into the next hole?

Joe's picture

The indexing pin sticks out of the arbor and seats in the holes of the cap.
The gear blank and cap can only orientate themselves to each other one way.
Since the gear blank is keyed to the cap, when you index, you can take the cap completely off if you wanted to and not worrie about anything.
You do not have to "feel" for any indents, you can see the end of the indexing pin through the holes in the cap.
Later tonight i will try and make alittle mock video with a pre-cut blank so you can see how it functions.

Joe's picture

Hello Ben.

I did not forget about the video, but was side tracked then the Resurrection-of-a-greenerd-press happened. For this arbor press project i will have to make a new pinion which will require a new gear cutter. So in a week or two when i start that, i will video the off set arbor being used. Sorry about the delay.

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