Darkplague's 16" Dob project!-Updated---------!!!!

[Darkplague]

My Mark Suchting mirror should arrive on Monday, so I need to fast track the building of my scope. In these pics is the progress I've made so far. On the whole, most pieces are finished, but there is a ton of small things to be made and little finishing touches to be done.

I don't recommend a project like this for anyone not good with power tools and cutting with accuracy. There is a lot of work involved even though it looks fairly straight forward in the end (imo).

The carpentry side of things was actually quite satisfying, even though I had never worked with wood before. I'd say the most challenging part to build is the mirror box, its not as easy to get everything square as I thought it would be. However everything turned out nice and square considering I had to hand cut everything with a jigsaw!! (didnt have access to a saw)

Picture 1: The Rocker box pieces being "laminated together"

Picture 2: The Rocker bottom and ground boards, and the 2 S/steel bearings

Picture 3: The mirror box

Picture 4: The secondary cage and homemade spider

Picture 5: The tailgate

Picture 6: Where the miracle happened ;)

What I would like is suggestions on how to finish the wood. Obviously I have to sand and radius all the corners, but can anyone suggest a stain colour that would suit this wood?

What is the best way to go about finishing the wood? Sand, then stain it 2 times, then spray it with gloss aerosol?

I am open to suggestions from other dob builders in to how to go about this. This scope will probably last me a lifetime so I want to get the best finish possible.

Thanks for reading!

[dugnsuz]

Hi Mark
I can't offer any suggestions, only praise for your work on this project.
It all looks excellent.
Good luck with the mirror when it arrives.
Cheers
Doug:thumbsup:

[cristian abarca]

Hi Mark. Don't spray finish the wood. If the wood is of good quality stain 1 coat and 3 coats of exterior polyurethane. You can use any stain you like as long as it is oil based, cabots are pretty good but any other manufacturer will do. There is a product that Solver paints make It's exterior polyurethane. It comes in a black can. Don't use a cheap polyurethane if you want it to last. Solver paints are an adelaide based company. It's not cheap but it's good. If the quality of the wood is a bit iffy then use a sanding sealer before staining and 3 coats polyurethane. I have used this product and it does the job well. Remember that when sanding in between coats always go with the grain of the wood and don't use steel wool use a light grade sandpaper with the stain say180 grit and 120 grit for the varnish coats. As for the colour a teak or a wallnut will look good. It's personal any stain will look good if it's done properly. Take care not to leave any paint runs behind. Where cabot's products are sold there are usually timber samples available just remember that you timber may vary the colour a little. To increase the shine ans give it a really glossy finish sand the last coat with 320 grit wet/dry sandpaper. Sand it wet and wipe the surfaces dry, then once dry wipe them with a rag wet with turpentine. You'll probably need 1 litre of turpentine 1 littre of polyurethane and 250 or 500 ml of stain, 1 sheet of 180 grit, 1 of 120, 1 of 320 wet/dry and a decent brush that doesn't lose any hairs. Don't use glass sandpaper use no fill sandpaper it's light grey and reasonably soft. You can pick up all of these materials from a Solver trade depot in adelaide. They are cheaper than most products. I use them. Hope this helps.

Regards Cristian

[drmorbius]

What a brilliant project... I especially like the custom lamination pressurisation device. And to think I only use my car to get to work.

You should turn this into a DIY article so others can follow in your footsteps... well done!

[stringscope]

Looks fantastic Mark :thumbsup: . Evene more so given you used a hand held jigsaw :bowdown: .

I feel the choice between spray and brush finish is a personal thing. I guess you might ask yourself the following question:

Do I want a mirror finish that looks like it has come out of a factory? This is fine, you just have to remember it will highlight every surface imperfection and every bump and scrape.

Or a careful brush finish? This to my mind looks just as good and says; "this scope is custom hand made and did not come off a production line".

If I recall correctly, Teters Telescopes in the USA indicate on their website a preference for to use a brush as opposed to a spray finish for the above reason.

Can't wait to see the finished product.

BTW what is the f ratio?

Cheers,

[Darkplague]

Thanks for the great advice. I was going to spray gloss everything but your post has swayed me to using a brush. Plus it is a cheaper option to boot!
The plywood I used is hoop pine and has nice markings on the faces, I was thinking 1 coat of walnut to bring out the features. Any more than 1 coat and it gets dark real quick. I too have used Solver in the past and found their paint to be of a better quality than anything you can buy at Bunnings.

The one thing I dont understand is why to sand in between coats of gloss? Doesnt sanding cause small scratches in the gloss making it less glossy?

Excuse my ignorance.


The scope is an F4.8.

Maybe when I have spare time I will write a DIY article on the project (If I ever get finished)

[Darkplague]

What I meant was I used a jigsaw to cut out all the shapes in rough, but afterwards I routed every single edge with a Router bit to make them all square.

If you had a decent table saw you could just cut them exactly as you wanted them. The router worked a treat though and it had the added benefit of giving you perfect 90 degrees edges, but was also very time consuming clamping a square on every side and following the straight edge with the router.

[cristian abarca]

Hi Mark. One of the reasons you have to sand is that the timber goes fury after you put a coat of clear on. The aim is to get it as smooth as possible. When we do mirror finish surfaces one of the things we do is remove all the shine from the previous coat then we recoat. It has to do with removing the surface imperfections that the brush/roller or spraygun leave behind. That is why you don't use glass paper and finish with wet and dry on the last coat. remember that when you sand the first coat you must be carefull not to sand too much or you will remove the stain. When you get to the final two coats you can sand in small circles if you wish but my experience tells me that you only need to do this with the wet and dry paper. Any scratches that you cause by the sanding as long as they are on the varnish only (not on the stain) will be covered by the next coat. The 120 grit paper is not very rough. If you find that it is a bit rough grab the piece you are going to use and rub it on your driveway for a second or two to smooth it out a bit. If you get stuck along the way or have any further questions let me know. Spraying is overrated unless you have excellent drying conditions. That is why cars are sprayed then they are cut and polished and the ones done in enamel or epoxy are dried in ovens to prevent dust settling on them (which is inevitable). In this same thread type in new telescope and click on the thread with my name on it. have a look at the truss telescope I made and have a look at the leaf at the bottom. if you look carefully you can see a reflection of it. it's not the red paint but the varnish that gave it the shine. I used the same varnish and method I explained earlier. I finally have a topic that I know a lot about, paint/painting.:thumbsup:

Regards Cristian

[Darkplague]

I checked out the 10" you made, The finish is awesome on it. Is that actually a red colour or just a deep red wood stain?

[cristian abarca]

Thank's Mark it was a bit of an effort but worthwhile. It's actually red paint and then two coats of clear over the top. Just remember easy does it with the sanding not too hard. I painted it because the plywood I used was actually offcuts I found at building sites so the quality was questionable. The timber you used is of much better quality so it should be easier to get a good finish.

regards Cristian

[Darkplague]

I've been reading some woodworking forums and am now swayed towards Giving the wood a "shellacking", and then a good few coats with a wax.

The wood has some nice fine detail in it and hopefully the shellack will bring it out.

I really need to begin on a test piece and see what it ends up looking like first!!:shrug:

[cristian abarca]

You can shellac if you want but you'll have to wax forever as the wax does fade a bit. Personally I'm not a great fan of shellac metholated spirits is not as strong a base as turpentine. It's great if you want to do french polish but much more work.

Regards Cristian

[Orion]

Congratulations Mark on a wonderful job.

Concerning the finish I personally like to lightly stain the wood and then use polyurethane. With the last telescope I made I brushed it on sanding between every coat although with the telescope I am now biulding I will be spraying it on.

[Darkplague]

So here's an update of my progress.

Today I was assembling the rocker box and drilling the holes for the Alt bearings.
I assembled everything together and found out that my mirror box was 1" too deep. So this meant a few hours lost cuttting 1" off of all the mirrror box sides. However this left too much clearance between the rocker bottom and the mirror box. So I had to recut the rocker sides also 1" less!! :mad2:

In the meantime I have finally chosen a nice coloured stain to use on the plywood faces. The sample piece on the rocker is painted with 3 coats of stain on the right, and 4 coats on the left. Which hue looks the better of the 2 in your opinions? All opinions valued. :thumbsup:

The bearings are also finished and painted. The only hiccup I had was that I found out the bearings had too much flexure in them and had to weld a strut in the centre for support. The bearings are DSC ready with a hole already drilled an tapped in the centre of the bearing.

All in all I am very happy with how its looking so far. I am striving for an obsession like scope in quality, and think I can achieve this especially with the Mark Suchting mirror.

So far the whole project has been very enjoyable and satisfying. Every weekend I have been looking forward to working on it in the garage. The trouble is the time goes by too quickly, especially when you are a fussy builder like me!! There is also the feeling of seeming to be almost finished building, and then realise there is still a ton of other small things to do.

Whoever has built one of these will know what Im on about :whistle:

Anyway stay tuned for the next weeks progress!!

[Astroman]

Hi Mark,

Looking the goods now mate :thumbsup:

As for the stain, I prefer the lighter stain so it stillshows off the grains but not overpowering.

Where did you get your Ply from?

[acropolite]

I'm with Andrew on the lighter colour, scratches and chips will show if the stain is dark.

[Satchmo]

Looks great ;) Also worth remebering that the plain plywood will take on a darker hue when the estapol sinks in and will show up the grain much better . A stained scope will always be more complex to fix if you get a guage or a deep scuff, becuase you need to sand , re-stain and estapol the area. If you leave the whole thing natural finish all thats required is a dab of estapol and you're on your way again.

Mark

[Darkplague]

Here are some more pics of the progress made this Sunday!

Once the corners are radiused and everything sanded properly, it should look very nice.

The results so far have been very pleasing considering I have never made a scope before. I havnt even seen a truss dob in person yet. The Kreige book has been my bible in this project, It really is essential if you have little knowledge of ATM.

[Darkplague]

I do have 1 question.
When doing the initial testing to get the length of the truss poles correct, where you put the UTA on a ladder and move it back and forth to gain focus on a star.

What EP should I be using for this? Should I go for a High power piece, or a low power EP?

The eps I own are: 6mm BO Planetary EP, 7.5mm Pentax, 14mm Pentax, 27mm Panoptic.

[Astroman]

Hey mark, did your mirror arrive yet?

[Darkplague]

Yes, It came 2 weeks ago, will have to take a photo of that too.

I just wish I had some annual leave so I can finish this thing! Just doing little bits each Sunday is very slow going. :sadeyes: The weather is also teasing me atm being very dark with no clouds to be seen. It seems to know that I dont have a scope to look through!!! :mad2:

When it is finally ready, get ready for the 1 month storm to come over Adelaide!!!!????!!!!!!

[Astroman]

WOOHOO storms :) I will be there with my camera then :)

[Satchmo]

I checked the Televue Website and the 27mm Panoptic has its focal plane 8mm below the shoulder , so that should give you a calculation point when you are trimming the poles to get all your EP's focused. In other words wherever the 27mm focusses your scopes true focal plain is currebtly 8mm below the 27mm 's shoulder .

Ideally putting your scope focal plane about 15mm above the racked in height is good for a low profile setup. You might have to take into account th eheight of your 1.25" adapter too.

Mark

[AstroJunk]

And leave enough in-travel for a paracorr/webcam maybe (about an extra cm). The good news is you can always lop that centimeter off later easily enough. Just make sure you get it right before you finalise your shroud!