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View Full Version : How was this sprocket cut?



Peter.
08-10-2011, 02:05 AM
I saw this yesterday - it's a replacement part for a mixer, about 3" OD. It's not a nicely finished part, not even de-burred but given the application it's probably got a short lifespan anyway.

What caught my eye was the unusual pattern on the teeth. What process would have been used to cause this type of pattern/faceting?

http://peterrimmer.myby.co.uk/images/sprok1.jpg

http://peterrimmer.myby.co.uk/images/sprok2.jpg

wierdscience
08-10-2011, 02:08 AM
Chatter from the Hobb.

Peter.
08-10-2011, 02:11 AM
That's it? Well I guess that clears it up. Have you ever seen such a poorly-finished 'new' part though? I could feel the burrs on every edge as I turned it over in my hand.

precisionmetal
08-10-2011, 02:14 AM
Dull hob, part not held solidly enough, runout in the hob -- a combination of those 3 or maybe more.

yf
08-10-2011, 02:23 AM
Where was it made?

The poor finish and burrs will likely be burnished off by the chain in a short time.

Peter.
08-10-2011, 02:42 AM
No idea who made it. It was on the desk with a length of keystock when I went into the site office at work.

Evan
08-10-2011, 03:18 AM
Time to replace the rats used to gnaw the sprockets. Have you tried applying a centre punch to the part to see from what sort of cheese it is made?

Black_Moons
08-10-2011, 03:25 AM
Time to replace the rats used to gnaw the sprockets. Have you tried applying a centre punch to the part to see from what sort of cheese it is made?

LOL, Made my day evan.

Peter.
08-10-2011, 03:32 AM
It's not my part or anything to do with me - I just spotted it on the desk. I did put it down carefully in case I dropped it and bent it though :)

form_change
08-10-2011, 04:07 AM
I'm going to go one better (worse?) and suggest that the sprocket was not cut on a hob at all.
The teeth (to my eye) look not to be tangential to the rounded part for the chain roller. Given that it's around 3" OD and 15t, it looks as if it would be a 5/8" pitch chain - not common, so I'm going to suggest that it was drilled out and then the teeth cut to match, and those marks are from a small grinder to blend the surfaces together.
As yf says, it will wear soon enough.

Michael

davidwdyer
08-10-2011, 05:48 AM
I'm going to go one better (worse?) and suggest that the sprocket was not cut on a hob at all.
The teeth (to my eye) look not to be tangential to the rounded part for the chain roller. Given that it's around 3" OD and 15t, it looks as if it would be a 5/8" pitch chain - not common, so I'm going to suggest that it was drilled out and then the teeth cut to match, and those marks are from a small grinder to blend the surfaces together.
As yf says, it will wear soon enough.

Michael

I was thinking of making a chains sprocket and that seemed to be the challenging part of the job making the rounded cut "mesh" with the two upper angled cuts on each side of it. Someone with a little die grinder probably did the "meshing."

tdmidget
08-10-2011, 06:07 AM
Crude but workable. I would have done it in a VMC. Drill the gullets and shape the teeth with a mill. And I'd deburr it.

luthor
08-10-2011, 07:03 AM
I don't see any evidence of a grinder being used on the sprocket.

aboard_epsilon
08-10-2011, 07:12 AM
I don't see any evidence of a grinder being used on the sprocket.

looks like dremel work to me ..very small bullet shaped stone

all the best.markj

Forrest Addy
08-10-2011, 07:36 AM
Looks like a fairly typical hobbed finish but maybe near the capacity of the machine, Could be they stacked too many blanks on the work arbor and those in the center didn't get enough support.

Ratty finish or not a chain sprocket sees only rolling from the link bushings so finish doesn;'t matter much. Esthetics? well - that's a personal perspective that may or may not affect the serviceability of the replacement part. Do the part a favor and replace the chain too. New to new is the rule in meshing gear pairs, power transmission chains, and the sprockets they run on..

Rustybolt
08-10-2011, 07:58 AM
It looks like it was milled in a not-too-rigid setup. A lot of places sub out thier common jobs to the lowest bidder.
When we did gear blanks for a company in Addison all the dimentions were + or = .005 except the bore which was + or = .0005.

pgp001
08-10-2011, 08:15 AM
Surely marks left by a blunt hob would pass through the tooth gaps not run round the curve of the tooth space.

It looks to be made by some form of crude milling to me.

Phil

wierdscience
08-10-2011, 08:46 AM
That's it? Well I guess that clears it up. Have you ever seen such a poorly-finished 'new' part though? I could feel the burrs on every edge as I turned it over in my hand.

Yup,some of the Chinese sprockets will draw blood just handling them.They are made in a hurry.They still work well enough,but they could also run them in a vibratory finisher for a few hours first.

sasquatch
08-10-2011, 08:53 AM
Come on you guys!!

Geez, all those grooves are there to keep the grease on the sprocket!!!:D

vpt
08-10-2011, 09:05 AM
I always thought heavy sprockets like that were just die punched out of a sheet of steel?

madwilliamflint
08-10-2011, 09:26 AM
Time to replace the rats used to gnaw the sprockets. Have you tried applying a centre punch to the part to see from what sort of cheese it is made?

Do you have any idea how hard it is to explain what I was laughing at here at work? (In Banking IT?)

:p

wierdscience
08-10-2011, 09:37 AM
I always thought heavy sprockets like that were just die punched out of a sheet of steel?

Nope,sprocket teeth are just like gear teeth,the profile changes with tooth count.

Some large sprockets are CNC flame cut,but they are most often found in papermills and sawmills and run conveyor and green chains.

Forestgnome
08-10-2011, 12:15 PM
Hand ground with a Dremel in a mud hut in India.

JoeFin
08-10-2011, 12:27 PM
Hand ground with a Dremel in a mud hut in India.

LMAO - so true it hurts

Arcane
08-10-2011, 12:39 PM
Surely marks left by a blunt hob would pass through the tooth gaps not run round the curve of the tooth space.

It looks to be made by some form of crude milling to me.

Phil
Apparently there hasn't been enough chat about hobbing in previous threads...

I think you're right about the crude milling. It looks like they used a roughing endmill that was used and abused and well past the time it should have been replaced.

dfw5914
08-10-2011, 12:58 PM
That part has been "Value Engineered".
Do not do anything to the part that does not increase the selling price.

Since purchasing decisions for basic parts such as the example shown are typically based almost entirely on initial purchase price, it only has to be not so bad as to generate a return. Any effort to improve the item beyond the absolute minimum degree of finish required to get the part sold (and not rejected) only lowers the profit. The part shown still has surfaces finished to an unnecessarily high standard (from a value engineering viewpoint).

Juergenwt
08-10-2011, 01:15 PM
Punch press part. Typical roll over and die break pattern. Than they used a shaving die and that produced another roll over and die break. Many, incl. US made products used this method to make large quantities of cheap gears - good enough for what was needed for a certain product.

Forrest Addy
08-10-2011, 04:39 PM
Nope. It wasn't milled. It was cut with a hob having and odd number of gashes. Look at the feed marks and tell me how I know that.

It was hobbed with plenty of feed, 0.090"/rev isn't uncommon in production stock gears and sprockets and heavy feeds aren't detremental to the product performance. It's may be a little unsightly but in a cement mixer that sprocket will work pretty well so long as a good chain meshes tightly.

Inadequate de-burring? What you aint got a file? I never ever bought a stock gear I didn't have to de-burr and detail. They make them by the zillions and since gears cannot be successfully tumbled and hand de-burring is so time consuming ad since stock gears are so competetive, it falls to the user to perform the seller's job. It aint right but like tobacco long tolerance of an evil practice has led to loathing acceptance and abuses.

John Stevenson
08-10-2011, 04:49 PM
Ditto on the hobbing.
Many of these cheap sprockets come from India and are made from reclaimed plates off the boats they break up.The problem with this ones is it shouldered so one sprocket isn't supporting it's mate.

Add a high feed rate and probably a dull hob and this is a classic cutting pattern.

I got a large one a while ago and had to take the boss off it, turns out the boss was a separate piece weld on and when I realised this I turned the radiused weld shoulder off, then the boss let go the inside of the sprocket and plate were badly pitted with rust, scabs going into the metal over 1/8" and then it was just skimmed up afterwards.

Most sprockets are low speed high horsepower drives and lets face it a chain isn't exactly rocket science. Peter's example looks rough and is rough but it more than capable of doing what it's made to do - probably off a Hardly Dangerous...........

davidwdyer
08-10-2011, 07:34 PM
Hand ground with a Dremel in a mud hut in India.

Just a note. I read recently that there are over 600,000,000 (six hundred million) people in India who do not have electricity.

That must mess with productivity. And that's why they cut these sprockets with their teeth, or train some rodents to do it.

Black_Moons
08-10-2011, 08:26 PM
Just a note. I read recently that there are over 600,000,000 (six hundred million) people in India who do not have electricity.

That must mess with productivity. And that's why they cut these sprockets with their teeth, or train some rodents to do it.

For only 24 cents a day, you too can support an indian family by paying for thier teeth sharpenings. Don't let them continue to make poorly made sprockets and harm your loved ones.

darryl
08-10-2011, 09:29 PM
Yeah, I'd say it was hobbed with a dull hob, then hand-ground to remove the burn marks. They probably didn't even use a dremel- one guy cranks the flex shaft and the other guy manipulates the handpiece. Takes a week and an ounce of hash to get through one.

Black_Moons
08-10-2011, 09:32 PM
Yeah, I'd say it was hobbed with a dull hob, then hand-ground to remove the burn marks. They probably didn't even use a dremel- one guy cranks the flex shaft and the other guy manipulates the handpiece. Takes a week and an ounce of hash to get through one.

Nah, Air tool... Connected to the hash pipe.

Scottike
08-10-2011, 09:43 PM
Naw,... No Hash here.. air freighted from china along with a hundred thousand Rong Fu's