Delmarva 108mm Schiefs.

[Chriske]

Due to a few reasons we cannot start grinding our 300mmbBrunn telescopes. Another 2 months before we can start grinding.
Eager as we are to start building/grinding something we've decided to start another smaller project.
We will build a Delmarva Schief each.

I don't have to build the scope because I already have a nice wooden version that I got from a friend  years ago. Mirrors were not included. I'll be making all the optics and the rest only need to build their scope.
The plan is to start grinding 250mm mirrors and cut 3 sets of 108mm mirrors out of the large 250mm mirrors. Because there four of us I need to grind 2 sets of 250mm mirrors. Just finished hogging to the correct depth, so I'll start finer carbo today.

This how my Schief will look like. The others will make their own version of coarse.
The Delmarva is a anastigmatic version both mirrors have the same ROC. It is a Dave Groski design btw, he knows 'a thing or two' about Schiefs...😁

[Chriske]

...one tool, two mirrors...

[allworlds]

It looks like a broomstick 😀 Just need a few twigs and it'll be ready to take off. Very fitting for Halloween night.

[Chriske]

1 hour ago, allworlds said:

It looks like a broomstick 😀 Just need a few twigs and it'll be ready to take off. Very fitting for Halloween night.

😳???

[Chriske]

Still busy planning, drawing some more and already made a few testprints.

As I said before I already have a wooden Kutter but the others need to make their scope. One more joined the group, so that leaves me with 1 set of optics.

So in total :
- a wooden will be made(mine)
- a second one will make the tubes out of aluminium
- a third will make a it's tube and wedge out a combination of wood, printed parts and a few sheets of acryl.
- the last two will be (almost) 100% printed. Almost because internally the printed parts will be reinforced with smooth or threaded rods. So in the end these scopes will be as stiff and strong as the other versions. Except for the collimation bolts no other metal part will be visible in these two scopes, that is the plan.

[Chriske]

Because this Kutter has a tilted focal plane the eyepiece needs to be tilted 3°93 forward.
For this I designed a special Crayford focuser in which a zenit prism is integrated.
I also need to construct a special lasercollimator to compensate for that tilt. A regular laser collimator is useless in this scope.

Laserunit not yet in drawing, only the red beam.
The black tube is in fact the 'eyepiece barrel'.  Because of the optical design I cannot rotate that barrel in it's Crayford. I probabaly will add a notch of some kind so the barrel is fixed in its correct position.

Same for the laser collimator. It only has one possible and correct way to be inserted in the focuser. It already has that notch in the drawing.

[Chriske]

Meanwhile a 'special' laser collimator(yellow) is in the making.
The laser beam is not in line with the eyepiece, it is with the rest of the scope.

[Chriske]

One of the printed versions of this Delmarva Schief project will look like this.
The printer of this builder only allow 180mm high prints. So the secondary tube needs to be printed in a few parts and connected with threaded inner rings.
He already printed and tested a few parts and it is incredibly strong and stiff. Each of the inner connecting rings has it's correct baffle on board. That makes these parts even stronger.

Together with the special zenith prism it will look like this. It is the one I drew and posted here earlier. Maybe, just maybe he will draw his own. I'll ask him...

[Chriske]

We developed a very (special) test to see how strong these printed tubes really are. And with success I might say.
The first test was a load of 75kg and a second was about  95kg. There was no deformation at all and the three parts could be screwed loose without any effort after the test.

This is our very special setup...🤭

[Chriske]

Zenith prism ready, a 5.5 hour print.

[Chriske]

Still at it...
Optics nearly finished so we can work on the scopes wedge, its angle and the width.

We decided to also print the rest of the scope, tripod, wedge/fork.

This is how the tripod will look like, V1 not quit finished. Busy adding some improvements.
A small container is in the making.
All printed parts are very thick.
The aluminium legs of these tripods are a gift from an old amateur. He gave us a box filled with these legs.