Excessive Mount Movement

[Mick1]

Evening all,
I've got a Skywatcher 102 f9.8 achromat refactor on an EQ3-2 mount and I'm having a bit of an issue with stability particularly at high power. And yes I did buy it and yes in hind site I should have parted with the extra 150 odd dollars and bought the EQ3 with the s/s legs or the EQ5, but it is what it is.
I had a good look at it today and came to the conclusion that one of the main problems lay with the leg and mount base connection point, there are 5 fasteners holding the 2 aluminium legs to the mount base per leg assy(3 assy in total).
Now because the telescope is 1000 mm long, there is about 500 mm either side of the mount center any movement and the telescope acts as a big lever and the mount twists at the leg mounting points.
So I'm thinking if I cut a triangular piece of aluminium plate about 6 mm thick
I could extend the mount securing bolt and wedge the plate between the 3 legs about 150 mm below the mount base the same method used on the EQ3 and EQ5 mounts with the s/s legs. I think this will be a more effective method to deal with the problem than hanging a weight from the center of the tripod.
Does anyone has any other suggestions apart from buying a new mount?

[ZeroID]

Sounds like those top bolts need to be tightened up a bit if they move that much but your triangle idea is worth trying. Doesn't need to be aluminium, a bit of decent ply will do the job, 10-12mm maybe. I'd still be hanging the weight as well to reduce the flex moment.

[Mick1]

Everything is tight, I was even thinking of getting a piece of plate cut at work to fit into the accessory tray and see how that works.

[xelasnave]

As well....Hang a bag of sand off the mount that can do wonders.
Alex

[xelasnave]

The mount can be made work well within certain areas...pointing straight up or best at 47 degrees..the best thing you can do is work with it and appreciate what you will need in time and what to look for.
I started with useless mounts but I tunned them as best I could and really with todays short exposures both those mounts would cut it uniguided...
And be excited that you have the gear you do as you can do some neat stuff really.
Alex

[xelasnave]

And I dont know if this worked but you gotta understand I was in the bush trying this and that to get things as good as they could be...so I cut up a blanket and covered my 150 mm on a mount with about 15 KILOS on the cross brace...but I reasoned that the two layers of blanket may dampen vibration a little...but a little is a step ahead...I cant remeber if it worked but you would think it would...still kept me from doing useless time wasting stuff☺
Alex

[raymo]

Its a good job you didn't waste your money on the stainless legs version, or
even the EQ5, because you would still have had vibration. A 980mm f/l
scope really requires an HEQ5, and even then it will still vibrate when you
touch it to focus it. Your best bet,[ as has already been stated] is the ply board with holes cut in it for holding eyepieces, and hang 5 or 6 kgs under
the tripod. You can also dampen the vibration somewhat by drilling a hole
on the inside of each leg about half way up the leg, and pouring sand into the legs, and seal the holes with silicone afterwards. Anti-vibration pads under the tripod's feet also help. An electric focuser from Skywatcher for about $90-100
is great, as you don't have to touch the scope and wait for the vibes to stop.
Another often overlooked point is that the further apart you can put the tube mounting rings, the less vibes you will get. A good idea is to get the 300mm long dovetail bar, then you can place the rings about 250mm apart which
will help immensely.
raymo

[brian nordstrom]

Good ideas so far guys , and as said one step at a time and your mount will be ok for visual .

I have an EQ2 mount that in its standard form easily holds my 60mm triplet and C90 Mak but my 90mm f10 saxon refeactor at 900+ mm long , completely overwhelmed it was , ' wobblertron ' city !! . Quite terrible actually !

So , reading up I started doing a few things ,

#1 , filled the bottom aluminium tripod legs with sand , don't forget to put a good blob of silicon rubber over the sand before you reassemble , stops any escaping if you tip the tripod for transporting . Helped quite a bit .

#2 , machined up a disc 200mm in diameter , lengthened the centre hold down bolt and reassembled , another quite big win ! , you can see this in the photo . It also made a very handy 1 1/4 inch eyepiece x3 , holder .

#3 , cut 3 pieces of alloy tube 20mm in diameter and fitted them inside the ( WAY TO LIGHT ! ) alloy tripod top where the 3 legs bolt on and refitted the bolts and tightened ,, this made the biggest difference yet ! :D .

#4 , machined up a stainless steel CW so the CW's are not right at the end of the CW shaft , this stopped nearly all the slow occillations that were present before this was done .

#5 , as said by Ramo I grabbed a 200mm long Vixen dovetail and fitted it on the OTA , also made a handle for the top of the rings and these two really helped a lot , more than I expected :thumbsup:.

These took about 3 weekends to do , in between testing and playing around has made a huge difference to this mount and it's now actually quite nice to use , not perfect but easily 70% better than it was .
I have also stripped , cleaned , made some teflon washers and re-lubed the mount and its very smooth now and it's able to be tightened to a much closer tollerance than standard .

Hope this helps ,

Brian.

ps. I have a Saxon 102mm f10 and its my most used scope now , do a search here of ' Frankensaxon ' here and have a look . Its mine and its a very good scope now as yours can be with a little ( lot ? ) of tuning .

[Oddity]

Interested in this thread as I’m seeking methods of stabilising tripod.

Have searched and can’t for the life of me figure out what a “CW” is.

[Oddity]

Nevermind just got it, counterweight. Took a while.

[brian nordstrom]

:thumbsup: Ha ha , good onya for sticking it out , here is my 21lb CW on my CI700 mount , note how close it is to the mount while balancing my C9.25 .

Brian

[Mick1]

Thanks everyone for your guidance, its all happening, I'm going to add a weight to the accessory tray,fill the main tripod legs with sand and cut a disc and buy some threaded rod to extend the mount securing screw/bolt before I spend more money and get a heavy duty tripod which as said previously will most likely have the same problem anyway. I think its a matter of sticking with what I've got and do a bit of fine tuning.

I have another question, what is the purpose of the middle cap on the main optical tube lens cap?

[brian nordstrom]

:thumbsup: Mick , its to stop down the main 102mm objective so not as much light reaches the eyepiece , not really much use in an 102mm scope ( this is used mainly in large reflectors as Jupiter in a 16 incher will almost blind you ) but some use it mainly for solar viewing , turning it from a f10 102mm scope to a f20 50mm scope as some Ha solar filters work best at above f15 , the ' Quark ' for one .

On your mod's you will feel a difference and don't forget some pipe/ wood packers in the tripod top where the legs bolt on , in between the casting .

Looking forward to lots of photo's .

Brian.

[doug mc]

This is how i stopped shaking at high power. It is just an alloy ring with4 threaded studs radiating out. A gentle push forward or backward at fine focus.

[brian nordstrom]

:eyepop: Doug , what a simple and easy fix for one of astronomy's biggest ' Bug Bear ' well done mate .

I found a photo of my ( wife's ) 90mm f10 Saxon on the supercharged EQ2 ,, yes , it can be done and done quite well .

Good luck with your endeavour Mick , but most of all don't rush , just enjoy the journey .

Brian.

[doug mc]

I have used the focusing collar on a C8 when I had one. Works on the mak as well as the dobs duel speed focuser. On my acro I had a similar idea. A small boss that slipped on to the rack and pinion shaft. It had a threaded hole into it that I screwed a longer stud into it. It swung free until I was close to focus. I then nipped it up and once again gently pushed forward or backward for best focus.

[brian nordstrom]

:thumbsup: , as we will learn being Amateur Astronomers ,,, we have to learn to ' tinker ' ,, here is my ' Supercharged EQ2 ' with a sweet 90mm f10 OTA 900mm fl .cool as and it is a good set up .

2nd photo is the same mount with a 60mm f7 420mm fl .

This is not about the telescopes . but the EQ2 mount , standard it was sold with the 90mm f10 OTA ,,, sad for all the X amateur's out there every where that got F2354'D over by Advertising . ! ( 675x ! can see the dawn of creation ? ) but with the 60mm f7 APO it's a tank ! and the EQ2 is a rock .

Brian.

[doug mc]

Here's a couple of pics of the fine focus attachment for the refractor.

[ZeroID]

Just added a much larger plastic knob to my fine focus. makes a heck of a difference with fine focus control and less vibration disturbance as well. Old copier foot which I turned the centre out of and just pushed over the knob.

[brian nordstrom]

:D Took a while but Mick here is a photo of my iStar 127mm f8 on the Vixen SP and Meade HD field tripod , not a bad combo if balanced well .

It shows how good these mounts really are . :thumbsup:. I would hesitate putting this OTA on an EQ3.2 with alloy legs , probably not even a standard EQ5 with SS legs .

Brian.