Tap top cap dob az bearings

[furrysocks2]

Been trying to improve my DIY Dobsonian...

I made the rocker box with a ring of smooth laminate wet-wall or something screwed on the underside of an 18mm MDF base - both were leftovers in the garage when we moved in to the house.

I'd settled for the gray furniture sliders, but it was always too stictiony. I recently tried a 12" lazy susan bearing but it was either too loose or if I preloaded the central bolt with a spring, not smooth enough.

I'd removed the lower base and ring when I installed the lazy susan but hadn't thrown then out, so I reassembled.

 

I scraped the top surface of the feet and put a single layer of £1-shop double-sided sticky tape on each - this was in fact my #2 favourite feel.

I then tried a 1" sqaure of old kitchen cutting board and played around with some 120/240 grit sandpaper, paste wax, lubricating wax and soap - soap was my #1 favourite, a thick and creamy feel with no greater pressure required to start moving than to keep moving - my favourite, until....

 

 

I was wandering around B&Q after checking the off-cut box next to the panel saw - there were two off-cuts of kitchen worktop with a rougher laminate than my wet-wall, but I'd have to make the ring in two pieces and would be too thick and heavy. So on my way out, I walked down the plumbing aisle eyeing things up with the Dob in mind and found these (94 pence for ten):

I drilled a stopped 11mm hole on top of each foot and press-fit one of these in each - now a light and creamy movement in az.

Yet to test and see how it weathers but I'm excited to try it - tap tops and soap on smooth laminate. 

[furrysocks2]

Having used it last night, albeit never having used a "proper" Dob to compare against, I LOVE how this feels! Certainly the best this scope has ever had.

I've got a broom handle screwed to the cradle. I used to grab the scope to push and pull, but the view would deflect before movement and settle afterwards - whether deforming the top trusses or the alt bearings, or just stressing the plywood base, I don't know, but always jerky.

I was imaging the moon last night - no drive and a 1/4" sensor and the FoV drifts pretty quickly. I could apply thumb pressure to the broom handle - some deflection with 3 foot free length, it's a softwood handle - but no jerk when it starts off, no more pressure to start it than to keep it going, at least not that I could tell. As the moon was nearish the Meridian, I was able to keep the target lunar features in view for ages with only the odd alt-tweak, and without introducing very much at all by the way of vibration, provided I held a steady hand. I've got dust bunnies, so I let it drift left and right within the frame by varying pressure on the pole, but could always keep it in frame if I paid enough attention to the screen. I guess it's a combination of the preload on the pole and the friction of the bearing, but it works.

I'm not sure I'd call it "light" having used it, but it's just so nice to use - maybe "buttery" or "syrupy" would describe it better.  For me, the tap top caps have done it for now, not looking to change them again. Might have another crack at improving the alt bearings, currently a rattly washing line prop and threaded-rod slo-mo control and I might add a turn handle slo-mo az control, but I perhaps don't need it with the az bearing how it is now.

Will be interesting to feel what a "proper" Dob feels like, as I never have.

[fiestazetecmk2]

Great work.I like to see passion in life an you have plenty of that with your dob.I'm already jealous that you have built your own.keep up the good work.

[furrysocks2]

Just now, fiestazetecmk2 said:

Great work.I like to see passion in life an you have plenty of that with your dob.I'm already jealous that you have built your own.keep up the good work.

Thanks.

So much time invested, I feel I owe it to the scope.