Setting Up A Dividing Head Question?

GarageGuy

GarageGuy

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I have a L-W dividing head that looks identical to the one Nels has. It's my first attempt to cut a spur gear, and I've gone through everything very carefully to make sure there are no mistakes. The gear I'm cutting is made of cast iron and will have 37 teeth, and I have a dividing plate with 37 holes in it.

The question: Because my dividing head has a 40:1 ratio, I should turn the crank less than one full turn to advance to the next tooth? Or, because I have a 37 hole plate, do I just do a full turn?

Up to now all my measurements have been careful and correct. The perfect gear blank, centering the cutter, depth of cut, etc. The more I thought about this, the more I confused myself. I just want to make sure I don't make scrap iron.

Thank you!

GG
 
Hi Garageguy
Please doublecheck my advise before cutting as i confuse myself at times. If you have a 40:1 ratio it means that you need to devide 40 by the nr of devisions you need to make.
Thus 40/37 = 1.08108108 turns per devision.
So now you know its one full turn plus a number of holes representing 0.08108108 tuns.
Now you take 0.08108108 and you multiply it by all the nr of holes you have on you different plates.
Once you find a whole nr or something very close to one you get the correct plate and the nr of holes you need.
For example i took 0,08108108 and multiplied it by 37 and got 3. Thus it means that you have to take 1 full turn and 3 holes on the 37 hole plate , per tooth
 
That makes perfect sense. As you advised, I'll wait and hopefully someone will corroborate, then I'll go to work. If my first gear actually works, I will be very impressed.

Thank you very much!

GG
 
40 divided by 37 = 1 full turn and 3/37 or one full turn and 3 holes in a 37 hole plate.
Machinist handbook is your friend.
Please show some pics of your form tool and setup
 
Thanks Jim! It is a Jet-15 mill/drill with a L-W dividing head and a Shars foot stock. The cutting tool is a #3 involute gear cutter for 35-54 teeth, 16 DP, and 14.5 degree PA. The cutter arbor is home made... and a little on the heavy side. The gear blank is on a 5/8" taper arbor. The hole in the blank is about .001 large, so my blank is off to one side more than I would like, but it should be workable.

The project is to make a pair of metric transposition gears for a friend's Logan lathe so he can cut metric threads on an imperial lathe. He wants a 37 tooth, and a 47 tooth gear. I'm trying the 37 tooth gear first.

GG

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That cutter is on a pretty long arbor, with no out board support. Any chance you can pull it in shorter?
 
The column on my mill is very large in diameter at the collet, and we had to make a longer arbor for it just so the column would clear the dividing head chuck when the cutter was centered on the gear blank. That's another reason we left the cutter arbor on the stout side. A little extra rigidity can never hurt. I suppose if the hole in the gear blank was .001 smaller, the gear would be further from the chuck and would ease the problem, too. I don't have a 5/8" reamer, but I will get one if it looks like we might be doing this regularly. Thanks!

GG
 
Thanks for the pics.
Whats keeping the blank from sliding off the shaft ? I cant tell if there's a shoulder in the pics.
Also, the chuck hasn't much grip on the arbor. It would be a shame to get half-way through and have it slip or worse, move just a bit out of time and it wouldn't
be noticeable until the last tooth was cut.
I hope to cut some gears this winter but have a lot of other projects to get done first.
 
You may want to make the arbor for the gear blank with a shoulder on one side and threaded on the other. I have messed up a gear before and now put it against a shoulder and back it up with a nut and washer. Its not going to move on me again.

It may be tedious, but I do a scratch pass all the way around, similar to single point threading initial pass. It will show if you have the spacing correct as the last tooth is either spaced correctly or it will look too small or big. Additionally, it will tell you that the gear is blank turning concentric and if there gear cutter arbor is cutting at the same depth all the way around. Next is to cut the gear to about 80% depth and then measure and cut the final depth on the last pass. Time consuming, but the gear will be correct when done.

I have several arbors set up now, different gear sizes required this. I make sure the arbor is plenty long enough to go past the chuck into the dividing head.
 
Odd man out here...why not use the table as an indexer, disengaging the drive and rotate to each of the 37 holes in sequence and machine each tooth after locking the table each time?
 
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