At last I think I have a design that can build and that is also built out of components that exist in this universe! By spinning the motor round and having the disc sander powered off the idler shaft I think I’ve incorporated all the features I wanted.
I’m not sure how well the disc sander will work powered off the idler shaft for two reasons: firstly, of course, it relies on the sanding belt to provide the power and the shaft. My gut feel is that it will be able to supply enough power, the belt is 90mm wide and presumably not slipping when 300mm is rubbing against a piece of wood so the smaller area rubbing on the disc should be a problem. Secondly, and I think this is the bigger problem, the idler shaft (probably) wont be perpendicular to the body of the machine so the table design for the disc sander will need a bit of thinking about. Access to the disc sander is also somewhat restricted but I think it’s probably good enough. There was always going to be a compromise somewhere and I think this is an acceptable one.
There are a couple of points in the design that I’ve not quite bottomed out. The first being the length of v-belt I need. At the moment I’ve just built a box around the motor and cut a hole for the belt to pass through. I have quite a lot of flexibility in this region though as I need to move the feet on the motor and can put them on either side. If necessary I can also make the motor box taller so that it uses a standard belt length.
The other main point I’ve not yet addressed is how I’ll fit the removable edge sander table and the removable (for bobbin sanding) platen. I’m currently thinking epoxied in bolts are the way forward. The springs are still giving me trouble. I’m concerned that the springs I’ve ordered won’t be man enough for the job. This grinder build uses a spring with a maximum working load of 26kg which, IIRC, is greater than the two springs my design currently has. On the up side there is easily space for a third spring if I need it only I don’t currently have a third 8mm shaft collar.
The four sanding modes this design supports are shown below:
Finally here is a shot of the internals of the machine. Most of the design features from version 2 and 3 are still in place including the tensioning mechanism etc. The box at the bottom that contains the motor may need to be made slightly taller but I think this is the final design. I haven’t calculated the hole for the belt, I simply eyed up the edge of the two pulleys and added a bit. I’m a little bothered by how little material will be present to the right of the pulley hole. It might make connecting the main board to the side a little tricky.