Ace Bodge

[John Stevenson]

Last thing tonight got a rush job in where a motor driving a small reduction gearbox had gone pear shaped.

Should have been a simple job just to bolt an off the shelf motor on but the coupling, made out of monkey metal had collapsed.

Should have got some pics but was rushing as it was needed on a production line.

Sketch of the coupling.

http://www.stevenson-engineers.co.uk/files/coupling.jpg

The OD is 14mm and the ID is 11mm the sticky up bit is 8mm diameter if it was a full circle.

So using a 5/16" round nose end mill I cut a groove in a piece of 14mm bar and silver soldered a piece of 8mm into it. Looked lovely until I came to drill and bore the 11 mm hole and it just pared the insert out.

Oh well another flat battery in the car park of life.

Then the bodge of all bodges hit me, actually it was Gert calling me for tea but that's another story.

Grabbed a piece of 3/4" plate and plunged a 14mm hole thru it, then using a 8mm milling cutter put a indent into the side, basically made what it has to fit in the gearbox.

Clamped it to the welding bench and got it stinking hot with the torch then kept feeding alloy welding rod in until I had a big pile on the top. Let it cool slightly and with another plate on top whacked seven shades of shït out of it and forged it into the hole.

Allowed to cool a bit and quenched it. the new bit tapped out and was a perfect fit into the gearbox, just had to bore the 11mm hole and bung a 4mm keyway into it.

Rang the customer and he came to fetch it, when he saw it he reckoned I hadn't made it but had found a spare one kicking about, wouldn't believe me that I'd made it but sod it, charge him double for being a philistine................


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[Liger Zero]

See I wish I had this kind of repair talent. I keep people like you on call locally because for situations like this.

[Mcgyver]

Clamped it to the welding bench and got it stinking hot with the torch then kept feeding alloy welding rod in until I had a big pile on the top.

i didn't follow that part, why heat the mold stinking hot?....and how does the feeding allow welding rod work? what alloy, ie what was the finished part made of?

[John Stevenson]

The heat from the mould caused the alloy welding rod to melt completely as opposed to melting the rod in the hole and getting voids.
the part was made of the alloy welding rods making what was basically an alloy forging.

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[oldbikerdude37]

Metal must cost alot in GB, seems like you could have some bigger stock to make it round inside and out.
Oh well if the people who need it are running again then that just dont matter

[John Stevenson]

Metal must cost alot in GB, seems like you could have some bigger stock to make it round inside and out.
Oh well if the people who need it are running again then that just dont matter

How do you turn the OD and leave a circular key on it that stands 4mm proud ?

[MTNGUN]

As usual, I'm impressed with Sir John's creativity and efficiency.

[oldbikerdude37]

How do you turn the OD and leave a circular key on it that stands 4mm proud ?

A circular key ? sounds like all you did is replicate a crappy idea. you will see that job again and have to fix it better then the customers silly idea and charge them some money.

[John Stevenson]

Yes I replicated a crappy idea.
Mainly because the gearbox had this internal shape machined into the hardened shaft.

It wasn't a customers silly idea, it was designed and built like that. Any jam up and it breaks the insert and so protects the gearbox

My brief from the customer was fit the motor to the gearbox in the shortest possible time.

[Mcgyver]

thx, i was thinking alloy rod meant something special for chrome moly or something, but sounds like it was AL or such?

OBD, sounds like the part fit in a recess in the gear box....whats the alternative; redesign and make a new end for the gearbox?

[oldbikerdude37]

Yes I replicated a crappy idea.
Mainly because the gearbox had this internal shape machined into the hardened shaft.

My brief from the customer was fit the motor to the gearbox in the shortest possible time.

Im a job shopper, iv done things quick and dirty too. maybe next time when they have down time you can fix them up better.

Whats the old saying? You can have it cheap, you can have it now, or you can have right? Pick any two..

[John Stevenson]

maybe next time when they have down time you can fix them up better.


Why, it lasted 14 years and only got pulled because the motor packed in.
It was still running with the broken coupling.

[mikem]

I guess I don't get how you did the repair. Can you explain that again?

[wierdscience]

Sounds like my kind of day John,had to remove a 55mm threaded OD bearing retaining ring on a quad gearbox.Honda I think it was,customer brought it in and said he couldn't budge it.I tried and couldn't budge it either,then I thought Honda=Japanese and Japanese love a good puzzle.......maybe it's lefthand thread?-Yup! $20 please:)

[danlb]

Yes I replicated a crappy idea.
Mainly because the gearbox had this internal shape machined into the hardened shaft.


Now it makes sense. The original post did not make it clear that the 4mm bump keyed it to one part, and the standard key locked it to the shaft.

I could not quite figure out why you'd done it that way either. Clever.

Dan

[Mark McGrath]

Whatever would Harold say? :D

Mark.

[dp]

I guess I don't get how you did the repair. Can you explain that again?

He bored a hole in 3/4" plate then milled out a key slot in it. The result is a die. Then he took his stock, placed it at the keyed hole, and beat the living crap out of it until it came out the other side of his 3/4" plate die looking like the pencil drawing.

[MuellerNick]

That's what shapers are for (if there's no CNC mill).


Nick

[Peter.]

So you had a motor that had gone pear-shaped and made it not pear shaped and then made a pear-shaped coupling to fit the no-longer-pear-shaped motor?

Think I got that right!

[Your Old Dog]

He bored a hole in 3/4" plate then milled out a key slot in it. The result is a die. Then he took his stock, placed it at the keyed hole, and beat the living crap out of it until it came out the other side of his 3/4" plate die looking like the pencil drawing.

Thanks DP, he likely did this post after lunch at the pub. Only part I really understood was beating 7 shades of sh1t out of it :D

[reggie_obe]

If I'm understanding your post correctly, the part was not a coupling in the traditional sense between two shafts, but a driver that coupled power from the motor to the transmission. It serves as a sacrificial link between the motor and the transmission or gearbox. You reference to "monkey metal" would mean, pot metal, white metal or ZAMAK?


http://en.wikipedia.org/wiki/Zamak

[gnm109]

Nice work, Sir John! A man after my own heart. I love fixing things without re-designing them.

I recently built three bushings for the steering on my Honda riding mower. Originals were rotted "sintered steel monkey metal" that had rusted themselves to the steering shaft - solid. They were round wth a key sticking up on the outside. I turned the bushings out of bronze and silver soldered the key on. Saved $25 I did. :)


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[ulav8r]

The quick bodge for an Ace bandage is Duct Tape.

[Limy Sami]

wouldn't believe me that I'd made it but sod it, charge him double for being a philistine................


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Works for me :D