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View Full Version : How are large sprockets for #25 chain manufactured?



doorknob
03-04-2014, 09:12 PM
I was wondering how sprockets like this one are manufactured:

http://www.monsterscooterparts.com/25chsp55to.html

I have examined one such sprocket closely. I was wondering whether it may perhaps have been cut out and had holes punched on a CNC plasma cutter, and then finished through grinding of the teeth (on one face only?) and other operations (because I saw what I interpreted to be scorch marks on the periphery of one of the bolt holes). But I suppose that other fabrication methods could have been used as well.

The sprocket appears to have been made out of steel. It is attracted by a magnet. But it seems to have some sort of plating on it.

I'm also wondering what kind of finishing operation may have made the thin concentric circles visible in the photograph on the linked page above. Perhaps some kind of wire brush to clean up the edges of plasma-cut holes?

Do ordinary mortals actually ever fabricate such things (in a home shop, for example), or are they made on fully-automated big-company production lines, or something in-between?

kf2qd
03-04-2014, 09:48 PM
Probably with some sort of hob. A stack of them cut all at one time.

Don Young
03-04-2014, 09:49 PM
Cutters similar to gear cutters are made to cut roller chain sprockets. I would think that production cutting would be done with hobs but I am not sure of that. A friend made a replacement timing chain sprocket for a small Honda motorcycle by laying out and drilling holes in the blank. He then cut the diameter down and finished the teeth with a file. Worked well.

Richard King
03-04-2014, 10:34 PM
Yep and Gear hob like a horizontal Barber Colemen https://www.youtube.com/watch?v=ahoXEEbF-ZA
or a vertical Liebherr , https://www.youtube.com/watch?v=F_4f44ASc_w

Pretty amazing how they cut sprockets and gears.....Look for a Gleason Spiral Bevel Gear Generator sometime..that's pretty cool too

"timing is everything"

Rich

EddyCurr
03-04-2014, 11:24 PM
The sprocket appears to have been made out of steel. It is attracted
by a magnet. But it seems to have some sort of plating on it.Perhaps that finish is a silver zinc wash, similar to what is used on some
vehicle brake rotors to inhibit corrosion.


I'm also wondering what kind of finishing operation may have
made the thin concentric circles visible in the photograph on the linked page above.
Perhaps some kind of wire brush to clean up the edges of plasma-cut holes?

If you mean the radial marks that are concentric with the axis of the gear,
another thought is that those indentations may be from stamping the gear
blank. Either during primary forming of the gear blank or perhaps as a post
process to ensure flatness of the finished product.


Do ordinary mortals actually ever fabricate such things ...Earlier posts give examples of HSM methods to make gears. However, note the
price of $9 for the gear in your link. No one makes their own for anything
like this kind of money.

Edit: On reflection, those radial marks are not from stamping.

.

Boucher
03-04-2014, 11:35 PM
Along time ago I took a tour of a factory that made large sprockets where they used a flame nitriding process to case harden the teeth.

darryl
03-05-2014, 02:50 AM
I've made a few of my own sprockets. One method starts with making a loop of chain, the same chain that will be used on the sprocket. The loop has the same number of links as the number of teeth you want on the sprocket. Then a pivot point is mounted on the mill table, and an mdf blank is drilled to fit the pivot point. By turning the disc under a milling cutter, an OD is created which will just allow the loop of chain to snugly fit onto it. A temporary setup is made on the mill table which will act as an indexing pin, nesting into the gaps in the loop of chain. Now you have an indexable disc.

A drill bit is set up and the table moved such that the drill bit is in alignment with one of the pins in the chain loop, and the axis are locked. Now you mount a sprocket blank onto this indexable disc, and you drill a hole for each index position around the loop. You also mill a central hole and whatever mounting holes you will need before dismounting the blank. All features that need to be concentric with the tooth circle are dealt with at this time. The diameter of the holes in the circle are drilled to the diameter of the chain rollers.

That's the basic setup for creating the gullets which the chain will roll into smoothly. I bandsawed into the holes to remove all unwanted material on the OD and leave a slightly oversize tooth which could then be milled to shape on both sides to suit the chain entering and leaving the individual teeth. I came up with a linkage which would move the indexing pin as the x axis was cranked, and this allowed me to form the teeth to a pretty close profile.

dp
03-05-2014, 02:51 AM
Pretty much any shaper can make them 6" or longer using a form cutter. Next op is to turn some relief into the "spline" that will become the sprocket teeth, part them off, bore them as needed, and heat treat the teeth. Shouldn't take more than a couple weeks if you don't stop at 1 or two :)

macona
03-05-2014, 03:39 AM
Cheap ones are stamped out of plate. I mean real cheap ones.

Peter S
03-05-2014, 04:42 AM
Here is a drawing showing a sprocket tooth form, it gives some idea why they are hobbed. Having said that...we have an injection mould to make a small 1/2" pitch sprocket in nylon. We also get some gears laser-cut from 5mm plate, but they used for the hand-cranked height adjustment of a welded frame, accuracy not critical.

http://img.photobucket.com/albums/1003/PeterS/th_Sprockettoothform-red_zps7288f087.jpg (http://smg.photobucket.com/user/PeterS/media/Sprockettoothform-red_zps7288f087.jpg.html)

John Stevenson
03-05-2014, 04:52 AM
The one in the OP post is what is known as a plate sprocket. These are hobbed in a stack on a mandrel and if you buy a stack you can often line up the machining marks so they show the typical slow hobbing spiral as the cutter moves thru.

I don't know if anyone makes sprockets any more unless they are special because plate sprockets like the one shown are for peanuts in blank form.

I have the facility to CNC the teeth out but unless its weird like a very low count tooth modified for conveyor drives it's not worth it.

sawlog
03-05-2014, 05:34 AM
I would guess the pars are hobbed like most posters have stated, and probally stacked 4 to 5 high when hobbed. the blankis look to be turned out of a piece of bar stock perhaps on a large bar feed machine, I know one thing they used some high feed rates across the face of the blank, it looks like the parts were feed at least .025 per rev.

SGW
03-05-2014, 06:38 AM
As Don Young said, they do make cutters like gear cutters to cut sprockets. I picked one up someplace years ago in a box of $5/pound tooling. Commercially, I'm sure they are hobbed, just as gears are.

vpt
03-05-2014, 07:39 AM
They keep telling me I can cut sprockets on the plasma table.

Willy
03-05-2014, 09:16 AM
The one in the OP post is what is known as a plate sprocket. These are hobbed in a stack on a mandrel and if you buy a stack you can often line up the machining marks so they show the typical slow hobbing spiral as the cutter moves thru.

.........................................

Like this.
https://www.youtube.com/watch?v=C2XU4JeHnGw

Secondary operations like final tooth profiling and hole/spline punching are done on other machines. Modern factories have the capacity to produce these in the millions annually hence the low cost.

doorknob
03-05-2014, 10:58 AM
Wow, what a wealth of information.

Thanks for all of the comments. There is more to it than I originally thought.

I first started looking into sprockets as a way of directly driving the wheels of an autonomous robot platform that a friend and I are building (and we may want to consider making a kit available for others, if things work out OK).

The available ones that we've found (like the one that I linked to in the OP) either do not have the proper bolt hole pattern that we'd like to use, or else the diameter of the central hole is too large for our purposes.

We had looked into what it would take to get a couple of custom ones made, but they were fairly expensive - and thus would not be suitable if we were ever to attempt to have them made in volume. The volumes that we are contemplating (I dunno - maybe 500, maybe 1K or 2K?) are probably too large to DIY, but likely too small to have fabbed for us at a reasonable price (but then we have not actually talked to anyone about doing volume mfg, since right now we don't have any funds).

Just understanding how the things are manufactured is quite helpful.

Of course, we will probably eventually decide that an even better way to go would be to fabricate our own gear reduction drives (because the available ones that we see attached as part of gear motors are uncomfortably expensive), but maybe that will be a post for some future time.

EddyCurr
03-05-2014, 12:13 PM
The available ones that we've found (like the one
that I linked to in the OP) either do not have the proper
bolt hole pattern that we'd like to use, or else the diameter
of the central hole is too large for our purposes.Some thoughts come to mind.

What access is there to machinery and skill to operate?
.
An autonomous robot of modest size and purpose might
get by with aluminum instead of steel sprockets. Al can be
less demanding to machine than steel.
.
Although sprockets are relatively complex to make, adapters
can be relatively simple.
.
It might be feasible to drive through the central sprocket
hole without needing to utilize the bolt holes of a purchased
part.

A single keyway would be easy to add to the ID of an existing
sprocket. Splines would be possible, but more of a challenge
and less economic. OTOH, if gears from bicycle applications
would work, these have tabs/splines that could engage matching
features on an adapter.

Lateral thinking.

.

tylernt
03-05-2014, 12:34 PM
"Performance upgrade" sprockets for motorcycle drive chains are often made out of a high-end aluminum like 7075. Many of those sportbikes put down over 100HP and the aluminum seems to hold up fine (although, I'm not sure how many miles they last!).

Boostinjdm
03-05-2014, 03:43 PM
On another forum, guys were having sprockets with custom designs and bolt holes laser cut. They seemed to be reasonably priced (for custom work) and pretty durable. Most of the time, I find it easiest to buy a toothed blank and drill/bore my own bolt holes and center hole.

Wheels17
03-05-2014, 04:09 PM
I don't know what size chain you are using, but there is a system called Weldasprocket for custom sprocket/hub combinations. You match sprockets with standard holes to hubs to make custom sprocket/hub combinations. I think it is mostly farm size stuff. Wholesale tools carries them at this link: http://tool.wttool.com/tools/Weldasprocket A 12 tooth size 40 sprocket is $4.05, and a 48 tooth is $15.99. Teeth are hardened, but you weld the hubs, so I would assume that you could put a custom hole pattern in the sprocket away from the teeth. Hubs are less than $5. They do Weldapulleys as well. Hmm, maybe there's a way to make a step pulley.....

Didn't pay close enough attention to the title.....

doorknob
03-05-2014, 06:45 PM
Some thoughts come to mind.

What access is there to machinery and skill to operate?
.
An autonomous robot of modest size and purpose might
get by with aluminum instead of steel sprockets. Al can be
less demanding to machine than steel.
.
Although sprockets are relatively complex to make, adapters
can be relatively simple.
.
It might be feasible to drive through the central sprocket
hole without needing to utilize the bolt holes of a purchased
part.

A single keyway would be easy to add to the ID of an existing
sprocket. Splines would be possible, but more of a challenge
and less economic. OTOH, if gears from bicycle applications
would work, these have tabs/splines that could engage matching
features on an adapter.

Lateral thinking.

.

Lateral thinking is always appreciated.

My skill and machinery are both somewhat lacking - sure, I can hack together hobby stuff, but I'm not sure that I'd be up to production quality.

Aluminum might be possible - we'd have to do some testing, but it might simplify things.

JoeLee
03-05-2014, 06:53 PM
They keep telling me I can cut sprockets on the plasma table.You can but they would need finishing.

JL.............

boslab
03-05-2014, 07:15 PM
I have heard that you can water jet cut them quite well, i dint have a clue if thats true as my knowledge of water jet cutting is limited to one experiment to see if tensile test specimens of 19mm plate was feasible, it was and in truth they were reasonably accurate, the guy at the water jet company said he had made sprockets for racing bicycles out of titanium, i didn't see one but had no reason to doubt him.
Something to explore anyway, laser cutting should work too, maybe the HAZ on a higher carbon plate would provide some surface hardness?
Mark

darryl
03-05-2014, 09:05 PM
Mine have all been done in aluminum- so far most are in low speed, low use applications, such as in synchronizing two threaded rods with a chain loop. Not even sure what alloys I used- some were 6061 that I know of, one large one was from sheet aluminum which was hard enough that it didn't like being bent, but machined well. Could have been 6061-