Lazy Susan bearing

[BeerMe]

I seen someone mention these on their Dobsonian mount, and never having heard of them before I was naturally intrigued.

They seem like a perfect solution for Dobsonian mounts like mine that aren't the smoothest on the azimuth movements.  Has anyone ever used one of these?  Was it easy to fit?

Most importantly, would it be suitable on my lil Heritage 130p base?

[furrysocks2]

I fitted a 12 inch bearing to my diy dob a couple of weeks ago. I used to have some wetwall running on kitchen chopping board, which suffered from "stiction" - you'd push and it'd eventually overcome friction and jump free and rotate too far - smooth, but you couldn't do small movements easily.

There is some lateral play in a lot of these bearings (not precision items, pressed steel), but with weight on them, the ball bearings should settle into the grooves and not shift about or lift too much, provided the center of gravity stays within the diameter of the bearing - ie get as large a bearing as you can fit and fit is as concentrically as possible, especially if you intend to run a bolt through the center - see below.

I've got a fairly large, long, heavy scope. It's a 215mm, about 5 foot long and perhaps heavier than it should be. I find that while it feels pretty smooth to turn, it will occasionally "stick" on a ball and require a bit more pressure to turn - won't jump forward, I still get small incremental movement. Another oddity is that it will occasionally run backwards a little when you stop moving, like it's rolling back on a not-quite-spherical ball, or settling into a low point of the race. Perhaps I've got some dust in the bearing already, and you can't clean them easily. What I'm trying to say is mine is not totally "uniform" and not what I'm going to stick with.

What it means for me, is that since I'm at high mag a lot of the time (my largest EP gives me >50x), it's still not 100% smooth. and requires some fettling to get an object in center of FOV.

For a smaller scope, I modded my Aldi/Lidl 3" base with a smaller bearing, but never used it as I intend to fork mount it it when I get time.

I found with both scopes, I needed to put a bolt through the center holes of the base and tighten it up a bit - I used a stiff little spring under the bolt head to help account for any wobble between two circles of the base. All of that helped to get the rotation a little bit stiffer, otherwise changing the EP would knock the scope off as the scope would rotate too freely - a lot more inertia in my big scope than yours. I initially found that with the bolt through the middle, turning the base could loosen the bolt, so I used a skateboard bearing with the outer race in contact with the top half of my base and a clearance hole under it to prevent the inner race from contacting - the bolt-head/spring was then bearing down on only the inner race, allowing the bolt head to remain fixed and not rotate, which the base rotated freely under it - preventing loosening - if that makes sense.

 

Hope some of that helps - if you've got the time and spare £5, give it a go. If it's not right, you'll learn something. Both scopes felt better but neither felt perfect - lazy susan bearings do a job, but there's a reason that there are other answers to the problem. My motivation for changing both scopes is I want to modify both of them to track with a couple of steppers and OnStep, so I need to engineer something much smoother than what I had.

[Joseki]

Hi, I used a lazy susan on my 10" diy dob base but I also have a 130p heritage and I don't think I'd put a lazy susan on that - it doesn't seem to need it as it's a lot lighter.  - I just had a go moving the 130p and it rotates smoothly on three teflon pads.  The wobble with the lazy susan, like furrysocks2 mentioned would drive me a bit nuts on a lighter scope.  If your scope's rough in the azimuth before trying the lazy susan solution maybe you should take the base apart and check that the teflon pads are dirt free and the pins/staples used to secure the pads are below the level of the teflon - i.e. they're not gouging the top part of the base.

[BeerMe]

Thanks for the prompt and informative replies gents!

My inclination was that my scope was a little too small for the LS bearing, I had a feeling that it would cause too much unintentional movements at the slightest knock.

I've had a bit of an issue with the base of my scope since I bought it.  This was a replacement  (the first one had a bent Secondary mirror support) and whilst I was still learning how to use it, I extended it too far beyond its centre of gravity once and it ended up wrenching loose one of the 3 bolts that holds the alt bearing to the base!  Since it was my own fault, I done a little diy on it by replacing the bolt and putting glue in to the areas where the blots come through from the base plate on to the alt support.  Once everything hardened, I sanded the bolts as replacing one and tightening all 3 had shredded a little wood in the base and I wanted to make sure I had removed any excess glue that had seeped down the bolts.

Perhaps some new, slightly thicker Teflon pads would help?

[furrysocks2]

24 minutes ago, BeerMe said:

Perhaps some new, slightly thicker Teflon pads would help?

Dove?

[BeerMe]

Ooh very interesting

What is this EbonyStar strip he speaks of?   I'm assuming this is a component of his base that I don't have, is it a circular strip which the Teflon pads move around?

So would I just apply a smear of soap around the circle the pads move around on my board, or directly on to the pads themselves?

[furrysocks2]

Check out this link.

Personally, I'd start with a wee dod on the pads - it'll transfer to the board and you're less likely to put on too much that way. I tried silicon grease on mine but it didn't seem to help much. Your scope, your call, but I can't see it doing any harm.

[brantuk]

This is the site I use for teflon products for alt/az dob bearings: http://www.awrtech.co.uk/miscprod.htm#PTFE. Their products and service are very good.

 

[BeerMe]

Thanks for the link brantuk.  Is the Tufnol material an alternative to the EbonyStar formica for the top board of the azimuth bearing?  I've noticed the EbonyStar material is difficult to get over here...

[brantuk]

I heard that ebony star is no longer made/available - so I went looking for other sources. It's like formica and rides very nicely on teflon pads. Here's where you can find the equivalent which works well but is expensive - it comes in 8'x4' sheets at £90 a pop:

http://www.idsurfaces.co.uk/c-3379-international-decorative-surfaces-f1782-stardust.aspx

The Stardust is the nearest one to ebony star. I use it on the underside of the rocker box which rides on teflon pads screwed to the top of the bottom board. If a few of us get together to split the cost I could deffo use a bit more of it for spare:

(the tufnol is similar but I've no experience of it)

 

[glowjet]

I am not into Dob`s, so please excuse my ignorance in these matters, however, I have been into DIY most of my life. I have often wondered, when reading threads on base bearings for the bigger Dob`s as to why no one seems to want to make their own roller race base, virtually frictionless I would imagine.

Just a question of screwing a number of those model car roller race bearings around the edge of a circular wooden disc of your chosen size, using washers where necessary so they can revolve without catching. Suitable holes and a central flange / bearing, fixed to a slightly larger circular wooden base unit, to enable both to be fitted together. The base should be covered with one of the kitchen worktop surface materials, Formica or whatever they use nowadays,  allowing the bearings to revolve on a smooth flat surface, should complete the project.

Some thought should possibly be given to strengthening the discs with stout hardwood rails or metal angle, as the timber may have a tendency to warp when used outside in varying temperatures, especially if using Beech ply. You may also need some friction control device, as the unit may well revolve too freely and need some adjustment.

As to the question of cost and availability of the small roller races, Ebay often has them listed in various quantities, I have seen as many as 8 for less that £4 from China and the like, if you want them from home counties, expect to pay in the region of £1.50 to £2 for the small ones.

It is effectually a DIY Lazy Susan, enjoy

[brantuk]

10 hours ago, glowjet said:

Just a question of screwing a number of those model car roller race bearings around the edge of a circular wooden disc of your chosen size, using washers where necessary so they can revolve without catching.

I did consider this method John - but I went with the formica/teflon solution cos the roller bearings don't have the required "sticktion" and would need a friction brake as you rightly mention.

I also considered reusing my lazy susan from the original LB rocker/turntable, but wanted a really simple remedy which is quieter and easy to maintain. I've also seen it working very well on mapstar's amazing dob design - in fact Damian did supply my az bearing from his left overs for which I was very grateful.

But yes - race bearings are an equally valid solution - I guess it's all down to budget and personal preference as usual.

[mapstar]

On Friday, December 16, 2016 at 22:37, brantuk said:

I heard that ebony star is no longer made/available - so I went looking for other sources. It's like formica and rides very nicely on teflon pads. Here's where you can find the equivalent which works well but is expensive - it comes in 8'x4' sheets at £90 a pop:

http://www.idsurfaces.co.uk/c-3379-international-decorative-surfaces-f1782-stardust.aspx

The Stardust is the nearest one to ebony star. I use it on the underside of the rocker box which rides on teflon pads screwed to the top of the bottom board. If a few of us get together to split the cost I could deffo use a bit more of it for spare:

(the tufnol is similar but I've no experience of it)

 

Looks a great job that kim and nice to see it coming together, I might have some of that myself.

They also sell some with the same texture called moondust but that wouldn't have been right on my dob (me and anything to do with the moon dont get on) 

The advantage over bearings that teflon/ptfe has is that it is virtually maintenance free and won't rust. Oiling bearings and optics is a no no in my opinion as it will eventually migrate no matter how careful one is.  

[knobby]

Old thread but might be useful ...

 

[brantuk]

5 hours ago, mapstar said:

Looks a great job that kim and nice to see it coming together

Thanks Damian - it's actually all assembled now and I've done a trial session with it - it moves beautifully. I've removed the bottom board ready for sealing and painting. Then all that's left is to add a nice colour coordinated Moonlite focuser that wifey is getting me for Xmas. I'll post all the pics up in the diy section once it's complete.

[glowjet]

17 hours ago, brantuk said:

I did consider this method John - but I went with the formica/teflon solution cos the roller bearings don't have the required "sticktion" and would need a friction brake as you rightly mention.

I also considered reusing my lazy susan from the original LB rocker/turntable, but wanted a really simple remedy which is quieter and easy to maintain. I've also seen it working very well on mapstar's amazing dob design - in fact Damian did supply my az bearing from his left overs for which I was very grateful.

But yes - race bearings are an equally valid solution - I guess it's all down to budget and personal preference as usual.

Thanks for your response Kim, I wondered why I had not seen or heard of such a device, it should be fairly straight forward to construct. As you say it would be very free running and require a form of friction device, you could also add a  slow motion cable drive for that added comfort.

Merry Christmas and a Happy New Year to you and yours