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Utilizing Skywatcher 33.5cm dovetail

souls33k3r

By souls33k3r
in DIY Astronomer

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souls33k3r

souls33k3r

Posted
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Hi All,

I have one of these Skywatcher 33.5cm dovetails which i'd like to utilize.

I currently have a two scopes: 

1) William Optics Star 71

2) Celestron EdgeHD 8"

Because the dovetail is right there to be used so what i was thinking on utilizing it to mount the (soon to be bought) Pegasus hub, guide scope, USB 3.0 hub and then plenty on room to mount a mini PC in the future if i wish to do so.

The issue is, the hole sizes are super weird.

5a97f90b6e2ed_Skywatcherdovetail.JPG.5fe4798060948766d12ad80242222e49.JPG

(1) Looks like a M4 or M5

(2) This is bigger than an M6 because i tried to put in the M6 bolt in it and it went straight through it

(3) It's bigger for the (1) but small for M6 bolt

Firstly anyone knows what these marked bolt sizes are?

Secondly all of these holes are tapped. I'd like to drill holes in the (3) to make it an M6 bolt size which lines perfectly with my WO Star 71 rings. But because they're tapped, will it be ok if i drill these and not bust my drill bit? or do i need to tap it wider or whatever the technical way to do this is.

Lastly because i don't know the bolt size of (1), is it the correct size for the Celestron scope tapped holes?

Sorry i'm not really a DIY person so tried my best to explain this but do ask if you have any questions.

 

Thank you

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parallaxerr

parallaxerr

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Hole #2 is a clear unthreaded hole for attaching tube rings, probably around 6.5mm ID.

Hole #1 is threaded to enable cone error adjustment. I won't try to explain cone error, Google that one!

Hole #3 is most likely a 1/4-20 photographic threaded hole for attachment to photo tripods etc.

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souls33k3r

souls33k3r

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1 hour ago, tooth_dr said:

Do you want to have M6 threads or just a hole big enough to fit an M6 bolt through in (3). It’s only aluminium so either way you won’t damage a metal drill bit. Do you have an M6 tap?

To be honest i'm not really fussed whether it's a tapped M6 hole or big enough. The (3) will be placed on the top of my WO Star 71 any way and will take the dovetail off if needs be and move it to my Celestron EdgeHD with everything still connected to it (Pegasus, Controller when i get around purchasing that, mini PC in the future and a USB 3 hub).

59 minutes ago, parallaxerr said:

Hole #2 is a clear unthreaded hole for attaching tube rings, probably around 6.5mm ID.

Hole #1 is threaded to enable cone error adjustment. I won't try to explain cone error, Google that one!

Hole #3 is most likely a 1/4-20 photographic threaded hole for attachment to photo tripods etc.

Cheers mate, much appreciated. Will definitely try to look at the cone error bit.

Does anyone know the thread size for the celestron where you attach the dovetail at the top?

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LightBucket

LightBucket

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A simple explanation of cone error, is that the tip of your scope is pointing either slightly up or down from the DEC axis, so those two screws you mention can be used to realign this error, either screwing in at the front to push the scope up, or in at the back to tip the scope down.... simples.. :)

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souls33k3r

souls33k3r

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2 minutes ago, LightBucket said:

A simple explanation of cone error, is that the tip of your scope is pointing either slightly up or down from the DEC axis, so those two screws you mention can be used to realign this error, either screwing in at the front to push the scope up, or in at the back to tip the scope down.... simples.. :)

Ah makes perfect sense. 

Sorry i should've researched in to this myself but i'm half asleep right now.

All what i want to do is to mount the plate at the top of my OTA so that i can put all these wizardry's on it.

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souls33k3r

souls33k3r

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2 minutes ago, LightBucket said:

there is a dedicated mounting bracket for the Pegasus, but think it’s only for fitting to a Losmandy plate..

Not really just losmandy, you can mount it on a vixen as well. 

Tbh i'm not really fussed about the bracket, i've got the heavy duty hook and loop velcro so will use that if it doesn't want to go on it with the screws.

I've spoken to my facilities guy here at work, told him what i need and he said he's got those things that we can tap the dovetail with and asked me to bring it in tomorrow so i'll get that done. 

@tooth_dr also mentioned these are aluminium so i'll see if i can have a few extra holes drilled in as well while i'm at it ;) 

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souls33k3r

souls33k3r

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Just checked this dovetail on my 8 EdgeHD. It's long enough but it's not wide enough for the screws to line up :( it's about 5mm short from both sides :(

I guess I'll have to look for some cheap aluminium plate and drill holes in it myself. 

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souls33k3r

souls33k3r

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Cheers matey, i never knew this site even existed lol 

I agree, this is a very good price BUT i don't want to be spending any more than i already have. Maybe a thin aluminium sheet is all what i need. Or worse case scenario, i'll use velcro lol 

This dovetail will serve no other purpose other than having these things mounted.

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LightBucket

LightBucket

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3 minutes ago, souls33k3r said:

Cheers matey, i never knew this site even existed lol 

I agree, this is a very good price BUT i don't want to be spending any more than i already have. Maybe a thin aluminium sheet is all what i need. Or worse case scenario, i'll use velcro lol 

This dovetail will serve no other purpose other than having these things mounted.

Fair enough, just an idea, but I understand it’s more expense... :)

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