Gear Repair.

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AllenH59
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Gear Repair.

Post by AllenH59 » Tue Apr 20, 2021 10:49 pm

Good Evening: I crashed my lathe, and took 2 teeth off a gear in the gear train for the Norton Gear Box. this gear is about 2-9/16" OD, and diameter at the depth of the teeth is about 2-5/16". It seems that my lathe manufacturer is not too interested in making me a gear. This lathe is out of production for quite a while. I know little about gear work. Here is my plan. 1. Grind out the area where the broken teeth are, and fill it with brazing rod. This is a cast iron gear. 2. Cut the outside of the brass off in the lathe to make it the same external contour as the the gear. 3. Put an involute cutter in the milling machine and cut the teeth.

My questions are:
1: Is there a better idea? Like should I make a complete gear?
2: What size involute cutter do I buy that will fit these teeth? It is 40 teeth, and 2-9/16" diameter.
Thanks
Allen

choprboy
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Re: Gear Repair.

Post by choprboy » Wed Apr 21, 2021 12:03 am

On #2... you would need to know the correct gear pitch to choose the cutter and it may not even be a standard size. Another option might be to use a single point cutter to cut the teeth. You can grind a tool to exactly match a good tooth profile and cut the brazed areas with that. There are several videos on Youtube of doing this. I forget if it was Keith Rucker, Mr Pete, or Abom that did a lathe gear repair that way a couple years ago.

AllenH59
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Re: Gear Repair.

Post by AllenH59 » Wed Apr 21, 2021 12:23 am

Thanks Choprboy..I am digging into the machinery Handbook and doing some math, and it looks like a DP of 16. that is as far as I am. I will measure tooth shape tomorrow

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Bill Shields
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Re: Gear Repair.

Post by Bill Shields » Wed Apr 21, 2021 6:04 am

I have fixed gears using the technique you are suggesting..it is time consuming and a lot of work..

Willing to bet that knowing the dp and tooth count you can find a stock gear -> and at worst modify the hub or center to agree with the original.
Too many things going on to bother listing them.

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liveaboard
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Re: Gear Repair.

Post by liveaboard » Wed Apr 21, 2021 6:39 am

Bill Shields wrote:
Wed Apr 21, 2021 6:04 am
knowing the dp and tooth count you can find a stock gear...
That's the way to do it.
Mostly gears are standard; there are metric and imperial standards. Find online gear catalogs and find a gear with the same number of teeth that is the same diameter as yours. That's the one you want.

They're surprisingly inexpensive.

Get the gear and cut it to fit; you can make a ring of the new one and press it onto the original after cutting it down, or if you have the means, make the new one fit the shaft.

earlgo
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Re: Gear Repair.

Post by earlgo » Wed Apr 21, 2021 8:58 am

Gear teeth calculations.jpg
...or you could check with Boston Gear. I have bought gears from them for my Atlas that fit perfectly.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

earlgo
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Re: Gear Repair.

Post by earlgo » Wed Apr 21, 2021 9:08 am

Boston gear catalog reduced.pdf
(300.51 KiB) Downloaded 50 times
Try this for your gear replacement.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

AllenH59
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Re: Gear Repair.

Post by AllenH59 » Wed Apr 21, 2021 2:12 pm

I may wind up fixing this one, or making one, or getting a quote from a custom gear maker. This is a 40 tooth 16 DP 14.5 Degree gear, with .750 face, and .875 bore, with a 6mm keyway broached into it, with a boss on each side, making the through hole length 1.237" , The bosses have an OD of 1.250". I know more about gears than I knew last night, and still have not yet cut one. No doubt still a long way to go. There are no gears in the catalogue that are wide enough. I thought about pinning two together, but that is probably asking for trouble, and I have no way to broach keyways.. Maybe this is the time to buy a press and a broach..

Harold_V
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Re: Gear Repair.

Post by Harold_V » Wed Apr 21, 2021 3:41 pm

AllenH59 wrote:
Wed Apr 21, 2021 2:12 pm
and I have no way to broach keyways..
You probably do have, but you have to use your imagination.
If you are adept at grinding HSS, you can grind the required profile on the end of a round piece, a size that will fit a collet (it can be held in a chuck as well, assuming it is blocked so it can't slip laterally). Once ground, it can be held in the spindle of your lathe or mill (a mill makes this real easy), then use the quill (or saddle of a lathe) to propel the tool. By taking light cuts (.001"-.003" depth per pass) you can broach a keyway almost effortlessly.

It's important for you to understand that the end of the tool is the cutting surface, in spite of the fact that the resulting tool would very much resemble a parting tool.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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liveaboard
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Re: Gear Repair.

Post by liveaboard » Wed Apr 21, 2021 3:44 pm

If you're patient, you can do it on a lathe; this one in the picture is a tapered bore, and I cut the slot by winding the compound in and out.

Ok, it was quite small and the hub is cast iron.
keyslot cutting with a lathe.jpg

AllenH59
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Re: Gear Repair.

Post by AllenH59 » Wed Apr 21, 2021 8:24 pm

Yes Harold... I could broach one on the lathe.. I knew that, I am considering buying a involute cutter, now that I know which one I need, and making a gear. I went down to the Boston Gear dealer here, and he confirmed that it is a DP 16 with 14.5 degree pressure angle, before he confirmed that Boston could not supply one. I have an index head for my milling machine, and I am reasonably sure I can cut 40 teeth. I have contacted someone who may be able to get me an original gear, I should know tomorrow how long that will take and if it is possible.

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Bill Shields
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Re: Gear Repair.

Post by Bill Shields » Wed Apr 21, 2021 9:05 pm

There are suppliers other than Boston gear
Too many things going on to bother listing them.

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