Old school large gear making video

[Bill D]

I was surprised they did no rough casting of the teeth. Most cutting was done wit the tool upside down. I suppose it helps clear the chips faster.
Bill D

 

[dalmatiangirl61]

That T-lathe was cobbled together from god knows what, the base for the compound is concrete? and bricks.

 

[EmGo]

It's not "old school" it's just crappy junk. And there's no upside-down cutting, they just put the camera on the bottom of the blank. Would have been nicer if the hob wasn't missing half its teeth, too.

 

[john.k]

Yeah ,but at least some of them had shoes .....and safety glasses too.....although cast iron chips do go everywhere......its called getn -R- dun

 

[dana gear]

Probably old Indian rail ways gear hob. If you watch closely the hob stalls out monetary during the cut, probably how the teeth got knocked off in the first place.
My hats off to these guys, wires and bent dividers are as close to precision measurement as thay come. hopefully the gear is going to turn very slow as the noise of the gear mesh running deep on one side and shallow on the other will drive anyone nuts.

 

[EmGo]

hopefully the gear is going to turn very slow as the noise of the gear mesh running deep on one side and shallow on the other will drive anyone nuts.

Doesnt work that way. The teeth will be the same on both sides, just the feedrate will be higher in the areas where the hob is missing teeth.

 

[john.k]

I think the comment is related to centreing the gear with a wonky caliper.......id say the gear is for either a jute mill or a sugar mill ..........gears that size run happily with a meshing difference of 1 - 2mm,so the caliper would be quite sufficient............when I was kid,the local brickworks had brick presses with large gears,some had broken teeth,and the local kids would play chicken putting fingers into the broken tooth space as the machine was running..........the really smart kids (me) would put a finger into the meshing gear tooth space ,and as the gear came round,there was no injury to the finger ........if you miscalculated ,then you got a flattened finger...it was a great place for budding engineers ,there was only one stoker on duty of a weekend ,and you could do all kinds of stuff with the machinery and the furnaces ......I loved stoking coal into the furnaces ...love the smell of coal smoke and the hot clay in the white heat inside the kilns.

 

[dana gear]

Sure it will, the center of its driven gear to center of the drive gear cannot possibly be correct, as crudely as their center of the hub to center pitch line was machined, (think out of round in relation to the center hub) as it ramps through the center pitch line changing depth. Depending upon what it's driving there could be all kinds of interesting noise.

 

[Vecair]

I was surprised they did no rough casting of the teeth. Most cutting was done wit the tool upside down. I suppose it helps clear the chips faster.
Bill D

Thanks for posting Bill D, a new 'can do' channel to watch and learn how it was done back in the day, but its today! Cheers mate!

 

[EmGo]

Sure it will, the center of its driven gear to center of the drive gear cannot possibly be correct, as crudely as their center of the hub to center pitch line was machined, (think out of round in relation to the center hub) as it ramps through the center pitch line changing depth. Depending upon what it's driving there could be all kinds of interesting noise.

Nope. That's a function of involute curves and the way hobs generate the shape. That part was 3' in diameter or so, even using a sharp stick to center it you can come within five thou-ish, it'll probably sound a bit like a freighter in a following sea but won't be bad at all. Thats one nice thing about hobbing, you can do a shit job and it'll still turn out pretty good.

 

[dana gear]

Nope. That's a function of involute curves and the way hobs generate the shape. That part was 3' in diameter or so, even using a sharp stick to center it you can come within five thou-ish, it'll probably sound a bit like a freighter in a following sea but won't be bad at all. Thats one nice thing about hobbing, you can do a shit job and it'll still turn out pretty good

 

[dana gear]

it's still out of round. But what do I know, we have only been manufacturing large gears since 1921, for those that use a sharp stick to measure that's over 100 years of gear cutting.

 

[john.k]

The casting is quite primitive..very rough....certainly not bearing comparison with what was done in England two hundred years ago.......the British iron masters were able to cast gear teeth that were servicable from the mould......typically traction engines had as cast teeth on the big gears ,with cut teeth on the smaller gears ......this generally allowed "flanged" teeth,where one side of the gear tooth was reinforced by the casting.............traction engine gears were "run in" by application of very fine sand into the gear train as it was running.

 

[john.k]

The "upside down" refers to the master machinist turning the rough casting to size (using a tape measure!)......IMHO ,the cutting is on the lower edge of the tool to direct the hot cast chips down to the floor........topside cutting would result in a snowstorm of cast iron chips all over machine and turner.

 

[EmGo]

it's still out of round.

No, being mounted and indicated that way makes it eccentric, not out of round.

If the blank WERE out of round, it would 't matter. The teeth would still be round, centered on wherever the blank was centered when mounted.

Due to properties of the involute curve and the way hobs generate the shape, that part will mesh fine with its pinion. These are not cycloidal teeth that are really sensitive to center distance variation.

But what do I know, we have only been manufacturing large gears since 1921, for those that use a sharp stick to measure that's over 100 years of gear cutting.

That makes you even older than me. Maybe the alzheimers attacked your understanding of basic theory.

For what it is, that part will be fine and it probably wont perform much worse than something cut with a class A hob on an L1800. The teeth are probably the best part of that ugly thing.

 

[ratbldr427]

Doesn't matter if it 's out of round or eccentric the sfpm at the tooth is slower at the root than at the crest , a simple matter of the radius from center of rotation. As long as both gears run true no matter where they mesh the velocity of the driven gear will be constant through a revolution. However if one gear runs eccentric it will cause the other to speed up and slow down each rev. The sfpm changes with the radial contact patch as it moves in and out of the gear, the pd moves in and out, not to be confused with the normal meshing where the involute gives a constant velocity as long as the pd doesn't change.

An exaggerated example is a feed gear on one of our earlier presses that has an 8" or so driven gear that has the shaft hole about 1" off set . It is used to speed up and slow down the feed belts in the feeder. Without seeing the whole mechanisim it would seem impossible.
How it works is it has an identical plastic idler gear that runs true but is straddle mounted in a sizzor linkage that is connected to both the driver and driven and moves in and out to compensate for the difference in the eccentric gear radius as it turns. It runs fastest on the short side and almost comes to a complete stop as it passes the apexs. The difference is the pitch line doesn't change on any of the gears just the pitch radius.

It is simple to prove, mesh two gears loosly and lock one,move the other one in deeper in a straight line, according to you there should be no rotation on the loose gear. The same thing happens when the eccentric driven gear moves in and out of mesh with the driver when they are moving. The ratio doesn't change,cant, just the periodioc velocity.

 

[dana gear]

No, being mounted and indicated that way makes it eccentric, not out of round.

If the blank WERE out of round, it would 't matter. The teeth would still be round, centered on wherever the blank was centered when mounted.

Due to properties of the involute curve and the way hobs generate the shape, that part will mesh fine with its pinion. These are not cycloidal teeth that are really sensitive to center distance variation.



That makes you even older than me. Maybe the alzheimers attacked your understanding of basic theory.

For what it is, that part will be fine and it probably wont perform much worse than something cut with a class A hob on an L1800. The teeth are probably the best part of that ugly thing.

Your right to a degree, the gear would be centered to the the hub of the hob machine, All I said is will be out of round, and I still do as the gear blank being finished bored and then the hap hazard attempt to center the gear blank to the hob drive will most certainly be out of round. Did you go back and look how it was centered on the hob drive? the hub will cut deeper on one side then it will on the other. Anyway, Will it make a big difference probably not, WHAT I did say is depending on the driven load and speed it very well make noise, more so if it reverses. Probably O.K. in your world certainly not in ours.( think returned defective work)
Backlash between a pair of gears will vary as successive tooth contact due to the effect of composite tooth errors, particularly runout and errors in the gear CENTER distance. Errors in boring the gear housing both in CENTER distance and alinement are of extreme importance in determining correct back lash.
And yes it is somewhat common in bevel gearing as well as Spur/Helical gearing when engineering permits to make slight changes between shaft centers to compensate for less then perfect manufacturing. I could go on forever about correct gear manufacturing, but what's the point, everyone is allowed there view here and I understand that, it's great to share different opinions , And yes maybe I should meet with my employees and part owner wife and see if my apparent Alzheimer's is affecting our multi million dollar a year business.

 

[Bill D]

Why did they not use a tapered washer to center the gear onto the hobber spindle. I was suprised to see the guy wipe each washer clean of chips/gunk before final placement.
It looks like the inner bore and outside rim were machined on one machine in one setup so they should be concetric?
Bill D

 

[EmGo]

Your right to a degree

No, I'm right entirely

The cutter spindle is square to the part center of rotation (tangent to that circle, actually) because thats how the machine is built, you can't screw that up. Both sides of the hob teeth will cut equally. It's a pretty shitty machine and a pretty shitty blank for a variety of reasons but it won't be any worse running forwards or backwards. You can get it plenty concentric for the purpose with a pointer and the eccentricity on that size part, doing what it does, will be fine.

This isn't "old school", it's just shitty clapped-out equipment but the process itself is pretty tolerant.

We were doing 3 meter AGMA 10 slewing bearings in 2 hours on gashers, one of our recent sales was two 5 meter Hofler Porta grinders, do you need charts ? I think I understand the basics.

This is nothing to ooh and ah over but it's not total shit either. The part will work as intended and won't be that much worse in slowspeed service than something done by Rush Gear. Those spindly long-ass spokes and the cheezy flange thickness and the low quality material already limit it a lot more than the teeth. In fact, the teeth are the best part.

Northern California, "we have only been manufacturing large gears since 1921" hmmm. Not Renstrom, they went tits-up. Not Custom, Bob started that when he left Renstrom. Not APG, they only do smallish stuff. Not Harbold, Steve kicked the bucket. Not Borg, he's a nice guy. Not me, I'm pretty sure. Not Leo Wickham, he's not that old. Not Howard Boom, he's also gone. Where you been hiding all these years ?

 

[johansen]

Doesn't matter if it 's out of round or eccentric the sfpm at the tooth is slower at the root than at the crest , a simple matter of the radius from center of rotation. As long as both gears run true no matter where they mesh the velocity of the driven gear will be constant through a revolution. However if one gear runs eccentric it will cause the other to speed up and slow down each rev. The sfpm changes with the radial contact patch as it moves in and out of the gear, the pd moves in and out, not to be confused with the normal meshing where the involute gives a constant velocity as long as the pd doesn't change.

An exaggerated example is a feed gear on one of our earlier presses that has an 8" or so driven gear that has the shaft hole about 1" off set . It is used to speed up and slow down the feed belts in the feeder. Without seeing the whole mechanisim it would seem impossible.
How it works is it has an identical plastic idler gear that runs true but is straddle mounted in a sizzor linkage that is connected to both the driver and driven and moves in and out to compensate for the difference in the eccentric gear radius as it turns. It runs fastest on the short side and almost comes to a complete stop as it passes the apexs. The difference is the pitch line doesn't change on any of the gears just the pitch radius.

It is simple to prove, mesh two gears loosly and lock one,move the other one in deeper in a straight line, according to you there should be no rotation on the loose gear. The same thing happens when the eccentric driven gear moves in and out of mesh with the driver when they are moving. The ratio doesn't change,cant, just the periodioc velocity.

Similar mechanism was used on the antekithra mechanism to generate the 19 year cycle regarding the eccentricity of the moon and earth vs the sun.