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Post your home made scope

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#151 mikey cee

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Posted 03 February 2013 - 09:30 PM

Ed doesn't it hurt to have that CW crack you in the head?? :lol: Mike

#152 Datapanic

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Posted 04 February 2013 - 12:16 AM

This is the Maynard Clark 8" f/8. I did not design nor build it, but somebody had it stored in a barn, in the back of an F-150 pickup truck outside of Tucson, AZ for years and years. The OTA was stored inside. I have been restoring it, very slowly for the past couple years - only one part left to be made and it will be finished. It has over 600 pieces to it. Not sure exactly when it was built, but it was pictured in the Oct 77 S&T and also received the RTMC Merit Award for Technical Excellence in 1980. You can read more about its restoration over in the Classics Forum here: Maynard Clark 8" f/8 If anyone knew Mr. Clark or remembers this scope, I sure would like to hear from you!

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#153 Pinbout

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Posted 04 February 2013 - 12:24 AM

The idea isn't that brilliant; it is a derivative of Porter's Springfield Mount.



I have something similar in my head but my counter weight hangs and uses the rocker box as a rail to glide on.

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#154 alistairsam

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Posted 04 February 2013 - 06:07 AM

Hi,
Here's my 10inch F4 Serrurier truss I recently completed.
Mirrors are from Orion Optics in the UK, trusses are carbon fibre, secondary spider is from guitar strings to minimize diffraction spikes, I've used guitar machine heads to adjust tension. Mirror Cell is a 6 point cell made from Aluminium square pipes rocking on a horizontal bolt held with clamps.

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#155 droid

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Posted 04 February 2013 - 06:09 AM

Gosh Dan; just spent like 2 hours drooling over that restore, and it dead ended, :lol:
So how did it turn out? was the mirror as good as you had hoped.???
Absolutely gorgeous, the most beautiful restore Ive ever seen.

#156 alistairsam

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Posted 04 February 2013 - 06:14 AM

Here's my home built Wooden Fork Mount.
It has a picaxe microcontroller based stepper controller with timing belt gear reduction to minimize PE.
RA Bearings are 50mm Bearings. Current RA shaft is Delrin with a steel Rod insert, but I'll be changing this to a steel tube.
I've added ST4 autoguiding by using a picaxe to monitor the 4 pins of the guidecam's ST4 output and adjusting the step gap duration in the stepper controller to either speed up RA or slow down RA.

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#157 Dick Jacobson

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Posted 04 February 2013 - 08:59 AM

The idea isn't that brilliant; it is a derivative of Porter's Springfield Mount.



I have something similar in my head but my counter weight hangs and uses the rocker box as a rail to glide on.

Unfortunately this counterweight device won't work well because as the tube rotates from vertical to horizontal, the amount of torque around the altitude axis increases greatly. The counterweight device in your picture produces a constant torque so it will balance at only one position. Possibly you could make it work by offsetting the center of the counterweight support disk so that the torque increases as the tube rotates to horizontal. But ideally the counterweight should hang from an arm that is parallel to the tube, in which case why not mount it directly on the arm or tube?

It is possible to build spring devices with torque that varies so that the tube is balanced at all positions. I've built one myself and have seen some others posted in this forum. But I think the simplest way to build a Newtonian that is balanced around the eyepiece is to just use a counterweight at the opposite end from the mirror.

#158 Pinbout

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Posted 04 February 2013 - 09:43 AM

Unfortunately this counterweight device won't work well because as the tube rotates from vertical to horizontal, the amount of torque around the altitude axis increases greatly.


i don't make changes in torque for my dobs, when I balance my dobs the torque is constant.

the only thing I see is an twist caused by weight on one side and not the other but that is easily remedied.

But I think the simplest way to build a Newtonian that is balanced around the eyepiece is to just use a counterweight at the opposite end from the mirror.



thats not consistent with your first statement.

#159 tag1260

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Posted 04 February 2013 - 10:46 AM

Here's a pic of my Frankenscope. Started life as a Tasco 11TR and has had several mods throughout the years. Mirrors are original as is the tube but I built the dob mount for it and changed the focuser to a 1.25" Orion and the finder to a Daisy Red Dot with and adjustable light. Always planned on building a "proper" looking mount but never got around to it

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#160 tim53

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Posted 04 February 2013 - 11:20 AM

Earle Dodds used to make Springfield mounts with counterweights on the tube plus a conventional weight in RA. For a dob mount, you'd only need a tube weight, so I think you could easily set it up so that it is less likely to jerk a knot upside your haid in the dark.

But a true Springfield is more better! :grin:

Tim

#161 etalon

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Posted 04 February 2013 - 11:35 AM

Danny, I´m sorry, but you are wrong. Dick explained it correctly. You have an increasing torque, when the tube move in a horizontal orientation. That´s the reason, why I used springs with different power moments and different fix points on my travel Dob. The springs have a nonlinear power moment, and normally you need more than one spring to compensate some hysteresis effects...

@all: Very nice scopes are shown here!!!

cs
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#162 Pinbout

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Posted 04 February 2013 - 11:55 AM

I'd appreciate if you spelled my name correctly.

show me your math...

#163 etalon

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Posted 04 February 2013 - 12:27 PM

Sorry, I have corrected it.

My (technical) English is much to bad for explaining such things, I´m sorry, but you can read it in every book about primary physics or technical engineering...

Maybe there would be some other guys, who speak English much better than I, and who can explain it. I also don´t know, whether, and when how, I can write math formulas here on cn...

Markus

#164 Pinbout

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Posted 04 February 2013 - 01:35 PM

the more the expansions springs are expanded the less effective they are.

the lever arm on the scope I drew is about 6in away from the center of rotation, and the 6in mirror is approx. 32in away from the center of rotation.

so if I rough in the torque balance eq.

6in*(x)lbs = 32in*(y)lbs

so in this equation where do you implement the angle of momentum.

#165 etalon

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Posted 04 February 2013 - 02:18 PM

The spring would not be less effective when it work in the range of elasticity. If you over expand the spring, it deform plastically, would became less effective and would be damaged.
Here is a link to calculate springs (compression-, extension- and torsion-springs):

http://www.federnsho...Berechnung.aspx

Maybe it would help.

In case of your Dobson, you get a torque moment depending on the length of the leverarm, the angel of the lever arm to the gravity force vector and the wight force at an arbitrary point on the lever arm.

Please excuse my bad English...

Markus

#166 Dick Jacobson

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Posted 04 February 2013 - 04:51 PM

Maybe it would help to imagine holding a heavy dumbbell, simulating the weight of the mirror. When your arm is about vertical, it takes only a little force to start raising it, but when it reaches horizontal it takes a lot more force on your shoulder. Mathematically, the torque due to the mirror is proportional to the sine of the angle of the tube away from vertical.

I hope we haven't totally derailed this topic. There are some wonderful ideas here. Markus, your travel scope at the top of page 6 is magnificent!

#167 Pinbout

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Posted 04 February 2013 - 05:49 PM

Mathematically, the torque due to the mirror is proportional to the sine of the angle of the tube away from vertical.



just one more thing.

on the mirror side,from angles 0-45, torque=Length*lbs*cos angle, from angles 45-90, torque= length*lbs*sine angle.

so at 45* the torque is the least.

Still working on my travel dob

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#168 droid

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Posted 05 February 2013 - 07:48 AM

That gonna be a carry on scope? looks almost ready to go. Nice workmanship

#169 Pinbout

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Posted 05 February 2013 - 09:01 AM

yep,

but I'm making different truss mounts,

like these

Posted Image

and my mirror is still hyperbolic

[I got a blank, but found it was polished figured and very,very hyperbolic now its only slightly hyperbolic]

#170 droid

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Posted 05 February 2013 - 09:33 AM

Cool video......my only concern would be Id get to the dark sky site and realize I didnt load the Allen wrenches, lol.
Could that be done with bolts with knobs??or would they get in the way of when packaging up for travel?

#171 Tom Clark

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Posted 05 February 2013 - 09:45 AM

Hows this for ugly? It is a 42" f/4. The reason for the square tube is to raise the balance point up towards the center of the tube. This allows for the scope to fit into a much smaller dome than the typical dob would - with a balance point closer to the mirror end. It also allows for the scope to be completely sealed up to keep dirt out when not in use. Interior doors close just over the mirror to keep the mirror clean.

The box near the focuser holds five of the most used eyepieces. The finder is a 5" f/9 to allow for wide-field views.

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#172 tag1260

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Posted 05 February 2013 - 09:49 AM

Looks like a fine piece of furniture to me!!! Beautiful wood working there.

#173 droid

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Posted 05 February 2013 - 10:07 AM

As an old ATMer told me years ago, after I fielding a dob uglier than the south side of a mule, " aint no such thing as an ugly telescope in the dark "

nough said, totally true
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#174 Pinbout

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Posted 05 February 2013 - 10:17 AM

that's what I'm working on.

since it's made out of 3/4 ply, I need to raise it about a 1/4 in, so I made plates to raise it up. I have press fit knobs for the allen head screws. i'm using them here on the alt bearings

Posted Image

also its better to come in from the aperature hole side with the screw, the alt bearings kind of get in the way, on the backside it fine. compare the previous pic with this.

Posted Image

so goes my life make it twice before I get it right. :lol:

#175 Pinbout

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Posted 05 February 2013 - 10:21 AM

Hows this for ugly? It is a 42" f/4.



I would have to agree, that is very ugly indeed. :roflmao:

now if you had a dragon [for heavan] or a tiger [for earth] burnt into the wood somewhere it would add the coolness back. :grin:






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