Does a finderscope have to be absolutely on top of the telescope, and how brave do you need be to drill holes in the OTA?

[JOC]

As you know me and finder-scopes are fraught with problems.  Hopefully later on tonight (clouds allowing) I have a Skywatcher RDF to try out.  If it works I am tempted to install both (the magnified RA Finder and the RDF).  Now I like those finder holders where you can put two finders on one bracket, but they are about £40 https://www.telescopehouse.com/orion-dual-finder-scope-mounting-bracket.html?gclid=Cj0KEQjwzd3GBRDks7SYuNHi3JEBEiQAIm6EI2rMnN3sDwczT_0hNtiT1uJp0KTBFQap9yV46-RG69EaAqT68P8HAQ.  Here at the moment I've got a Skywatcher mounting bracket that was a fiver!  It is identical to the one already on the telescope for the current finder scope.  Could it be successfully mounted for a finder shoe next to the existing one (i.e. not exactly on top) and would the finder work?  Do people drill holes in their tubes?  The existing one has a additional plate on the inside of the tube (for strength?) - would I need another plate for the second bracket if I used it?

Finally how brave do you need to be to drill holes in your nearly new telescope?

[Bizibilder]

I would be wary of drilling holes in the tube as the swarf (bits of metal from the hole) will fall inside and may scratch the optics.  By all means drill if you can dismantle the scope first so that you can clean it out and then reassemble.  Better may be to buy some double sided "sticky pads" and use those to mount your RDF finder.  The sort I mean are used for fixing rear-view mirrors onto car windscreens etc.  They can be bought from car accessory shops.

Alternatively attach the RDF to a base - maybe wood? - and use cable clips to hold it onto the tube - should last a while.

I suspect the plates you mention are there to locally thicken the tube wall so that the screws holding the finder bracket in place have enough metal to screw into.

[knobby]

Finders can go wherever they work for you, why not try cable tieing the new bracket to the stem of the old one as a trial.

As for drilling a new scope ? Bravery is proportionally related to the cost of scope divided by weekly income multiplied by diy skill rating and the amount of time planning said drilling.

Plus time spent protecting inside of scope from metal shards ...

[Cornelius Varley]

The only two requirements for the location of the finderscope are that it should be in a comfortable viewing position (this is usually on top of the tube) and that it is aligned with the telescope, it doesn't need to be absolutely on top of the tube.

[mikeDnight]

If you have firm hold of your drill, a bench top drill is best, and you drill slowly, not at full speed, the blur will be pulled out of the hole. Be careful if you're drilling near optics so that your drill bit doesn't come into contact. There shouldn't be a problem if you drill carefully and slowly! If a Newtonian, it will be easy to vac out any blur or dust.

Mike

[JOC]

I Like the idea of cable ties :-D  As you can probably guess I wasn't overboard with the idea of drilling the OTA, but £40 is £40 and I already had the other shoe.  I like the idea of mounting it onto something else and then cable tying / sticking that something else to the tube.  The RDF isn't heavy and I might get away with some sticky pads, but black cable ties sound best as they won't leave a sticky mark on the tube.  I'll ask my engineering type bro. if he can mount the new mount on to a slightly longer bit of metal and then I could cable tie it into place.

BTW love this:

23 minutes ago, knobby said:

Bravery is proportionally related to the cost of scope divided by weekly income multiplied by diy skill rating and the amount of time planning said drilling

LOL

[knobby]

Thankyou  and good luck

[D Wright]

If you have a Skywatcher then there will be 2 x 1/4" holes on the top of the rings. I a pice of wood lengthways between the 2 rings then screwed a cross piece at 90 degree angle and I have a Telrad at one end and a RACI finder at the other nicely balanced. It also helps to balance the tube in the rings as all the weight is in the centre.

[JOC]

D Wright, great idea, but unfortunately no rings on my Dobsonian mounted 200P Flex tube

[davyludo]

I drilled holes in my little newt. I turned it upside down  then drilled holes and made sure I'd cleaned all the swarf out before turning it back up (so that nothing was left to small down onto the primary. It only took a couple of minutes. 

I'd be a lot less brave if it was a sealed OTA (something like a frac or a mak)....or if it was an expensive scope.

[Daz69]

I drilled a hole for my Rigel quick finder shoe. Don't be afraid to do this so long as you feel confident enough, but you really have to be reckless to do a messed up job.

Eyeball where you want the shoe to go, and lay down some masking tape. Replace the shoe to confirm position, and if happy, accurately mark out for your hole/s. Remove the primary mirror IF you are clear of the secondary, but if you are directly over the secondary, remove it also. To not remove the optics is where people go wrong, so don't chance your luck. Preferably I'd remove both. 

Use a 2mm pilot drill to start each hole. Drill straight and slowly, keeping the bit perpendicular to the tube to stop any slip and scratching, and keep the drill light (don't press down, just use the drill's weight and if the bit is sharp it will go through). After each drill size, clear out the swarf ensuring the tube is clean. Once you've taken the hole out to the size of the bolt you'll use, check the inside of the tube to ensure that there is no swarf still hanging from the hole. If there is, break it off and thoroughly clean the inside of the tube before attaching the shoe. Once the shoe is secure and tight (use a nyloc nut for security), make sure all tools are out of the tube, and then re-fit the optics. Job done............ apart from collimation   10 minute job maximum, not including a tea break. 

[BeerMe]

Thanks for bringing this up JOC, I've been wondering about the implications and knowhow for drilling holes in an OTA too!

I seen a 10" Dob on ABS and the seller had attached a long (bathroom towel rail long) handle on to the OTA for ease of carrying. 

The method I had considered, so that I wouldn't have to remove the primary, would be too stick self-adhesive pads inside the OTA where I wanted to drill the holes, then drill lightly through til I hit the pads, vacuum out anything from the hole on the outside of the OTA, then remove the sticky pads and any shards that would have dropped in to the OTA are hopefully stuck to them.  In theory, I think this could work but I'm terrible at DIY....

[Daz69]

5 hours ago, BeerMe said:

Thanks for bringing this up JOC, I've been wondering about the implications and knowhow for drilling holes in an OTA too!

I seen a 10" Dob on ABS and the seller had attached a long (bathroom towel rail long) handle on to the OTA for ease of carrying. 

The method I had considered, so that I wouldn't have to remove the primary, would be too stick self-adhesive pads inside the OTA where I wanted to drill the holes, then drill lightly through til I hit the pads, vacuum out anything from the hole on the outside of the OTA, then remove the sticky pads and any shards that would have dropped in to the OTA are hopefully stuck to them.  In theory, I think this could work but I'm terrible at DIY....

Why not remove the primary? For 2 minutes work you could save the heartache of having a scratched mirror. Personally, and this is my thought, I certainly wouldn't trust a ha'penny sticky pad to save damaging an expensive mirror. As an expert DIY'er (IMO) and having a woodwork workshop, I have had many times when both my Dewalt and Bosch battery drills unknowingly release the drill bit whilst removing the bit from the drilled hole. That's not user error, but an unwanted trait of quick-release speed chucks. 

Of course you may very well be lucky and all will work out fine doing it your way, but in case someone else is looking at doing this job themselves, I advise against it. 

[BeerMe]

6 minutes ago, Daz69 said:

Why not remove the primary? For 2 minutes work you could save the heartache of having a scratched mirror. Personally, and this is my thought, I certainly wouldn't trust a ha'penny sticky pad to save damaging an expensive mirror. As an expert DIY'er (IMO) and having a woodwork workshop, I have had many times when both my Dewalt and Bosch battery drills unknowingly release the drill bit whilst removing the bit from the drilled hole. That's not user error, but an unwanted trait of quick-release speed chucks. 

Of course you may very well be lucky and all will work out fine doing it your way, but in case someone else is looking at doing this job themselves, I advise against it. 

I wouldn't do it myself, I just wondered if that might be an easier way.  Removing the primary just scares the hell out of me.

[Dave In Vermont]

Another good reason to get a RACI-Finder: You can position the eyepiece to a comfortable position for easy viewing. No dilling needed:

 

 

I'd also consider the double-sided tape as an excellent option for mounting the finder' 'shoe.' I have a GSO 200mm F/4 Rich-Field Newt from 2000ish that came with this. It was for a cheap red-dot finder Orion mounted (un-asked for) post-production. As a Newt on an EQ-mount is supposed to rotate as needed to position the draw-tube/eyepiece, Orion had managed to put the sticky-taped bracket for this 'toy red-dot' in a terrible location. The tape is still on this excellent scope. My caveat: Think carefully before you proceed.

Dave

 

[JOC]

I actually think I am going to try and avoid drilling mine, but following the above train of thought, if the holes are near the open end of the tube it might be possible to G clamp in a disposable block of wood inside the tube to drill down into.  I also see no reason why if you found something non-particulate like a large squishy polythene bag or a scrumpled bit of bubble wrap you couldn't stuff that down the tube beyond where you are drilling and put a paper jiffy bag over the secondary, I even have visions of blowing up a balloon in the tube except for the fact that the swarf might puncture it .  Of course with a truss tube you do also have the advantage of a gap between the secondary and the primary sections of the OTA. 

9 minutes ago, Dave In Vermont said:

Another good reason to get a RACI-Finder: You can position the eyepiece to a comfortable position for easy viewing. No dilling needed:

Oh, I've got one of those, I was looking to mount the RDF alongside it.  I could spring for the £40 for the double finder mounting bracket, but I have a job to get the RACI angled low enough to match the OTA view now without adding more height to it. 

[Daz69]

11 minutes ago, BeerMe said:

I wouldn't do it myself, I just wondered if that might be an easier way.  Removing the primary just scares the hell out of me.

I understand what you're saying, but the easiest way is not always the best, or safest way. There is no right way as such, you do it however you want, but the best way to protect your expensive glassware is to remove it.

In regards to removing the mirrors, don't be afraid to. So long as you work on a table with a soft towel under the OTA , and place the mirror face up away from where you work, and without any kids/pets that may grab it or knock it, you'll be fine. Learning how to collimate isn't difficult, my first attempt to get my Celestron set up (secondary was literally hanging by a thread when I unboxed it) took my quite a while, but when my SW200 came (secondhand), the first thing I did was whip both mirrors out to thoroughly clean the inside of the OTA, to check the mirrors, and do the secondary mod of fitting a large washer and plastic disc. Collimating that took a third of the time. I've got to take mine out again soon as I'll be fitting the shoe for my Rigel finder, and fitting a fan to the rear of the primary. Just work slowly, and methodically. 

[rockystar]

taking it all apart and refitting it is a good way to get to know how your equipment works. And is a great way to force you to learn collimatation

I've moved the finder shoe, added a carry handle and replaced the finder - all of which required drilling new holes. I removed both mirrors first and then constantly reminded myself that It's just an aluminium tube.

the only other thing, is that you will need to cover the previous holes to prevent stay light.

after I'd done it once and knew I could put it all back together, it wasn't such a scary prospect to do it again.

[Paul73]

If it is for your Dob. Drill away. Just be a bit careful how hard you press. 

Make sure that the scope is horizontal, then just sweep the swarf it of the open end.

RDF / RACI Finder combination works a treat. The other option, is a Telrad instead of the RDF. Works better and you don't need to drill holes (about £40).

Paul

[Charic]

Ive used an alternative to the ever-so sticky 3M pads when I mounted my Telrads! but belt and braces security, they were also tie wrapped, but tie-wrapping allows you to find a suitable position before sticky or bolt mounting. Don't forget try all the angles once temporary mounted. Its ok setting up your finder when the scope is at say 45° but will it be comfortable for you anywhere between horizon to zenith?

I have an idea for a ring of holes 12.5 to 25mm diameter with the lower edge of each hole in a position that aligns with the surface of the mirror? as viewed with the scope upright? but if I actually go ahead with this idea, both end cheeks of my Sky-watcher can be removed, and if carefully marked and handled, I'm certain  for one that no swarf or tool damage will occur inside the scope, and with careful re-application of the cheeks, the scope will, in all probability, still be collimated! if not, thats not an issue for me to correct. Like I said its just an idea for now.

Do what you feel is best. but once cut or drilled,  there's really no going back, although drill holes can be plugged with rubber grommets. Also consider the re-sale value after any modification?

[Astro Imp]

5 hours ago, Paul73 said:

The other option, is a Telrad instead of the RDF

Unfortunately there is insufficient room for a Telrad on the OP's scope. I recently bought the same scope and was very disappointed my trusty Telrad would not fit. I now use a Rigel Quickfinder alongside my RACI, works a treat.