Gear repair fixture !

[Bob Kelly III]

A friend of mine, Gary Bower a long time enthusiast of several lathes milling machines and what not. told me how to repair a gear that I have never heard of before
... although brazing up the busted tooth area of a gear is not new, his method for re cutting the tooth area was....
what I knew already was that it takes an indexer to turn the gear so the next slot is in line with the cutter in the milling machine
and rotary indexers like that cost a fortune ....when you can find them and it's hard to justify one for a single gear repair Right?
well Gary told me that he came up with the idea to help his friend about 30 years ago when he had a gear that had busted teeth on his lathe
if you take a stout piece of flat bar , I used 1.5"x 1/4"x 3" steel scrap I had laying around. used my Logan lathe to make the pin that the gear will sit on
and afixed that to the top right corner of the piece of bar stock when it was laying horizontally in the milling vice.
and I welded the pin in from the back side .... then ground it flush again.
next i put the gear on the pin and with my awl scribed a arc using the good teeth on the back side of the gear to guide the awl
I guessed at the horizontal line from where the bad teeth would be re cut to the back side of the gear and scribed a mark then used a center punch and frilled a small hole
( this hole needs to be between the teeth of the gear) then I found a small nail that fit the hole and cut it off about 1/8" from the top of the gear ....
i welded the nail in place then hand filed the nail to shape ( like a "V" ) and then put the gear back on.... after several tries at fitting it like this I had a very good strong fit
.... I thin found a scrap piece of steel suitable for a flat bar across the top edge of the bar stock so it would not twist in the vice when putting this thing in and out of the milling vice... and it was done....
the idea here is that you have one side that you can squeeze in the vice on the gear and lock it down for the milling....
after you set it up and take your first cut and lock the quill down you should be able to take it out and return it to the exact same spot,
once the first tooth is cut you remove the device with the gear intact and ease the gear off and turn it one tooth (to align it up with the cutter on the other side) and put it back in the milling vice and do the next tooth. and repeat till all the teeth are cut anew !
Gary's Idea had a peg that had a tooth on the top to align the teeth to the next step, my version used a nail instead. the disadvantage to the nail is that you must take it out of the vice in order to move it one tooth... with Gary's version you simply loosen the vice, use the peg to align the next tooth and then tighten the clamp again.
there is no doubt in my mind that Gary is one sharp cookie !
I call this the "Gear self indexing device" no need for a rotary indexer.... it took me about an hour to make up is all and I did a dry run to make sure I would not run into any limitations when actually doing it..... I saw no problems at all !
.... my only problem is getting the gear brazed up !.... my O/A torch burned up in the ranch fire about 5 years ago and it hasn't been replaced yet !
so I'm on the hunt for a welding shop that can braze that gear now !
.....
Koodos to Gary ! he saved my bacon on that one ! ..... index the gear with the gear itself ! who'd have thunk it !!!!!!
hahahhah
.....
I think I will add a piece of metal on the end of the thing to make it set in the mill vice the same way each time.... right now it can slide horizontally.... just welding a scrap piece of steel over the corner will stop that from happening ...it'll be ...put it in the jaws, push down on the top to make sure it's level and push it in till it stops... and tighten it down...... cut the tooth,pull it out advance it a tooth and put it back in...

....
now I can take my time with my lathe indexer and not have to find a 34 tooth saw blade !
his method is far easier !
....
Thanks Gary !
Bob.........

 

[Bob Kelly III]

something that I forgot to mention.... the Peg for the gear to sit in cannot protrude beyond the face of the gear when installed...that very important
if it does, the gear itself won't be clamped tight ( the jaws of the milling vice will hit the peg and not the gear )
......
Bob.

 

[HarryJM]

Hi Bob,

Any chance of posting a picture as this is something that I will be interested in making once I get my shop setup. I did run across a post/picture (and cannot find it now) on Practical Machinist where the author made a self indexing fixture, mounted to a mill table, which looked like a sturdy L bracket that he mounted the gear on vertically with a indexing pin at the bottom.

Thanks,
Harry

 

[Bob Kelly III]

sure ! I didn't spend much time at this, maybe an hour ...and I'm slow in my old age ! LOL
and there may well be a better way to do this sort of thing but for me this is the cats meow !
if you look real close you can see the nail I used as a pin between the gear's teeth on the back side of the gear
it doesn't hold any pressure it is just there for alignment, the mill vice holds the gear against the flat stock....( to which I added 2 other pieces of steel for alignment purposes)
here's 5 pictures including how I plan to cut the teeth on the 3 in 1
hope this helps !
Bob.........

 

[HarryJM]

Thanks for the pics!

 

[Bi11Hudson]

I have used a similar method in the distant past to repair a small gear. Long before I had a milling machine, or even a lathe. Using just a stick of brass key stock and a file, it is a time consuming but doable process. No welding or brazing, just screwed together. But it worked... and held up for several months while a replacement was located. This before the internet...

 

[Bob Kelly III]

it may well be worth the time to put some greater effort into this, by having a alignment Pin that is bolted to the back ( by counter sunk and flush screws so you can accommodate different size gears to repair... like those of the change gear verity. you might have to have different Main pins also
to mount the gear on....
the problem comes when the gear is a large diameter like a bull gear....
it's a thought anyway !
....
Bill, the gear was already repaired by a old method of drilling small holes straight down into the gear and screwing in machine screws, cutting off the heads and then filing the screw shaft into a tooth form.... there is repairs like this on the bull gear on my lathe also 3 screws across the width of the gear.... replacing 1 tooth that had busted off.... evidently some one mistreated the lathe in the past by not stopping the lathe to shift in and out gears.
after seeing the damage done... I stop the machine to shift things..... the split nut and clutch being the only exceptions !
....
I could just add a few more screws in the wide gaps on that small Idler gear....there is room to do that, but I would rather see full teeth across the gear width..... and quiet down the machine a bit when it is engaged and running. i think brass would do that for me !
.....
there is also the dove tail method to hold a piece of metal in the gear, but that takes an accurate mill and a tiny dovetail on this tiny gear
so that method is usually reserved for large gears...but it works.... too.
.... I am sure variations of these methods would repair most any gear....
.....
....if any of you guys have a different method to repair a gear, no matter how ! I'ed love to hear it !
.....
Gear repair has been something I've been interested in most of my life....and Knowledge is power !

Bob.....

 

[savarin]

tumbler reverse

I'm looking into making a tumbler reverse for my 9x20. I'm sort of following the 9x20 LATHE TOP MOUNT REEVERSE TUMBLER by Jeremy Taylor. I'm considering making the shaft for the reverse gear (45t in Jeremy's plans) to fit the 42t gear but making the position adjustable for a 45t when I can find...

www.hobby-machinist.com

post 26
I made this fixture 6 years ago to cut gears successfully so I expect it could cut the repaired gears.
That aluminium gear is still going strong.

 

[Bob Kelly III]

that was quite an undertaking ! but look at the results ! Well done !!!!!!
that is indeed making a gear from scratch ! without using a $900.00 rotary indexer ! FANTASTIC !!!!!
.....and I did bookmark that index printer site...been looking for that for about 5 years now ! HAHAHAHA THANK YOU !
......
I've made 2 aluminum gears so far on the 3 in 1 and they worked very well,..... aluminum stands up really well gear to gear but for something like I tried to do it was folly from the start ! I made a small gear for a starter pinion on my lawn tractor..... it lasted about 6 to 8 starts and was gone and to make matters worse it took a few teeth out of the flywheel too !
so it is Pull rope time when I want to start that thing now ! Bah !
.....
that gear you made just happens to be the same one I am trying to repair on my Logan lathe the forward /reverse idler gears that engage to the spindle.....and then transmit their power down the chain to the lead screw .
...... after discovering the damage,...... I stop the lathe to mess with that lever !!!!!!
.....
I wonder if anyone has tried to Braze with propane alone ????
I'm going to try it by first firing up the weed burner, and putting it in my small forge, and pre heat the gear and rod it will be on then turn the heat down a bit and then try brazing it with a propane torch.... if it works I'll show ya how I did it LOL.....
so that is my next project...brazing with propane ! LOL......
later guys !
Bob.........

 

[just old al]

Re: Brazing with propane: Yes, you can. I do it often for fittings and brackets in antique car restoration. Brazing is more than strong enough for things like mounting brackets and the like and I can do it downstairs in the workshop rather than having to run out the car and fire up the MIG or TIG in the garage.

As you say, heat control is important. Do use firebricks to make a muffle to retain heat and preheat on cast iron is always a good idea.