[itsme]

Hello,

Today I made the spur gear for my engine. After some fumbling around, I figured out that the Emco's dividing head could actually divide 14 holes, so it turned out to be easier than I had originally thought. It is a light press fit into the rear housing and will use 4 M2 grub screws to hold it in place permanently. It took a bit of effort to make sure that the gears and screw holes would all align properly, but then on rough assembly, it seems to be fine. Just a word of warning to anyone who is going to use the SW92 plans for the gear dimensions - DON'T! I machined the spur gear using these dimensions. It had a 16.8mm outside diameter. I finished the gear and was very disappointed when it would not mesh with the internal gear. I then went and got a proper drawing for this gear and it turns out that the outside diameter should be 16mm, not 16.8mm. I re-made the gear (16mm this time), and it now meshes very well with the internal gear. There is no slop and they are very smooth. I have attempted to take some photos, but was battling with the light.

The next challenge is to get the side clearances right. The rotor and housing were originally faced on the lathe and when I measure them, they are not 100% parallel. Both are off by about 0.01mm. I did machine both of these parts oversize by about 0.2mm. I'm not sure how I am going to do this. A surface grinder would probably be ideal, as it would give nice parallel sides - the only problem is that I don't have access to one. The only other method I can think of is getting a flat surface and working the housing and rotor by hand on sand paper starting coarse and moving on to finer paper for the finish. I'm not overly keen on this method, as I'm not sure how easy it will be to get the sides parallel. The other problem is finding a flat surface. I have got a piece of glass which seems very flat, but I have no way of measuring it to see if it truly is flat or not.

I need to do these clearances next so that I can make the apex seals, which are then needed to balance the engine properly. The clearances are extremely important if I want this engine to run.

Regards
Warren