Dampening on gs dobs

[Starkler (Geoff)]

Ken could you let us know the bolt size and thread just for reference purposes thanks?

[ballaratdragons (Ken)]

Don't know, I'm not much of an engineer. The original assembly manual calls them 'Philips Head Screw Black'.

The thread length is 38mm. The thread itself I don't know, but the O.D. of the thread is 6mm. It is the bolt in the bottom spring mount. I took one of mine to the Bolts and Fasteners shop and they matched it for me.

I just went and compared it to other bolts I have and it is the same thread as a standard Gal Coach Bolt of the same diameter.

I've never been good with AF and Whitworth etc.

[ausastronomer (John Bambury)]

They are standard 6mm metric.

All the bolts and nuts on the GS dobs are standard metric sizes of 3mm,4mm,5mm and 6mm, I can't remember what the centrebolt on the groundoard was because I had to replace mine with a 1/2" UNC centre bolt to tie in with argo navis (long story) and I can't remember whether I had to drill the hole out. The only non standard bolts are the 3 collimation thumb screws on the bottom of the mirror cell which are 7mm metric which is a non standard metric size in Australia but used in Asia.

Clear Skies
John Bambury

[ballaratdragons (Ken)]

Well, there you go! Thanks John.

They are 38mm X 6mm Metric domed head philips bolt.

[slice of heaven]

Fitted the extra teflon pads to the alt bearing and they removed all the sideways travel.....Thanks AUS.
. Also added some self adhesive foam strips to the alt bearing support to stiffen the alt movement. I used 5mmx12mm strip , this suits my (standard ) setup with no springs & barlow & ep fitted , test before you stick. Most benefit came from the 2 placed above the teflon strips. This has stopped the OT from dipping when near horizontal and over balancing when near vertical due to the height of the the finder. We have since replaced the finder with a telrad, their so much easier.
. With the dustcap fitted the OT will still nosedive so we've made a padded brace (prototype:just clamped) to prevent any damage and stop flexing of the 2 side supports. This has improved the dampening greatly and the real one should fix it totally when made.
. While at the cabinetmakers sourcing material I queried about Ebony star. It's a laminate made by Westernart , ebony star is a pattern , the texture is the real point of concern. The Touchstone texture is a 50 point dimpled surface with a gloss and feels like the right stuff. " Anybody know for sure?" It's roughly $90 a sheet 6'x4' but I can wait for an offcut for $15 (fitted) .Hopefully this would fix the sticky az movement problem. Mines 'ok' but Ive had to use 6 teflon pads,3 on the LP for slide & 3 on the outside for stability.


Slice

[ausastronomer (John Bambury)]

[QUOTE]Originally posted by slice of heaven

Also added some self adhesive foam strips to the alt bearing support to stiffen the alt movement. I used 5mmx12mm strip , this suits my (standard ) setup with no springs & barlow & ep fitted , test before you stick.


Geoff,

This is a bandaid solution only IMO.

The proper or recommended way to adjust the altitude motion of your scope is to move the teflon pads that the altitude bearing rides on. The 1st thing to do is replace the supplied nylon pads with proper teflon pads. If you want to make the motion stiffer you move the pads further apart (I would try about 1/2 to 3/4 of an inch for starters) if you want to make the motion lighter you move them closer together.

PS You can re-use the nylon pads but they are stapled so you would need to re staple them when you reposition and thats hard to do without the staple staying proud of the surface. I used new teflon pads with 2 small 4 gauge c/sunk screws.

CS-John B

[slice of heaven]

I better get a bigger note book for all these facts and figures , a little bit of knowledge goes a long way ....Thanks Aus.
. Any idea about ebony star? I only have a sample piece ,it feels right.

What I'm after is a mount with a slick featherweight movement but stays put , and a perfectly stable view at the ep. As per the Parks. The kids have to be able to use it comfortably and enjoy it.
More like a family car with power steering rather than a truck without.
I'll definitely try repositioning the pads later on to fine tune it and I'll let you know the results. Then I can pull the 'bandaids' off. I've already thrown away the crutches supplied ( the springs ) had no intention of fitting them. In my experience with teflon, if teflon is mated to a flat surface and too much pressure applied it takes a greater force on startup to break the suction , which results in jerky operation' exactly what you dont want on a scope. Hence the long term use and recomendation of the dimpled laminate 'ebony star'. Their choice of materials on the az/alt is far from ideal. The az should have had the teflon riding on a surface similar to ebony star and a less slippery surface on the alt, or as you stated, better positioning of the pads. Minimal cost and effort to them for a better product. They should have done more R&D. Still ,it makes for a good project and keeps little hands busy.

Slice

[ausastronomer (John Bambury)]

[QUOTE]Originally posted by slice of heaven
>[B]I better get a bigger note book for all these facts and >figures , a little bit of knowledge goes a long way ....Thanks Aus.
> Any idea about ebony star? I only have a sample piece ,it >feels right.

Yep, Ebony star is a specific pattern of Wilson Art in the USA. It has a dimpled finish and that is the critical thing. You need to get a laminate that has a matt dimpled finish. Any 1 of 100's from several different manufacturers work equally as well as ebony star. My scope actually uses a Wilson Art pattern called Mystique Night, works just as well, the surface texture is the critical factor not the colour. I suggest you go to a kitchen refit company and buy a scrap sheet of laminate with the same texture as ebony star. I have done that on a couple of occasions and they will sell it about $20 per 1/2 sheet. Which prolly does 2 scopes.

>What I'm after is a mount with a slick featherweight movement >but stays put , and a perfectly stable view at the ep. As per the >Parks. The kids have to be able to use it comfortably and enjoy >it. More like a family car with power steering rather than a truck >without.

You will have that after you do the teflon pad ebony star thingy.

>They should have done more R&D.

Couldn't agree more, but it all comes down to cost

>Still ,it makes for a good project and keeps little hands busy.

CS-John B

[slice of heaven]

Thanks Aus
I'll be back to the cabinetmakers tomorrow. I'll finger all their samples and see what comes up.

Hmmm...Ebony star....Mystique night...suitable names for materials to be used in telescopes.

Slice