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An Observing Chair from Dobstuff Astronomical Telescopes

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14 replies to this topic

#1 Dennis Steele

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Posted 10 September 2019 - 07:28 AM

These beautiful observing chairs are made entirely from Baltic birch. They stand 30" tall and adjust from 10" to 22". Other heights are available to your specification. $169.95 plus shipping.

 

Dennis

dobstuff astronomical telescopes

http://dobstuff.com

tel: 650-315-6578

 

We build parts, kits, remake your telescope or entire telescopes to specification.

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#2 rockethead26

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Posted 10 September 2019 - 10:02 AM

Is that seat being supported in each position by a single brass wood screw?



#3 Dennis Steele

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Posted 10 September 2019 - 12:15 PM

The screws are stainless-steel, NOT brass. Yes, a single screw is all it takes to keep the seat in a fixed position.

 

Dennis


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#4 Dennis Steele

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Posted 10 September 2019 - 12:16 PM

On another note, the "cross bar" that holds the seat in position is a 1/2" steel bolt with a brass sleeve. Dennis


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#5 Mad Matt

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Posted 15 September 2019 - 02:35 PM

Look nice! I would use at least two screws. Stainless Steal is actually quite „brittle“ and will break quicker than you think.
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#6 Jon Isaacs

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Posted 17 September 2019 - 04:26 AM

Dennis:

 

What is the load capacity?  

 

What is the range of seat heights?

 

My engineering eye questions the single screw as well.  There's probably a significant amount of friction involved but a worst case scenario is zero friction on the front side putting the observer's full weight on the  brass cross piece.  If it somehow were near the end of the screw, it would be putting the maximum bending moment on the screw.  It could bend or it could deform the wood.  

 

Another worst case scenario is that the observer thinks the chair is hooked on the screw, it's not.  The observer sits down, the chair slips and now the next single screw has to deal with the momentum and weight of the observer. 

 

I weight about 230lbs. One time a heavier member of Cloudy Nights was wondering how the Starbound chair handled it's rated load of 350lbs so I had someone sit on my lap.  It was around 360-370 lbs total and it felt rock solid. 

 

Jon



#7 Dennis Steele

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Posted 17 September 2019 - 07:35 AM

As this is a prototype, getting these comments is great. As far as the cross pieces are concerned -- it isn't brass per se'. The light brass tube slides over a 1/2" steele carriage bolt to cover the threads. I thought the threads would damage the wood backing. I will add a second screw.  

Comments????

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#8 Goodchild

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Posted 17 September 2019 - 01:04 PM

I'd like to see the screws replaced with dowels.



#9 Dennis Steele

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Posted 17 September 2019 - 02:24 PM

I thought of dowels. That'd be easy. I note that all the "metal" chairs use rivets and and machine-screws. So I figured it'd work pretty well and be a bit easier to deal with. But the dowels would keep with the wood construction. I think if I were use a 1/2" dowel in the center, protruding about 1/4", that'd be more than adequate.

 

What do you "engineers"  think??smile.gif

 

 

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#10 mogur

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Posted 17 September 2019 - 04:52 PM

Either way I agree that two is much safer than one!



#11 Starman1

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Posted 18 September 2019 - 05:46 PM

Look, the comments show people don't understand how the seat works.

It doesn't even really need screws at all, since this is not what keeps the seat from sliding down.

What keeps the seat in place is pressure of the top pin against the back of the wood and the pressure of the bottom pin against the front of the wood.

These chairs have been constructed for years with completely smooth surfaces, like the Starbound, and they work just fine.

The key is to put your weight forward on the seat, away from the vertical plank.

 

So let's assume someone sits too far back on the seat.  Is there sufficient pressure on the pins to hold the seat in place?

Maybe, maybe not.  Hence, the screws.  and it would only take one screw--the pressure is still mostly horizontal, not vertical.

 

And yes, a 1/2" dowel would be sufficient.



#12 Starman1

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Posted 18 September 2019 - 05:52 PM

My criticism is that there is an insufficient range of adjustment.

I have used a Starmaster Chair (6" to 31" seat height range) with the 12.5", and it is barely adequate.

My Berlebach Charon goes up to 36", and it is more comfortable at the zenith with the scope.

A larger or taller scope might need more.

When I used an LX200 8" SCT, I had a chair with a 21" to 28" range and the top setting got used, but I wished it went lower to, say, 14" or so.

10" to 22" would have been inadequate for that scope.

The Starbound chair goes from 9" to 32", OK for a 6" to 14" dob.

 

So I have to ask, is this seat only for refractors?

How much would you gain by raising the hinge to the top of the board?


Edited by Starman1, 18 September 2019 - 05:56 PM.

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#13 Dennis Steele

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Posted 18 September 2019 - 07:47 PM

Wow and thank you for the input. I can make the chair any height I want. So higher is better. I can do that. I'm making a second chair now so I can put them both of CN classifieds -- so I'll make it taller and more range of movement.

 

So, I'm thinking 6" to 32" would cover all the bases.....

 

THANKS AGAIN, I'll make the second chair higher.

 

Dennis


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#14 Dennis Steele

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Posted 18 September 2019 - 07:48 PM

To answer your question. No it isn't specifically for refractors. I want to make a good "general" purpose chair -- and will offer custom-heights....

 

Make sense??


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#15 Starman1

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Posted 18 September 2019 - 09:15 PM

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