Skywatcher Newtonian 10", Cheap & Easy Cell / Spring Upgrade
Anyone interested in upgrading their Skywatcher Black Diamond 10" newtonian mirror cell? I have a thrifty home mod that will allow you to use most of the stock cell & parts (along with some Bunnings bits n pieces) to:
provide WAY more tension / support by adding better springs;
push the primary mirror up the tube to allow the use of MPCCs and change the balance point (slightly);
allow better 'back side' ventilation of the primary mirror; and
provide 9 points of contact to support the primary mirror (vs. the 3 x stock cork points).
And the parts you'll need (I'll provide specifics if anyone is interested):
3 x bigger springs;
9 x stiff rubber spacers;
Dremel (or my $20 Chinese knock-off from Bunnings);
silicone;
hand drill and bits (or a drill press if you're lucky);
screwdrivers etc.
Will attach pics or a vid later if anyone is keen.
But I also know that there is a 'real science' behind mirror cell support points; but I'd perfer not to go there as I don't have the time to get that particular: http://www.cruxis.com/scope/mirroredgecalculator.htm
Logan,
I would be interested to see what you propose, my 8" Skywatcher seems not to have springs but compresses down onto rubber "cushions". It all seems pretty crude, but it works.
Cheers
Graeme
I used 3 x C-774 Utility Compression Springs (made by Centurey Spring Corp or CSC). They provide a rediculous amount of tension compared to the stock springs. (See pic 5). And no need to buy spacers to keep the springs from moving, just leave the 3 x stock springs in there, and place the new springs over them! They keep the new springs perfectly centred
And you can just make out the 9 x black mirror supports. They are furniture spacers / supports from bunnings, and look like Cadbury Choclate squares - only black chocolate! I just used silicone to secure them in a standard 9 point configuration. (See pic 3)
And I upgraded both the mirror lock bolts and tension bolts, 65mm M6 from memory. They don't have to be sunked head, as the black mirror supports raise the mirror a good cm above the mirror cell. I also added wing nuts to the end of the lock bolts. I had to grind the inside of the wings for the head of the bolt to fit, and I secured them with a nut and loc tite. (See pic 2).
I drilled holes through the end of the 3 x tension knobs. This was easy, and done with a hand drill. I then test fitted the M6 bolts to see if they could pass through. I had to grid the inside of the head with a dremmel to make it super smooth for the bolts to pass through. (See pic 2). Alternatively, you could buy nice tri-head knobs from a specilaty faster store. They'll be easier to grab and will make collimation a sinch. But I was happy to mod the stock parts for now: http://ganter-griff.com/Standards,35...c94a&LCID=2057
This mod pushed the primary mirror 2-3 inches up the tube, and will allow air to pass more freely around the mirror and up into the tube when the fan is used. It was kinda cramped back there before the mod. (See pic 3). I will be getting an MPCC shortly. Nice to know that I won't have to cut the tube!
Cheers,
Logie.
Last edited by Logieberra; 08-02-2011 at 09:20 AM.
It has taken a bit more work, but it’s worth it. I now have tremendous compression and greatly reduce mirror movement within the cell.
Recap – the issues:
The 10” mirror was slopping around in the stock configuration. The stock springs were not strong enough to support the weight of this heavy mirror, and I was losing collimation with minor movements – hence the need for stiffer springs. The stock springs were so bad that I found myself using the mirror lock screws to collimate – not ideal.
I will take pics soon to explain these details, but in the meantime here’s the list of my latest problems and solutions:
-The 3 x T-shaped collimation adjustment knobs do not fit snugly into the back of the mirror cell. The stock holes in the cell are too wide, so the knobs slop around 2mm+ in any direction.
-SOLUTION: I decided to use the existing lock screw holes and widen them to 10mm. This provides a prefect fit for the T-shaped adjustment knob.
-I also found that b/c I’m using longer springs, they were warping when compressed and not sitting straight within the cell. This made turning the knobs almost impossible.
-SOLUTION: I grabbed heaps of washers, glued them together, filed them to fit the ID of the springs, and OD of the bolt. I also added some shrink tubing to the bolt so the washers are a perfect fit (I could not find washer that matched the ID of the spring or OD of the bolts – so I had to grind them down by hand… struth!). This keeps the springs centred and makes turning the knobs much easier.
I did a test of the new configuration (by moving the scope around by hand) and the mirror shift is significantly reduce. Looks like I’m on the right track.
Any advice from you expert tinkerers out there?
P.S. my tools are limited, so please forgive my ‘backyard’ ideas and methods
Ummm, sort of, sort of not. I used what is available at most engineering supplies, from memory in my case M5 bolts, with an Allen head (cap screw I call them, perhaps incorrectly), and on the head of these fit a plastic push on cap, with knurling on the edges. It changes the Philips Head screw that was the secondary adjustment to finger turn bolts, and in minutes.
If you need any more I can go shoot a picture. I can also source these if you wanted, or can get the guy who lives near the firm to source them, but am sure they will be about your neck of the woods as well.
Gary
I had a chance to mess with my setup and collimate with Catseye this weekend. Just to confirm - it really does 'stiffen' your cell. The Mirror will not slop around within the cell like it did in the original setup.
I am VERY pleased.
The springs can be purchased from Bunnings (I checked), or from any Speciality Fasters / equivalent speciality store.
Good luck!
P.S. if you can make plastic spacers - do that - to keep the weight down, or wood / dowel. Anything that keeps the springs centred.
I certainly did. I'll check the lengths for you at home. I got them from bunnings.
P.S. before you do the mod, collimate your scope (as good as you can), whack her on your mount and slew about the sky, or do it by hand (gently - to simulate slew movement). I found that my mirror shifted quite a bit under these conditions.
When I perform the same test now, it holds collimation much better across the sky. But, as with all newts, you will still need to perform minor collimation adjustments throughout the night. It's a good practice to check it often.
someone out there:
