The Mapstar 22" build

[mapstar]

Moving on it was time to attach the bearings to the mirror box. I was going to use steel hex drive screw in insert nuts as these are a lot more durable than the alloy types. Downside is they are a little more expensive.Like these

http://www.ebay.co.uk/itm/M8-x-18mm-Headed-Hex-Drive-Steel-Screw-In-Inserts-For-Wood-Zp-10-Pcs-100093-/271416559691?hash=item3f31b0084b:g:iLYAAOxyTMdTNY5S

I again used the same jig I had used to put the holes in the bearings orientating it so that the bearings were at the correct position. Once I'd done this I put a flat cut on the Jig so that It lined up with the front surface of the box. I could  then screw another piece of ply to the top which would locate on the top of the box with an overhang so it could be used on either side of the box matching everything up with a datum line drawn squarely across the mirror box. Probably the picture tells the story better below

The hole's were then cut in again with the router (1/2"bit) utilising the 30mm guide bush in the highlighted holes. Two cut already above. Once finished I have found that a small chamfer cut in reduces the amount of break out when screwing in the insert nuts

 

I made a cross brace for the bearings next using pretty much the same technique's as for the bearings

Edited March 28, 2016 by mapstar

[mapstar]

The cross brace was cut from 24mm thick material and the obligatory hole's cut in. All the edge's and hole's were then chamfered. Here it is before I chamfered it on the router table

Again using the Jig for the the bearings I lined all this up so that I could cut the insert nuts into the ends.

Again a small chamfer allows the nut a better start. Because the nut was going into the end ply's I waxed the thread before putting it in and also clamped across the ply to prevent splitting which can occur if the hole is too tight which it is being screwed into. A trial is always good.

Now the bearings and cross brace were finished it was time to assemble it just to see how it looked

 the knobs came from ebay and were cast bakerlite type

http://www.ebay.co.uk/itm/5pcs-40mm-Dia-Star-Shape-Head-M8-x-40mm-Male-Thread-Clamping-Screw-Knob-/181888137816?hash=item2a5960ba58:g:oOYAAOSwoydWraCy

So I'd now got both the UTA and Lower optical assembly finished it was onto the rocker box which would be a little different from the square norm

 

Edited March 28, 2016 by mapstar

[mapstar]

After looking around at various designs of rocker box I settled on a Sumerian type design which would be round. The main parts would be made from 18mm with the actual bearing carriers being 24mm.  The design would have a solid base and a doughnut on top which the mirror box would run through.

Here's how I started by cutting out a circular piece and then dividing it up with 16 'spokes'

All these I would dowel on and then fill each section with a stretcher. The 'spokes' I would put hole's in to lighten the assembly slightly but having a heavy base would add a bit of stability too, making the whole assembly bottom heavy.Here's the assembly drilled for the dowels and with the holes cut. Each hole was chamfered 

Once I'd put the stretchers between each I then glued one half up ready for the top. I used the same technique as the UTA with the router trammel bar to put all the dowel holes in the lower and upper ring of the rocker, so they matched, then did the glue up in two sessions. The bottom first with the top in situ dry to keep everything aligned.  

Before gluing the top on I had to make up the bearing carriers. These were again cut with the trammel bar and router then all drilled for dowelling them onto the top of the rocker. Here they are ready for fitting. They are complete with the teflon pads 

Into the top doughnut ring I put in the dowel holes and could then move onto gluing up the upper ring, after that the bearing carriers were glued on top making sure they were parallel,in line and square with each other across the rocker box. They also had to be just a fraction wider than the mirror box with bearings attached.  

 

 

Edited April 3, 2016 by mapstar
More info

[mapstar]

Here's the assembly during a trial fit before I attached the teflon and bearing edge guides.

I put four hole's around the the middle and also a bushed hole in the centre for the bearing. It was all sanded ready for finishing. I then made the ground board on the next post.

Cheers

[mapstar]

I made the ground board out of 3 pieces of 12mm triangular ply glued together. To keep the alignment I again dowelled everything together.

The central bearing and pivot boss I had made quite a while ago, like the rest of the metal work whilst I has access to my friends machine shop

I set the boss into the top, attaching it with three brass screws and a large aluminium washer from underneath. The teflon pad would fit on top of the central boss

Below with the addition of feet pads and teflon. The feet would eventually have rubber glued onto the underside

 

I stripped it all down for a final sand and also added some hole's to lighten it up which again had the obligatory chamfered edges even though not much of this would ever be seen

All the construction completed it was ready for finishing and re-attaching everything when the final build up happened. The truss poles and attachment would be next on the agenda

Edited April 2, 2016 by mapstar
Alterations

[faulksy]

On 26/03/2016 at 11:53, mapstar said:

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 

 

 

 

hi damien , great idea about insulating the spider but it will leak through the bolt thread

[faulksy]

awsome thread. love it. keep it coming

[mapstar]

1 hour ago, faulksy said:

hi damien , great idea about insulating the spider but it will leak through the bolt thread

Hi Mike thanks for commenting. 

Here's what the shouldered washer does to prevent what you are thinking of. Insulators like this have been used in Industry for quite a number of years. Made from Tufnol for HV systems. Here's a cut away drawing of how the insulation is put together. The shouldered washer effectively insulating the bolt from the vane 

The plastic insulator also wraps underneath the vane to insulate it from the collimation ring as can be seen on the fully built up photo above

Sorry for not posting a drawing about it before

Edited April 2, 2016 by mapstar
Extra details

[Stub Mandrel]

The same, but much smaller, is used for attaching transistors with uninsulated tabs to heat sinks but I guess you know that already :-)

[mapstar]

6 minutes ago, Stub Mandrel said:

The same, but much smaller, is used for attaching transistors with uninsulated tabs to heat sinks but I guess you know that already :-)

Thanks Neil, I did try to find a diagram of such a thing but none turned up that were suitable

[swamp thing]

I bet sanding that rocker box was a nice job. I like the sanding part it's very therapeutic seeing and touching the smooth wood hmmmmmmmmsmooth. I need to get out more yes?  

Good job matey  

[mapstar]

Just now, swamp thing said:

I bet sanding that rocker box was a nice job. I like the sanding part it's very therapeutic seeing and touching the smooth wood hmmmmmmmmsmooth. I need to get out more yes?  

Good job matey  

Cheers Steve

O.k. when everything is flat, but it was a proper pain when glued up! I'll give you a shout next time I've a sanding job on the horizon 

[swamp thing]

I like sanding Damian but not driving to Yorkshire mate  

[mapstar]

Just now, swamp thing said:

I like sanding Damien but not driving to Yorkshire mate  

Ha ha, thought you may spot the catch 

[Soupy]

Looks great Damian, brings back memories!

[mapstar]

5 hours ago, Soupy said:

Looks great Damian, brings back memories!

Yeah seems like years ago now though.

[Physopto]

Nice set of pics Damian. A lot of careful work there. 

But do you never sleeeeeep????

[mapstar]

I try Derek, but at present think job worries are putting paid to that?

[Physopto]

Yes, really sorry to hear of all this trouble. Whatever happens, I hope you get sorted quickly. Never nice not knowing if you are secure in work. 

[mapstar]

6 minutes ago, Physopto said:

Yes, really sorry to hear of all this trouble. Whatever happens, I hope you get sorted quickly. Never nice not knowing if you are secure in work. 

Nothing a cuppa won't sort at this time in the morning!

Edited April 3, 2016 by mapstar

[Physopto]

At present Trying to convince the other half to make one. 

[mapstar]

Here's another shot of the rocker 'box' with the extra hole's cut in the bottom, the central bush fitted and the teflon refitted until I came to finishing it.

To complete the base and bearings I needed some laminate/formica.

The last scope used quite a textured surface and was replaced by bearings eventually due to the scope being motorised. I wanted something smoother this time as the scope would only be used manually. Finding a suitably textured material and supplier proved to be quite a long task. The wilsonart ebony star that so many books mention is no longer available so an alternative was needed.

I actually went through a book of over 500 samples at a supplier I chanced upon whilst travelling on the motorway. I don't normally look at the side's of trucks but I noticed one with International Decorative Surfaces on it (mental note to self was left). I checked them out and fouund a branch only half an hour from me.

The laminate I ended up with is superb stuff and is actually from the brand Formica. It's full designation is:-

Formica Pattern range StarDust HGP Quarry F1782 CW

They also do two others called Lava Dust and Grey Dust. It's the quarry finish that makes all the difference though. It just so happens that these three are that finish

Here it is being cut and ready for attaching to the rocker bottom

 Just the same to do for the alt bearings and then glue it on. I use Evo stik 528 Instant Contact Adhesive (this used to be made by Dunlop) to attach the Formica to the surfaces. It is the best I've used as contact adhesives go. I have a little bit left over so may need to build some more scope's to use it up 

 

Edited April 3, 2016 by mapstar
additional technical information

[Soupy]

4 hours ago, mapstar said:

Yeah seems like years ago now though.

It does indeed buddy... But the excitement has rarely dwindled. Keep going it's a great read.

[Gina]

Amazing work there - great stuff

[mapstar]

16 minutes ago, Gina said:

Amazing work there - great stuff

Thanks Gina