Machining spur sprocket to accept rim

[srcarr52]

If you can find a clutch drum with the correct OD and the spline you want an insert could be made and brazed into the ID of the bearing surface that has the double flats for the drive.

 

[Nutball]

Might even figure a way to pin something in place and peen the pins in place.

 

[Ketchup]

The 2500 oiler design eliminates the need for the sprocket to drive the oiler, so it’s simpler than modifying a 2511 sprocket.

We need a 2500 drum…for science.

Edit:
Anybody got a guess what the original drum is brazed with?

 

[Ketchup]

https://www.amickssuperstore.com/Echo_1_4_Sprocket_CS_2511T_p/ami001710.htm

Out of stock BTW

 

[vrex]

My original intent with this query was to be able to run husqy sp21g, a .325 nano chain, seems to split 3/8 .043 and 1/4p .050 and I’ve run it on our shop saw and like it plenty. Today after work I checked what the t540ixp uses for a setup and found it has a replaceable spur and no clutch drum. It uses an electronic brake I suppose. The echo 2500t uses a clutch drum/spur because it had a mechanical brake (brake band from chain brake applied to the drum). Probably less good for an electric motor with no clutch or slip but then, why would you go slamming on the brake? Anyways, lo and behold, something of a solution towards my goal, but not an actual rim drive solution. The husqy sprim (r)(c)(tm) has two flats. It doesn’t fit perfect in the pto of the 2500t, it’s a couple thou too tight, but I expect that could be cleaned up easily enough. So then, that thing brazed to a 2500t drum that has had the original spur removed somehow would net me the result I'm looking for? But I don’t know how to braze at that level or if it’s feasible. If I can do this, it becomes possible to buy readily available Oregon speedcut nano bars and chains (same as the sp21g). Otherwise it’s fiddf*ckery finding a good 1/4p bar (the stihl e mini light has my eye but is dumb money) and 3/8lp bars are everywhere but good chain sans safety bumpers are available but few reviews (archer and I believe Carlton/woodland had one).

 

[Ketchup]

My original intent with this query was to be able to run husqy sp21g, a .325 nano chain, seems to split 3/8 .043 and 1/4p .050 and I’ve run it on our shop saw and like it plenty. Today after work I checked what the t540ixp uses for a setup and found it has a replaceable spur and no clutch drum. It uses an electronic brake I suppose. The echo 2500t uses a clutch drum/spur because it had a mechanical brake (brake band from chain brake applied to the drum). Probably less good for an electric motor with no clutch or slip but then, why would you go slamming on the brake? Anyways, lo and behold, something of a solution towards my goal, but not an actual rim drive solution. The husqy sprim (r)(c)(tm) has two flats. It doesn’t fit perfect in the pto of the 2500t, it’s a couple thou too tight, but I expect that could be cleaned up easily enough. So then, that thing brazed to a 2500t drum that has had the original spur removed somehow would net me the result I'm looking for? But I don’t know how to braze at that level or if it’s feasible. If I can do this, it becomes possible to buy readily available Oregon speedcut nano bars and chains (same as the sp21g). Otherwise it’s fiddf*ckery finding a good 1/4p bar (the stihl e mini light has my eye but is dumb money) and 3/8lp bars are everywhere but good chain sans safety bumpers are available but few reviews (archer and I believe Carlton/woodland had one).

Could you just grind the sprocket off the 2500 drum and then stack the t540 sprocket on it?

 

[vrex]

Could you just grind the sprocket off the 2500 drum and then stack the t540 sprocket on it?

I’m not sure the answer to that. I assume yes but I really have zero working knowledge of fabrication, just understand it on a basic level. If you mean grind the spur down to the drum then braze the husqy paddle rim on, I don’t see why not, except for that flange adding thickness maybe? Plus, I know diddly about brazing. @wcorey @srcarr52 @davidwyby ?

 

[Ketchup]

I’m not sure the answer to that. I assume yes but I really have zero working knowledge of fabrication, just understand it on a basic level. If you mean grind the spur down to the drum then braze the husqy paddle rim on, I don’t see why not, except for that flange adding thickness maybe? Plus, I know diddly about brazing. @wcorey @srcarr52 @davidwyby ?

Maybe I’m missing something, but why do the drum and the sprocket have to be attached?

 

[wcorey]

Maybe I’m missing something, but why do the drum and the sprocket have to be attached?

Drum is part of the brake.

 

[vrex]

Drum is part of the brake.

Bingo

 

[wcorey]

I’m not sure the answer to that. I assume yes but I really have zero working knowledge of fabrication, just understand it on a basic level. If you mean grind the spur down to the drum then braze the husqy paddle rim on, I don’t see why not, except for that flange adding thickness maybe? Plus, I know diddly about brazing. @wcorey @srcarr52 @davidwyby ?

I’d be attempting it by tig welding as you have more control over the temp and maybe avoid mucking up the heat treatment on the hub. Though as srcarr mentioned there could be an issue with cracking.
I was tig welding rim spline/hubs onto keyed hub adapters as part of the driveline on saw dynos and had no issues.

 

[Ketchup]

Drum is part of the brake.

Don’t the sprocket and the drum both have a keyed slot that goes directly on the crank? The drum would have a lot less grip on the crank, but it would still have some.

I agree that TIG is worth a try. This is a pretty tiny saw.

 

[Ketchup]

I thought I’d have a go with a 2511t drum mated to the spline off a 455 rancher drum. I figure it would be nice to have a 2511 spline drive and the process would be very similar if I wanted to do a 2500, but with out the oiler concerns.

Cutting both drums is quite difficult but the sprocket is the worst of it. Best to remove most of the 2511t sprocket with a cutoff abrasive. I burned several carbide tips doing it all on the lathe. The 455 drum is softer on the inside, so you can bore out the point where it connects to the spline with HSS.

I over sized the fit because I couldn’t get the 2511t sprocket to shave down perfectly even. My plan was to sweat silver solder into the seam and see how long it held up.

But I didn’t get that far. I froze the drum and heated the spline, but it wouldn’t drop on completely. I pressed it the rest of the way and it cracked.

I think I just botched the machining. I’ll revisit the 2511t drum. I think it has some run out and needs some more trimming at the drum/shaft connection.

I’m a little more skeptical about welding now too. The spline cracked very easily.

 

[wcorey]

I'd likely just cut the whole spur off flush, then cut the donor spline/part off of the other drum with a good sized flange left around it and do a small mating lip for alignment purposes.
That way the tig welding is a good distance away from the spline and a piece of wet cloth in the center hole can keep it from losing temper. Still chancy for warping and fracturing...

EDIT... Oh wait, I forgot this one isn't direct fit and needs the center bearing. I guess you could only do the flange if the thickness allows it.

 

[Ketchup]

I'd likely just cut the whole spur off flush, then cut the donor spline/part off of the other drum with a good sized flange left around it and do a small mating lip for alignment purposes.
That way the tig welding is a good distance away from the spline and a piece of wet cloth in the center hole can keep it from losing temper. Still chancy for warping and fracturing...

EDIT... Oh wait, I forgot this one isn't direct fit and needs the center bearing. I guess you could only do the flange if the thickness allows it.

Yeah. The bearing and the oil gear make this more difficult.

I talked with a machinist friend about it. He said the spline is sintered metal and probably won’t tolerate welding. Even if it goes together it has a high chance of failure under load. He suggested brazing, which is clearly how the original was put together. I’m just a novice in the brazing world.

Off to the school of YouTube…

 

[wcorey]

He said the spline is sintered metal and probably won’t tolerate welding.

Maybe I didn't explain it well enough.
That's why I say to cut way out around it, leaving a good sized flange of drum material on it, the drum is relatively weldable.

 

[Ketchup]

Gotcha. I think that could be done with a Stihl
260 drum. It has the same crank bore as 2511t. It’s a lot more welding than I was thinking and there may be important differences on the inside of the drums. I’ll look into it.

 

[Al Smith]

You could use a brass bushing in place of a needle bearing if it would be easier .

 

[vrex]

Sorry for my absence, 13 straight days of tree work and I’m cooked. @Ketchup thank you for your efforts. I think I follow what @wcorey and @Al Smith are saying. I’m curious what needs to be done to decouple the drum and braze on a new spur. Would a torch gently heating the parts cause the brazing material to flow out again? Or does an industrial process like echo may use be more heat intensive and cause tempering issues if we were to try it at home?

 

[wcorey]

Melting braze pretty much requires heating to cherry red which would certainly mess with the temper.