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LeeRich

Never say never ? bespoke wedge.

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Hi all, well as the title suggests I seem to have made the mistake of thinking i knew best at the time lol. Hands up...it was me.

I recently built a new obsy based on the idea I was going to purely be a visual and casual CCD web cam photographer but guess what...yer, I am now hooked in the fact that long exposure is an avenue I want to stroll down.

BUT, already having designed my obsy around an alt/az mount I am now realising just sticking a EQ wedge under my LX90 isn't possible as scope position is critical to it not hitting the dome. 

SO,  I am now in the midst of design and the build of a bespoke wedge to accommodate these factors and i will post my progress for your perusal.

Please feel free to offer any constructive critism in case it appears I have over looked something.

Here are my initial drawings. Pics to follow as I start cutting the steel plates, not sure on gauge yet? I'm hoping 6mm will be enough but i will compare with 10mm next week.

Cheers, Lee.

Edited by LeeRich

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Apoloigies for the creases, paper looked flat when I took the pic lol ?

20190202_114024.jpg

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Personally, I'd go at least 10mm, more like 16mm plate, but then I tend to over-engineer everything....  

In theory, as you know your latitude (55.7) ?? you could almost make a fixed angle plate, which should make things a little easier....

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I agree, i too like to beef things up and as I have nearly a 12" overhang from peir centre I will need to consider what gauge won't flex.

I would love it if a fixed angle would suffice but reading about doing a (DRAV)?? I know that polar alignment is critical for long exposure so I will need adjustment to do it right ?

My latitude is 53.7 deg so I'm making the plate angle 54 with a 2deg adjustment for fine tuning either side. My pier top is 100% level so hopefully this will work ?

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As long as you adequately brace the underside of the S end of the wedge to your pier then you should be ok. I would up the plate thickness to 8mm at least but I would avoid too much off axis weight hanging off the pier.   ?

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Defork your SCT and get an EQ6 EQ Mount, as you will do in the end trust me...

I started exaclty like you, visual with fork mounted SCT then moved to imaging and bought the Meade heavy duty wedge, was great for a while, then I de forked it and bought an NEQ6... you will end up there too, as the SCT is great and you can image well with it, and guide it to, but it’s a lit of faffing about, as balance is absolutely critical especially when your guiding, which you will end up doing too, the. You will want a small frac to piggyback for wide field objects...and so on...why not just re engineer once and be done with it...

You know it makes sense...

If you do go down the wedge route, I had a fixed angle one to start with, but had adjustment bolts under it to make altitude adjustments...so it can be done if it’s set on three threaded bars..one at North and the other two at back in triangle, get the back two level and adjust the North facing bolt under wedge...simples.. :)

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50 minutes ago, Peter Drew said:

As long as you adequately brace the underside of the S end of the wedge to your pier then you should be ok. I would up the plate thickness to 8mm at least but I would avoid too much off axis weight hanging off the pier.   ?

Thanks Peter. Yes I'm now thinking of 10mm thanks to all the input thus far. As far as over hang is oncerned I'm governed by position so i will have to accommodate this in the final design. Fortunately I built the pier to hold a tank so should be ok ??lol

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18 minutes ago, LightBucket said:

Defork your SCT and get an EQ6 EQ Mount, as you will do in the end trust me.

Lol one step at a time LighBucket ?? I was thinking 50 quids worth of steel plate and some stainless fixings just for now hahaha although I don't doubt your absolutely right and somewhere down the road we may be having this discussion in another thread called "Never, never say never"lol

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Ok, just finished the 1:1 scale drawing and all seems to work. Only thing I will change is the sheet gauge which i will decide at the metal shop next week but this doesn't effect the calculation on this plan. Will also probably fine tune a couple of ideas like the alt adjustment and dec adjustment while building it. I always find for myself when designing things on paper there is always an element of change while actually building but that's just me I guess, I ain't no professional after all so changing things on the fly is what works for me.

Cheers.

20190202_164220.jpg

Edited by LeeRich
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Looking good, any particular reason to make it out off steel, are you planning on welding it ?

Remember when mounted on the pier the forks need to point north.

Dave

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3 hours ago, Peter Drew said:

I would avoid too much off axis weight hanging off the pier.   ?

Despite what first appears as quite a large over hang which is about 12" the OTA is actually well seated over the pier so until I I do a balance test I'm quietly confident the wedge will sit nicely balanced ??

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2 minutes ago, Davey-T said:

Looking good, any particular reason to make it out off steel, are you planning on welding it ?

Remember when mounted on the pier the forks need to point north.

Dave

Thanks Dave. Yes I will be welding the base plate to the sides and then running bolts top and bottom of the scope plate so once aligned and tightened it should be solid. ??

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This project just got interesting as a good friend of mine has now asked if I can build one for his 8" LX90 which has the same base dimensions as my 10" so as I already own an 8" LX90 myself, this thread has officially turned into 2 builds. A 10-12mm gauge pier mounted wedge and a possibly 6mm tripod mounted shorter wedge. 

??

Edited by LeeRich

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There is a lot of friction between a wedge and the pier top which makes fine adjustment tricky as when the adjuster overcomes the inertia it tends to move with a sudden jump.

I put a sheet of 3mm PTFE between them to aid smooth movement.

Maybe make some way of reducing the actual contact area between them, a "proper" wedge has a circular rim about 10mm wide that it rests on.

Dave

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6 minutes ago, Davey-T said:

I put a sheet of 3mm PTFE between them to aid smooth movement.

Nice one Dave. I didnt think of this great idea ✊ thank you for this vital information.

I will most certainly do exactly what you have done here to smooth out that fine adjustment motion.

As I have never seen a wedge up close little things like this are exactly why having forums like SGL are a brilliant thing.

?

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My Astro Engineering wedge is made of 15mm steel.

Teflon under the wedge gives a nice smooth movement but unfortunately Teflon "creeps".

(8" LX200GPS)

Michael

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17 minutes ago, michael8554 said:

My Astro Engineering wedge is made of 15mm steel.

Wowzers. I think i will have to find a happy medium of gauge bearing in mind I only have an LX90 and no plans to upgrade....but !!! Lol if I ever did then a totally different set up is what i would probably go with so this wedge I'm building is a one off for the scope I have so cost, time and stability all play a part.

The Teflon creep is an interesting one, i shall be looking into that. Cheers.

?

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42 minutes ago, LeeRich said:

The Teflon creep is an interesting one, i shall be looking into that.

Be interested in it too, once aligned mine is bolted down through the Teflon  so not sure where it can creep to.

Dave

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Just out of interest would one of these polar scopes work as a semi accurate set up if I were to drill an appropriate sized hole in the wedges scope plate ?  I'm thinking I can set the wedge up pretty accurately before bolting the scope to it and drift testing ? Obviously they are for a specific mount but I'm thinking if I adapt it to fit on my wedge it would work the same ? Cheers for any input ?

Screenshot_20190205-172712_Samsung Internet.jpg

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Don't think it's necessary you can use the scope as a giant polar scope by aiming it north aligned with the forks and getting Polaris to stay in the FOV as you spin it in RA.

You need a bit of AZ' adjustment in the wedge base anyway, slots about an inch or so long should be enough.

Pic' of mine, pier was aimed magnetic north but you can work out the true north offset to get it more accurate.

Dave

Dave

Wedge-adjustment.png.5eb6cf39853ef624340e8b9336244465.png

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Cheers Dave. I did think of just using the scope but I'm not 100% convinced the fixed setting circle on the mount is accurate ? so I would indeed have to continually rotate the thing to get close. Just wondered how accurate/easy these polar scope are for the money as it would eliminate all the weight of the scope on the wedge for initial adjustment but that said i will still need to fine tune with it in place so you're probably right ?

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Setting circles aren't great, a long time since I did mine but I think I used a combination of spirit level and protractor to get it level east / west and aimed north at 45 degrees.

Using finder scope initially to get Polaris centred then rotating the main scope, this get it near enough for drift aligning or DARV.

Dave

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Sounds like a plan. Save me sen 30 squid eh lol off to see the steel man tomorrow so hopefully this little project will start to take shape very soon.

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