50mm shaft, flange bearing mounting. Pt 3. Rapid progress.

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After scouring the small ads and ignoring sales of 6 meter lengths of stainless 50mm shaft a local engineering company kindly sold me enough [82cm, 32"]  for my intended declination shaft. I'm hoping my 40cm, 16" stump of 50mm shaft will be long enough for the polar axis. These shafts are heavy! It took two of us to lift a ~3m length of bar comfortably onto the bandsaw rollers.

Now comes the hard part. I have to decide if pillar blocks or pillow blocks are the way ahead. Pillar blocks will require a stiff and flat support plate to carry the loads directly down into the pier. Nope.

The images show my final choice. Self-aligning and rubber sealed  flange bearings secured by heavy studs to the ends of a [virtual] box. The inner nuts are unnecessary but avoid the components sliding around. The shaft turns with silky smoothness and almost no friction at all. Worries about a tight fit were groundless. Provided the shaft was square to the bearing it slid through without shake.

Flange bearings [pillow blocks] can be clamped to the ends of an almost solid [plywood] box via the threaded studs. The box avoids flexure modes in a potentially undersized flat plate. The PA box can be pivoted to allow adjustment for polar altitude. A turnbuckle or screw jack can make fine adjustments easy. One slight worry is indentation of the plywood at the polar axis junction with the declination box. Adding an alloy sheet in the 'sandwich' won't help unless that sheet is considerably larger than the flange to spread the loads.

I am quite tempted to see if another local engineering company has any square steel tube large enough to fit over the studs but resist the pressure from the flanges. The ends of the tube would have to be carefully squared to avoid twisting the bearings via their flanges. Though the bearings are self-aligning it still pays to have them square to each other..

I have ordered the wormwheels from Beacon Hill and should have them within a month. I decided to go with an 11" for the RA and 8" for the declination. Though Barrie tells me these are nominal sizes and it sound as if they will end up 3/4" larger in both cases. Which is all the better provided bits of the telescope and mounting don't strike the RA wheel. This may need a slightly larger overhang beyond the bearing nearest the saddle to allow for when the telescope is vertical on either side of the pier. This is where closest approach to the PA wheel is most likely.

Beacon Hill have settled on 287 teeth for their wormwheels for a 1/5th RPM motor. These will need new motors so I can't just swap the old ones over from the MkIV which uses 359T on both their 7" wormwheels. The slightly longer, thread pitch of the BH worms will make the aluminium teeth on the wheels thicker and more robust. I'll be glad to get away from the constantly rusting MkIV worms! No oil or grease has ever proven to stop the rust with the mounting living outdoors but protected against the weather. The worm housings and their adjustment have been a regular problem.

Now I need a price for a large diameter, taper locking bush to give me a really solid and accurate connection between the RA and Declination shafts.

The bearings were incredibly cheap at under £10 equivalent. The galvanized threaded rods and nuts were more expensive! I was able to obtain the 50mm stainless steel shafts for half the price of the studs. Online sales prices for 50mm SS were 7 times higher per meter!   

My idea for alloy channel stiffening didn't work out. The channel was too narrow to go over the studs and too wide to go between them.

The scale and sheer weight of the present assembly is quite unbelievable! 16kg as shown.  The long studs will be halved to build the declination assembly. The present overall length to the fronts of the flanges is about 11" for the Polar Axis.  Though I may go back to my source for a longer length of shaft now I know it is affordable. The flanges are 143mm square or about 5 3/4". The shafts are 50mm in diameter or about 2". The threaded rods [studs] are M16 or about 5/8" in diameter. The massive shaft itself resists flexure while the studs add their own stiffness at a distance which rises as the square of the radius from the center of the shaft. I shall really have to find a suitably stiff pier to maximize the upgrade to 2" [50mm shafts].

Click on any image for an enlargement.

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