making sprockets for chain drive

[Sam Longley 1Participant @samlongley1]

I want to avoid buying pre made sprockets for the drive on my PYRTE traction engine & would like to have a go at cutting them myself from 3mm plate. the chain sold by Reeves is 8.3mm gauge but I can obtain 8mm fairly cheaply so could go with that.I need 2 sets to give me 4:1 twice , thus 16:1 approx but not critical I am told

Then i thought about cutting the teeth. I started looking for a cutter & sprocket cutters can cost hundreds of £'s & I cannot see anything in model shop sites. I may be missing some thing

Then it suddenly occurred to me that chain rollers are round so the tooth cuttout should possibly be a semicircle & do not actually mesh with another gear. So what if I drilled loads of holes of the correct diameter at the correct radius & at the 8mm pitch of the chain then milled the excess metal away

Would that leave me with a working sprocket?The teeth would need little points on the end where the rollers drop off  for clearance & there must be a way to file/mill those off or just cut the teeth a bit short to reduce the engagement.Or even go round again drilling overlapping  holes with a bigger drill/mill at a wider radius & catch the teeth ends to form the points. Not really correct but would get me to a position where I could touch up with a file

Or am i talking rubbish. If so what is the correct way to go about it please- if it does not involve too much explanation that is !!! & if it is the way to do it are there any tips? I do have access to a CAD programme so could set it out first— if I can remember how to use autocad after years of retirement

Thanks

Sam Longley

Edited By Sam Longley 1 on 07/11/2016 11:57:46

[Sam Longley 1Participant @samlongley1]

[HopperParticipant @hopper]

Your theory would hold good if the chain and sprockets did not move. Unfortunately they do. The chain in a linear then circular path and the sprocket purely  circular. The design of sprocket teeth is about as complex as that for gear teeth. The root of the space between two teeth is as you suggest, a semicircle about equal to the roller diamter, but the tops of the teeth need to be clearanced so they roll smoothly into and out of contact with the chain as it arrives and departs on a linear path,, while the sprocket moves in a circular path.

See details here: **LINK**

That said, for your low-power, low rev application, you could probably make a suitable cutter using close-enough dimensions, eg bottom radius, angled straight sides and pointed tops. An alternative might be to look at using a standard size chain from a small motorbike or mini bike and readily avialable and cheap sprockets. Or bicycle chain and sprockets, available at any tip recycle shop by the bootload for a few pence a piece.  Is there a need to re-invent the chainwheel?

Edited By Hopper on 07/11/2016 12:08:11

Edited By Hopper on 07/11/2016 12:10:30

[John Stevenson 1Participant @johnstevenson1]

Take a look at this program.

Sprocketeer

[Sam Longley 1Participant @samlongley1]

Ok thanks for that. It is cleary a complicated and complex subject. Any tips on where to get cheap cutters please or does one not buy them like standard gear cutters?

Edited By Sam Longley 1 on 07/11/2016 13:12:35

[Martin ConnellyParticipant @martinconnelly55370]

You have not stated what machinery you have but the implication is that you could cut the basic roller diameter semi-circles in a plate. Maybe with what you have you could get a full size printout from Sprocketeer as suggested by John and stick it on your plate. You would then be able to either mill off a lot of the excess material and finish with a file or just use a file alone to shape the sprocket (depends on the size and number of teeth as to whether this is appealing or not.

Martin

[Douglas JohnstonParticipant @douglasjohnston98463]

Just a thought, would any bicycle sprockets fit the bill or are they the wrong size.

Doug

[Chris Evans 6Participant @chrisevans6]

I made the rear sprocket for my pre war motorcycle and very pleased with the results. However it is one of those never again jobs, to long on the mill/rotary table and calculator as they are not an easy thing to make. I now buy cheap sprocket blanks from a commercial power transmission/belt supplier and modify to suit. Most come with a centre hole read to open up.

[duncan webster 1Participant @duncanwebster1]

I have made sprockets by co-ordinate drilling the holes, then filing the tooth profiles using a link from the chain as a gauge so that the chain will roll smoothly on and off the sprocket. It takes a very long time. As you are presumably not making the chain, I'd just buy the sprockets, especially if as others have suggested you can use bicycle cogs. The last sprocket I wanted I got cut by a local gear cutting firm for not a lot of money

[John Stevenson 1Participant @johnstevenson1]

Is it worth it ?

From 60p upwards depending on size.

Beltingonline

[Sam Longley 1Participant @samlongley1]

I do have a milling machine plus dividing head& tailstock etc so I could soon sort out a gear cutting set up. I thought such a project would be a good starter for learning the process as they do not have to mesh with other gears. Being only 3mm th steel they should be easy to cut. But now you are all putting me off.

I had considered bicycle sprockets & I know I can buy the correct gear sets from Reeves, but that is not the point of the hobby. & any way I want to know how so i will buy some chain, set up some drawings & have a play.

(Then I will buy the bits from Reeves !!!!)

[Gordon WParticipant @gordonw]

I too have made chain sprockets in the past. Steel plate, dividers ,steel rule, center punch, hammer, hacksaw, file, and wolf drill. Long job, hard work, but they did work. These were for m/bikes, used on the grass and sand. Chains did not last long, but they didn't using bought sprockets.

[Bob RodgersonParticipant @bobrodgerson97362]

I bought a couple of sprocket cutters from Tracey Tools a good few years ago. At that time they had common sizes used on British motorcycles.

[John HaineParticipant @johnhaine32865]

If you hunt around on Google you should find details of making sprockets for bikes, I recall seeing some quite detailed how-to articles. Possibly associated with the name Sheldon Brown who is a US bike guru. IIRC these are made with fairly simple tooling, but the makers are aiming at good performance (which is the whole idea).

[Sam Longley 1Participant @samlongley1]

Posted by John Stevenson on 07/11/2016 15:44:37:

Is it worth it ?

From 60p upwards depending on size.

Beltingonline

Thank you John

items ordered

But i am still going to make some to prove I can. I used to profile grind my cutters for my moulding machines & once I have drilled the root of the sprocket I reckon I can rig a simple profile unit on the grinder & grind the tips. Profile grinders can be really complicated but they can also be very simple & I have the grinding wheels already.

Just needs a few arms on the grinder plus a follower & a pattern against a pin that matches the grinding wheel profile

[Chris Evans 6Participant @chrisevans6]

Sam, glad to hear you are going to persevere. I enjoyed making my sprocket to prove to myself that I could but as said before I felt it just took to long working out the pitches was easy enough. Shifting either side for the ramp angles was fiddly.

[HopperParticipant @hopper]

Ah well, if you have a mill and a dividing head, you should be able to use an end mill cutter that is 2 X R in the drawing posted above and traverse it in a straight line to cut one side of each tooth. Then flip the sprocket over and use the same setting and traverse to cut the other side of the teeth. Then all you ahve to do is put the little point on top of each tooth, which could be filed at a pinch, or cut with the same end mill cutter with the sprocket set at the appropriate angle, again flipping the sprcket over to use the same set up to do the other side of the teeth.

[Ian S CParticipant @iansc]

I have made sprockets by drilling holes and filing the tip profiles, the sprockets on the power feed on my mill are made that way. In a larger size, we have used sprockets profile cut (oxy acetylene), cleaned up with an angle grinder, I think the chain sizes were 30 mm x 15 mm, and 2" x 3/4", run at low speed, The large ones on the bed of a machine for feeding 3ft x 4ft large sqare hay bales to stock. The smaller chain drives the drum that distributes the hay. 60 plus machines built, very little problems mechanically, a few more with the opperators. Ian S C

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