Good link for dob bearings.

[spaceboy]

How did you fix the LS to both bases??? You would need the 225mm LS for your 8" as the 10" is a 520mm base board so I don't have the problem with the cradle fixing bolts getting in the way. I know the ones you are on about and they are a pain. I made laminated setting circles to fit between the base boards and those bolts kept catching that and in the end I had to give up on the idea. I decided to fit a gemred rotary decoder instead of setting circles.

[sixela]

I think I'll try the ebony star,

You'll still have to experiment with pad placement and size when you get the Ebony Star; the ultimate goal is for the static and dynamic friction on both axes to be well matched with the scope pointing roughly 45° up; in other words, when you push the scope's end up and away from you at the same time, it should start to move up and away at the same time and move in the direction you pushed.

That's what's actually more difficult to achieve with a lazy Susan (though perhaps not impossible): building an Alt and an Az that behave the same way so that you can move both axes simultaneously with ease.

Move the pads closer to the centre to reduce the force necessary to move in Az.

Try to size pads for 15psi loading at least, certainly not significantly less.

[spaceboy]

How can you improve on ALT or do you just balance the scope to the EP using some thing on the back of the OTA??

[scogyrd]

How did you fix the LS to both bases??

I drilled 2 holes through the bottom board (it might've been 1 actually, the base is in the garage atm and it's too cold outside to check), to line up with the big holes in the LS, and screwed it to the top board through them.

I was tempted to do it to my 200p but chickened out in the end.

You would need the 225mm LS for your 8" as the 10" is a 520mm base board so I don't have the problem with the cradle fixing bolts getting in the way.

I tried the 225mm LS first and it wobbled even worse.

I think it's mainly because of the centre bolt though. If the weather's not too cold at the weekend I'm going to have a go at fixing that to the base board.

TBH I'm half tempted to buy a sheet of MDF and make a new base. I'm not really impressed with the one skywatcher gives you, it's too stiff and heavy for my liking.

[spaceboy]

Strongly recommend you don't use MDF!!!!

[scogyrd]

Strongly recommend you don't use MDF!!!!

Why not? My last one works fine. It's not like skywatcher gives you good quality wood either.

[sixela]

How can you improve on ALT or do you just balance the scope to the EP using some thing on the back of the OTA??

Personally, I don't need to improve my Alt bearing or the scope will move as soon as I even think of switching eyepieces .

Do you have a sticky Alt? I'd suggest trying Sailkote on whatever bearing you already have, if you just mean you have too much friction.

But yes, if the problem on Alt is that you have to somehow make the friction colossal before the scope stays put, counterweights are the solution. The first thing to do is to make the scope as close as neutral as possible in the middle of your eyepiece range (i.e. heaviest_eyepiece/2).

Sometimes it's tricky, because you have two dimensions for the centre of gravity to wander; you have to place counterweights so that it works well both at the horizon and at the zenith! If it's perfectly neutral at the horizon but not at the zenith you need to move the counterweights to another spot on the same tube section.

[spaceboy]

Why not? My last one works fine. It's not like skywatcher gives you good quality wood either.

My point exactly Scogyrd. If your going to go to the trouble of making a replacement board why not make it out of a wood that not easily effected by the elements. The idea would be to upgrade not replace with the same mediocre stuff Skywatcher send out.

Thanks Sixela. I noticed I have to make small adjustments on ALT which can have the object zooming out of view but I will try sailkote before looking to make a balance beam. Where do you get it from ??

[scogyrd]

My point exactly Scogyrd. If your going to go to the trouble of making a replacement board why not make it out of a wood that not easily effected by the elements. The idea would be to upgrade not replace with the same mediocre stuff Skywatcher send out.

TBH I think mdf would be an upgrade from the chipboard skywatcher use.

I was only thinking about using mdf to make a prototype with anyway, mainly because it's pretty cheap so I won't get too upset if I make a mistake.

Once I'd made something I'm happy with I'd probably remake it with some decent wood.

[spaceboy]

Sounds like a plan to me. TBH I have only used MDF once. At the time every show on TV ranted about it so I thought I'd give it a try. Never again! stuff was found to have a mind of its own. I know wood swells and shrink etc but MDF dose it's own thing. For the difference in cost I found the more conventional alternative much better.

[Hypernova]

I have JUST received my ring of Ebony Star from Teleskop Service, via UPS. The product I have got is a ring of the laminate top surface on it's own, no actual work surface underneath. The texture is quite knobbly, kinda like the finish on my old SkySacn eq3-2 mount.

[sixela]

Yup. you stick it to the existing surface (preferably sanded) using thixotropic contact adhesive (and a lot of pressure!)

Knobby is -50 finish. Knobby is good!

[scogyrd]

I have JUST received my ring of Ebony Star from Teleskop Service, via UPS. The product I have got is a ring of the laminate top surface on it's own, no actual work surface underneath. The texture is quite knobbly, kinda like the finish on my old SkySacn eq3-2 mount.

I received mine earlier too. How are you planning on fitting yours? As usual the screws are in the way on my dob so I'm going to fit it to the bottom board and put the teflon bearings on the top.

I've already removed the bearings so if anybody knows of a good source for some new ones it'd be much appreciated.

[Hypernova]

I've just cut around the screws , rather roughly but it won't matter when it's all put together.

[spaceboy]

I've already removed the bearings so if anybody knows of a good source for some new ones it'd be much appreciated.

Teleskope do the best upgrade pads but I would imagine you'd be looking at another £10 P&P. Ebay have strips you can cut to size. Just search under PTFE sheet.

[Moonshane]

I have used this seller on ebay a few times. very reliable and sells odd offcuts cheaply.

benchrisseb items - Get great deals on Business, Office Industrial, Photography items on eBay UK!

[scogyrd]

Teleskope do the best upgrade pads but I would imagine you'd be looking at another £10 P&P. Ebay have strips you can cut to size. Just search under PTFE sheet.

I had a look there before ordering the ES but didnt see any pads, only teflon sheets which seemed a bit expensive. I bought this in the end anyway.

PTFE SHEET 3MM (ETCHED) 150MM X 60MM (CLEARANCE) on eBay (end time 15-Dec-10 10:50:33 GMT)

Thanks for the link as well Moonshane.

[spaceboy]

I always wondered if you could use this sheet instead of ebony star. Or would Teflon on Teflon be to slippery???

[sixela]

Teflon on teflon is actually quite sticky: it's not at all rigid and flows a bit under pressure, so teflon on each side tends to make the pads sink into the teflon at the other side.

You need the "flowing" teflon on one side and something hard on the other. Teflon on aluminium actually also works quite well (but gets dirty as the aluminium oxide layer tends to be rubbed off and clogs things), and teflon on some untextured hard plastics works surprisingly well (and on textured FRP it works even better); there are also some textured plastic sheets to stick onto windows that also work quite well.

Experiment, experiment, experiment. As long as it's hard on the other side and has just the right kind of grainyness (not too small and not too large scale) it'll work; there's nothing magical about HPL laminate.

[irishbloke]

I received mine earlier too. How are you planning on fitting yours? As usual the screws are in the way on my dob so I'm going to fit it to the bottom board and put the teflon bearings on the top.

Hi Scogyrd,

I've read and heard from others the teflon is best on the bottom board because it can be placed near the feet. This means the weight of the scope is constantly distributed in the same way to the feet. If you have the teflon on the top the weight will move around the bottom board so it's more likely to flex and needs to be much stronger to avoid flexure.

It might be easiest to cut parts of the ring off to fit round the screws.

Brian

[spaceboy]

I'm assuming you will be fixing the Ebony star with solvent adhesive???

Make sure you both get down the DIY store for some kind of mask. From my experience of Evostick impact solvent it could have you thinking your in the 60s again. Oh and don't forget some disposable gloves if you like having skin on your fingers.

Once you stick with this stuff it stays stuck. It can get a bit messy if you end up with excess solvent squishing out as every thing you touch afterwords wants to stick to you.

[scogyrd]

Hi Scogyrd,

I've read and heard from others the teflon is best on the bottom board because it can be placed near the feet. This means the weight of the scope is constantly distributed in the same way to the feet. If you have the teflon on the top the weight will move around the bottom board so it's more likely to flex and needs to be much stronger to avoid flexure.

It might be easiest to cut parts of the ring off to fit round the screws.

Brian

I looked at a few plans for dobs and saw that nobody else had put the bearings on the top board so I bought a 16mm flat drill bit and countersunk the offending screws. I'm just going to cover them with the ES ring when I glue it down. I know it means I won't be able to take it to bits again but I'm not planning to and I can at least experiment with different sizes of teflon to get it how I want it now.

I was hoping to finish it today (glueing it at least because the teflon hasn't arrived yet) but I've just spent 2 hours looking for a lost screw and have had enough of it for now.

Does anyone know if you can buy replacement screws from anywhere? Otherwise I'm going to use a bigger wood screw. Which is no big deal, it'd just be nice to keep them all the same.

[spaceboy]

You could try eBay (the one stop shop) I would imagine you can find the same type on the net, ask at a local joiners or DIY centre. The one thing I have found with items like this if you find some where on the net they will want to sell you 1000 or a £50 minimum spend.

If you will be unable to take the cradle apart again It may be worth making sure any joints are sealed and waterproofed to avoid future water swelling the chipboard. I used silicone sealant, it's a bit messy but should give peace of mind.

[scogyrd]

I had planned to replace the skywatcher screws with some that had a countersunk head but after going round B&Q, Focus and a couple of local hardware shops this morning and not finding any, quite a few had the right size but they had different threads, I decided to buy a flat top drill bit and countersink them that way.

It's times like this that convince me that parallel universes do exist. It's the only explanation I can think of for what happened to the missing screw, one minute it was there and the next it'd vanished!

I had planned on sealing it with silicone. I'm a tiler by trade so I'm used to dealing with it. A good tip is to spray any surfaces you don't want it to stick to with soapy water, e.g. when I'm tiling a bathroom I'll fill the joint with silicone, spray it with soapy water and then run my finger down it to smooth it off. If you try doing it without the water it sticks to everything and gets everywhere.

[Moonshane]

It's times like this that convince me that parallel universes do exist. It's the only explanation I can think of for what happened to the missing screw, one minute it was there and the next it'd vanished!

I bet it's in the cleats of your shoes!