Measuring a chain sprocket

[Tony Wells]

Here is a decent discussion of the problem. It's a bit lengthy, but comprehensive:

http://www.heinrichbrothers.com/store.asp?pid=28589

 

[Tony Wells]

As far as the actual chain pitch, the tips of the teeth are the same spacing as the center of the roller grooves. If you took a couple of dowel pins the size of the rollers, you could measure over a pair of them in adjacent grooves and establish the chain pitch. Since the links, when viewed individually are held in a straight, static distance by the side plates, subtracting one diameter from the "over the pins" dimension would yield the chain pitch. Their are only a few standards, so even an estimate with a pair of dial calipers compared to a chart would get you the chain ID.

Am I correct that the chain pitch (or chain #) is what you are needing? Oh, and yes, the roller pretty well seats in the bottom of the groove, until the pull side of the groove begins to wear, and then it has a tendency to climb up, and eventually out of the groove.

 

[Tony Wells]

According to ANSI, it appears to be a #25 chain, assuming the other dimensions are correct:

Chain number Pitch Roller Diameter Roller Width Sprocket Thickness Working load
25 1/4" 0.130 1/8" 0.110" 140 lbs

 

[Tony Wells]

It is difficult without a scale to get a feel for what condition that sprocket is in, but it looks to be a bit worn. Since you need to buy the chain and other sprocket, you might want to consider replacing that one as well. The can be bought as blanks to be bored, keyed, or set screwed as needed. If that sprocket is worn, it will be hard on the new chain and sprocket.

 

[Tony Wells]

Well, that causes me to question the #25 chain. 1/4" pitch chain isn't all that large. If you confirm the other dimensions, fine, but just by appearance, those holes make it look more like #41. You may need to take it to the power transmission supply to match up. Most here would be glad to fetch a bit of chain to lay in it and match it up. If you are planning on ordering from McMaster-Carr or someone like that, we need to be more sure.

Peak to peak what do you measure with calipers?

 

[Tony Wells]

Oh, that changes considerably. More in line with the scale of the holes.I didn't realize you were dealing in radius. That won't be a #25 chain then. I thought it sounded a little small and light.

Check out http://www.gizmology.net/sprockets.htm for the dimensions for other chains.

Best go fully armed with information if that's the sort of supply house you have.

 

[4R8]

G'day guys.

Simple chain measuring method on an unknown sprocket is with a straight edge. I've used it successfully a few times.

Being that the points of the sprocket point away from each other you cannot get an accurate measurement from them.
BUT, by placing a straight edge at the base between two grooves and measuring the distance will give you an accurate pitch.
The deepest point is always going to be perpendicular to the pin on the chain.

Not sure if that makes a whole lot of sense.
I'll do a quick drawing

 

[4R8]

Here we go.

I've quickly added over the top of a sprocket design I had done a while back.

It's a 40 tooth but still shows the method. On a smaller sprocket, the angles are exaggerated more and this is where this method comes in handy.

The Blue section represents the use of a straight edge.

The green shows where the pins would be.
The Yellow shows the pitch distance.
The green and yellow are purely for representation to show the pins would be perpendicular to the deepest part when a straight edge is used in this fashion and NOT the deepest part towards the centre or between the points.

 

[4R8]

Roughed out another but with a smaller sprocket

 

[Tony Wells]

That is correct. Everything should be measured as though "over the pins". That's why I earlier suggested a couple of dowels to represent the rollers, then measure over them and subtract one diameter. You want C-C between the rollers, as that is the chain pitch.