20" f/4 Dob build

[swamp thing]

I am really daft sometimes. Never even considered cutting with two blades. I'll remember that one.

Yeah! It's a trick that my Dad showed me, he was a tin basher of considerable skill, then turned he's hand to carpentry and taught me a huge amount ( no easy feat to teach a bricky woodwork ).

Remember to wind a nut down lower than you want to cut too, or the burs that the cut induce may make trying to start a nut off down the threads pretty tricky.

Regards Steve

[Adz]

Great work so far Steve, I am following with much intrigue

[Matthew]

Nicely done Steve .

[swamp thing]

Great work so far Steve, I am following with much intrigue

Glad your following my attempts.

Nicely done Steve .

Thank you.

I've taken the whole cell to pieces again now for painting. I was going to get it powder coated but have had some experiences with that on off roaders that I've built and it's not very hard wearing and cannot be simply 'touched up' like paint whenever required.

Regards Steve

[Matthew]

Personally I wouldn't powder coat it Steve , the last place I worked had electro static paint bays and a walk in oven to cure the paint but like you said it chips so easily and isn't very hard wearing, in the end they galvenised everything then powder coated that.when you finish the cell and mirror box I wouldn't mind popping down to take a look ( if that's ok )

[swamp thing]

Started to paint the mirror cell. I've given it a coat of Galvafroid, I'll give it another or two before a paint finish.

The next part I'll be starting on will be the UTA. It'll be a little while before I start on the mirror box. Mat you're more than welcome to pop along and have a gander when Ive built the mirror box buddy.

If we get some decent dark skies I might well be heading your direction with my other scope. If so, I can always bring any parts with me so you can have a look.

I have a few ideas on the mirror box I've been thinking over and over in my head.

Do I stay with the traditional KB design and go for a plywood with mitred corners (I'll biscuit joint them too for extra strength)? Or do I build it from laminated kiln dried timber, this could have dovetailed corners....:rolleyes:Nice.

I could dovetail the ply but it'll never look like proper wood.

I must admit I do like the idea of real timber rather than ply but it's not the usual way of doing things and I worry I'll be making problems for myself in the long run. A scope should be beautiful but function must come first.

Decisions, decisions.

Steve

[Moonshane]

I am sure you know this Steve but as I understood it, the main benefit of ply (decent ply) is that it is very stable and unlikely to warp and move if well sealed cf with boards of solid timber. that said, I bet you could get away with it if well put together. if I'd have had the tools I would have done finger joints but in the end I just glued and screwed straight butt joints. worked well for my needs.

you seem more skilled than me so I'd go for finger joints and ply. that would be rock solid and does look good too.

[swamp thing]

You are absolutely right about the benefits of ply Shane. You are probably right about sticking with using it. It's just the beauty of a natural wood is very appealing. I was thinking a kiln dried timber once treated with an epoxy finish shouldn't move at all but is it worth chancing it just for looks?:

The main function of a scope is to look through not at. Maybe if I was building a smaller scope that would be the time to play around with some new ideas.

Perhaps my 10" could do with a new look in a couple of years time.

Don't be to quick to assume I'm more skilful than you at scope building Shane yours takes some beating.

[Moonshane]

cheers matey. don't get me wrong I wanted my scope to look good too but like you working well was more important to me. whatever you do, it looks like it will be a stunner. I have already started planning a truss/box design for my 6" f5 so I can take it on planes and camping. my mother in law has just moved to Tenerife so Teide here we come!

[swamp thing]

What a muppet I am.

Ordered the ply for the UTA (5/8" HVHC). It arrived today. Got it cut for easier transport, got it home. I got it cut too small.

Be ordering another tomorrow.

I should know better. Measure twice cut once, not cut first then measure.

Still at least I've some nice new spot boards for work.

[spaceboy]

Your not on your own Steve. Story of my life

[Daniel-K]

that cell is a work of art mate good job

[swamp thing]

Your not on your own Steve. Story of my life

Annoying aint it. I've goota wait now until mid next week before they get another sheet in.

that cell is a work of art mate good job

Thanks Daniel.

I've made a couple of changes to the cell namely, the outer plastic circle. I cut another to contact the outer triangles better.

And the side pins. Although the cam cut dowels worked I felt they could be improved on by using 'mopstick' this has a small flat on it. I felt this would allow me to index their positions to one another much more accurately, lessening the likelihood of one being in a different place relative to the mirror.

The whole cell has also been painted with a Matt black paint.

Here's one with the glass in place. Wrist watch for scale

[Moonshane]

looking super Steve - sorry about the timber. nothing like a mistake to focus your mind.

[dtr42]

been following this post, what a great project, wish i had your patience good luck for the completion

[Don Pensack]

PLOP can be downloaded here:

Automated Mirror Cell Optimization

Don't want to configure your own?

Try here:

Design Techniques for Mirror Cells

and don't forget the edge support is critical:

Dobsonian Mirror Edge Support Calculator

[swamp thing]

looking super Steve - sorry about the timber. nothing like a mistake to focus your mind.

Indeed Shane. Captain Cockup sure does whip you back into shape.

been following this post, what a great project, wish i had your patience good luck for the completion

Patience.....me? I think not. I'm the least patient person you could ever meet. It's just if you rush things like this, you have to live with all the corners you cut and compromises you made. I'm too impatient to live with something that doesn't work properly.

I've built a few overland campers, and nothing drives you up the wall quicker than when you've rushed something and it therefore doesn't wrk properly when you need it too most.

[swamp thing]

PLOP can be downloaded here:

Automated Mirror Cell Optimization

Don't want to configure your own?

Try here:

Design Techniques for Mirror Cells

and don't forget the edge support is critical:

Dobsonian Mirror Edge Support Calculator

Some great links here.

Nice one Don.

I couldn't get the PLOP to work on my mac.

[Moonshane]

I made a few mistakes when routering my shapes but a few days of sanding sorted that and made me remember for the next time!

[swamp thing]

I made a few mistakes when routering my shapes but a few days of sanding sorted that and made me remember for the next time!

Its easily done for sure. You can't beat that sinking feeling you get when you realise you've cocked it up.

Project for this weekend is just to make a trammel up to assist cutting the UTA circles for when the next sheet of ply arrives.

[swamp thing]

Well I made the trammel up at the weekend and the ply arrived yesterday. Got it all set up only to find my router bit knackered.

I'm not lending my tools out ever again. Period.

So bought the new 1/4" bit and routed the UTA rings out of the 5/8" hardwood ply.

I've given them a quick sand but nothing to bring em up to a finish yet as there is still some work to do on them namely drill out upper tube pole seats and drill for fixings.

Gotta get my backside in gear and order the ally tubing, the threaded inserts for it and the focuser and finder in the next few days else they'll be holding me up.

[Moonshane]

lookimng good steve, very sharp cuts. you ca tell it's a new bit

I'll be interested to know where you get your tubing/inserts

[swamp thing]

Was gonna give this mob a shout?

Round Threaded Tube Inserts - Metal

These look like the kiddies I'm after. The 38mm ones should do for the 1.5" truss tubes I'm going with.

[Moonshane]

look good mate. unfortunately the tubing I am using for my 6" f5 will be only about 13mm ID. I may have some inserts that will do though with some epoxy.

[swamp thing]

The truss tube hardware arrived today.

I was going to make my own truss blocks but TBH just couldn't be A&E&£@d. The problems with wooden split blocks needing to be accurate for frequent assembly/disassembly when made of even hardwood is obvious.

I had seen the Webster telescopes hardware and had always been Impressed with the quality of the fixings. Some PM,s exchanged with Umadog (cheers buddy) convinced me this was the way to go.

I must add the service and speed the parts arrived from Detroit was very impressive.

Here's a couple of pics:

The lower mirror box clamp is at the top right. With the UTA clamp below.

The upper clamp locator is just placed on the UTA ring for the photo.

They didn't come with instructions but Eric Webster remembered to email me the fitting instructions. Which are excellent.

Another of the chief reasons I chose these was they leave both ends of the tube open so cables can be run up the truss tube keeping it tidier and safer than cables hanging everywhere.