Gear Made in Single Operation?

[Geof]

The metal is not exotic but it is a kind of composite which is why I put it here.

It is a gear from the steering mechanism of one of my lawn tractors; a broken gear now.

The first picture shows how it looks when it is together and you can see the interesting through hole. Interesting because the two straight sides are parallel while the curved sides are tapered, and the corners between the straight and curved parts are really sharp, no discernible radius at all.

How do you make such a hole?

The answer is you don't, you make all the stuff that surrounds the hole by a process called powder metallurgy also known as sintering. Steel powder is compressed at extremely high pressure and temperature in a die fusing the particles into a solid mass. Much the same as the procedure for making carbide inserts.

I should put in a caveat here: It is my personal conclusion that this part is made by sintering based on the overall appearance, the appearance of the fracture, the hole shape that would be extremely difficult to make any other way and the fact that this part is in a not very expensive consumer product.

[Einstein_1985]

The hole can be easily made with a wire EDM machine, costs next to nothing have those made in a factory in India.

[DaveKennedy]

Well, I'd drill and tap it and recess 2 socket head machine screws either side of the hole. Through the 2 halves. Then I might recess a ring with a hole saw around the hole and super glue a steel ring in. Assuming it's going to be 'sandwiched' in place. I like to think some of my 'professional repairs' are more of an improvement than a bodge.

It might have been cheap to produce (in numbers) but it clearly wasn't up to the job.

[Paulo E.]

Cool looking part.
I agree with Einstein, EDM is the way to go.

[templecorran]

I guess you've tried all the 'simple' things like searching for a replacement part from the tractor manufacturer?

[Paulo E.]

ROFL

Maybe the part is no longer manufactured or he wants to do it as a special project but yes LOL you do bring a valid point. Having said that, Geof is one sharp dude so if there is a reason he has one

[peterpan3]

Wire EDM is the only way to go with this, or a really good welder.

[AMCjeepCJ]

I don't think he wants to build one. He started this thread to keep his other thread on topic because myself and a few others kind of started talking about this type of technology instead of his original question, which was, "What has been the Single Biggest Advance in Machining Technology in the last 50 Years"...


See post #20, 22, 28 and possibly others but post 31 directs everyone here:
http://www.cnczone.com/forums/showth...244#post629244

I think he posted here only as a way to keep everything on track in the other thread and to show an everyday example of what we had been discussing.

Note he said, "gear made in single operation?"

You can't make that part on a wire in one operation, it has a counterbore...

[Geof]

I started a new thread because I didn't want to clutter up the other one.

Where did I say I was going to repair it?

I agree that shape could be done by EDM, I guess even the counterbore, but I seriously doubt this one was made that way. It is easy to see there are no tool marks on the sides of the gear and around the end of the hub there is a very small flash as if it came out of a die, I think it probaly came out of a multi-part die.

Nobody is seriously suggesting the OEM made this part by EDM are they?

No I haven't tried the simple things yet. Give me a break, it broke Sunday afternoon, I started the thread Sunday evening and my time is 6:36 am Monday and I am having a cup of coffee.

My title is wrong anyway because it would not have really been made in a single operation because powder metallurgy requires preforming of the powder mass.

Dave's comment about it not being up to the job is correct. The lawn mower is only a few years and I bought it the year it was introduced. It is the style with the steering connected to individual hydrostatic transmissions on each rear wheel to vary the wheel speed depending on the radius of the turn. It is fun to drive because the front wheels can turn a full 90 degrees making it pivot around the center of the rear axle.

[Geof]

What was AMC saying about the Internet and information in the other thread?

The coffee kicked in and I realised I could enter the part number impressed in the side of the broken gear into Google.

Seven hits and all of them say something like: part# 717-04282A replaces part#717-04282.

No prize for guessing which is my part number; maybe this is not the first one to break.

Maybe I should order the opposite side one while I am ordering?

[LeeWay]

Just an observation and perhaps a wrong one, but those sharp crisp corners may have contributed to the parts demise. I think it would be better to actually have a small radius in there. Don't know if the shaft is as crisp, but a radius would seem to make it stronger.

[tjwal]

Originally Posted by Einstein_1985 The hole can be easily made with a wire EDM machine, costs next to nothing have those made in a factory in India.

Hmm this must be the CNC group, what is really needed is some old technology, think blacksmithing. Make up a mandrel that matches the hole. Heat up a gear blank in your forge and drive the mandrel into the hole. Clean the blank up in the lathe and cut the teeth.

Then with the $15 you've saved by not ording a new one buy a six pack and enjoy the fruits of your labor.

JohnW