Telekit progress

Vermin (Tom) · #1 09-03-2005, 09:17 PM

I'm finding this quite easy going so far.

I've got the main components glued together as can be seen below. The mirror box is only dry fitted in this photo but is glued now:

http://www.webclot.com/scope/images/DSCF0002.JPG

Still plenty to do including lots of sanding and routing.

The mirror cell is this weekends planned work.

Striker (Tony) · #2 09-03-2005, 09:31 PM

Yes but what is it.......kidding..

ballaratdragons (Ken) · #3 09-03-2005, 09:46 PM

Thanks for the update Tom, looking good.

Certainly looks like a big task.

Did you end up making any templates before gluing? and were you able to get the aluminium rod?

Vermin (Tom) · #4 10-03-2005, 01:21 AM

No need for the aluminium tube, I don't know how he did it, but a sheet metal worker mate from work managed to repair the crushed tubes to like new condition. A talented man.

I did not make templates, the kit is not a great design IMO, it's much lager than it has to be.

I had another setback tonight:

I'd been trying to make some sort of symmetrical arrangement of the mirror cell for over half an hour. I used a drafting triangle to draw an equilateral triangle through the collimation bolt holes to assist with alignment of the cross bars but this did not help.

I took the pieces apart again and noted there are 2 sets of different sized floatation pads! This coupled with a hole spacing error on one of the crossbars (~ 1/8" different from the rest) makes it impossible.

Just sent off another email to Astrosystems. If they say anything other than "replacement parts are on the way" I will not be a happy chappy.

I have a mirror cell I built a couple of years ago (see the for sale forum), I may just end up using it yet.

.

iceman (Mike) · #5 10-03-2005, 06:12 AM

Looking nice Tom, shame yuo're still having issues though.

Can't wait to see it when it's all together.

Vermin (Tom) · #6 10-03-2005, 09:50 AM

Well I did not get the response I was hopeing for:

"the bottom line is this cell, with some variations in dimension, will perform flawlessly in supporting your mirror. There is a good article written by a Japanese engineer about wavefront error vs support points and he shows that optically, a 9 point cell would be sufficient for a 16" It is in the Sky and Telescope for November 1994. And last, I have almost a match to your scope with my 16" f/4.6 with a 1.6" thick mirror and similar variation in the cell pad placement. When you see the central star of the Ring Nebula, mottling on the surface of Io, and detail withing the festoons on Jupiter you know the construction is well within needed tolerances.
Last, I wanted to relate a time last year when I observed two nights with with what I and others that used my telescope considered premium views, only to come home, remove the mirror for cleaning and find one of the flotation pads had broken loose from the orientation ring and had rotated 30 degrees.
It had been that way all weekend from the dust imprint on the back from the flotation points."

Personally I think it's an excuse for yet more shoddy workmanship.

Anyone else care to comment on this?

ving (David) · #7 10-03-2005, 10:01 AM

glad to see some progress

seems like one thing after another though!

janoskiss (Steve H) · #8 10-03-2005, 10:52 AM

Just "smoke & mirrors" Vermin. Very poor service! Maybe your mirror cell will be allright for the job, but you wouldn't be happy if a few wheelnuts were missing on a new car, even if all the engineers in the world agreed that three per wheel are more than enough. And what about the resale value! How are you gonna explain to a prospective buyer that it just looks bad but it works just fine! Give them hell Vermin! Don't let them get off so easy.

I have online access to back issues of S&T through uni, and there is no article in the Nov 1994 issue by some "Japanese engineer" about mirror cells. They must mean this one about finite element modelling of mirror plate deformation:

Toshimi Taki, "Mirror support: 3 or 9 points?", Sky and Telescope. Cambridge: Sep 1994. Vol. 88, Iss. 3; p. 84 (4 pages).

There is one real problem with the study. It assumes that the mirror lays flat and the weight of the mirror is spread uniformly across its surface area. So the results can only apply when you're looking at the zenith. There's a followup article with more data tabulated here:

Toshimi Taki, "More thoughts on mirror-cell design", Sky and Telescope. Cambridge: Apr 1996. Vol. 91, Iss. 4; p. 75 (3 pages)

PM me if you want copies of the articles.

Vermin (Tom) · #9 10-03-2005, 01:58 PM

Well I read the articles (thanks Steve) and found an old email from Mark where he did suggest a 9 pt cell would be adequate, so it looks like the current 18pt cell with small asymmetries will do the job.

I like your other arguments Steve, I can't be bothered trying to push the point though. I just want to get this scope finished and start observing again.

I'm taking the week before Easter off to really get stuck into it.

Dave47tuc (David) · #10 10-03-2005, 06:33 PM

Keep working Tom

The end result will be

Good luck.

rumples riot · #11 10-03-2005, 11:29 PM

Looking good Vermin, nice work so far, all the components look put together well.

Just noticed that I am on 999.

Vermin (Tom) · #12 19-03-2005, 11:56 PM

Spent a while trying to get the filter slide / focuser board to line up on the secondary cage tonight. Then realised that Astrosystems had drilled two pilot holes in the wrong place.

I guess I should expect this sort of thing by now.

Should be easy to fix.

janoskiss (Steve H) · #13 20-03-2005, 12:05 AM

Geez, it's going from bad to worse. I can send you some scrap plywood if you want to start over

Seriously though ... Best wishes. Hope it all works out in the end, and all 200+ of us can come and visit to look thru yer massive scope.

ballaratdragons (Ken) · #14 20-03-2005, 12:05 AM

Geez Tom,

Did they do anything right?

Vermin (Tom) · #15 20-03-2005, 01:37 AM

Another one: Mirror cover handle screws were too long, had to grind them down or they would have punched right through the cover.

Most of these problems are little things, and none of them insurmountable, but the list is growing:

Shipping damage to truss poles, mirror cell back, mirror box sides, secondary cage cover.
Wrong ground board foot supplied.
Lower truss clamp block split almost in half.
Lower truss clamp blocks not square
Poor accuracy of mirror cell components.
Altitude bearing extension inner radius wrong diameter.
Secondary cage struts too long.
Filter slide mounting pilot holes wrong.
Mirror cover handle screws too long.
Azimuth brake too short.

ballaratdragons (Ken) · #16 20-03-2005, 01:46 AM

Yes Tom, they sound like small things, but so many of them.

It's not good at all for a company. If it was built by a mate down the road you could excuse some mistakes, but a company to have that many problems on one item. Not good advertising for them is it!

Imagine the heart-ache and problems if the kit was purchased by someone with no carpentry skills at all.!!!!!!

Vermin (Tom) · #17 20-03-2005, 02:03 AM

Yeah this kit could be so much better if they just took a bit more care in the packing and inspection of parts.

I hope it's going to be worth the effort. I'm really worried about how well it's going to balance and how smooth the bearings are going to be. This should all have been easy to calculate in the design phase, but I'm not filled with confidence in them at the moment.

Time will tell... should be ready for a first light by the end of this month (would have been sooner but I've just gotten over a nasty case of the flu).

ballaratdragons (Ken) · #18 20-03-2005, 02:27 AM

Even if it turns out that the balance is wrong and the action is not smooth, you'll fix it! I can tell you are the type of person who will make it work even better than the original.

Vermin (Tom) · #19 20-03-2005, 02:33 AM

Well I doubt I'll turn it into expensive firewood, just depends how fed up I get

Don't you ever sleep?

ballaratdragons (Ken) · #20 20-03-2005, 02:46 AM

Yeah, going to bed now as I am making heaps of mistakes on this computer from tiredness. Catch you soon.

Good luck with the firewood . . . oops, I mean 'scope'.