Anybody REALLY like doing big gear repairs?

snowman · Aug 8, 2017

Ok, it's not really THAT big, but good size. Probably 20" in diameter give or take a few. The piece that is broken off has been broken multiple times, and welded. Welds have held well enough to then break elsewhere on the gear.

Replacement cost makes machine scrap.

I've seen a few of you post projects like this in the past.

Milland · Aug 8, 2017

That's not pretty. What overloads the gear and leads to breaking? What sort of machine is it?

If you're feeling adventurous I'd be tempted to look at some way of spreading the load out so it's not as stressed. If you can reverse the input direction you can setup an intermediary gear stage with two idlers, then a smaller gear to replace this one. But with two sets of drive teeth engaged it should be more robust.

snowman · Aug 8, 2017

It's an old mechanical baler in the scrap yard. People overload it.

It has an overload clutch, but ya know, if you keep pushing that button...sooner or later it's bound to work right?

I'd also wager a guess that misalignment came in to play some for the breakage past the first weld, as there was likely no machining done.

snowman · Aug 8, 2017

Actually...after talking about laser cut gears.

Is this a place where a laminated gear may actually be able to work? Something along the line of cutting the whole damn thing out of 1/2" pieces of steel, then having it bolt up to a hub.

Milland · Aug 8, 2017

snowman said:
Actually...after talking about laser cut gears.

Is this a place where a laminated gear may actually be able to work? Something along the line of cutting the whole damn thing out of 1/2" pieces of steel, then having it bolt up to a hub.

Yeah, that thought popped to mind on my end too. Get some numbers and see if they make sense. I'd be curious what the quote(s) is(are).

johansen · Aug 8, 2017

snowman said:
It's an old mechanical baler in the scrap yard. People overload it.
...
I'd also wager a guess that misalignment came in to play some for the breakage past the first weld, as there was likely no machining done.

laser or water jet cut gears for sure. make it too strong and something else will break. maybe replace the keyway with a sheer pin?

Probably just happens to break wherever the shock load is applied, and the gear could have stored stresses in it from prior weld(s), as it looks like cast iron?

DDoug · Aug 8, 2017

snowman said:
Replacement cost makes machine scrap.

....meaning fix it cheaply..... :toetap:

snowman · Aug 8, 2017

digger doug said:
....meaning fix it cheaply.....

Not necessarily...it either needs to work again, or it needs to be replaced. The quoted replacement cost for that one gear put it in the "replace" machine category. I don't think it was an off the shelf gear.

I don't do gears...but for the replacement cost, I would have made an exception.

snowman · Aug 8, 2017

johansen said:
laser or water jet cut gears for sure. make it too strong and something else will break. maybe replace the keyway with a sheer pin?

Probably just happens to break wherever the shock load is applied, and the gear could have stored stresses in it from prior weld(s), as it looks like cast iron?

Very good possibility. It didn't break at the weld, but at the next tooth root...meaning it likely wasn't preheated enough or cooled too fast.

johnoder · Aug 8, 2017

See if my guess is any good.

51 teeth
9.5 Module
20 degree PA

tdmidget · Aug 8, 2017

Soooo, is this a "baler" or an alligator shear? There's no shock loads on a baling press and the old ones were chain driven. This has the look of a alligator shear, a machine apparently designed to remove fingers and hands but often used to cut scrap.

Dan from Oakland · Aug 8, 2017

Looks like a pretty simple job from the picture. Have a circle burned out of plate, turn the blank, have the teeth cut. Done. Whats the replacement cost of the bailer versus a gear? What was the cost of a gear? Whats the pinion look like?

snowman · Aug 8, 2017

tdmidget said:
Soooo, is this a "baler" or an alligator shear? There's no shock loads on a baling press and the old ones were chain driven. This has the look of a alligator shear, a machine apparently designed to remove fingers and hands but often used to cut scrap.

It's a baler....but I have no clue how they break it. Haven't really looked at it. He just asked me about something else and I saw it sitting there and asked.

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adama · Aug 8, 2017

No need to weld the laser cut gears to a hub, don't go too greedy on the thickness and just cut the mounting hole + key way on the laser. Add a few bolt holes and just slide em on the shaft one at a time and bolt them up as a stack, get em cut in something harder than mild steel and they will happily chew up the gear it runs with, but hay its not then your repair that’s failed!

Tony Quiring · Aug 8, 2017

First repair the gear to where it fits and works then stop and upgrade the gear.

We are guessing there was a great amount of sudden load when the interface was in the unsupported area between the spokes.

So get some 1/4 or thicker plate and make disks.

Machine the gear to allow the disk to rest in a recess in each side.

Weld the disk in place then drill holes as required to allow molten lead to be poured in then weld cover on opposite side.

Magna flux the unit between steps to check and repair cracks.

Heat up then fill with melted lead yo make it solid.

Now any high point loads are spread out across wide area.

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Monarchist · Aug 9, 2017

Tony Quiring said:
First repair the gear to where it fits and works then stop and upgrade the gear.

Nah. Not worth f*****g with in this day and age. Not spoked CI anyway.

Belt conversion candidate, rather, this one is.

Belt technology has moved waay faster and farther than gear technology so long as the space (width, mostly..) and speeds fit. As they should do on a baler.

Not silly-cheap, high-capacity belts, no, but more affordable than large gears

Also way more damage-resistant / cheaper to fix if/as/when damaged.

Milland · Aug 9, 2017

That's a surprisingly reasonable idea. You must be slipping, your reply is to the point and not enough obfuscation.

Monarchist · Aug 9, 2017

Milland said:
That's a surprisingly reasonable idea. You must be slipping, your reply is to the point and not enough obfuscation.

Ah, well. Statistical accidents do happen.

Forrest Addy · Aug 9, 2017

Make a stronger gear and something else will break, probably something more expensive than a gear.

I suggest a new gear and install a break-away clutch. One that trips and free wheels until reset. Like a circuit breaker but mechanical and a lot more expensive. Or a belt drive.

pressbrake1 · Aug 9, 2017

Just a couple of weeks ago I converted a similar arrangement and load (i assume) to triplex chain under customer s orders. I thought It was a nasty idea but its holding up so far

Anybody REALLY like doing big gear repairs?

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