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Hello all!

I am mounting an Explore Scientific 8x50 Right Angle Erect Image Illuminated Finder Scope on my Skywatcher Dobsonian. The original Skywatcher mount only had one bolt hole. The Explore Scientific base requires two bolts. I was told to make sure to have the primary mirror cover in place and to place a cotton sock over the secondary mirror.

My concern is drilling into the tube itself. Are there any other precautions I need to take so that that it doesn’t look like it was drilled by a bunch of Wallys? LoL!

Greg

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As above and use your smallest bit as a pilot first.

Maybe hold or get someone to hold something like a cup under where you are drilling to catch swarf?

It's harder to explain than do.

Use washers on inside and paint matt black when you have the chance.

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I would be tempted to remove the secondary and spider and then drill with the OTA on its side.  If possible I would wedge a block of wood in behind the site of the new hole to support the tube whilst it was being drilled.  Masking tape or insulating tape over the site of the hole can help stop the drill bit from wandering when you start drilling.

James

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11 hours ago, Alan64 said:

I tape a sandwich bag, with blue painter's tape, to the inside of the tube over the area to be drilled, and to catch the debris.

Alan you beat me to this. A poly bag taped behind a hole is a good idea for any drilling - not just scopes.
Swarf cannot end up in places should not be.

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Enlarge the pilot hole up to the required size by proceeding with successively larger drills. I enlarge in increments of 0.1mm (or 1/64th inch if you have imperial drills) if possible but never more than 0.5mm at a time. This will prevent or minimise the chance of the drill snagging and distorting the hole which will often leave a rough edge and/or torn metal. Also if possible only drill at a very low speed; this will give you a chance to stop proceedings if things begin to get out of control.

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Just a thought, but if you know someone with a 3D printer could they print you an adapter which would fit into the existing SW fitting and allow the mounting of the new finder without drilling any holes?  I use a 3D printed adapter to mount my RDF and SW RACI side by side and this works well - I've looked at your finder and there certainly looks like scope for making a base to fit the ES fitting onto a SW fitting.  Even if not 3D printed my dad even carved me a little adapter one day from a small piece of wood, or I guess something could be engineered from a bit of metal if you have a mate with a workshop. 

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