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A new focuser - BDF


Chriske

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I'm just having Friday musings maybe a focuser for an imaging scope could be quite different in design to today's conventional designs, the required travel distance is in reality is tiny for any given setup.

 

If you used M4 (maybe even fine) configured like your BDF but 3 or 4 threaded rods and no slides you could have pretty precise adjustment on the image plane distance but also pitch/angle, either 1 motor and 3/4 pulleys or 3/4 motors for motorised planar adjustment, the drawer tube needn't be a tube but simply an adapter plate to the filterwheel, you might want a tube for the purpose of blocking stray light.

 

I'll think some more about this.

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Thanks to you all Guys N Gals, very much for that open minded attitude..!!
It's a bit surprising that you members do offer and allow to use/host your own projects to be hosted on that site I'm planning to set up....:thumbsup:

Some time ago I was a member at another forum. Just before I left that forum I was making plans also to start this very same project.
When I announced that idea on the forum I immediately got a PM of the forum-admins. They told me I was ab-so-lu-te-ly not allowed to copy or use projects/files from members of their forum. They added : if you do start harvesting objects from our forum you will be banned from the forum.
So that is in fact the reason why I left that forum. I Told them I was not happy with their 'rules' and also told them I would leave the forum(after contributing for 15+ years). The only reply I got was : That's your choice sir..!
Ending up here at SGL, I do not regret..at all..!

The only thing I have(and had) in  mind is gather all these Astro-'things' in one location. I will do that unconditionally, for free and accessible to everyone. As a matter of fact I will not gain from it, on the contrary I will invest(buy a domain) and there's lots of work involved... BUT...! ... there are already two members of this forum willing to help me a out with this project.

THANKS..!..:thumbsup:

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3 hours ago, John78 said:

I'm just having Friday musings maybe a focuser for an imaging scope could be quite different in design to today's conventional designs, the required travel distance is in reality is tiny for any given setup.

 

If you used M4 (maybe even fine) configured like your BDF but 3 or 4 threaded rods and no slides you could have pretty precise adjustment on the image plane distance but also pitch/angle, either 1 motor and 3/4 pulleys or 3/4 motors for motorised planar adjustment, the drawer tube needn't be a tube but simply an adapter plate to the filterwheel, you might want a tube for the purpose of blocking stray light.

 

I'll think some more about this.

Hey thanks for the ideas John

The reason for these linear bearings is to have the focuser-barrel run straight without any 'wobble'. And imo if I would have used 4 threaded screws friction would intensify. Friction was my enemy in this project because these timing belts are running in contact with PLA..!
Another solution for precise-focusing would be to use a dual speed knob.

But as I understand it you do have a complete other goal. Using 4 threaded rods and a stepper would be a very good idea indeed.

Chris

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Well as my ally tube in stock was a bit short, I've decided to rip off your idea for a printed focuser tube with metal running strips. Printing beautifully with a brand new nozzle, and the latest Cura seems to give better results too.

DSCN1086.thumb.JPG.cd0a961769c70af34c2ff673133273d0.JPG

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Woow...! nice one Neil..!
The first time I used shims way to thin.(.2mm) and because of that it was not a smooth ride at all for that focusing barrel, it was kinda jumpy. You need at least shims .4 or .5mm thick. And also they need to be absolutely flat, no bends allowed.
These printed tubes are not straight so I also installed a spring on that focusing-rod. That spring will eliminate all errors in that barrel.
And what's more, you'll be surprised how smooth that focuser will go.

Keep us informed..!
:thumbsup:

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1 hour ago, Chriske said:

Woow...! nice one Neil..!
The first time I used shims way to thin.(.2mm) and because of that it was not a smooth ride at all for that focusing barrel, it was kinda jumpy. You need at least shims .4 or .5mm thick. And also they need to be absolutely flat, no bends allowed.
These printed tubes are not straight so I also installed a spring on that focusing-rod. That spring will eliminate all errors in that barrel.
And what's more, you'll be surprised how smooth that focuser will go.

Keep us informed..!
:thumbsup:

I've gone for 2mm thick anodised aluminium extrusion, should do the job ?

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28 minutes ago, Chriske said:

Hey Neil,

Can't see it from this angle, is there more than one flat..?

Three, one 15mm wide for the spindle, two 10mm wide for bearings.

The extrusions are constant thickness +/- 0.01mm over a metre, which should be more than good enough over 100mm. More important to sand off any high points on the print beneath the strip. Don't want to damage the anodising as it will promote wear.

This is my metal one, working up the courage to anodise it myself ?

DSCN0254.thumb.JPG.de6ad33d14380c8a9df80583772b9450.JPG

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33 minutes ago, Stub Mandrel said:

Three, one 15mm wide for the spindle, two 10mm wide for bearings.

The extrusions are constant thickness +/- 0.01mm over a metre, which should be more than good enough over 100mm. More important to sand off any high points on the print beneath the strip. Don't want to damage the anodising as it will promote wear.

This is my metal one, working up the courage to anodise it myself ?

DSCN0254.thumb.JPG.de6ad33d14380c8a9df80583772b9450.JPG

WOW!!  That's delightful!  Beautiful engineering. ??

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23 minutes ago, Chriske said:

But again in the printed version you really need to spring-load that focusing-rod. That printed barrel is not straight enough, you'll see.

I will try supporting the spindle only at its ends first, flex in the the 3mm rod should hopefully be enough.

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Little scope with Crayford focuser inspired by @Chriske's design using metal rails.

I did find the extrusion awasn't flat - crosswise! I had to gently scrape  the two edges so the spindle could  have more contact. Block crudely adjusts tension, then the central screw works on a teflon pad for fine adjustment.

DSCN1118.thumb.JPG.d7cbe2618a400e26fd1a9000f9d62594.JPG

DSCN1117.thumb.JPG.320579bf5d6d744a1095ab9bc0415b92.JPG

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Nice, very nice indeed..!!...:thumbsup:
You did not choose to install a spring to compensate for the irregularities in the printed barrel's surface. (I always do for this type of focuser)
So Neil my question is : is the focusing action smooth over the whole length of the focusing range...? Maybe that's not exactly what I wanted to ask. I should ask instead : is the tension on the focusing-rod the same over the whole range..?
Using a aluminium eyepiece-barrel there's no need for a springloaded device. But printing that barrel, you can't tell whether that barrel is straight or not.

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3 minutes ago, Chriske said:

So Neil my question is : is the focusing action smooth over the whole length of the focusing range...? Maybe that's not exactly what I wanted to ask. I should ask instead : is the tension on the focusing-rod the same over the whole range..?

Smoother than a rack and pinion, so plenty good enough for this application ?

I used a 4mm (I couldn't find any 3mm or 1/8" rod) spindle, which also had the benefit I had a couple of bearings to suit. This has a degree of flex that will take in any small variations.

One advantage of 3D printing is that any x-y errors in printing are pretty much constant regardless of part size, so make use of the good repeatbility and 'design out' reliance on absolute sizes as far as possible. I think surface finish is as much of a peril as absolute accuracy, which is of the order of a couple of thou. In this case all I did was use a file to ensure there were no 'pips' in the corners to lift the bar out of alignment.

 

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  • 4 weeks later...
On 26/07/2018 at 10:26, Chriske said:

This very moment I'm busy designing and printing a set of focusers of different type. Purpose is to show visitors but especially members during open door (in our public observatory) what can be achieved with a 3D printer. As a matter of fact two years ago our club bought a 3D-printer and guess what, it is hardly used. So what I'm actually doing is to show our youngsters what can be done with that thing. I really do not understand why that printer is 'ignored'...!

Well this is what I've got so far,
Next weekend Open Door...

Starting at 9o'clock and clockwise.
1- Helical(ball bearings)
2- Reversed Crayford
3- Collapsible focuser - dual speed
4- Rack and pinion
5- Crayford driven with a rubber O-ring(planes are Tie-wraps)
6- Timing-belt driven focuser
7- Regular Crayford  - dual speed
8- Helical(ball bearings - with dual speed function)
9- Helical (with threads)

In the centre are three reduction adapters('springloaded')

image.jpeg.29b0b59291069f71d91837a22c9e2b6a.jpeg

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