"Make me one just like it!"

"Make me one just like it!"

Doc Nickel
Doc Nickel

June 13th, 2011, 8:50 am #1

Several weeks ago, I had a guy come by and bring me some big parts. Big broken parts.

He said, "I need one just like it".

Naturally, I replied, "Exactly like it? Why don't you use that one, then?"



Every machine shop, repairman or heavy-equipment guy has heard the old story, where they (or a friend of a friend, etc.) were doing this job off in some distant locale in a foreign land. It was some tough repair of some big old equipment, and during the process, a part is found to be damaged, but no suitable replacement can be found.

So the boss/foreman/machinists mate/etc. takes the part to the local indigenous people's blacksmithy/knifemaker/machine shop. He hands it to the guy at the smithy and says "make me a new one of these". The smith, who has barely a passing knowlege of english nods, smiles, and says "yes, sir. Come back in two day."

The foreman returns in two days to pick up the new part, only to find the smithy was as good as his word- he'd duplicated the part exactly, right down to the stripped threads and wallowed out keyway, including copying the scoring on the shaft precisely.

I've heard one version or another of that tale a hundred times. Sometimes it's the ships' machinist mate who disappears into the engineering spaces to produce an exact copy of a broken mixer part for the galley, other times it's an oil or logging company out in the South American jungles who gets a perfect copy of a winch-drum shaft from the local blacksmith.

But I digress.

Anyway, this fellow brought me the remains of a planetary geartrain that turns the cab of an older excavator. Replacement parts can be had- at a price. That price is high enough we're making new ones, and even after heat-treating, he'll still be thousands ahead.

But, they're big enough and tricky enough that these are "get to them when I can" parts. They're also 4140, meaning HSS tooling doesn't last long.

So far I've blanked out the three big gears and now the shaft...





In both cases I had to sort of extrapolate what wasn't there.

But, now the fun begins. The last time I had to spline some 4140, I had to make a cutter specifically to do it- HSS just didn't hold up. These teeth are mighty large (comparatively) and that might not be possible- or at least, as easy.

I went and looked at a tool-and-cutter grinder in the hopes I could possibly grind one of the dozen or so spare carbide-faced cutters I got in that big horizontal-cutter stash a while back, but it looks like I'd have to buy a pretty expensive diamond wheel and make my own fixtures to do it.

Neither of which is impossible, of course, but as always, I'm trying to come up with an easier- or perhaps just different- way.

Doc.
Quote
Share

FireFrenzy
FireFrenzy

June 13th, 2011, 9:45 am #2

Now i'm extrapolating from 32dp and 48dp (rc gearing) and someone either ran that piece of kit WAAAAAY to long or did something HORRIBLY wrong with it! i'm genuinely surprised it lasted this long....


Insert a smiley with a MOAR sign where appropriate!
Quote
Share

Doc Nickel
Doc Nickel

June 13th, 2011, 11:05 am #3

As I understand it, one of the bearings in the system somewhere, failed, and one or more of the bearing rollers dropped into the planets. And better still, it happened during a big job, and the operator didn't notice right away.

The center shaft is the worst- the planets still have most of their teeth, just badly chipped and cracked.

I just wish I had substantially bigger machines for this sort of thing.

Doc.
Quote
Share

Snowtroll
Snowtroll

June 13th, 2011, 11:43 am #4

Several weeks ago, I had a guy come by and bring me some big parts. Big broken parts.

He said, "I need one just like it".

Naturally, I replied, "Exactly like it? Why don't you use that one, then?"



Every machine shop, repairman or heavy-equipment guy has heard the old story, where they (or a friend of a friend, etc.) were doing this job off in some distant locale in a foreign land. It was some tough repair of some big old equipment, and during the process, a part is found to be damaged, but no suitable replacement can be found.

So the boss/foreman/machinists mate/etc. takes the part to the local indigenous people's blacksmithy/knifemaker/machine shop. He hands it to the guy at the smithy and says "make me a new one of these". The smith, who has barely a passing knowlege of english nods, smiles, and says "yes, sir. Come back in two day."

The foreman returns in two days to pick up the new part, only to find the smithy was as good as his word- he'd duplicated the part exactly, right down to the stripped threads and wallowed out keyway, including copying the scoring on the shaft precisely.

I've heard one version or another of that tale a hundred times. Sometimes it's the ships' machinist mate who disappears into the engineering spaces to produce an exact copy of a broken mixer part for the galley, other times it's an oil or logging company out in the South American jungles who gets a perfect copy of a winch-drum shaft from the local blacksmith.

But I digress.

Anyway, this fellow brought me the remains of a planetary geartrain that turns the cab of an older excavator. Replacement parts can be had- at a price. That price is high enough we're making new ones, and even after heat-treating, he'll still be thousands ahead.

But, they're big enough and tricky enough that these are "get to them when I can" parts. They're also 4140, meaning HSS tooling doesn't last long.

So far I've blanked out the three big gears and now the shaft...





In both cases I had to sort of extrapolate what wasn't there.

But, now the fun begins. The last time I had to spline some 4140, I had to make a cutter specifically to do it- HSS just didn't hold up. These teeth are mighty large (comparatively) and that might not be possible- or at least, as easy.

I went and looked at a tool-and-cutter grinder in the hopes I could possibly grind one of the dozen or so spare carbide-faced cutters I got in that big horizontal-cutter stash a while back, but it looks like I'd have to buy a pretty expensive diamond wheel and make my own fixtures to do it.

Neither of which is impossible, of course, but as always, I'm trying to come up with an easier- or perhaps just different- way.

Doc.
When you do something, do it properly...
And when you break somthing, break it thoroughly...

I can't understand that the driver didn't realise something was seriously wrong and stopped earlier.

This is the mechanism that turns the cab?
We're talking a big hydraulic excavator that moves around on crawlers, bucket at the end of a long boom?
Please tell me that the bearing that failed isn't the one that the entire upper secion rests on. (It's made up of pins/rollers/whatever you call them, not balls, so fits the description, and it is rather close by, after all)
If the races are damaged...
Quote
Share

CTPatt
CTPatt

June 13th, 2011, 12:09 pm #5

As I understand it, one of the bearings in the system somewhere, failed, and one or more of the bearing rollers dropped into the planets. And better still, it happened during a big job, and the operator didn't notice right away.

The center shaft is the worst- the planets still have most of their teeth, just badly chipped and cracked.

I just wish I had substantially bigger machines for this sort of thing.

Doc.
One would think a kerplunk of that magnitude would be noticed, if nothing else than for the fact that the parts in question would start jamming.
Quote
Share

Snowtroll
Snowtroll

June 13th, 2011, 1:15 pm #6

Those parts looks like they would chew up just about anything. A few bearing rollers probably just took a few seconds...

And even IF they jammed, have you any idea what kind of inertia would be forcing them to continue turning, if the machine was in 'mid swing' when it happened?

But, yeah, the operator SHOULD have noticed.
Also, these things doesn't 'suddenly fail' often. Not without a good reason.

Quote
Share

Russ Kepler
Russ Kepler

June 13th, 2011, 1:36 pm #7

Several weeks ago, I had a guy come by and bring me some big parts. Big broken parts.

He said, "I need one just like it".

Naturally, I replied, "Exactly like it? Why don't you use that one, then?"



Every machine shop, repairman or heavy-equipment guy has heard the old story, where they (or a friend of a friend, etc.) were doing this job off in some distant locale in a foreign land. It was some tough repair of some big old equipment, and during the process, a part is found to be damaged, but no suitable replacement can be found.

So the boss/foreman/machinists mate/etc. takes the part to the local indigenous people's blacksmithy/knifemaker/machine shop. He hands it to the guy at the smithy and says "make me a new one of these". The smith, who has barely a passing knowlege of english nods, smiles, and says "yes, sir. Come back in two day."

The foreman returns in two days to pick up the new part, only to find the smithy was as good as his word- he'd duplicated the part exactly, right down to the stripped threads and wallowed out keyway, including copying the scoring on the shaft precisely.

I've heard one version or another of that tale a hundred times. Sometimes it's the ships' machinist mate who disappears into the engineering spaces to produce an exact copy of a broken mixer part for the galley, other times it's an oil or logging company out in the South American jungles who gets a perfect copy of a winch-drum shaft from the local blacksmith.

But I digress.

Anyway, this fellow brought me the remains of a planetary geartrain that turns the cab of an older excavator. Replacement parts can be had- at a price. That price is high enough we're making new ones, and even after heat-treating, he'll still be thousands ahead.

But, they're big enough and tricky enough that these are "get to them when I can" parts. They're also 4140, meaning HSS tooling doesn't last long.

So far I've blanked out the three big gears and now the shaft...





In both cases I had to sort of extrapolate what wasn't there.

But, now the fun begins. The last time I had to spline some 4140, I had to make a cutter specifically to do it- HSS just didn't hold up. These teeth are mighty large (comparatively) and that might not be possible- or at least, as easy.

I went and looked at a tool-and-cutter grinder in the hopes I could possibly grind one of the dozen or so spare carbide-faced cutters I got in that big horizontal-cutter stash a while back, but it looks like I'd have to buy a pretty expensive diamond wheel and make my own fixtures to do it.

Neither of which is impossible, of course, but as always, I'm trying to come up with an easier- or perhaps just different- way.

Doc.
I think your HSS might be suffering from a lack of coolant and some small excess of speed, as long as it's just 4140HT and not something you've hardened up special. I cut gears from 4140HT with regular HSS gear cutters and haven't had any real problem with it, but it is something that will point out the difference between a sharp cutter and a slightly dulled one.

It's the spline end that would bother me - got the specs on it? If not is the mating part available? If not it may be a fun time in the shop to make something to fit without something to test against.
Quote
Share

lakc
lakc

June 13th, 2011, 4:18 pm #8

The splines should be made to standard specifications. The standard silver soldered carbide bits can be ground with a green wheel into the proper form tool for cutting. Thats an awfully expensive chunk of 4140 there.
Quote
Share

Austin J
Austin J

June 13th, 2011, 4:49 pm #9

Several weeks ago, I had a guy come by and bring me some big parts. Big broken parts.

He said, "I need one just like it".

Naturally, I replied, "Exactly like it? Why don't you use that one, then?"



Every machine shop, repairman or heavy-equipment guy has heard the old story, where they (or a friend of a friend, etc.) were doing this job off in some distant locale in a foreign land. It was some tough repair of some big old equipment, and during the process, a part is found to be damaged, but no suitable replacement can be found.

So the boss/foreman/machinists mate/etc. takes the part to the local indigenous people's blacksmithy/knifemaker/machine shop. He hands it to the guy at the smithy and says "make me a new one of these". The smith, who has barely a passing knowlege of english nods, smiles, and says "yes, sir. Come back in two day."

The foreman returns in two days to pick up the new part, only to find the smithy was as good as his word- he'd duplicated the part exactly, right down to the stripped threads and wallowed out keyway, including copying the scoring on the shaft precisely.

I've heard one version or another of that tale a hundred times. Sometimes it's the ships' machinist mate who disappears into the engineering spaces to produce an exact copy of a broken mixer part for the galley, other times it's an oil or logging company out in the South American jungles who gets a perfect copy of a winch-drum shaft from the local blacksmith.

But I digress.

Anyway, this fellow brought me the remains of a planetary geartrain that turns the cab of an older excavator. Replacement parts can be had- at a price. That price is high enough we're making new ones, and even after heat-treating, he'll still be thousands ahead.

But, they're big enough and tricky enough that these are "get to them when I can" parts. They're also 4140, meaning HSS tooling doesn't last long.

So far I've blanked out the three big gears and now the shaft...





In both cases I had to sort of extrapolate what wasn't there.

But, now the fun begins. The last time I had to spline some 4140, I had to make a cutter specifically to do it- HSS just didn't hold up. These teeth are mighty large (comparatively) and that might not be possible- or at least, as easy.

I went and looked at a tool-and-cutter grinder in the hopes I could possibly grind one of the dozen or so spare carbide-faced cutters I got in that big horizontal-cutter stash a while back, but it looks like I'd have to buy a pretty expensive diamond wheel and make my own fixtures to do it.

Neither of which is impossible, of course, but as always, I'm trying to come up with an easier- or perhaps just different- way.

Doc.
That new part you made there is mighty shiny...
Quote
Share

Derek
Derek

June 13th, 2011, 8:04 pm #10

That's how the old one once looked.
Quote
Share