Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

elliot

Lazy Susan...no thanks.

Recommended Posts

I've just received a 12" Lazy Susan bearing to see if I can ease the Azimuth movement on my 10" SkyWatcher Dob.  Before I drilled any holes I thought I'd just put it in between the baseboards to see how it moved with the weight of the scope. Sure, it moves very freely and of course I'd have needed some kind of clutch to stop it flying around in the wind, but when it gets down to really fine movement, the cheep pressed steel bearing really isn't up to the job. I couldn't get the super-fine movement I had with the Teflon pads, it was just a wee bit too jerky. The Teflan pads are not as easy flowing but you get a load of control with Teflon if you apply some carefully applied muscle. 

That's two dob mods that haven't worked for me so far, caster wheels and now the lazy susan bearing. Next upgrade will definitely be something simple like an eyepiece.

IMG_2694.thumb.JPG.1ff48d06bc16a2f250ababda6085bf2e.JPG

Share this post


Link to post
Share on other sites

Not all Suzans are as lazy as one another.

This particular Lazy Suzan is manufactured by GSO and used on their Dobs.

Teflon or no Teflon, nothing I have had the chance to use so far comes near its smoothness and precision.

  • Like 2

Share this post


Link to post
Share on other sites

I must admit I've never quite seen the practicality of caster wheels on a Dob mount unless they very positively lock into place with no flexion or wobble - I get that they make moving the larger Dobs into a basic viewing position easier, but surely such things would work against the movement of the scope?

  • Like 1

Share this post


Link to post
Share on other sites
4 minutes ago, JOC said:

but surely such things would work against the movement of the scope

Exactly...it was a terrible idea :D 

Share this post


Link to post
Share on other sites

I've owned a couple of dobs with a "lazy susan" type bearing on the azimuth axis but I've always preferred correctly spaced teflon pads for smooth motion with the right level of sticktion.

The scopes with lazy susan type bearings seemed too loose in a breeze and a little rough in motion when I was using the scopes at high magnifications.

My current 12" dob uses well sized and positioned teflon pads and it's spot on :smiley:

  • Like 2

Share this post


Link to post
Share on other sites

I'm testing a lazy susan bearing with furniture glides - the glides are a skoche taller than the lazy susan. The reason why I went with this design is that the GSO LS starts to stick after a few years. It will be interesting to see how I get on (If I ever manage to finish the dob build)

  • Like 1

Share this post


Link to post
Share on other sites

" sticktion  "   .....  I'm liking that word, is it official Dob-speak ??

  • Like 2

Share this post


Link to post
Share on other sites
13 minutes ago, Craney said:

" sticktion  "   .....  I'm liking that word, is it official Dob-speak ??

It's "Stiction" as in "Static Friction" not "Sticktion" which sounds like it has something to do with small tree branches :)  It basically refers to the fact that two surfaces in contact can require more force to overcome friction when they are not moving than is needed to keep them moving thereafter.  The main effect with a dob base is that you try to nudge the tube along and it won't move, so you push harder and then it suddenly moves and overshoots.

  • Like 2

Share this post


Link to post
Share on other sites
46 minutes ago, IanL said:

It's "Stiction" as in "Static Friction" not "Sticktion" which sounds like it has something to do with small tree branches :)  It basically refers to the fact that two surfaces in contact can require more force to overcome friction when they are not moving than is needed to keep them moving thereafter.  The main effect with a dob base is that you try to nudge the tube along and it won't move, so you push harder and then it suddenly moves and overshoots.

I might have used the wrong term then. A good dob bearing will stay put when you want it too but move smoothly without jerking when needed. What ever that property is called, Moonshane / Shane put just the right amount of it into the dob mount that he built for me :icon_biggrin:

 

oo12dob01.JPG

Edited by John
  • Like 2

Share this post


Link to post
Share on other sites

At Stoneleigh  this year I looked at all the Dobs big and small. The optics were never in question, but every one on display had some degree of stiction. The small ones also suffer with being too light weight so the whole base moves when you turn them. The bigger ones sit quite solidly at least. I find it so odd when products are displayed that clearly have faults.

Share this post


Link to post
Share on other sites
1 hour ago, TSRobot said:

At Stoneleigh  this year I looked at all the Dobs big and small. The optics were never in question, but every one on display had some degree of stiction. The small ones also suffer with being too light weight so the whole base moves when you turn them. The bigger ones sit quite solidly at least. I find it so odd when products are displayed that clearly have faults.

I know what you mean. When I was at Stoneleigh this year I had a good look at some large refractors. With one exception they were all undermounted and would have been hopeless to use at anything like high power. I realise that the mounts were being used to display the scopes but some folks I overheard clearly thought that they were demonstrations of what would be suitable for the scope :rolleyes2:

Share this post


Link to post
Share on other sites

I remember saying to one nice sales chap about a small 150 Bresser dob that maybe it just needed a little Mr Sheen to get it moving. He didn't seem to understand what the problem was. I was actually pondering buying it right then, but wanted to see how well it turned. Hey ho ?

Share this post


Link to post
Share on other sites

At our society when we built our 18.5 inch we actually used steel bearings that work very well.

Share this post


Link to post
Share on other sites

There was a nice article in "Telescope Making" magazine [years ago now] regarding the static friction versus the dynamic [moving] friction of Dobsonian bearings. [Stiction]

There is a fine line between the two forces best served by PTFE [US. Teflon] and Formica where the effort of the slightest push exactly matches the freedom to keep moving. 

There is a sense of light, buttery smoothness without loss of control, or sensitivity to wind, regardless of the telescope pointing angle or the direction of travel.

Only at the zenith does the friction seem to rise because the azimuth bearing cannot enjoy the usual "leverage" applied instinctively by the instrument user at the eyepiece.

This is true of both the Dobsonian mounted reflector and refractors mounted on Berry-style, counterbalanced, offset forks.

A suitable lever could replace shoving the instrument itself when viewing only at the zenith.

Perhaps a vertical pole extending upwards from a corner of the usual Dob supporting "fork" or side boards for maximum leverage.

This would provide a standard torque around the azimuth bearing regardless of the uprightness of the OTA itself.

The azimuth push pole would only be needed when viewing at the zenith. So could be simply slid into and out again of its location tube or rings.

Then discarded again when not in use. A refractor would need an inverted pole for zenith viewing and could even be cranked outwards for ease of use.

Share this post


Link to post
Share on other sites

According to simply bearings, the pressed steel bearings need a dose of lubricant to smooth out the balls motion and also add some damping, at which point they will glide. I suggest some dabs of normal lithium grease will provide the smoothness and sticktion you want. 

I don't see the point of using a bearing like this and then raising the base onto ptfe gliders such that the bearings aren't running in their races properly - there's no advantage of a bearing there at all other than to provide a centre of rotation.

I like the idea of transport bearings if you have a hard enough base surface. 

Share this post


Link to post
Share on other sites

I've always thought people wouldn't pay hundreds of pounds for a decent commercial mount if you could make something just as good with a bit of wood and some teflon pads at a fraction of the cost. I've had a home made 8.75" f7.2 Newtonian for thirty years which has been on several home made dobsonian mounts - all scrapped for the reasons mentioned on this post. Partly my own fault for not following proper designs or plans but I've wasted untold time on this and this post has reminded me not to waste any more time on dobsonian mounts. I've read some articles which indicate that you really need to know what you're doing to design and build a good dobsonian mount otherwise you can waste a lot of time and effort.

Share this post


Link to post
Share on other sites

This one was built by an SGL member who knew what he was doing. It works superbly :icon_biggrin:

 

oo12dob01.JPG

Share this post


Link to post
Share on other sites
11 hours ago, Davidv said:

I've always thought people wouldn't pay hundreds of pounds for a decent commercial mount if you could make something just as good with a bit of wood and some teflon pads at a fraction of the cost. I've had a home made 8.75" f7.2 Newtonian for thirty years which has been on several home made dobsonian mounts - all scrapped for the reasons mentioned on this post. Partly my own fault for not following proper designs or plans but I've wasted untold time on this and this post has reminded me not to waste any more time on dobsonian mounts. I've read some articles which indicate that you really need to know what you're doing to design and build a good dobsonian mount otherwise you can waste a lot of time and effort.

I'm not sure what you are doing wrong but none of my Dobsonian builds has offered anything but smooth, effortless movement.  :thumbsup:

Except one. Which was a plywood equatorial with large disk bearings. The cantilever forces required the bearings be bolted through and tightened.

This  increased the friction beyond the acceptable. It might have worked better on a stiffer pier than my 4" x 6' steel pipe.

Share this post


Link to post
Share on other sites

Think I goofed a wee bit on my dob build...the azimuth movement is fantastic on the furniture gliders and Lazy Susan but I need to sort the Alt bearings...

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By Simple-Human
      Just wondering what peoples thoughts are on the pro's and con's of the different types of mounts out there? Do Dobsonian mounts have issues on non-flat surfaces (like a garden) or can Equatorial mounts ever have issues getting out of line too easily?
    • By Piero
      Very happy with it! Wish the sky were clear, but as we all know, when we buy astro equipment, it's cloudy! Argh!
      The telescope was collected from David Lukehurst at noon and then we travelled back to Cambridge. 
      John Nichol primary mirror: 37mm thickness, Suprax. Hilux coated. Optics 1/8 PV wavefront  1/27 wave RMS. Strehl .95. Secondary mirror: 62mm MA.
      Here a few photos:



       



       

       
       



       


    • By markastro
      Hi,
       
          Looking for a 12" DOB (or larger) which can be transported to Prestwick, Ayrshire. Any brand, as long as the telescope is optically sound and in good working order. I'm a reliable buyer who has bought and sold on this site before.
       
      Thanks,
       
      Mark
    • By Ships and Stars
      Hi all,
      Last night was the best night of astronomy I've had in my short time delving into this passion. It was simply incredible. Fortunately my dear friends the midgies have departed Scotland for another season. This means I can now stand at the scope without ingesting a lungful of tiny biting insects and concentrate on what I am observing. Always a plus!
      Two nights ago I went to my local dark spot with my 200p SW reflector. It was wonderful. LP map shows Bortle 4, but I would actually say it was a 3 or possibly a 'bright 2' when the lights go down a bit in the wee hours.
      Last night, I took the 20" dob and parked up. I am finding it easier and easier to move this beast around, but it's still a little bit of work to set up at the end of the day (literally). It can't all be so easy!
      I'm fairly new to astronomy and my scopes haven't seen a huge amount of use. After several failed attempts to get the GOTO working, I finally sussed it last night. It was just a few simple things really - small errors on my part such as a misplaced washer which blocked the azimuth from using its full range of motion, combined with a limited view at home which prevented me from doing a successful align. A huge relief to get the GOTO up and running, but I now feel a bit like I'm cheating!
      I don't feel guilty enough to not use the GOTO however😁 Frankly, it's brilliant and was putting objects bang in the centre of the EP.
      I arrived about 6pm yesterday so plenty of time to set up. I left my counterweights at home and thus ended up strapping a small vinyl bag of tools and tyre jack to the underside of the mirror box with a tie-down. Worked really well actually! Can fine tune by removing a spanner or two.
      A few drops of rain blew through just before dusk but then rapidly cleared off, so all systems go.
      I tripped over the power cord after my first successful align. And then did it again a minute later after my second align! Will need to tidy that arrangement up or put some of my glow tape on the cable. Plenty of practice then doing an alignment, haha.
      M57 Ring Nebula for starters, I've been playing with my Baader 36mm aspheric quite a lot lately, I like the wide views. The Ring was fairly small through the 36mm but bright and crisply defined with an apparent faint blue tint. I then swapped to the 21mm Ethos and OIII which stayed in the focuser most of the night. 
      Next stop was NGC6960, Western Veil Nebula or 'Witch's Broom Nebula' which was mind-blowing. It appeared as a silvery apparition which threaded right across the sky and extended well past the FOV from the 21mm Ethos. Scanning along its wispy tentacles was amazing. There's something unnerving about viewing it, it gives me goose-pimples, just otherworldly. The Eastern Veil and Pickering's Triangle in the central area were also clearly prominent, albeit slightly less luminous than 6960. The Veil was also clearly visible without the OIII, but with much more 'background noise', i.e. stars competing for attention.
      Following this, I slewed over to the Cocoon Nebula, but only saw a very dark lane practically void of stars. That was interesting in itself as it was so apparent by virtue of its darkness.. I don't know if I bumped the scope alignment of if I was just too impatient to punch another object in to the handset, but didn't spend a huge amount of time chasing it. In hindsight, I think I slewed to the wrong end of the dark lane. I'll find it next go.
      I then lined up on the Crescent Nebula which was easily visible, lots of fine filamentary details observable after some time studying it. A beauty.
      Next was Dumbbell Nebula which practically looked 3D through the big dob, just jumped right out at me. Another simply amazing sight. I spent quite a long time staring at it and could easily see the entire shape and structure extending from the 'Apple Core'. I remarked last night it looked like it was hanging inches in front of the scope. That's sheer aperture working I suppose!
      At the end, I spent some time just slewing around and having a mesmerising look across the sky, just taking in the depth and variable magnitude of stars that a big scope can display. I was already running on three hours' sleep from the previous night and by this time, I was starting to crash but was on a natural high. I crashed into the bed happily.
      Can't wait for another clear night with the big dob. I was a bit worried a few weeks ago that I'd bought something I didn't have the time or skill to fully appreciate, but getting the GOTO up and running and being able to rapidly slew to various objects really put things into perspective. My 200p is a wonderful, portable scope, but in comparison, 20" of aperture is simply a completely different level. It is like the difference between a small grainy 640px video and high definition 4k with the brightness cranked right up.
      Tonight I shall stay in, sleep well and dream about how much discarded glass is needed to cast a 36" mirror blank and how many years it would take me to figure it...
       
      Clear skies all
       
       
       
       

    • By astrorg
      Hello
      I have been away from this forum from possibly July - I never find a lot of time to do anything these days, same to be able to relax reading and interacting Astronomy forums.
      I asked here a few ideas about making a solar scope or modifying whatever I had and I was recommended to also see Solar Chat Forums and I did.
      Thanks to solarchatforums I have been able to do something decent and here is what I have done so far - very slowly!
      1. I purchased a second hand PST and replaced its ITF with Maier one from the US and it finally had a clear image coming through + moved Etalon screw to third position - all the usual thing everybody does [after I researched it]!
      2. used a new SCT screw-on short focuser [used once or twice on a LX200 R Classic] and using Teflon tape I screwed the PST Etalon to the focuser and purchased a 2" adaptor to fit on Etalon.
      3. then used a Chinese 2" to 1.25 and modified the 2" side socket taking internal ring off and making 3x 120° threaded holes and 3x nylon thumb screws and used that as an adaptor to fit the original PST eyepiece holder - strangely enough at present this adaptor is also used as a tilter ... until I buy a proper camera tilter
      4. then fit the above eyepiece holder into the SCT focuser with 2" to 1.252 adaptor in it and screwed the whole Gold PST tube with Etalon in it and made a BETTER PST - see image

      5. I also initially tried a 2.2x DSLR camera Lens magnifier in front of PST and it decently works too - so PST will be fine for full solar disk mainly and without the 0.5 angstrom - not forcibly needed, I am probably around 0.7 as it is!
      6. more importantly, I decided to make my own 90mm solar scope using the above bits and pieces.
      7. with the help of Solar Chat Forums [great guys with a lot of knowledge, some are professional - i.e. they know the optics mathematical details - which helps] I purchased a cheap Bresser AR90/900
      8. the ONLY usable thing there ... is the main tube, a nice and thick tube - the rest is ALL plastic!!!
      I dismounted all parts and saw tube shorter ... a bit too much ! - I could have saved ~6cm really as I went with original ideas, but forgot I was using a different telescope from my initial thoughts - silly me!
      So, I added a 6cm extension - no problems there to reach the 20cm inward needed for the PST Etalon which has ~20cm FL
      9. initially I used a Tuna Fish 100g tin to adapt the SCT focuser onto my AR152 and fit Etalon inside the focuser to get near the 20cm needed- lets call it Quark unit - which it is really!
      It worked well, so I decided to add a second focuser to tune the Etalon ... getting back to AR90/900 ...
      10. I was trying to avoid overspending, I could not afford to spend too much - then I remembered I had a unused AR102SX which in my mind I guessed ... the focuser should over AR90/900 and it did!
      It just fits perfectly - then drilled three holes for the holding screws et-voila'
      11. I purchased a second hand 75mn Baader D-ERF and fit it INSIDE the AR90 tube at about 20cm inside from the front air-spaced doublet lenses, as there are the usual internal rings soldered in and just sit on it and I have about 70mm aperture  - i.e 70mm width from the D-ERF for photons to get through.
      At that ~20cm distance from front lenses the beam is still very large - probably about 60-65mm - there is no heat in between - no need for air-escaping holes
      12. when I have the time I will make a solar finder scope and fit it on the tube - not that is really needed - I usually use CDC to get there almost over The Sun [having an almost exact spot on the yard!] - then use my eye without eyepiece and look thourgh the PST eyepiece holder for solar shinging and centre the telescope over The Sun.
      Well, it works well after tuning Etalon focuser correctly and then focusing/tuning Etalon etc. - the usual.
      See some images - still learning imaging/processing and a lot more to learn about Solar ... a lot!
      I will probably need to get a Power-mate 2.5x when I can afford it!
       
       

      1st mod - without the original black box - it works so much better - better focusing and sharper viewing too.


      This is the AR90/900 shorten tube with AR102SX focuser and adaptors to test it normally
       

       
      This is complete with the Quark Unit on the right side
      Since this image there have been some changing - do not use the revelation adaptor any more and added a 6cm 2" extension.
       
      Here are some images:

       
       
       

       
       
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.