The Mapstar 22" build

[mapstar]

Onwards and upwards as they say

After gluing up the other ring onto the spreaders I then glued on more strips at the rear of the focuser board. I made myself a little jig to run around the inside so I could get the same curve as the rebate for gluing the aero ply on.

 

 

The aero ply was glued inside in two halves using brads to nail it in place. Here it is when completed. The main aim was to keep it as light as possible

To actually mount the focuser (Feathertouch LW with SIPS) I decided to sink a 4mm aluminium plate into the focuser board and open up the hole inside so I could easily get my fingers around the SIPS unit to remove it for collimation. It was a job I wish I'd done when the board was still loose but you live and learn. This would be held on by M5 setscrews from inside the Upper Tube Assembly (UTA) Here's the plate being hand tapped on the pillar drill (I seem to be brilliant at tapping holes by hand at angle's!!!!) so the use of the drill is good for getting it perpendicular to the surface

I discarded the silly sized imperial screws that came with the focuser kit and fitted M4 cap heads instead. The plate was drilled to suit and tapped M4. Now the levelling grub screws had a decent base to work against instead of wood.

The spider was next up and I changed it's design a couple of times as the weight of the 130mm minor axis secondary is considerable (650g) This creates a rotational force so I countered this with thicker vanes and 4 M6 collimation screws. Here's the spider central boss which was made from a 2" piece of round aluminium bar and then had the collimation plate bolted on with M4 countersunk allen cap screws.

This wasn't the finished item as I had to lighten it with a series of holes in the collimation plate. The vanes would be bolted on with the 8x M4 holes. 

More soon

 

 

 

 

Edited March 26, 2016 by mapstar
additional information

[JRM]

great work Damian, things  fitting together nicely,gonna look awesome. keep them coming.

Rick

[mapstar]

8 hours ago, JRM said:

great work Damian, things  fitting together nicely,gonna look awesome. keep them coming.

Rick

Thanks Rick coming on a bit quicker than the mirror thread 

[Stub Mandrel]

I wish I could work wood that neatly.

[Gina]

Me too.

[mapstar]

21 minutes ago, Stub Mandrel said:

I wish I could work wood that neatly.

Thanks for the comments Neil and Gina

There was just a little too much glue about for my liking, but as you say it would be more than adequate for most. The clean up takes a while but I was going to paint the scope when everything was finished 

Edited March 27, 2016 by mapstar

[Physopto]

I would rather too much glue than not enough! Easily wiped of later when almost set, as I am sure you did. Having seen your work, I could not fault it even if I wanted too. Really nice job Damian.

Derek

[mapstar]

Not wanting to have unbalanced diffraction spikes I insulated one of the spider vanes so that I could supply the dew heater through the metal work. You can see the plastic insulating washers under the screw heads. The central boss had been machined to account for this 

The insulating washers are these if anyone want's to do something similar 

http://www.ebay.co.uk/itm/Packs-of-10-M3-M4-M5-M6-M8-M10-M12-M16-NYLON-Plastic-Shoulder-Washer-/400481731718?var=&hash=item5d3e924486

Here's the spider before the bottom collimation plate was added 

The top of the actual secondary holder I had a friend machine up from aluminium plate to accept a spherical bearing so the whole assembly would tilt nicely. A 22mm end mill was used to put the counter bore in so the outer race of the bearing would fit, the offsetting is clear to see with this being such a fast scope at F3.4. This plate would also be lightened in it's final guise. Here it is with the collimation ring

Here it all is in it's final assembled state (apologies for the poor quality of the image) I still had to attach the dew heater wiring so it was just dangling

More soon 

 

 

 

Edited March 27, 2016 by mapstar
additional information

[mapstar]

17 minutes ago, Physopto said:

I would rather too much glue than not enough! Easily wiped of later when almost set, as I am sure you did. Having seen your work, I could not fault it even if I wanted too. Really nice job Damian.

Derek

Agreed Derek starving the joint is far worse than having a bit of glue to wipe off. I cleaned off as much as I could but it always leaves a film on the wood as effectively you are just watering it down. Luckily the glue is suitable for painting over. It would be a different matter if I was going to stain it though.

[Physopto]

Yes I tape the bits, but that does not always stop the glue migrating through the wood under the tape.

[Gina]

I like the idea of connecting the dew heater through the spider - nice one

[Physopto]

Puzzled, why two wires if you used the vane?

Or am I missing something?

Derek

[mapstar]

20 minutes ago, Physopto said:

Puzzled, why two wires if you used the vane?

Or am I missing something?

Derek

Here's another pic. Effectively the kendrick dew heater pad has two wires to it so I lugged them up and connected them to the vanes (1 vane positive, 3 vanes negative) and then run wires up the inside of the UTA to the outer ends of the vanes as in the photo's which are hot of my rubbish camera

A bit better quality shots 

 

[Soupy]

It's all looking rather tasty Damian. Amazing woodworking and metal working, it's great to see it all coming together.

[mapstar]

15 minutes ago, Soupy said:

It's all looking rather tasty Damian. Amazing woodworking and metal working, it's great to see it all coming together.

Yeah although you already know what it looks like it's an interesting walk through how it got there.

[mapstar]

1 hour ago, Gina said:

I like the idea of connecting the dew heater through the spider - nice one

Cheers Gina. Something I wanted to do on the last build I just didn't get the time as the owner needed it quickly.

[Physopto]

Yup, I was not seeing where the wires went.

[mapstar]

Just now, Physopto said:

Yup, I was not seeing where the wires went.

They weren't connected in the first shot 

[mapstar]

The actual secondary holder I had many thoughts on and I will come back to that nearing the end of the thread so I'll move onto the truss mounts for the upper tube assembly.

The last scope I built used a threaded rod into a threaded insert nut on the bottom of the upper tube assembly. This time I wanted something faster to assemble so went for the usual bike skewer method. Because I wanted the trusses to be as solid an assembly as I could get I decided that every truss pole would be clamped. No rattling! I made four mounts which were made from 40mm 5mm thick T section aluminium.

I made a jig so that all the mounting holes were in exactly the same place (M5 screw sticking through) I then used the jig to drill the skewer clamping holes (8mm) which would be slotted down to the left hand edge when complete

Once finished I made up a jig out of scrap ply so that I would get them all mounted squarely onto the bottom of the Upper Tube Assembly. See pic below

Once all the mounting point's were drilled it was a case of finishing before refitting all the components. 

 

 

Edited April 4, 2016 by mapstar
additional technical information

[mapstar]

I had to work out the bearing size for the balance so for this I refer to Albert Highe's book:- Engineering, Design and construction of portable Newtonian telescopes

In it is a little disc with XL files which do all the work for you.

With that sorted I knew the bearings had to be 385mm diameter. Knowing this I set up a jig to cut the bearings from two pieces of 24mm thick ply. I used a CAD program to draw them out until I was happy with the shape. I used the CAD quite a bit to figure out all the other bits (Mirror box/Rocker). Here's the Jig and drawing before the cutting commenced

The 1/2" router making easy work of the chore and creating lots of saw dust in the process! My home made trammel jig is a god send

And after they were finally cut. Because I'd worked out where the hole's would be (the five drilled holes) I used these scrap pieces to keep the 2 bearings in the correct orientation when the upper curve was cut

Next onto the hole cutting just for a bit of aesthetic appeal 

 

 

Edited March 27, 2016 by mapstar
additional information

[mapstar]

Onto the hole's for the bearings which would be various sizes tapering from the middle.

After these were cut I used them to make a jig to cut in the screw holes for the attachment screws that would fix the bearings to the mirror box. Photo below shows me setting up the jig from underneath first and then on top where I had cut holes to use the 30mm guide bush on the router to accurately drill the bearings with a 10mm cutter. The use of bits of scrap and an old jig in evidence.

From above with a few marker pen highlights so I used the right holes!

Here's how the bearings looked once the attachment holes were drilled. The holes would be bushed with 10mm stainless tube having a 1mm wall thus an 8mm hole to stop the wood wearing as the scope was assembled/disassembled. Just a bit of sanding to finish off next

There are three holes for the mirror box (left side) and two for the cross brace (right side)

More soon and thanks for reading

 

[Uplooker]

Having had a look through the finished article, it's lovely to see it at all stages of construction.

Are you sure you are not a Tech Pubs writer in another life? Very well written and documented.

You would certainly have need a few pies as sustenance during this build?

I suspect that you're telescope building antics will result in many people's downfall as they attempt to replicate you're workmanship?

Cracking job and cracking scope ?

[Physopto]

Oh Dear Ian, I missed that connection, it is a pie measuring device in disguise!

Derek

[mapstar]

Cheers Ian

That's why I'm filling in the secondary holder last, it's a secret pie holder to cook the pies whilst the scope is aimed at the devil's light bulb! 

[mapstar]

28 minutes ago, Uplooker said:

Having had a look through the finished article, it's lovely to see it at all stages of construction.

Are you sure you are not a Tech Pubs writer in another life? Very well written and documented.

You would certainly have need a few pies as sustenance during this build?

I suspect that you're telescope building antics will result in many people's downfall as they attempt to replicate you're workmanship?

Cracking job and cracking scope ?

You may notice the amount of edits I do when I think of something else to add in that may be useful to others.

I only wish it was as easy to make as write about!