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Graham

I can wait no longer

34 posts in this topic

Go for it Graham, but wear some eye protection just in case :thumbsup:

 

Looking forward to some more updates :)

Graham likes this

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Nice one Graham but take it steady, if you damage your eye you cant use it for the proper side of astronomy that you have just discovered.

 

:)

Graham, Big Al and Tweedledee like this

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Stay safe Graham - but I understand the frustration. :)

Graham likes this

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Thanks folks.

The eye as such is not a problem as it has never worked properly since the year dot. :)

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Don't blame you Graham, just take twice the care with your good eye! 👍

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Got the new lap finished last night and even managed to get an hour of figuring in as well. :2thumbsup:

Ibbo, Tweedledee and Smithysteve like this

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After I got home from work this afternoon I decided it was time to design my mirror cell.

Decided on a 30 point cell.

Four Whiffle trees take care of any lateral forces.

During collimation the complete cell will move. It pivots on the top link and collimates using the 2 Orange screws. These will fit to the main scope frame.

 

 

Mirror Cell 1.jpg

View from underneath.

 

Mirror Cell 2.jpg

Tweedledee, Werisit, BAZ and 1 other like this

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No messing about there Graham, that's going to be solid enough to park a truck on.

Where do these Whiffle Tree's grow? :lol:

Graham likes this

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Thats what I am aiming for Martyn.

They come from a very special place not too far from you.

Whiffle dale :rofl:

BAZ likes this

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Great to see you are cracking on :thumbsup:

 

Never seen a 30 point cell before Graham.

 

From your drawing I can't quite see how all 30 points would let the mirror float with equal pressure on each, without an intermediate layer of suspension. But maybe I have misunderstood the drawing. 

 

I used the PLOP program for my mirror and found that a 27 point suspension would provide such marginal reduction in deviation over an 18 point that it would not be noticable or worth the extra engineering complications.

 

If you don't already have it, you might like to download it here and have a play...

http://www.davidlewistoronto.com/plop/

Graham likes this

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Looks great Graham. I like the way you are going to achieve collimation. I've also thought of supporting the mirror in the lateral axis by using rollers positioned around the circumference the same way you have done.

Graham likes this

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14 hours ago, Tweedledee said:

Great to see you are cracking on :thumbsup:

 

Never seen a 30 point cell before Graham.

 

From your drawing I can't quite see how all 30 points would let the mirror float with equal pressure on each, without an intermediate layer of suspension. But maybe I have misunderstood the drawing. 

 

I used the PLOP program for my mirror and found that a 27 point suspension would provide such marginal reduction in deviation over an 18 point that it would not be noticable or worth the extra engineering complications.

 

If you don't already have it, you might like to download it here and have a play...

http://www.davidlewistoronto.com/plop/

 

Thanks for that Pete

I have downloaded it but could not get my head around it :facepalm2:

The drawing was mainly for me to be able to get all the dimensions I will need to make the bits.

I have not shown in the drawings but all the supports float on ball and socket joints.

 

7 minutes ago, Doc said:

Looks great Graham. I like the way you are going to achieve collimation. I've also thought of supporting the mirror in the lateral axis by using rollers positioned around the circumference the same way you have done.

 

Thanks Mick.

If you are making a Dob you will only need the bottom two Whiffle trees, I need four as I will be fitting this scope to my Horseshoe mount ( when I build it ) so it needs the extra couple to allow it to go right over in the Dec axis.

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10 hours ago, Graham said:

 

Thanks for that Pete

I have downloaded it but could not get my head around it :facepalm2:

The drawing was mainly for me to be able to get all the dimensions I will need to make the bits.

I have not shown in the drawings but all the supports float on ball and socket joints.

 

What I was trying to say is that the support points should work on the same principle as your whiffletrees on the edge. Can't see how you would maintain that principle in your drawing, as it looks as though the 10 triangles of 3 points are all supported on the same rigid non floating base. The positioning of each support at the centre of gravity of the points above is also important. Ultimately, no matter how many support points, the mirror is supported from just 3 initial points on the frame in order to allow all points to contact the mirror with exactly the same pressure, otherwise unwanted distortions will occur and the mirror will not perform. the PLOP program does take a bit of getting into, but it specifies the optimum positioning of the points and intermediate suspension parts.

 

I'd never heard of whiffletrees until I started looking into mirror cells in detail - the name just rolls off the tongue :D

 

The following pics should better explain what I mean...

 

This 18 point has 3 pairs of triangles independently floating on 3 bars allowed tilt on their centres.

cell18.jpg 

 

This 27 point cell has 3 groups of 3 triangles independently floating on 3 larger triangles which are also independently floating on 3 points.

cell27.jpg

 

Sorry, I'm not attempting to describe this 54 point one :lol:

cell54.gif

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Pete.

Thanks for the info, I now get what you mean and you are right.

I am going to need to do a revision of my design. :facepalm:

I do like the 18 and the 54 point patterns.

Much more symmetrical.

I like symmetry, appeals to my engineering bias. :)

Whiffle trees were devised way back in the days of horse drawn implements. ( other animals were also available to be used )

They were used to spread the load from the horses harness to the implement being towed a kind of early constant velocity joint.

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4 minutes ago, Graham said:

Pete.

Thanks for the info, I now get what you mean and you are right.

I am going to need to do a revision of my design. :facepalm:

I do like the 18 and the 54 point patterns.

Much more symmetrical.

I like symmetry, appeals to my engineering bias. :)

Whiffle trees were devised way back in the days of horse drawn implements. ( other animals were also available to be used )

They were used to spread the load from the horses harness to the implement being towed a kind of early constant velocity joint.

I have done quite a bit of study on it over the last month or two, and just want you to get well practised before I send you my mirror cell design ;) :)

 

Horses and carts. :rolleyes: Who'd have thought that the same technology would have ended up in telescope design. :)

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8 hours ago, Tweedledee said:

I have done quite a bit of study on it over the last month or two, and just want you to get well practised before I send you my mirror cell design ;) :)

 

Horses and carts. :rolleyes: Who'd have thought that the same technology would have ended up in telescope design. :)

 

No problem with making a cell for you Pete.

I will be making inquiries to a supplier to the company today about the ball joints.

Should be able to get a decent discount if I get a bulk buy order in. ;)

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Hi Graham, and Pete...

on the subject of 'whiffle trees' etc, Kim (Brantuk) posted an excellent thread to SGL's  Mapster who has built a 22" absolutely awesome dobsonian!

 

Kim posted this link in his rocker box build thread... Just scroll down the thread...

 

https://stargazerslounge.com/topic/266267-the-mapstar-22-build/#comment-2915131

 

Mapster shows his whiffle designs (and the rest of the build) for the 22" mirror support system ( an 18 point support frame )

It's well worth a look 👀

Graham, Brantuk and Tweedledee like this

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Cheers Steve, that certainly is the best home built scope I've ever seen :thumbsup:

Brantuk likes this

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Nice one Kim.

That has certainly given me some food for thought with different design ideas. :)

Brantuk likes this

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Redesigned Cell.

Have a much better design for the Whiffle trees just not the time to draw it tonight.

 

new cell 1.jpg

Side view.

 

new cell 2.jpg

Other side.

 

new cell 3.jpg

Smithysteve and Tweedledee like this

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Thanks Pete.

Good job you pointed out the error on the first one :blush:

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You can tell at a glance, that your new design is perfect for the job! 

Nice work Graham 👍

Graham likes this

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1 hour ago, Graham said:

Thanks Pete.

Good job you pointed out the error on the first one :blush:

You're welcome Graham. :thumbsup:

 

We're all on a learning curve. 3 months ago I would have thought that a whiffletree was something magical growing in the forest around Hogwarts castle :facepalm:

Graham and Smithysteve like this

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