Broken gear - Calling all machinists/ welders

[markct]

is it a straight cut gear or helical? i have repaired a few gears for atvs and stuff that were straight cut by simply welding them up carefully and then machining them with a fly cutter ground to match in the milling machine. where in northwest ct are ya, im from northfield ct

 

[CT_Tree_Guy]

Hiya Mark, it's straight cut. Glad to hear you've had success with welding them up, that might be an option. Heck, if I was on Gilligan's Island I'd just mig it up, grind a new tooth with a die grinder, slap it back in and crane myself off the island. (The S.S. Minnow carried a full complement of welding tools, and the professor made a coconut-powered battery to power the MIG).

Anyway, sounds like I'll be up and running again soon. It'll be interesting to see what turns out to be the best/most feasible way to do it.

I'm in Collinsville, part of Canton. And Northfield has GOT to be a part of some other town, cuz I've lived in the Farmington Valley for 40 years and I have NEVER heard of Northfield, no offense intended. /forums/images/graemlins/smile.gif

I can't even find it in my Rand McNally road atlas! Where da heck you at?

 

[JustGary]

I didn't mean to suggest that welding would not work, just that dovetailing is certainly an option. The fact that you are dealing with a pinion gear might make dovetailing harder in this case (a single flat gear provides lots of room to cut in a decent sized dovetail to support the stress; your example does not look like the best candidate).

See what the machine shop suggests. If you can't find a machine shop that will help you, talk to the machine shop instructor at the local community college or vo-tech. They may have a set of gear hobs for your particular gear. As a previous poster mentioned, the proper hob makes recutting the teeth a simple task. It also reduces the stress on the new tooth since it meshes best with the existing teeth.

Heck, you might even talk the instructor into a repair for a free tree job...

- Just Gary

 

[CT_Tree_Guy]

Gary - Wow, thanks for all that information and detail. Great point about the dovetailing on a tall gear like this, could be tricky but we'll see. A friend of mine is the son in family machine shop here in town. They're world-class and they do it all, including aerospace, so they should be full of ideas.

It's been interesting learning about hobs, they probably have them and can show me how they work.

On the machining-for-tree work thing, it is amazing how many people need tree work done, and it does come in very handy for bartering. Of course, if you're with the IRS, I never said that. /forums/images/graemlins/smile.gif

Thanks for the help, John

 

[JustGary]

</font><font color="blue" class="small">( I've lived in the Farmington Valley for 40 years and I have NEVER heard of Northfield, no offense intended. )</font>

Also no offense intended, but you guys from the Northeast just crack me up. You can live your whole life within ten miles of a particular town and never know it. Of course, if you go twenty miles you're in another state!

Anyway, I'm surprised that you didn't post a photo of the actual gear. You know how we like pictures.

I tried to surf up an example of a dovetailed gear repair and didn't find one. I did find a web page from a guy who made his own gear hob for a gear set he needed to make. It turns out the poor guy used the wrong pressure angle on his first try... I hate it when that happens!

Gears are very interesting critters, and we tend to take them for granted until something happens to them.

- Just Gary

 

[CT_Tree_Guy]

Gary -

For a small state, Connecticut has more cities, towns, burroughs, districts, sections and villages than you can believe. That, coupled with a tendancy for people in this state/region to keep to themselves (almost to a fault), makes things like this pretty common.

As for not posting a picture of the gear itself, it's still in the turret - I've been too busy hauling logs to take it out yet. I'll post a pic of it as soon as I do.

Thanks for looking for dovetail examples, that'll be one of the things I ask my machinists about.

Gears are very interesting creatures, and we really do tend to take them for granted. I always make sure that my guys know what is going on inside machinery, like a transmission for instance. It's easy to just mash a gearshift lever around if you're not aware that it's connected to cast steel shifting forks that are sliding expensive gears around that are trying to mesh at high speeds. /forums/images/graemlins/tongue.gif

 

[AntrimMan]

Dude, put some air in those front tractor tires.
Any gear that breaks under load will likely affect the mate, so look real close at that one too.
Gears follow standards and the pressure angle and circular pitch are usually standard values. On a spur gear like this one there can be some undercutting that results from the hobbing and that is what weakens them.
A decent shop with at least one old timer and a lot of cake on the floor will be able to help you. If you need to make an entirely new one think about 8 hours start to finish at $55 per hour plus heat treat.
If it's a cast iron spur, and lots are since iron on steel is a decent wearing combination, then you are buggered because fixing a small cast iron spur is next to impossible.
The easiest thing is to find NOS or used parts at the knackers.

Good luck and all the best,
Martin

 

[AndyMA]

I suggest you may want to give Ken a call at Ken's Repair in N Franklin Conn. 860 642-6599 Ken can repair most anything, has more parts sitting around than 10 Junkman's and spent years in the utility business. If a parts available from any source (including his yard) chances are Ken know where to get it.

Andy

 

[AntrimMan]

I just remembered where I heard about making gears to replace obsolete unobtainable ones.
Find someone with Model A's or the equivalent. They will know who can make what. Most parts can be had but I had a shop instructor who told us about actually making a ring and pinion set for some old model car because the owner couldn't find replacements.
Todays wire EDM capability makes gear cutting easy. The first one is gonna cost you though.

Good luck again.
Martin

 

[CT_Tree_Guy]

Martin -

Yeah, I'll have to check that LF tire, hadn't noticed. I had a slow in that tire from a nail and slimed it 4 weeks ago, maybe she's still leaking. On the other hand, they're just 6-ply turfs and that's a heavy log. Just doin' what I gotta do. But thanks, I'll check it to make sure I've got 30 psi.

Will definitely check out the main ring gear, but that thing would be frighteningly expensive to replace. It's the big one at the bottom of the first schematic.

Thanks for the cost estimate, it bears out my WAG of $500.

Pretty sure the whole gear is machined with no part of it cast, but we'll see.

Thanks for the help and tire observation, John

*Edit*

Just checked my tire pressures. LF 25, RF 28, should be 30.
LR 16, RR 16, should be 20. I'll have have some words with the folks from Slime, and with my head mechanic - oh wait, that's me. Not all that low, but I'll obviously boost them back up. Like I said, that was a heavy log, and even with an 800 lb. grapple on the back of the tractor the rear was very light. That's a lot of weight on the front axle, but like I said, just doin' what I gotta do.

Maybe a good reminder to everyone that now that the cold weather is here (well, for some of us anyway), re-check those tire pressures.