Dobsonian DIY mount

[kg4kpg]

My new XT8 I bought without a base has arrived so now it's time to build the new base. I'm going to grab some birch 3/4" plywood from the home improvement store and build one. The birch will last a lot longer than the original base would have anyway. I have found several samples on the web with good descriptions on building but I'm curious about the cuts I need to make for the altitude bearing. I see a lot that use two straight cuts making a V but not many cutting a half circle. How much bigger should the cutout be compared to the bearing surface? Is there a reason why the V cut is better other than probably being easier?



Thanks,

Chris

[Moonshane]

hi Chris

Good luck with the project. A curve on the rocker side in my view is more aesthetically pleasing as you can match the shape of the actual bearings, plus the thickness of your teflon pads or whatever materials you use. it also ensures that the bearing is more in line with the bearing surface with more of it making contact.

A straight V cut is OK and slightly easier in some ways but to be honest I find it easier using a router for a curved cut. I'd recommend a round cut.

whatever you do, make sure that the pads are fixed at a position about 35 degrees either side of the centre of rotation. some make their Vs with a 90 degree but which creates jerky movements. see below

[michael.h.f.wilkinson]

Birch plywood is a lovely material I find. Built the kids' mini-dob mainly from birch

[NGC 1502]

Hi Chris, all good advice above.

I'd go for a round cut as well.  If using 3mm thick Teflon pads, just add 3mm to the radius or 6mm to the diameter of the azimuth bearing for the curves in the base.

A router is best for cutting curves in plywood, but you can get away with a jigsaw ( saber saw in US ).  Go slowly, don't force it, for a nicer cut.

You can experiment for the best position on the curves for the Teflon pads.  Further apart makes the movement less light, closer together gives a lighter movement but more prone to balance issues, especially if changing from heavy to light eyepieces.

All the best for the build, Ed.

[kg4kpg]

Thanks gents.

Regards,

Chris