13" F/3 telescope build

[Mitch Alsup]

There is a freely downloadable program called PLOP (Plate Optimizer). Plop has been designed for parabolic mirrors and models the surface distortions that the <point load> supports will imposed on the mirror.

In my case, PLOP suggests that the support is better than 1/128 (4.5E-6 m) wave of surface distortion--a figure so much better than the expected surface that it is essentially invisible.



I have also seen that several professional mirror makers serving the amateur market support their mirrors on mirror cells on the polishing machines.

 

[StevSmar]

...I have also seen that several professional mirror makers serving the amateur market support their mirrors on mirror cells on the polishing machines.

Thanks for the reply. That’s good to know that some mirror makers take the intended support method into account when polishing their mirrors.

I’ve enjoyed reading this thread, and the others you linked to.

 

[pdentrem]

I was following your cell build on cloudynights until the take over by a couple well respected guys got into it. Any ways I made my own cell for my 13” Zambuto but I am not happy with the upper structure and it’s support system. Keep this going, I hope to learn a few ideas for my rebuild.
Pierre

 

[savarin]

I'm well jealous of your Zambuto mirror.
My financial controller would have a fit If I wanted to get one of those.

 

[pdentrem]

I'm well jealous of your Zambuto mirror.
My financial controller would have a fit If I wanted to get one of those.

Took some dollars to get it and time but well worth it.
I currently have a two truss system but may return to a 6-8 truss scope.
Pierre

 

[Mitch Alsup]

A 2 truss has vibration written all over it. It is just not stiff.

But note, It took me about 2 years to find the one <pair of> connection that was allowing flex into my 6-pole truss.
I beefed it up and the scope works like binoculars (i.e., without vibration.)

Zambuto makes fine mirrors, but stops at F/4. I am using a Lockwood mirror (who is willing to make <about> anything you are willing to pay for.) Your financial controller would have a hissy fit instead of just a fit..

 

[Mitch Alsup]

I thought you guys would enjoy the means by which I made the vanes for the upper assembly.

{After 4 unsuccessful attempts over 1.5days, I gave up on making the triangles and trying to adapt them to the upper assembly at hand.}

So, after thinking about is over night I came up with a plan whereby I would hold the secondary frame in place, and also hole the upper assembly in place so that I could cut, cut, fold, mark and drill the holes in the vanes with the rest of the structure not moving.

The secondary frame is raised off of the table saw bed by a 1/4" thick 45 degree triangle. The frame is clamped to a 1-2-3 block with a setup bolt and nut. The frame is then held down with setup clamps and the tension adjusted so the frame was perfectly square to the bed of the table saw.

The pickup point beams were then placed at mid adjustment and bolted to the upper assembly so that they were stiff for the duration. One side of the beam was removed for easier access.

Then one by one each vane was constructed, cut out of raw stock (roofing flashing material--lifetime supply for $8.00). After being cut two 0.111 holes (4-40 thread diameter) at the proper separation. after the holes are drilled, the vane is screwed and clamped to the bending jig and bent to 45 degrees. Back at the assembly table the vane is screwed into the secondary frame, a corner is colored with dikem and marked with a scribe from teh other side. this hold is then located and drilled 0.111. brought back and tested. Repeat 3 more times.


Then, finally, after all for vanes are fitted and brought into tension, the entire setup jig is disassembled and the upper assembly stuffed with fire proof blanket then the vanes are silver soldered in situ. This produces vanes that are absolutely square to the optical axis.

Here is an image of the upper assembly assembled onto the scope with the secondary (less optics).



I am very happy with this spider assembly. It is stiff enough one can grab the upper assembly from the secondary frame and hoist the upper assembly around with little chance of even harming the collimation! It is stiff. And to the extent I can measure it, it is perfectly square.

Other than the somewhat cramped quarters of the assembly jig, this means worked quite well.

 

[Mitch Alsup]

I'm well jealous of your Zambuto mirror.
My financial controller would have a fit If I wanted to get one of those.

My optics came from Mike Lockwood:: Set of 3: 13" F/3 for wide fields, a 30" F/3 for deep space, and a 20" F/3 for when I'm too tired for setup the 30".

My financial controller has no observations into spending from my slush fund, nor I to hers. It is better that way--for both of us.

 

[Mitch Alsup]

Introducing Margot::


Margot is my Grand Daughter, and grand indeed; but that is not the reason I reintroduced this thread.....

 

[Mitch Alsup]

Today I dedicate this telescope to Margot, and naming it Margo::
But this thread resurrection is about the assembly of the telescope.

So we start by installing the primary mirror in the mirror cell (frame):


You will notice the measurement devices, in order to place the primary in the middle of the mirror cell one has to be able to measure where that middle is, and when the mirror cell will move under any touching, one has to know when the cell has moved and when it has not.

There are 4 ball transfers in 4 machined cylinders, and each BT is being positioned such that the top of mirror to top of frame and bottom of mirror to bottom of frame are equal (similar side to side--except different measurements) with the bottom of the mirror touching BT on the frame. The BTs on the top of the frame are used to create space so the mirror is not pinched in any way.

The BT outward distance is adjusted by a 1/4-20 screw and bolt pushing on the back of the BT with the nut pulling on the block the cylinder was machined into. In any event, after fiddling with it for a while, I was able to get 0.004" clearance at both top BTs with the mirror positioned within 0.002" of where I wanted it.

By the way, the "top" of the frame is the far side in these images.