WCD Bearing Blocks

[AdamHeard]

Originally Posted by craigboez

I have a question regarding West Coast Drive bearing blocks.

Based on many of the pictures and CAD models I've seen, the "standard" way to create them is to cut a pocket all the way thru your 2 x 1 x 1/8 siderail, and then slide a bearing block into the pocket from the side. Once in place, the bearing block gets a plate bolted to it from both sides to hold the block captive in the slot while allowing it to slide front to back.

It seems a simpler approach would be to cut the same pocket in the siderail, but then slide a 1.75 x .75 bearing block in the siderail from the end. This would just fit inside the inside dimensions of the tube, and would eliminate the need for the sideplates and fasteners.

I can see a downside to the simpler approach, and that is that you need access to the end of the tube you're installing the block in. That doesn't seem like that big of a deal. I would think the two would be comparable from a weight standpoint. Is there another downside to this approach that I'm missing?

A long, long time ago (before my time even) 973 used to do this.

The problem is the inside of extruded tube is all over the place dimensionally, so this blocks end up being really finicky.

[sanddrag]

Also, there is some benefit to having the bearings outboard of the 1" tube. Having both bearings only 3/4" apart to the outsides seems a bit narrow.

[ablatner]

Bearing blocks are probably the trickiest part to design and machine of a WCD. At this point, they've become pretty standard for various reasons. Many teams use something like this.

As Adam said, the relatively poor tolerances in tubing makes bearing blocks on the inside difficult. The tubing from McMaster-Carr has tolerances of .044" for the outside dimensions, and it's probably much worse for the inside.

One benefit of the standard method (linked above) is that you can put a CAM on the pointed ends for tensioning.

[craigboez]

Originally Posted by ablatner

Bearing blocks are probably the trickiest part to design and machine of a WCD.
...
One benefit of the standard method (linked above) is that you can put a CAM on the pointed ends for tensioning.

The only CAM tensioners I've seen appear to be very difficult to machine on a manual mill and very custom. How do you approach the tensioner?

[Cory]

Originally Posted by craigboez

The only CAM tensioners I've seen appear to be very difficult to machine on a manual mill and very custom. How do you approach the tensioner?

A cam could be square. Or you could sand a radius into it. It doesn't need to be as fancy as what we make, for example. You just need something with a non-constant radius. They don't even need to all be perfectly the same since you're not going to get the exact same tension across all your chain runs.

[wilful]

For our chain tensioner cams we used a ~1/4" thick piece of 3/4" or 1" (I don't remember which) steel shaft with a hole close to the edge and welded a #10/32 socket head alan bolt into the hole.

[Mark Sheridan]

Originally Posted by wilful

For our chain tensioner cams we used a ~1/4" thick piece of 3/4" or 1" (I don't remember which) steel shaft with a hole close to the edge and welded a #10/32 socket head alan bolt into the hole.

As a "customer" of 766, I can attest that these work well. We even discussed removing the cam after tensioning to save weight since the bearing blocks we use can grip the box tubing so well. The cam tensioner looks like a automotive Cam bolt. I could never find one small enough to work. I suppose this design could be improved by using an aluminum 1/4-20 bolt and a 1/4" thick piece of aluminum to save weight. I don't think the loads are high enough to wear out the aluminum bolt. Plus it is nice to have more area to weld to.