My SW Skyliner 200p additions and modifications

[Avocette]

A couple of people have asked me to write up the additions and modifications I have made to my SW Skyliner 200p mount so (before I forget) here goes.....

Water Butt Stand (WBS).

The SW Skyliner 150p, 200p and 250px Dobs are all fitted with mounts of 52cm diameter. If you want to stand up to observe, and to give some protection to the mount from a damp lawn (it’s basically made from melamine coated chipboard so would be susceptible to swelling if it gets wet) you can easily support the mount on a WBS. In addition, if the lawn/patio isn’t level, then you can add some levelling feet to the WBS.

-       the most suitable WBS is one as shown in the photos. If you just want to mount the scope directly on it then you can find a way in which all three feet will balance on it (precarious!) or better you should drill two holes in the top surface to allow two of the three mounting feet to pop through, the third foot sitting comfortable in the large recess (used for the watering can in the normal usage with a Water Butt).

-       Pick up ropes – I added 4mm rope loops in several places around the WBS.

-       Levelling supports. The ones I use are the adjustable feet sold for kitchen cabinets. I hope the photos show how I fitted them into the top of the WBS. With a two axis bubble level fitted to the mount top circle it’s easy to adjust the mount to compensate for sloping ground.

Lazy Susan (LS) bearing:

-       the bearing I chose is around 21cm diameter. Although there is still a bolt in the usual place between the top and bottom mount circles, it no longer plays any part in defining the rotation of the mount. Its role now is partially visual (no empty holes in the top and bottom mount circles) and partially security during transport of the mount. When carrying the mount base by its carrying handle, or the whole scope by the tension adjusting handles, the LS bearing is not under top pressure of the weight of the mount and scope, and depending on the type of LS bearing, without the bolt, there might just be a risk of a ball bearing slipping out of place.

-       The LS bearing is held by two sets of 4 screws, 4 downwards into the bottom mount circle and 4 upwards into the top mount circle. Access to the upper screws (one at a time) is through a hole in the bottom mount circle which matches exactly the hole in the lower surface of the LS bearing which is provided for this purpose.

Teflon furniture sliders:

-       The three rectangular white Teflon pads which were originally stapled into the bottom mount circle are removed entirely and the pairs of staple holes and an area a few centimetres around them is covered with white Fablon (sticky back plastic).

-       Three Telfon 25mm furniture sliders are screwed within a few mm of the edge of the bottom mount circle to form an equilateral triangle. Depending on the thickness of the furniture sliders, a number of layers of plastic (damp-proof) shimming material (jug milk bottle sides or other packaging) must be placed under them until the total thickness (furniture slider plus shims) is equal to the thickness of the LS bearing allowing the furniture slider Teflon surface just to touch the underside of the top mount circle.

Assembling and adjusting the mount:

-       In a first stage the mount is assembled with only the downwards pointing LS bearing screws in place but with the central bolt used to define the centre of rotation. The original bolt should be replaced with one about 5mm longer and ideally made of stainless steel. I found a 60mm M12 bolt, two washers and a Nyloc nut to be ideal used in conjunction with the original black plastic tubular bearing. By a process of trial and error the shims under the furniture sliders are adjusted to give the correct smooth acting rotational friction ‘feel’ for Dob nudging. Of course, it’s essential that this trial and error testing is carried out with the telescope OTA in place.

-       In a second stage, ideally when the system has bedded in for a day or two, the four upwards pointing LS bearing screws are put in place. They are needed to define more precisely the rotation of the mount. Without them and just relying on the coupling bolt, the mount top circle can slip a few mm sideways. The LS bearing screws should be tightened just enough to hold the LS bearing upper face in position against the underside of the top mount circle. This should not affect the friction ‘feel’ of the mount, but be prepared for a second phase of shim adjustments if needed.

Adding the setting circle:

-       The setting circle was made for me by an exhibition poster print shop using matt coated vinyl on a 3mm Foamex backing. This is light, robust material and damp-proof. The circle needs to be around 46 or 47cm diameter so that it is contained without touching the three furniture sliders, and the degree calibrations should be appropriate to match the position of the bezel and alignment wire. The printed Foamex panel was supplied as a large rectangle for me to cut to shape and carry out the final trimming myself. The inner circle sits neatly around the lower half of the LS bearing and rotates smoothly around it. The outer circle is cut at around 47cm diameter except for about 20° where it extends out to form a tab which projects beyond the mount bottom circle by a couple of cm. The final rotational adjustment of the setting circle makes use of this tab.

-       Bezel and alignment wires. In the 200p Dob (Photo 8) pictured the bezel was made (the hard way!) from a cut down non-stick-coated steel ‘Dariole mould’ from Lakeland http://www.lakeland.co.uk/16034/4-Dariole-Moulds . The bottom edge was drilled (pillar drill) with two 1.5mm holes and a length of straightened (stretched) galvanised wire placed through the holes and soldered into position. All exposed metal was then painted with smooth black Hammerite paint. (PM me if you’d like to do the same - I’ve a couple of spare Dariole moulds left).

-       The bezel and alignment wire unit was fixed in place in a circular hole in the mount top circle with white outdoor silicone sealant.

 

As you can imagine the modifications were carried out in an experimental fashion and not step by step in the order given above.

I have also modified a SW Skyliner 250px and took a different approach. The 250px OTA being quite a bit heavier than the 200p, I worked out a way of using six furniture sliders in a circle about half way out from the centre to the edge of the bottom mount circle. This permitted a slightly wider setting circle but entailed a lot of curved slot trimming (Photo 9).

For my next scope modification (SW Skyliner 300p Flextube) I plan to use a plastic desktop cable tidy obtained from a DIY superstore for the bezel, and the galvanised wire will be attached to the underside of the mount top circle. I haven’t quite finalised where to place the furniture sliders and how many to use. Some of you may know that the 300p Flextube comes fitted with a form of LS roller bearing but no Teflon friction control pads. It’s also significantly bigger and heavier than the 200p or 250px, so needs a more powerful technique of nudging to move it and then if you don’t reverse-nudge it to stop, it will continue spinning for some seconds!

[sbooder]

Nice mods, very tidy.

[rob0971]

Great idea with the stand.

[Glennith]

I'm showing this to my husband! He is busy making a deck to stand it on as he wasn't too happy about the chipboard stand but of course the deck could also get damp. We have a couple of water butt stands, great idea.

[asset189]

Great stuff , i like the water butt mod , where did you get the adjusters you added to it? Currently i have a basic 360 degree strip arou d the circumferance of the top base board and a moveable pointer so i can align on any bright star but its a real pain bending down to read it and you mod will solve this. With regards to your base it looks like you have tried a couple of set up with the lazy susan and gliders, what works best? Thanks in advance

[Mr Spock]

Nice mods. You've done a great job there and I'm sure others will do the same having seen this.

[Avocette]

Great stuff , i like the water butt mod , where did you get the adjusters you added to it? 

They're industry standard cabinet feet used in the kitchen fitting industry. I think they should be available at lots of DIY supermarkets. I'd probably start at Wickes or B&Q.

 With regards to your base it looks like you have tried a couple of set up with the lazy susan and gliders, what works best?

The answer is both I'm afraid - the lazy Susan bearing to make a really smooth rotational action followed by careful adjustment of Teflon furniture sliders by the use of shims (packing washers) made from various materials until the thickness giving just the right touch is found. 

The setting circle fits smoothly around the bottom (fixed) half of the LS bearing and at first I just allowed the scope to sit on the bearing and the furniture sliders, with the bolt defining the centre of rotation. I quickly found that this method allowed a few millimetres of slop in this rotation so the best I could achieve with the setting circle was about + or - 2 degrees which can mean you miss the target. So I ended up attaching the upper half of the LS bearing to the mount with 4 more screws (pointing upwards) which are accessed through a hole in the bottom circle of the mount. So now, in fact, the bolt is redundant although I left it in place for cosmetic reasons (looks better than a hole showing the chipboard material).

I'm struggling now with the addition of a setting circle to my 300p Flextube. It doesn't have any Teflon pads at the moment (it comes from the factory with a flat form of LS bearing) and it spins very easily. The bearing is effectively held in place by the bolt and cannot be fixed in place with screws. I may have to replace it with a conventional screwed down and up LS bearing.