Focuser BBH + BBH2S (dual speed version)

[Chriske]

Yet another printed focuser. It is a variant of the well known Helical focuser.
In this case the eyepiece barrel is supported by 8 small ball bearings(6x10x2.5). These bearings are mounted at a 6° angle. So when rotating the eyepiece-barrel in the main unit it will very slowly go up or down. That's why 'BBH' : ball-bearing-helical.
In this focuser it is absolutely necessary that the focuser barrel is made of aluminium(sorry guys). Maybe just maybe it would also work with a printed eyepiece barrel, don't know to be honest.
The unit is spring-loaded so the pressure on that barrel is adjustable.

[Gina]

That's clever ??

[bottletopburly]

should the bearings not be facing in the direction of draw tube ?

[Chriske]

They do,

[bottletopburly]

7 minutes ago, Chriske said:

They do,

no i meant in direction of tube so wheels turn as drawtube goes in  and out 

[Chriske]

Oh now I understand...!
The bearings you would add in the focuser tube are not needed. As a matter of fact when these ball bearings would be added(in the direction of the barrel's movement) the function of the angled ball bearings is completely lost. What's more these 'straight' bearings would completely block the focusing movement.

Look at it this way : A Helical focuser is based on the movement of very course thread, just the same movement as a bolt and nut. Well, think bigger, lots bigger, and add a eyepiece and you have a Helical focuser. Now replace the thread by ball bearings and you're done. Because of the friction of the ball bearings against the tube it will stay in place. Only when turning the barrel the eyepiece will go up or down.

[Gina]

It's rather like a Crayford applied to make a helical mode.  Turning the tube rotates the bearing outers and, being at an angle, this causes the tube to move in or out at the same time as turning.  I hope that adds to Chris's explanation and makes the action even clearer.

[bottletopburly]

4 hours ago, Chriske said:

Oh now I understand...!
The bearings you would add in the focuser tube are not needed. As a matter of fact when these ball bearings would be added(in the direction of the barrel's movement) the function of the angled ball bearings is completely lost. What's more these 'straight' bearings would completely block the focusing movement.

Look at it this way : A Helical focuser is based on the movement of very course thread, just the same movement as a bolt and nut. Well, think bigger, lots bigger, and add a eyepiece and you have a Helical focuser. Now replace the thread by ball bearings and you're done. Because of the friction of the ball bearings against the tube it will stay in place. Only when turning the barrel the eyepiece will go up or down.

Got it now?

[Chriske]

This one works incredibly well...!
As a matter of fact if I can find a way to add a dual speed function I'll consider working with this focuser.
I was planning to make the rotating part of the main body itself spring-loaded(as in the drawing higher up), but it even works perfect without it.
Until now I made lots of focusers but this one is the most simple to draw/print/assemble and on top of it it's action is very smooth.
The ball bearing's 6° angle position was a good choice imo. The speed is not to high or to low. But it could do with a dual speed knob.

This one cannot be made with a printed eyepiece barrel.  The outer surface of my aluminium barrel had a few very small irregularities(it was on old barrel). While focusing I could feel this irregularities, although very faint I don't like it. So I sanded the barrel's outer perimeter until it was very smooth again. After sanding the action was perfect.
To be clear, it actually can be used with a printed barrel of course but then you must ignore the rather 'bumpy ride' while focusing. A printed perimeter will never be able to produce that same smooth action like a aluminium barrel does.
But again using a printed barrel I do think it'll need that spring loaded system to overcome these little perimeter-irregularities.

[Chriske]

I did find a way to add that dual speed function.
Made it as small as I possibly could.
Let's hope this thing works... fingers crossed..!

Dual speed unit is mounted at the same angle as the bearings and is springloaded of course.
Contact wheel with the eyepiece barrel is a thick rubber O-ring
Speed reduction is 4:1 -  Partly  done with that little red gear and the rest is done with the contactwheel itself.
A bevel-gear  pair to have the focusing knob ergonomically correct.
To eliminate friction (except on that rubber wheel of course) there are 8 ball bearings. (3x7x2.5)
Going to make a 'release' system for the focusing knob. When not in use the bevelled gear slides a few mm away and releases from that other bevelled gear.

Pivot point is on the left;  spring will be mounted on the far right side of the unit (light brown)

[Gina]

Looks very good - be interested to hear how it does in practice.

[Chriske]

Dual speed unit done.

[Gina]

That looks excellent ??

[Chriske]

This dual speed focuser does its job perfect. Very smooth, no issues at all.
Reduction is not  4:1 as I first thought but 7:1, but that's ok, it's not to slow.
I'll call this one : BBH2S (Ball BearinHelical-2-Speed)
Notice that the dual speed unit is at an angle(the same angle as the ball bearings 6°)

[Gina]

A very interesting unit.  Unfortunately not suited to imaging but I know it's for observing with eyepiece attached directly and a rotating eyepiece is no problem..

[Chriske]

Is it because of the rotating barrel..?

1 minute ago, Gina said:

A very interesting unit.  Unfortunately not suited to imaging.

 

[Gina]

My editing crossed with your post...   But yes.

[Chriske]

Well Gina, I have good news for you...
This very moment busy drawing the same focuser(Helical) were the barrel does NOT rotate at all...! Also supported by ball bearings btw.

[Gina]

That's clever!  Thought that was how it worked...

[Chriske]

Renamed this thread because a dual speed version was added.

[Astrobits]

A couple of pics of crude versions of this design that I snapped at an ATM meeting about 10 years ago:

Nigel

 

[Chriske]

Thanks for posting Nigel..!
..and yes, crude is the correct word here.... BUT it works, and that is important.