Gear repair fixture !

that's interesting ! because I's seen 5 videos on you tube that say you can't do it ( not enough heat!)
and 3 videos that say you can ....
any idea what kind of temps your propane torch can reach ?
it's weird.... as it looks like every propane torch out there burns at a different temp !
LOL....
THANKS for the Response ! it's been about 12 to 15 years sense I've tried to braze anything ! LOL....
Bob....
 
Honestly, they all burn at the same temp - air fuel mix is air fuel mix. Amount of heat on the other hand...there's your magic.

You need to reach temp to melt the bronze and that is the issue. A small, wimpy propane pipe soldering torch isn't going to bring a 30-pouind casting up to temp with any speed - and it'll fail. My present one is a torch and regulator made for plumber's use - runs off a midget propane bottle in its original application but I just use a 20-pounder to run it. I think the brand is a TurboTorch.

I have brazed with a conventional torch on a disposable gas bottle - but careful heat retention is the name of the game,. Firebrick over, under and to the sides to form a pocket to retain the heat helps tremendously.
 
ahhh ! thank you for that info Al !
yah I figured overkill with the heat and heat retention is the only way to go with trying to braze with Propane....
......
ages ago when I had a good Oxy/Acetylene torch i switch from acetylene to propane and actually saw very little difference in cutting 1/4" steel plate
I did have to buy a few tips for the torch though. at $30 bucks a whack !
but the money saved in the long run was in the hundreds of dollars !
.... but when the Ranch fire went through the place all that was left of most of my tools was untempered tools and puddles of aluminum all over the place....Brass did not melt! steel warped cast-iron survived like nothing ever happened ! the cart and bottles we the only thing salvage able.... and I doubt the bottles can be re filled ! the torch though I still have it, has no O rings in it and of course the hose is gone regulators toast and so on.... but I do have a older but still usable 20 gal propane tank and I was thinking of getting a propane torch just for shop use...... or perhaps just use a 5 gal tank I have plenty of those. that happened about 8 or 9 years ago now...but losing 98% of 50 years of accumulation is a hard thing to get over !!! LOL....
.....
just came back in from some lathe work.... "practice threading" and I got a problem with that ! but I'll post it in another thread !
thanks again Al !
Bob.........
 
Yes as has been said before propane burns in air at a fairly fixed temperature, but will burn quite a bit hotter if used in a torch that you can feed oxygen with. While a propane flame is hot enough you have to have a suitable size burner to provide enough heat, particularly on large jobs and metals that have a high heat conductivity because they soak the heat away from the work area.

Another thing to watch for is not all propane is the same, some some places and brands are mixtures of propane and butane and even straight butane. Here the main difference is in boiling temps. 100% propane will work much better at low ambient temperatures . Remember also that boiling off the gas will lower the temp of the liquid in the tank so even at moderately low temps your supply of gas may reduce, resulting in lower heat output.
 
Interesting ! I thought propane and Butane were the same thing ! Ok very interesting
yah I figured using my 5 gal bottle powered weed burner would make a dandy pre heater ! get that thing as hot as I can with it and then go to town with the hand held propane torch...... I have no idea what the temp is of the little propane torch is but I got it at Squall Mart ( wall mart ) a few years back because it had a self ignition button on it, found it in the camping section ...i'm hoping it will get hot enough , if not I have another older one that is quite a bit bigger and i'll use it !
but first I gott'a come up with $20 bucks for brazing Rod ! that stuff has really gone up over the last 30 years same amount used to be $5.00 !
I haven't brazed anything in AGES !!!!!
Bob.......
 
The actual flame temp between the various blends of propane and butane are all very similar, it's the size of the flame size that counts.

And Yes using two or even more torches, if the situation requires it, to preheat, and maintain the large job at a good temp is quite useful.
 
Interesting ! because I have seen the cheaper torches claim max temp of 1700 degrees and others 2800 degrees
it seams most of the bigger soldering torches do indeed reach about 2700 to 2800 degrees in temp ( if my memory serves me correctly)
but yet the little torches that run off the same small bottles struggle to reach those temps. or so they claim !
......
my bigger torch in the shop is an older one and it has a slow leak around the valve but it is a torch for soldering large copper pipe
it's one of those torches you don't leave the bottle on or it's empty the next time you try to use it ! ...a pain in the arse !
.....i don't hold out much hope for the little auto ignition torch reaching a high temp... as I have used it to try and temper stuff being held in the vice and it is very hard to even get it red hot that way.... ( the vice wicks away the heat too fast) I did get the job done but I had to hold the part with a pare of needle nose vice grips and that held in the vice..... that worked really good )
this torch is mainly for starting my wood pellet stove.... and it does a great job of that.
.....
years ago with my Hydroxy gas setup, I hooked up a small torch on a hose and melted a spot in a rock ! with a needle size flame !
but that is a different gas all together ! LOL..... ( i used a AC/DC welder on DC to power the 3 cells to get enough gas volume in order to run the torch off the bubbler.... still I popped the safety lid on the bubbler 3 or 4 times when I was farting around with it ! LOL.... the lit flew 250 feet straight up each time ! lol....
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I have some oven thermal insulation out there and I will try to make a pocket out of it to hold the gear and short shaft.....
I have 6 teeth that need repaired ..... that is a big area almost 1/4 turn on that gear most of the teeth are just missing pieces but I would like to bring it back up to snuff !

....
Bob......
 
There was a possibly useful technique some while back for smaller gears that could be cast from aluminium. It involved using Hydrocal, a type of plaster used for molds. The gear was set in a divided form with the good half of the gear being cast. Pins had been set on the dam for later use.

When the Hydrocal had set, the dam was removed and the gear reversed to expose a usable side with the pins acting to reinforce the joint. Then the other side of the mold was cast. Once that side was cast, the original would be removed and the mold touched up.

Before use, the plaster mold was preheated to drive out residual moisture and a replacement part cast. Hydrocal will hold up well enough to make two aluminium castings. This I know from experience. It probably would make more before degrading beyond use.

This tecnique is useful for repairing a gear where gear machining facilities are not available. Hydrocal reproducing the teeth in finest detail. I never tried a large gear but 4" by 1/2" thick worked well. I have heard of it being done with brass, but I'm not that good.

.
 
that's a cool idea ! i bet if your real careful you get a part that just bolts back in !
I've only done a bit of casting of aluminum,...and I have yet to get the green sand ... I just filled copper pipes and beat the copper till it expanded enough to get the aluminum slug out and used it on the lathe ! LOL.... I did several large round disks that really didn't turn out very well they always had a big dip in the center so I learned to make them 2 times as thick as I needed ! LOL....
I made a forge from a short 2' section of 11" well pipe and made a burner for propane for it and I melted aluminum for a long time with that setup...
what I did was cut a hole about 3" in diam for the heat source to go into...and then used a piece of 6" stove pipe to go in the center of the 11" well pipe and then just made tin flanges for the top and bottom and filled the gap with Kitty-litter as insulation .... I made my crouseable from a large washer 1/2" thick and a 4" pipe 1/4" wall .....and welded it all up and that worked very good....i use it to this day,
.....
I've got nothing against aluminum gears , from what I've seen they hold up very well in hard work !
.....
I suppose I could use my bad gear to act as a pattern to cut an aluminum blank into a gear and have a completely new gear !
that would take a completely different fixture to do that but it can be done ! and they're not that hard to make up from the looks of things !
same idea as the other one but 2 gears wide and the nail or Pin is only for the first gear....
clamped tight in the milling vice you can copy the original gear quite easily !
I would think that you would need a locating pin between the gears though so they can't turn and get out'a sync !

.....
Bob.....
 
Repairing a gear without gear cutting equipment. OK making a new gear from scratch is not easy, but repairing an existing one is not too hard. I had an idler gear on a large diesel engine driving a 3 ph alternator, about 1200HP. The cast iron idler gear was the intermediate gear on the timing gears for the camshaft it was a good size about 14" from memory. It was too big for our mill an dwe didn't have any rotary indexing device nor any suitable cutters.

The camshaft had jammed up and the steel driver gear had chewed out about 5 teeth in one spot on the idler. The rest of the gear was good. The process was to fix a sheet of steel shim about 2 or 3 thou, to the gear and carefully scribe the gear profile from a good area covering a few more teeth than the damaged area, also pick up a couple of other spots opposite and at about 90 deg.

carefully cut out the teeth as marked this has to be very accurate. when finished put the pattern aside and prepare the damaged gear for welding or brazing, I chose to braze it as I didn't have any suitable cast iron rods. grind out and prepare the damaged area, then fill it with brazing or welding make sure to overfill all over.

Then set up in lathe . I used a previously prepared mandrel so that I could be sure it was running true. Face both sides leaving 1 or 2 thou. proud and turn the OD again leaving 1 or 2 thou. proud. Paint both side faces with layout blue.

when dry, afix pattern to one side and scribe tooth profile onto gear, then repeat on other side. Rough out tooth cut out with hacksaw, then file to scribed lines. It's a good idea to test fit into machine before filing too far. At this point you can file the last thou or two from the OD and the sides, and dress up the finished gear to a good fit.

The rebuilt gear was able to run for the next 6 weeks until we got back to home port where a new gear was waiting for us. Examining the repaired gear showed it had stood up fairly well so it was put away in the spares box for that engine.
 
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