F12, 4" newt Build.

[Nathan_Pembs]

Nice one! You're storming through this

How did you calculate where to cut the focuser hole in the tube?

[mapstar]

Fantastic work and very neatly done. The body filler definitely does it's trick and look's like it was meant to be part of the focuser.

Well done and great to see 

Damian

[bluemaxroe]

hi nathan_pembs, i made a cardboard tube mock up. 2 short pieces of carpet tube. one with the primary at the back, and the other with the focuser and secondary in. next i took some more carpet tube, sliced that down lengthways so i had a long 1/4 section or 1 quadrant and screwed that to a straight length kf wood.

i fixed the tube section with the primary to one end and left the secondary end free to slide up and down.

took it upstairs (it happened to be a clear night. focused on a star. measured the distance between front of mirror and centre of focuser. job done.

with the dia. of tube being so small, i had to make sure that i would reach focus without the focuser tube being in to far, as this seriously blocks the light path by almost 1/5.

so before i slid that part of the tube up snd down, i ser the focuser out just over halfway (clear of the inside) i then checked this again using a 2xbarlow as well.

hope that helps. sorry for no pictures.

[bluemaxroe]

thanks Damien. a trick i learned as a modelmaker. its pretty foul stuff to work/sand. but with wet and dry gives a lovely finish. especially coupled with P38. if your not to worried abiut weight that is.

[mapstar]

thanks Damien. a trick i learned as a modelmaker. its pretty foul stuff to work/sand. but with wet and dry gives a lovely finish. especially coupled with P38. if your not to worried abiut weight that is.

I'll agree with you on that, I've had the same experience with it myself and can confirm it is horrid stuff although I'd definitely not swap it for polishing pitch.

Like the Innovative use of it for astro and I'm sure you'll inspire others to make use of it in the future adapting focusers to different tube size's

Great stuff

[Soupy]

Really clever work on the focuser, looks like it was machined to fit! Well done.

[bluemaxroe]

Thanks soupy. That kind of work I find fairly easy but the spider and secondary positioning on the other hand is a real pain, as it is so small. I seem to have it in the right place now, but the arms of the spider are a little off square.

[valefor]

You have always been a little off square. Lol. But it shouldnt make to much difference. Makes the defraction spikes look interesting. Doing an amazing job tho. Cant wait for the finished scope

[bluemaxroe]

i resent that monseiur P. thanks for the guide on the cell design too. should soon havevthis wrapped up. ps i wanna see the registax'd jupiter soon mate.

[bluemaxroe]

Ok next step, create method to hold mirror. I decided to replicate the style of most cells where the mirror has three clips that can be tightened down to hold, but not put pressure on the mirror. Then I will use a little silicon for grip...to steady the mirror.

Here is an image of the 2.5mm aluminium sheet cut, and now stuck to the back of the brass cell.

Not sure if this will put tension (different contraction rates of brass and aluminium?) but it's all I had, and wood would have been too thick for the cell spring depth to deal with....

The three spots are where the standoffs will be that hold the clips for the mirror.

[bluemaxroe]

Ok so, a little cutting, filing and wet and dry later and some more 2.5mm sheet aluminium has turned into three mirror clips. Mounted on 3 x M3 bolts.

These clips were so small it was incredibly fiddly to cut any felt of rubber to fit under these. Might buy some small rubber washers to fit these instead. For the mean time I have stuck some fabric plaster to the underside of them to provide cushioning.

Thoughts?

[valefor]

I think it looks great. Rubber washers sound like a great idea

[bluemaxroe]

And here is a shot of it mounted in the tube.

Still a lot to do...this is just a test fit...I will check it collomates and comes to focus as expected, then I willstart finishing the tube. The rings came today.....just standard skywatchers - the external dim of the tube just happens to be 140 so that's what I management to get of astronomy for a tenner.

[skybadger]

Velcro pads

[mapstar]

Looking good

[Soupy]

It's looking great.

Just one question now I see it almost complete. With it being a long wooden tube, it will be pretty well insulated, does that not mean you will set up some small thermal currents in the tube with no way for these to escape?

[bluemaxroe]

Good question Soupy.

It is my thought to have the scope stored in a dry outdoor area/ shed. This should mean the scope starts at a lower temp. Then I have left as much space as possible around the cell to the rear to hopefully help with temp variations.

Other than that, any suggestions? I don't want cavities in the tube..and there is no room for fans etc....it's just too small, and the mirror itself is only 12mm thick, so this should cool down pretty quick.

[Soupy]

I am sure won't be too much of a problem and without cutting some ventilation holes in the tube I am not sure what else you could do, other than what you are doing...

[astrolunartick]

Very interesting build. Very enjoyable to watch you build this. Im looking forward to seeing the scope mounted. How are you mounting it? Keep up the good work. 

Pete

[bluemaxroe]

with rings...140id rings fit nicely. picked some up off astroboot a few days ago. its ready to test. which explains the cloud...sorry everyone

[Ajohn]

You might be able to find some cork mats to use for contact points on the mirror.  Just cut small pieces stick them to the locations and adjust so that they grip the mirror lightly. As cork varies I suspect that the gasket material that's around 1 1/2 to 2mm thick would be best. It's cork binded with rubber. The natural stuff may turn out to be too soft unless you can find some thin dining table type cork mats but they may be too thick. Put  3 pads under the mirror as well.

At this size and even larger I don't think you need to worry about tube currents especially with a wooden tube. The main thing is that the air is stable in the tube. You could simply cut a hole through the centre of the wooden part of the mirror holder to allow air to pass through the tube if your concerned about this aspect but looking at your holder there is already plenty of space for air to pass through the tube.

John

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[Laurie61]

An interesting project, if you would like to flock but feel the tube is too small dia try flocking some thick card and then slide it in from one end.   

[bluemaxroe]

its a cunning idea Laurie61, i like it and would probably do it as it seems even easier than painting. it would add to the thermal issues though. as this is a budget build i am not sure yet if the scope warrants flocking. i think my commercial head is winning as i already have some left over blackboard paint.

[valefor]

Its nice to see how cheep you can make a decent scope for. Try the blackboard paint and if it dont work out you can flock it later.

[Laurie61]

I doubt you will have too much trouble with thermal prob's, especially if the scope is stored outside. Something similar has been tried before and the chap was happy with it.