- Joined
- Dec 3, 2020
- Messages
- 177
When changing spindle speeds (jockeying belt positions), I got tired of loosening the two screws that allow the middle pulley swivel arm to swivel, then tightening them again after.
BTW, how necessary is it to tighten those two screws? How bad would it be to just let the swivel arm swivel? It won't move in use, only when tightening the belts, right? When it floats to the position that balances the belt tensions? I bet that's a FAQ...
But on the assumption those do need to be tight, I replaced the regular M8 screws with cam-locks, borrowed from a bicycle rack, the kind that carries bicycles on the car. You could make you own cams, but using these bike rack parts made it easier.
Now, I flip those two levers up to let it swivel, flip the levers down to lock it. Read on if interested.
This (below) is the cam open, swivel free to swivel:
If you want to make some this way, the bike rack part you need is called a quick-release skewer ("QR" for short), but it's not the normal one that holds QR wheels in the bike, those have a 5 mm shaft. You can't cut M8 threads on a 5 mm shaft. The ones I used have a 9 mm shaft, and AFAIK they are only made for car racks, such as certain kinds of Yakima, Thule etc. The kind of rack where you take the front wheel off the bike and clamp the fork into a QR that's built into the rack. This is a somewhat unusual part, but most bike shops will know what you mean, from this description. Hopefully the part is available separately, but I'll leave that to you to discover. I used QRs that I've had kicking around for some time because, on my rack, I replaced them with locking skewers. As in with a key, anti-theft security.
Here's the QR disassembled:
You can't chuck that end with the cross-hole, it's imprecisely made and the shaft would flail all about. So I made a shim to hold the shaft in the 3-jaw, for reducing the diameter from 9 to 8 mm:
Shim can be any diameter that's larger than the head of the QR shaft; I used 1/2" 6061. Drill the ID to ~9 mm — I used a letter "S" drill (8.8 mm), and it was pretty tight. A "T" drill (9.1 mm) might have been better. Then one slit with a hacksaw to allow it to tighten. High precision is not needed.
Turn the diameter of the part that needs threads, and thread it to M8 x 1.25 mm. That's the thread in my RF-30 anyway (an Enco clone from the '90s), but I'll bet yours has the same thread.
The cam-lever and "helmet" parts of the QR have to be assembled onto this shaft after it's threaded down into the head casting, because the lever is too big to spin, it hits the column. Assembly is a little fiddly, but only needs to be done once.
The position of the lever in the closed position might need to be adjusted with a shim washer, if it tightens at an inconvenient angle. You turn the QR and find the spot where it tightens best, by trial and error, and if that position had the lever facing the wrong way, then you'd add a washer under the QR where it bears down on the swivel arm. Use a washer that's not 1.25 mm thick, because that'll make no change in the lever position. You have to go thinner or thicker than the thread pitch to get a change in the tightening position. Mine just worked out, by luck I guess, no washer needed under either QR. Don't forget there are two ways to pass the cam lever through the oval hole in the shaft, so if one way puts the lever at a bad angle, try inserting the cam from the other side.
Dunno if I explained this well, so feel free to hit me with questions.
If you think this is a stupid idea, please be gentle, to spare my tender feelings... NOT!
No really, let me know what's wrong with it.
Thanks
Mark
BTW, how necessary is it to tighten those two screws? How bad would it be to just let the swivel arm swivel? It won't move in use, only when tightening the belts, right? When it floats to the position that balances the belt tensions? I bet that's a FAQ...
But on the assumption those do need to be tight, I replaced the regular M8 screws with cam-locks, borrowed from a bicycle rack, the kind that carries bicycles on the car. You could make you own cams, but using these bike rack parts made it easier.
Now, I flip those two levers up to let it swivel, flip the levers down to lock it. Read on if interested.
This (below) is the cam open, swivel free to swivel:
If you want to make some this way, the bike rack part you need is called a quick-release skewer ("QR" for short), but it's not the normal one that holds QR wheels in the bike, those have a 5 mm shaft. You can't cut M8 threads on a 5 mm shaft. The ones I used have a 9 mm shaft, and AFAIK they are only made for car racks, such as certain kinds of Yakima, Thule etc. The kind of rack where you take the front wheel off the bike and clamp the fork into a QR that's built into the rack. This is a somewhat unusual part, but most bike shops will know what you mean, from this description. Hopefully the part is available separately, but I'll leave that to you to discover. I used QRs that I've had kicking around for some time because, on my rack, I replaced them with locking skewers. As in with a key, anti-theft security.
Here's the QR disassembled:
You can't chuck that end with the cross-hole, it's imprecisely made and the shaft would flail all about. So I made a shim to hold the shaft in the 3-jaw, for reducing the diameter from 9 to 8 mm:
Shim can be any diameter that's larger than the head of the QR shaft; I used 1/2" 6061. Drill the ID to ~9 mm — I used a letter "S" drill (8.8 mm), and it was pretty tight. A "T" drill (9.1 mm) might have been better. Then one slit with a hacksaw to allow it to tighten. High precision is not needed.
Turn the diameter of the part that needs threads, and thread it to M8 x 1.25 mm. That's the thread in my RF-30 anyway (an Enco clone from the '90s), but I'll bet yours has the same thread.
The cam-lever and "helmet" parts of the QR have to be assembled onto this shaft after it's threaded down into the head casting, because the lever is too big to spin, it hits the column. Assembly is a little fiddly, but only needs to be done once.
The position of the lever in the closed position might need to be adjusted with a shim washer, if it tightens at an inconvenient angle. You turn the QR and find the spot where it tightens best, by trial and error, and if that position had the lever facing the wrong way, then you'd add a washer under the QR where it bears down on the swivel arm. Use a washer that's not 1.25 mm thick, because that'll make no change in the lever position. You have to go thinner or thicker than the thread pitch to get a change in the tightening position. Mine just worked out, by luck I guess, no washer needed under either QR. Don't forget there are two ways to pass the cam lever through the oval hole in the shaft, so if one way puts the lever at a bad angle, try inserting the cam from the other side.
Dunno if I explained this well, so feel free to hit me with questions.
If you think this is a stupid idea, please be gentle, to spare my tender feelings... NOT!
No really, let me know what's wrong with it.Thanks
Mark
