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Posts Made By: Tom Lacovik

March 6, 2004 10:45 PM Forum: Telescope Making

What is your upper cage weight?

Posted By Tom Lacovik

Hey everyone.

I am looking for a sampling of weights (honest weights that is, no prizes for lightest cage! smile from people who have made 13.1 or 12.5 obsession style (2 ring + struts design only please) for their completed upper tube assembly. I realize there are many different designs out there and materials too, but if you happen to know what your completed cage weighs (optics, focuser and all) I would really appreciated knowing that as it will really help me at this juncutre...if it's not too much trouble, can you please weigh it and let me know (include info like w or w/o telrad etc).

Thanks to anyone/everyone who can help.
Tom.

March 9, 2004 04:16 PM Forum: Maksutovs

MK67 Eyepiece recommendation

Posted By Tom Lacovik

Hi All.

Can someone recommend an WIDE field eyepiece, 2" that goes nicely (and comes to focus smile in an MK67. It will be the first time I get to buy a 2" EP!

Already in use:
2" TV Everbrite diagonal.
1.25" Pentax XL 14 mm (all the XLs are nearly parfocal and are easily focused)
1.25" Pentax XL 10.5 mm
1.25" Pentax XL 7 mm
1.25" Celestron Ultima 30mm (barely comes to focus racked all the way in)

bonus points if the EP is also a good match for a Swayze 13.1" f/4.5 dob I'm building.

Thanks.
Tom.

March 20, 2004 07:14 AM Forum: Telescope Making

Thinking about making a filter slide

Posted By Tom Lacovik

I'd like to build a lightweight filter slide for my the 13.1 string dob I'm building. But I haven't really found any plans (suggestions?) perhaps there is an alternate way to flip one in or out (a la moonlite or something similar) without lots of threading in the dark...I'd be interested to know what others have done and if there are any plans anywhere or descriptions you could point me to. Thanks.

TomL

March 22, 2004 04:31 PM Forum: Telescope Making

Mirror box minimum height

Posted By Tom Lacovik

Hi Guys,

What would you say the minimum height/dimensions is for a mirror box for a 13.1" primary for correct baffling? In addition to the wall heights as baffles, I suppose one also inserts a square board with a primary-sized circle cut out of it down to a certain height (if so, what height?) above the primary's face.

Thanks for helping.
TomL

March 23, 2004 06:06 AM Forum: Telescope Making

Are shrouds unavoidable?

Posted By Tom Lacovik

If shrouded viewing is unavoidable, then I will make a shroud.

However, my cage blocks out all light from the top of the cage to the focal plane. But from the bottom, I can see some ground (crescent) with the eyepiece removed and looking at a sharp angle down through the fully racked in moonlite focuser. I wonder what the practical effect will be when I'm done. Is this normal, or better or worse than average? I've seen a lot of cages with the focuser right at the bottom of the cage, and having tested that position too, I can see a full circle of ground, not just a crescent as seen in my sketch below. My sketch is really my cage and dimensions, and about as high as I can get the focuser without more aggresive measures.

So, Should I worry about this? Is a shroud necessary anyway? will a filter slide/focuser baffle eliminate the need for a shroud? anyway what do you guys think?

Thanks for sharing your thoughts on baffling/shrouding.
TomL


March 26, 2004 04:08 PM Forum: Telescope Making

Weight vs Performance: Aluminum or Steel Cell?

Posted By Tom Lacovik

Hi Guys, I'm wrapping up the cage for my 13.1" today and you may have seen some of my progress here, some of you helping out along the way - thanks!

This being my first scope, I am really feeling a kind of "You have to build one to know how to build one" sensation...

In particular, I am moving on to the cell and though trying to keep the whole scope light and in balance with a low profile box, I don't have a 'gut' feeling as to whether I will actually need extra weight in my box or not (except for some vague notion that more scopes seem to fight top rather than bottom heaviness, balance-wise).

This is affecting my decision to make my cell out of steel, aluminum, or even 1/2" plexiglass. The other side of the coin is strength of course, and although I and many others believe that most dobs are overbuilt (not necessarily a bad thing until you have to put lug them in and out of your car trunk like I will), I don't want to totally neglect the important issues of strength/flexure...and so my question (finally smile is....drum rolll....

Given where I am coming from (goals: lightweight, low profile 13.1"), is aluminum (or even plexi) an option, or is steel still the only good performer for a dob cell? What is the weight versus performace trade off here? If big gains on weight savings can be made for very little performance trade off if any, then I will go with aluminum.

Please note that my mirror is a 1 1/8" THIN 13.1 and is quite light (about 12 pounds).

I await your experienced responses...(thank you)

TomL

March 27, 2004 04:14 PM Forum: Telescope Making

13.1" Mirror Cell

Posted By Tom Lacovik

I'm confused. Is the K-B steel ladder and seatbelt sling out-dated. Is it the best. Does anyone care to suggest a cell design for a 13.1"? or should I just make the KB one and be happy?

HELP
TomL

April 2, 2004 01:35 AM Forum: Equipment Talk

2" WideField EP on a budget

Posted By Tom Lacovik

Can someone recommend an EP that is WIDE field 65° or more in a 2" format...for a 13.1 f4.5 dob. I want a spacewalk feel / emotional impact, more so than dead on color accuracy etc. if you follow me...what's out there?
Tom.

April 8, 2004 08:23 PM Forum: Telescope Making

On-board 12v DC Battery?

Posted By Tom Lacovik

What are people using for an on-board 12V DC source. I'd like not to carry a car battery powerpack, and just have a small-medium sized cell doubling as dob counterweight, but not weight 10 pounds either if you follow.

I was eyeing some of my cordless drill batteries. These can often be found cheap ($10 for 9.6 or 14.4V ones, but harder to find 12V ones). However, these don't often list amp-hours on them just voltage. A few do though, and they tend to range between 1.7Ah and 2.4Ah.

Considering that 8 (or 9 I guess since rechargables are 1.2V not 1.5V like alkeline) AA rechargeables in series will make for a 12V source, and each one is listed at 2100 mAh (ie. 2.1 Ah) it's harldy any benifit to having a bigger drill battery. I've seen some square "hobby batteries" (like at radio shack) that cost more, but are 12V, though I don't see any rechargers sold for them? Basically those look like miniature car batteries.

I would like to find something with slightly more Ah, like say 4Ah that isn't one of those big heavy portapower packs (I have one btw), rather something I can leave on-board on the dob so I don't have to carry yet another item with me. Motors (fans) eat lots of power though, so maybe its unavoidable?

Thanks,
TomL

April 9, 2004 05:32 PM Forum: Telescope Making

Test: Filament Wound Epoxy Tubing vs. Aluminum

Posted By Tom Lacovik

Hello Gentlemen,

I enjoyed your responses to my battery thread. I have also enjoyed all manner of threads here. In particular I like when someone undertakes a scientific test for the good of the group (eg. I was building my cage when the results of the flocking test came in. When it came to buying velvet, I walked right into my fabric store and there was a bolt of JB Martin Fidelio Black 1000 staring me in the face. Lucky me).

So to give something back to the group I bought and tested a couple of different truss poles. Naturally carbon fiber is very expensive at about $60 per 3/4" tube. But I found an interesting alternative that cried for a deflection test at a plastics, fibers, and materials store. It's called "Filament Wound Epoxy Tube" from Tap in Portland (see http://www.tapplastics.com/shop/product.php?pid=144 )

I plan on building a string scope with four 3/4" tubes and string "V"s between them. My scope is to be a 13.1 f4.5 and my cage with hardware weighs 5lbs.


Test results for the Filament Wound Epoxy Tubing ($12 / tube)
OD .745" WALL 0.0375" Weight .098 oz per inch
(eg. 48" tube weighs 4.7 oz -- So, four of them weigh: 1.174 lbs)

With a 4 pound weight hanging off of a tube at a distance of 60",
the Filament Wound Epoxy tube deflects 16"
But at 40" (more like MY final tube length), it's only 6"

Aluminum ($8 / tube)
OD .75" WALL 0.055" Weight .183 oz per inch
(eg. 48" tube weighs 8.78 oz -- So, four of them weigh: 2.194 lbs)

With a 4 pound weight hanging off of a tube at a distance of 60",
the Aluminum tube deflects 12"
But at 40" (more like MY final tube length), it's only 3.5"

Note: to test this I drilled a hole about 4" deep into my work bench and inserted the tubes firmly using masking tape on the tubes to make them snug). I marked the starting position for each tube (same) on a stick. I then hung a drill press vice weighing about 4 pounds off of the tube at 60" and marked the deflection on the stick. Repeated for both tubes twice.

What do you think? Further tests needed? Maybe with 4 of them rigged up to a cage type jig? The weight savings up top translates to 5x as much below (or 6x as much overall) so it counts for something, but not if the deflection is too much (vis a vis collimation). I look forward to hearing your thoughts on this alternative material and my tests.

Thanks for providing me with your varied tests in the past and here's one right back atchya.

TomL