Another ebony star question

[halo1234]

Sorry I just want to get this right before I order stuff & I get it wrong. This is for my SW 300P again.I wondered if anyone had found a good UK source for Ebony Star. I can see TE in germany do it as pre formed rings. Just would be nice to source locally.

I've found the below source which seems to be the same stuff.

EBONY STAR 60 - Laminate Edging 3m x 42mm

Also what dia do you have the ebony star ring in relation to the centre bolt?

I've found the below source which seems to be the same stuff.

EBONY STAR 60 - Laminate Edging 3m x 42mm

I've also found some PTFE sheets, but what thickness do I go for?

eBay - The UK's Online Marketplace

Am I right in thinking the load is mainly on the PTFE & Ebony star?

The declination is very sticky.I've noticed the load is really just on the bolt & mount hole. I'm wondering if lubrication will reslove this?

Thanks

[scogyrd]

I don't think the sources you've found would be any good as it's just a thin strip of ebony star to do the edge of a worktop that you've just cut. You'd need to buy a sheet of it to do the base of a dob instead.

TBH I'm not convinced ebony star is the holy grail that some people like to make it out to be either. I didn't notice that much of a difference when I fitted it to my scope, when compared to the laminate that skywatcher used, and it certainly wasn't half as good as I'd been led to believe. There are many other alternatives that are just as good, if not better, imo. However, having said that, I've only got an 8" scope and it may well work better on larger, heavier scopes.

[Rusty Strings]

The strip you've found isn't the same, I know I bought some along with an ebony star ring. The texture on the ring is far lumpier than the strip. The ring did make a huge difference to the stiction on my homemade dob mount but it was replacing a 12" vinyl LP. I did use the strip on new, larger diameter alt bearings and it does feel better than the old PVC ones.

[asteria]

Hi there - I'm interested to know whether a bearing can be made from a piece of acrylic and PFTE/Teflon. I am thinking of making a dob mount using an acrylic disc (say 2-3mm) and PTFE pads. Any thoughts. Thanks. Ed

[johninderby]

You can get the proper Ebony Star in pre-cut rings for your dob base from Telescope Service.

http://www.teleskop-express.de/shop/product_info.php/language/de/info/p3876_.html

The problem with using an acrylic disk is that the surface is smooth and you will have problems with "sticktion" when you start to move. You need something like Ebony Star which has a lumpy surface that gives low friction when moving but has no "sticktion" as well.

John

[asteria]

Hi John - that's helpful, so there needs to be a bit of 'texture' on the disc. I'll look at the TS site. Thanks. Ed

[johninderby]

Hi John - that's helpful, so there needs to be a bit of 'texture' on the disc. I'll look at the TS site. Thanks. Ed

Yes it needs just the right texture.

TS also sell the Teflon.

John

[asteria]

Hi - the disc seems a bit big for my needs - I probably need something about 7" in diameter as the scope isn't going to be big. I just need an offcut or scrap. Will keep my eyes open. Thanks again. Ed

[johninderby]

While TS do squares of Ebonystar, the smallest is 40cm by 40cm. That would give enough extra to do the alt bearings as well and I'm sure you could easily sell the rest on SGL.

http://www.teleskop-express.de/shop/product_info.php/info/p2472_Ebony-Star-Platte---40x40cm---Zum-Selbstbau-von-Gleitlagern.html

John

[asteria]

Perfect!! Will track this down - it's just what I want. Thanks. Ed

[halo1234]

So I get this right. I have a SW 300P. I was planning on getting the Ebony-Star Ring D=40cm zum Selbstbau from TE. I was also planning on getting some 3mm think PTFE from ebay. Does it matter how much I use? Do I also need to replace the PTFE washer on the main bolt?

Thanks

[johninderby]

So I get this right. I have a SW 300P. I was planning on getting the Ebony-Star Ring D=40cm zum Selbstbau from TE. I was also planning on getting some 3mm think PTFE from ebay. Does it matter how much I use? Do I also need to replace the PTFE washer on the main bolt?

Thanks

Just make sure it's good quality "virgin" Teflon/PTFE if you get it from eBay. You don't need to make the PTFE pads too large. 30mm to 40mm dia. will be big enough. TS also sells the Teflon you'd need. The PTFE washer is OK so that doesn't need changing.

John

[halo1234]

Does the dia of the ebony star matter releative to the ota or base of the dob?

[johninderby]

The Ebonystar ring wants to be a fairly large diameter. Have a look at where the little Teflon pads are on the basebaord now and that will be a good guideline.

John

[callump]

There is quite a lot of myth and legend around "ebony star".

Ebony Star is(was) made by Wilsonart a US laminate manufacturer. Formica is a competitor business.

But Ebony Star is just a colour - the important thing was the finish. The finish as used in K&B book was, i think, called crystal, and sheets with this finish had the suffix -50. So the classic Ebony Star has the code 4552-50.

Dave Kriege liked the colour and the name, so that is what he recommended, but in fact any Wilsonart laminate with that finish would work just as well.

I understand from discussions on Cloudynights that the Crystal finish is not made any more. But there may be stock of it still around.

Some Cloudynight ATMs suggest using Wilsonart laminate with a finish of -45. Others have tried Formica finish -42. These two seem to perform about the same.

Legend has it that Dave Kreige went into a laminate shop and tried sliding a small piece of teflon one the samples to determine which worked best, and that's how he came to find 'Ebony Star' - you could always try the same test if you get a few samples of different surfaces.

K&B also suggests FRP (Fibreglass Reinforced Plastic) but I have never been able to find out what this is called in the UK, or find a supplier (though I am sure it must be used somewhere).

Callum

[Hypernova]

If it is any help, when I purchased a ring of ES for my 200p dob I bought the 50cm diameter ring. It was the most appropriate for my 'scope as it fitted right over where the rock box contacts the teflon pads on the base, I had to cut notches out where the fixing bolts come through though but this wasn't much of an issue. The ring was glued to the rocker box with a 2 part strong adhesive which is mixed just before application.

I will agree with Scogyrd that it hadn't provided the massive improvement that I was hoping for, the stiction has reduced and the movement is smoother but not massively so and I feel that better results could've been achieved for less outlay by making use of a lazy suzan bearing instead, an option which I also considered at the time. I will go about applying a finish of wax to the surface at a later date to see if it makes any improvement to the motion, a fresh set of PTFE pads might be added as well.

[Moonshane]

a couple of points here based on my experience with my 16" dob (home made)

1) unless you want to screw / nail your teflon pads then buy sheets with one side etched. this allows them to be glued down. I got them off ebay and they are fine.

2) I thought about buying ebony star but to be honest I was a little short on funds. I took a chance and went with a sheet of laminate that I found at a local kitchen supplier (not a major chain). this was sold at £2 per square foot so £8 in total. it was not as 'bobbly' as ES but had a slight roughness to it. the alt bearings were a different material but had the same texture.

3) for the azimuth bearing I used three pads as normal and an extra one of the same thickness around the central bolt. two each side on the alt.

4) I turtle waxed the laminate before putting it all together.

the bearings are very smooth with very little stiction. maybe the weight of my scope helps but it worked for me.

if you can afford ES then get it but make sure you wax the surface every now and again to aid flow.

hope this helps.

[johninderby]

It should be emphasized that you MUST wax the ebonystar with Turtle Wax for it work smoothly. If it's not waxed it simply won't work properly and you'll wonder why you fitted it.

Also the cheap little Teflon pads that come with SkyWatcher/GSO dobs are poor quality and you won't see the full benefits of the ebonystar.

It's the combination of the ebonystar + Turtle Wax + good Teflon that make it a good system.

John

[Moonshane]

totally agree John.

it's important to estimate the weight of the fully loaded scope too. teflon / laminate bearings should have a weight of 15psi so if your scope excluding the ground board weighs say 50 pounds, you need pads which are 50 / 15 / 3 = 1.1" square so about 1 inch x 1 inch for the azimuth and about the same for the alt.

[johninderby]

A common mistake is making the Teflon pads too big which will simply add drag. Also should mention that with the Alt bearings the two Teflon pads on each side should be fairly close together to reduce drag.

Taking a different tack I wonder if anyone has tried an air-table base for floating the scope. By varying the air pressure you could adjust the drag. Of course there would be one major downside....if your battery was flat no observing.

John

[Moonshane]

the standard spacing for the alt bearings is 65-70 degrees apart i.e. from the centre of rotation or another way at just under 24 mins past and 36 mins past. worked on my mounts really well.

[halo1234]

For some reason I didn't see all the recent posts on this subject. So I may have not made the best choice. In the mean time I bought some pre-cut ES with a 40cm dia I did this based on advice from a US website suggesting this size for 10'' to 14'' dobs. I also picked up some MaxGlide 5cm pads. They are supposed to have a heavy coat of PTFE, plus they are drilled & have sticky pads on one side. I picked 5cm since the ES ring thickness is 5cm. So I need to figure out how many pads I need to use. Due to the width of the pads & ES I might go for 3. I'm glad you all mentioned the wax. I would of missed that.

I'm also making a new base this weekend. I've bought some adjustable feet & M10 X 25mm Hex Drive Screw-In Threaded Inserts to match. I was going to cut a square based & mount 4 feet on each corner. I'm also going to nip to Staples & get a setting circle printed off & laminated.

Cheers

[Moonshane]

hi Halo

it's essential you only use three pads and that they are spaced at 120 degrees from centre and directly above the (three) feet. if you do more than three you'll lose stability (as you will if you don't put the pads above the feet).

[halo1234]

Thanks again Moonshane. So really 40cm dia of ES is too small since the feet would provide limited stability that far away from the edge of the base.

[Moonshane]

not necessarily. you could make slightly bigger feet which sit on and outside of the pad placement and then that would still work. the main thing is that the weight is transferred directly to the feet.