dob base modifacation

[SHUTTLE ATLANTIS]

hi guys i have been having a wee bit of trouble with the dob base

not running smoothly seems to stick ive tried washing up liquid, to a bit of grease and polish to make the base plates run smooth with out much joy. so today i came up with this

omnitrack ball transfer unit saturn mount 3 of thease between top

base and bottom . then smooth turning

[coulthamst]

I think that this modification may remove an important feature of the original Dobsonian design - "stiction", provided by the teflon pads. Using ball bearings of any sort will result in unwanted azimuth rotation, which will take place at the least unguarded touch or slight gust of wind. The method outlined in many previous threads of shimming the centre bearing with home-made washers cut from old milk containers will produce better, more effective results.

[johninderby]

It should work OK, but don't forget you'll probably need some "friction pads" as well to stop it from turning too easily. Spacers with some teflon on top will work well, but you'll have to shim them a bit at a time until you get the friction just right.

John

[RikM]

I've just this afternoon cut some milkbottle washers for mine.

[jimmyjamjoejoe]

I've done the milk bottle washers. 3 was too many and produced rocking, 2 is just not quite enough. I still get stiction at high powers, making nudging difficult.

I also considered the ball transfers, but having to countersink them etc is a bit of a nightmare. It'd be much easier to use a lazy susan bearing, then upgrade the crappy nylon pads that come with the base to virgin teflon, and pack them up until perfect stiction is achieved.

Alternatively, there is ebony star laminate, but after trying a lazy susan on a 12" dob, i can't imagine that laminate could be better.

[scogyrd]

I tried ball transfer units before settling on a lazy susan. They probably would've worked fine but I fitted them to a plywood base and they formed separate grooves in the wood because the wood was soft (compared to steel) and none of them were fitted completely uniformly. They were close but not quite close enough that they all ran in the same groove. Which meant that, when I let go of my dob it wouldn't always sit still because the btu would want to settle into it's own groove. It didn't move a huge amount but it was enough to annoy me at higher magnifications.

I think this could probably be eliminated if the base was laminated or you had a sheet of steel or something for the btu to roll on though.

In the end I fitted a lazy susan and did this mod instead.

http://stargazerslounge.com/diy-astronomer/177296-lazy-susan-dob-brake.html

I doubt it'd work too well with ball transfer units though. You would probably end up putting too much pressure on the btu and they'd form grooves.

[jimmyjamjoejoe]

I still havent found a place to get a steel block or a place to get it tapped

[scogyrd]

I still havent found a place to get a steel block or a place to get it tapped

It is hard to get metal now most of the scrap yards have closed down. I had to resort to ebay to buy mine.

I couldn't find anywhere to tap it either so I did it myself. It's not hard, it's just a bit daunting if you've never done it before. I bought 2 blocks in case I messed it up but I managed to do it first time.

[SHUTTLE ATLANTIS]

okay guy thanks for replys i think i will put this project on hold for now, there is allways a way of finding a happy soluction .

[devlin]

Iv just put a 12 inch lazy Susan Bering in my SyQuest and just added some sticky backed Velcro on top of the Teflon pads works great runs smooth as silk and just drags enough to stop unwanted movement total cost about £20.

[Moonshane]

I think the problem with most of the skywatcher type bases is that they use smooth laminate. get down to your local kitchen cabinet maker and they will have sheets of 1mm or so laminate that you can buy cheaply. buy the one with the most stippled pattern. glue this to the bottom of your rocker with contact adhesive, wax it and it will work smoothly. if not then replace the teflon blocks for ones a little thicker.

for me this is the most consistently good method. waxing makes a difference.

[johninderby]

Having done the Lazy Susan mod a while ago

http://stargazerslounge.com/discussions-mounts/154447-lazy-susan-bearing-dob-mount.html#post2072992

I still prefer the Ebonystar mod, but unfortunately no one seems to stock it in the UK. As Shane says a pebbled or wrinkly finish laminate does work even if not quite as well as the Ebonystar. I've also found you need the right wax as well (Turtlewax) as some brands don't seem to work very well.

John

[Moonshane]

yes, I agree John - the paste type turtle wax has been working well on my dob for almost a year now. I used this onehttp://www.amazon.co.uk/Turtle-Wax-Paste-250g-Polish/dp/B0054JW8WA I also think that the heavier the dob, the smoother the base.

[johninderby]

I've recently experimented with using Turtlewax Glaze on top of the wax. It's a silicone based glaze that is slipperier than just the wax on it's own. Don't know if it makes that much difference really but it certainly hasn't hurt.

John