How hard is it to build a telescope?

[swamp thing]

Looking forward to seeing this John. Not as much as you though no doubt

[gooseholla]

Well my spider is still a work in progress - awaiting the hardware to install the rulers as vanes, and got a bit of trimming etc to do to keep wood hidden behind the secondary, but here, after many hours toiling and a couple of prototypes I improved on... I unveil the Goose Astro Systesm BHW 3000 (Bloomin' Hard Work!).  

It is a hefty lump but hopefully It will do the job. Got some inserts to go into the collimation holes for the bolts to go through. Yes, essentially it is a few lumps of plywood glued together, but hopefully I can now put this sage behind me, install some vanes and get round to testing!
 

What type of silicone to install the mirror - heard clear silicone, but are there different kinds of silicone? Is the stuff that goes round sinks etc. the same as that which installs mirrors?

Regards

John

 

[mapstar]

Great name for the spider John

Its getting closer but a bit more work yet so onwards and upwards.

Some clear Unibond glazing silicone will be fine the stuff that's used on aquariums just have a read on the label what it sticks to.

Generally it's like pitch it sticks to everything you don't want it to!

[gooseholla]

Had I of been more prepared and well not a cheapskate, I would of ordered one from the states ages ago. However, thanks to modifying rustysplit's design you sent me a link to, I think I've come out with something solid.

Cheers

John

 

[mapstar]

That's what it's all about getting something individual

Imitation is the sincerest form form of flattery

[gooseholla]

Hi,

Is this the stuff? Only unibond thing that came up for unibond glazing silicone

http://www.screwfix.com/p/unibond-silicone-frame-sealant-clear-300ml/86958

Cheers

John

[gooseholla]

Some good progress made today.
 

The final coat of varnish went onto the mirror box. The Kydex ring went into the tailgate to hold the triangles in place.

The spider was painted black with two coats today. Bit annoyed as no postman today so I couldn't build the vanes up or put a washer on top for the collimation bolts to ride against. The construction is of plywood and is glued and today I countersunk some drywall screws to hold the 45 degree angle to the round part - just incase!!

Also the Beech split blocks were varnished - they went a lovely colour.

They need a second coat and the insides doing tomorrow.

Also to do tomorrow:

• I have to semi-align the blocks so I can decide how much of the side bearing to cut out. That is going to take up most of tomorrow I think.
• The mirror posts have to be installed as well and I'm going to tweak the split bolts for the strap so it sits in a little further.
• I'll also cut the focuser board to length and width and glue some reinforcing strips on and decide where to install it on the secondary cage. The secondary cage will then get its final varnish.

Then if all goes to plan Saturday I'll try and silicone the secondary mirror in place and then hopefully by Monday the focuser can be aligned and the beast finally tested.

John

 

[Ajohn]

You should be able to get the adhesive style clear silicon rubber from a builders merchant rather than the one that is intended to use as a sealant.   well you could at one of our local ones, not sure now as they have been taken over by a national chain.

John

-

[gooseholla]

Well I think a mirror test is going to have to wait another week or so. Woke up today feeling rough - caught my neighbours cold/flu and I'm not going to make fine  cuts and measure fine angles while my head is spinning.

I did finish off varnishing the split blocks today and primed the spider vanes ready for black paint and also managed to get the focuser board trimmed down to size.

John

[gooseholla]

So those who are observant among you who have been following the build will notice I haven't ever shown how I am going to fix the truss tubes to the upper cage. Well here we are...

They are made from the same beech as the lower split blocks. Instead of a clamp there will be a bolt going through with a star wheel/knob on the end. The eyepiece and adapter are 1.25" and I cannot pull them out by any amount of force. They still need to be sanded and varnished.

I will be ordered the knobs tonight and varnish them tomorrow, when I shall also build the spider up with vanes etc.

John

[swamp thing]

John 

How did you calculate the angle to drill the top clamp holes? 

Just wondering as I'm not very good at working this sort of thing out. Is there a formula in the KB book I missed? 

[gooseholla]

Yeah, you can use trigonometry using half the length of one of the sides of the mirror box and the focal length between the cage and box. ie if your focal length is 1840, as mine is, I took away how much of the mirror box, cage, and length to focuser from secondary it would be, fudged in about an inch or two extra to make sure I had wiggle room, then worked out I had 1160 mm between the two. I then used tangent to work out the angle. It turns out that for my mirror box, anything from about 1100 - 1300 gives a 13ish degree angle.

Pages 235 and 236 of the book explain it.

So do, for example 11 inches (half mirror box side) divided by 46 inches (height between two halves) then press shift tan on a calculator to get tan-1 which will give you the degrees. If you want to, you can then work out the length of pole you'll actually need using trig as well... but that is a risky thing.

As an aside - I have NOT ordered my poles at that specific length, I have ordered them quite a bit longer, as the calculations are rough and the split block location liable to change etc. So they are coming at 1400mm each, a lot longer than needed so I can cut them to required proper length once tested the mirrors .

John

[gooseholla]

Today was another good day. A lovely sunny day so my day began with  some varnishing and painting.The upper truss clamps were varnished, they'll get another coat tomorrow. All the parts for the spider were painted with another couple of layers of black paint.

The mirror box had some edges varnished that had only received one coat. Tomorrow the inside will have a final black coat, after it has been de-dusted! All the hardware was installed today - mirror posts, sling and corner braces. The first picture shows a way to clamp them into place if you haven't got massive clamps. Lay the box down flat and lay some 2x4s across them. Another way is to have a lump of wood which spans the gap between 2 corners.

The angles of the triangles need a bit of adjusting, so will be restuck with new foam pads to the kydex ring.

Here is the top part of the spider with vanes attached. I didn't quite get consistent 90 degree bends, but I am sure I can sort that out whilst mounting. The ends will attach with some stud connectors I am cutting a channel into. This is one of the jobs for tomorrow. This is the bottom of the spider hub. On the other side are 3 holes with threaded inserts for M6 bolts to run through for collimation.

Also my truss poles turned up today!!! They are lighter than I thought. The package contains the poles cut to 1400mm, a lot longer than needed, and some offcuts measuring about 800mm. I will use one of the offcuts to practice using a tube cutter. The plan will be to mount the lower split blocks and run the poles through them, then slide them up and down until I achieve focus, then mark and cut them all to that length. I think that will be easier than holding an entire secondary cage and moving it in thin air!!

So tomorrow and Friday:

- Build spider

- Paint mirror box inside with final coat of black

- Assemble ground board and rocker board together with pivot bolt so I can spin the mirror box while testing.

- Silicone secondary mirror to spider

- Install truss clamps

- Test sometime over the weekend - hopefully!

 John

ps anyone know where I can get the right heat-shrink for the tubing? It is 32mm tubing.

[gooseholla]

Secondary Spider - Final Design

So you probably are aware I had a lot of spider trouble during the build. But here it is, in all its glory. And it was certainly worth persevering!

The hub part is made from a sheet of 18mm plywood and two 6mm sheets laminated onto it either side of the 18mm. 3 bolts provide the collimation. They run through threaded inserts. The bolts are M6 and the inserts required an M8 hole drilling 28mm into the hub. The bolts ride against a stainless steel plate that was cut from some 2mm thick steel which was epoxied onto the lower assembly. Everything that is glued to something else on the 45 degree part of the spider was also held in place with countersunk dry wall screws. I just hope the glue holds where I laminated the wood for the hub - I used a lot of glue and a lot of clamps, so fingers crossed!

The white thing in the pictures is a template from the K + B book I cut out to test sizes.I will use another one tomorrow to centre spot the back of the secondary so I can align it. The board it is going to be siliconed to has a layer of epoxy across it and a hole cut out of the middle so that I can peer through and line the mirror up under the centre of the secondary hub. The board still has to be attached to the 45 degree blocks with wood glue and countersunk screws. It is made from a sheet of exterior plywood I purchased for something.

The vanes were made from 4 stainless steel rulers. Nothing special, cheapest I could find. They start off as 30cm ones and cut down to 22.5 cm. They were bent 90 degrees and ended up being 21 cm long, the length I needed each side to span the gap of the secondary cage. They are held in with some self tapping screws I had for my car.

Everything was primed and given about 5 layers of matte black paint - mostly because as I reworked things and sanded down bare wood started to show. But it looks a lovely dark smooth black in person so was probably worth it.

So there we go. After building one far too small to start with, and having troubles with some other designs, it seems I have something useable at last. Thanks goes to mapstar and rustysplit, whose simple plywood design I copied and modified.

John

[swamp thing]

Think I bought my heat shrink tubing from eBay TBH. Plenty of different places about with similar prices.

[gooseholla]

Good day today and lots was done. Ready I think to silicone the secondary mirror tomorrow  and install the primary on Saturday.

Made the connectors for the secondary vanes today. They are a stud connector with a hole sawed half way down and a hole drilled across for a bolt/grub screw.

I used one of these machines to make  the slots as it has the right width blade for the vanes. It is best to start a little groove with a hacksaw first so that the bit doesn't bounce off and wander.

Also I cut the Teflon pads for the bearings. They are a little large than the K + B book suggest as I do not know the total weight of the scope, only a rough figure nor the kind of laminate I will be using. They are held in with 4 panel pins punched below the surface.

This is what the  rocker will spin around - an M12 nut through a lock nut which has been epoxied to a washer which will be permanently installed to the lower side of the groundboard.

The final part of the spider was glued together today. A hole is drilled in the board for the centre of the mirror to align with the centre point of the stalk. We lined the board up by blutacking a needle upright on the bolt and moving it to the centre of the hole. It was then twisted a bit so the lines on the board matched the 4 vanes of the spider. This will make it easier to plonk the secondary mirror in the correct place tomorrow.

There is still a bit to do, like install the truss clamps in the right place and drill 4 holes for the spider vanes to attach to the secondary cage but it should then be testable. After that I need to buy some laminate for the bearings, find some material to seal the upper cage in and build the rocker box sides up and cut the arcs. So still a bit till it is fully useable, but good enough for a mirror check and determining pole length.

I forgot to add.... I also need to drill the hole and install the focuser. I will do this before I silicone the mirror on so that I have my reference marks on show.

Regards

John

[gooseholla]

Today was a mixed day. Everything really should of been ready for tomorrow to test but I was overcautious in making my cuts for the vanes so the spider doesn't quite fit in when tensioned - the vanes bend out, so tomorrow I've got to chop something off somewhere by a mm or two.

Other than that, focuser went in and was lined up. I put the K + B secondary template on the spider and used the Moonlinte focuser with a laser to align where the focuser board would go. I was going to install the upper truss clamps but I got side tracked wanting to silicone the mirror onto the 45 degree part just incase tomorrow I can still test things.

The secondary mirror had three large blobs of silicone put onto the board, and a small one for luck !! I then placed some toothpicks on it and let the silicone settle for a minute. I then lined it up the best I could and plonked it down. It has its cover over it now so it doesn't get dusty or dirty.

The jig to hold it flat is a lump of plywood, my drill press held at and my drill press set to an angle until it is flat.

So really excited I could be testing tomorrow or Sunday... but the spider issue has to be sorted first, and I am not going to rush it, even though I am excited!

John

[gooseholla]

Well I redid the secondary so the vanes are now tensioned nicely and fit in the cage. I had a quick go at trying to line some truss clamps up with the poles in ,but some things have come up and since the weather is forecasted cloud for the next few days I've knocked it on the head for this weekend and will start again Monday while I sort a few bits out.

[mapstar]

Looking really nice there John and well done for getting to this stage, think the weather might also give you urgency to finish as it's not at all what they forecast

Damian

[swamp thing]

That UTA looks sweet John, nice job mate

[gooseholla]

Thanks for the comments guys.

I'd love to get it finished this weekend but an unexpected trip from niece and nephew, a visit to see someone and having to cover two services at church on the organ tomorrow mean it won't be done this weekend :-( In better news, the secondary mirror stuck to the holder, so I could test the mirrors at least by holding the UTA!

John

[gooseholla]

The weather was a bit grim today so I didn't get a chance to assemble the telescope but I did some modification to a couple of bits. My neighbour also came over, who was an engineer, and we looked at ways of improving the truss clamp system, especially the upper part. He drew a more sturdy way to do it, using the same kind of design, so I will crack on and make those tomorrow. Got a couple of other bits to modify slightly as I've thought of better ways to do it whilst looking in detail at all my parts over the weekend. So I may get to test the mirrors sometime... Good ol' British weather - must be a major astronomy event coming up!!

John

 

[gooseholla]

Today was a good day. The rocker bottom was built up and glides effortlessly on top of the ground board. I know it didn't have the full weight on it but it was good to see it working. Then the angles for the poles were measured through some testing and the split blocks started to be installed on the mirror box. I only got two done in the end as I was having a natter with a few people and my neighbour throughout the day. But now I know the measurements the rest will be installed tomorrow. The upper clamps have to be installed on the upper cage as well tomorrow. The secondary mirror made an appearance earlier in the day as well. I think I need to adjust the moonlite focuser a bit. Lots of fine tuning to do over the coming weeks I suspect. But all being well, tomorrow the two halves will be joined together!

I had a scare early on in the day. The focuser was above my head and about 5 inches higher than expected. Stupid me being tired was reading mm wrongly so had it way too high! Phew... thought I was going to have to get a ladder!!

The blocks are installed like the K + B book says. A coach bolt goes through and eventually a hand knob will go on - I am still waiting for them. Some reinforcing strips and drywall screws need to be added to make them solid and say in the right place.

The top clamps will hopefully work better when one surface is flat against the cage. At the moment it is hard to get everything lined up whilst they wobble about. Again some knobs will go on them when they arrive. n.b the left hand pole was damaged when I got it! It wasn't the clamps that did it. I will be cutting that off anyway when the poles are the right height.

John

[swamp thing]

Blimey I think my eyesights gone all blurred

Have a word with the camera man John. 

[mapstar]

Lot's of progress John keep up the enthusiasm as first light is getting near (thats if the weather plays ball)