GSO 10" - spring tension - bad design ??

srv · #1 20-02-2008, 01:06 PM

I have a problem with my 10" GSO.

Because of the amount of tension on the azimuth spring
the lower bolt has pulled and loosened the nut/collar
seated in the chipboard base.
( see attached picture)
http://members.iinet.net.au/%7Ematth...s/IMG_0699.jpg

Anyone else experience this?

I have some idea on how to fix this
using a metal plate with a nut/collar welded to it.
I'm also interested to see if anyone else
has some ideas.

Another problem I found is that the azimuth tilt causes the scope to move
sideways. I thought of using the metal plate to cover the sides further up
to stop the black round plastic from moving sideways.
I'm also finding that one of the 'teflon' pads is scratching the black plastic/OTA mountings.
http://members.iinet.net.au/%7Ematth...s/IMG_0702.jpg

Any thoughts/suggestions?
thks

Matt.

rmcpb (Rob) · #2 20-02-2008, 01:44 PM

Matt,

First the scratched bearing. Have a look at the plastic pad and you will probably see a small staple that is raised above the surface of the pad. Knock it in below the pad surface and your problems will not get any worse. Smooth the scratches and the surface of both bearings with some very fine wet and dry and your movement will be improved, reduces the stication.

As for the pulled out spring. Well there must be some serious tension on that bolt to pull out like that. Before I made my mount with oversized bearings I did not use the springs at all. I got a couple of large magnets out of some old speakers and covered them with some self adhesive felt from Spotlight. I then used these to balance the scope with great success.

As for the sideways movement, have the nuts that hold the bearings come lose? Its a common thing with the GS design and when it happens to one bearing it slips which could cause the off axis movement. Line them up and tighten the nuts and use some Loctite to stop them coming lose again.

Have fun

srv · #3 20-02-2008, 02:05 PM

Thanks for the info.
I will recheck the bearings for alignment.

Here is a sample mockup picture of what I had in mind.
Using a fabricated metal plate, welded nut/collar for the spring bolt.

http://members.iinet.net.au/%7Ematth...osed-plate.jpg

GSO only supply 1 spring/ring per side.
I added the second, but then found the tension wasn't enough to stop the scope moving by itself.
I don't have any extra parts on the OTA, only the viewfinder and focuser.

Matt.

rmcpb (Rob) · #4 20-02-2008, 02:15 PM

Matt,

If you can just try the magnet trick, its really commonly done and it very easy.

Cheers

erick (Eric) · #5 20-02-2008, 03:34 PM

I have two of these bases and I guess it's a matter of you get what you pay for - and we didn't pay that much, really - certainly not the price of a well-machined precision optical device and mount.

So many of us end up fiddling around. Away you go - add plates, put bolts right through the particle board etc.

I see that Bintel add an extra sheet of notes, including advice to watch the staples working up above the surface of the teflon. I purchased some new pads and they came with screws and countersunk holes in the teflon. You might try replacing staples with screws, if the staples persist in misbehaving.

I've already swapped the springs upside down on my 8" having seen them this way in a Zhumell manual I saw on the web. (I think Zhumell is a beanding of GSOs in the USA.) That meant some new bolts (stainless) added. By this I mean the spring is fixed to the base and I put them up onto the OTA. (Remembering to put my foot on the base first or the whole lot lifts off the ground!

I don't have a problem with lateral movement on the Alt bearings on my 8", but I know the previous owner observed it on the 12". He had added digital encoders to the axes, so it was a bit of a problem. It may be flexing of the larger 12" base. I've been thinking of how to add a brace between the top two corners of the base, after the OTA has been put into place. Might even put a nice eyepiece rack on that brace!

Magnets covered in felt - yes, I use those for balance. Neat, because you can just reach down and slide it up and down a bit as you change eyepieces or elevation. However, a bit of dew and too much elevation and the magnet takes off. No worse sound then a brief swish, followed by clunk and thunk as the magnet slides down, hits the primary mirror flange and falls off into the dirt!

Have fun - make it better!

srv · #6 20-02-2008, 03:35 PM

Can you let me know where you purchased replacement teflon pads from
with the countersunk screws . thks.

erick (Eric) · #7 20-02-2008, 03:37 PM

Quote:

Originally Posted by srv

Can you let me know where you purchased replacement teflon pads from
with the countersunk screws . thks.

USA supplier - I'll have to look it up. Supplies upgrade kits with bigger pads, a central supporting pad and new central improved bolt.

erick (Eric) · #8 20-02-2008, 03:41 PM

OK, here we go.

http://www.astrosystems.biz/pivot.htm

He has lots of other neat stuff as well.

Also read up here:-

http://www.iceinspace.com.au/index.p...41,451,0,0,1,0

This is the 12" I purchased, but I got the Astrosystems bits prior to that and upgraded my 8".

Starkler (Geoff) · #9 20-02-2008, 06:25 PM

Theres a lot that can be done to improve the motions of a gso dob.

http://www.iceinspace.com.au/forum/s...ad.php?t=13760

GrahamL · #10 20-02-2008, 08:00 PM

True .. the best thing I ever did to those springs was lose them in a cupboard somewhere ..I'm not sure its a bad design as such ,works great with focuser weights you buy them with but adjusting for heavier eyepieces and assorted extras the old speaker magnet fix can be tricked up pretty well.

srv · #11 12-03-2008, 11:09 PM

For interest - here are the finished pics.

I had a friend make steel plates for me and used a
threaded hole for the spring bolts.

I painted the plates with some rust proof/undercoat
and then finished them with a black mat spray paint.

Here are some pics of the finished design.
http://members.iinet.net.au/~matthew.../finished1.jpg

http://members.iinet.net.au/~matthew.../finished2.jpg

I also put some new teflon pads in, much thicker than the original teflon (plastic ?) -- new teflon ones sourced from Astrosystems.
Thks Erick for the info.

GTB_an_Owl (Geoff) · #12 13-03-2008, 12:18 AM

to save getting your fingers caught on the spring/ring when attaching - tie a shoelace on the bottom ring and use that to pull down on

geoff

erick (Eric) · #13 13-03-2008, 12:18 AM

That looks very neat and solid, Matt. You've given me an idea for my 12" base I'll have to work on.

I used it two nights last weekend and didn't put the friction springs on. No wind helped the situation, but it was still very sensitive and would easily move if I didn't get the balance right.