Helical Crayford Focuser - v2
Description
A zip tie is used to close the 'petals' onto the tube. Perhaps you can use a large rubber band as well, which would be a bit better for instances where the tube isn't consistent in OD. Maybe one of those silicon bracelets? A large hose clamp could also work.
Half of the bearings are also inverted. This moves the bearings into two planes, so that it only moves along one axis and doesn't tilt to the sides. In v1 this was done with steps, but I think this design is cleaner.
One revolution yields about 35 mm of travel with the standard petals, which have a 15 degree angle. The fine petals have a 5 degree angle, and I assume should be ~11.5 mm/revolution.
All the sketchup files are in the zip below. Add a comment if there's any trouble opening it.
Video: youtu.be/bW7UEPq3LA8
Instructions
Assemble as in the pictures, except use smaller screws :-). Everything is M4 except the M3 on the eyepiece screws. I think m4x30 is a bit conservative, and you might be able to use smaller, like 20-25mm. In the pictures of mine, i used 40mm 'cause that's what i have on hand, but there's at least 15-20mm extra.
You might also like a focus tube lock, and if so print out one lock petal and only 5 petals, replacing the 6th petal with the lock petal (only in the fine pitch for now)
There is a base plate for a 6 inch tube like a PVC drainage tube, and one for a truss like design, which has a flat bottom face. The truss base plate is more multipurpose; it can be used on all sized telescope tubes and trusses. You just need to print an adapter to attach it to, so i would recommend the truss design.
You must be logged in to post a comment.
Can it be locked in position?
Is it strong enough to connect an DSLR camere?
Very nice project, thanks for sharing!
The bearings spin too easily to support the weight of a DSLR, and spining/focusing it would be tricky. Perhaps if you replaced the bearings with rubber wheels it would have more resistance and grip.
There is a lock "petal" that i've included in the design, but haven't tried yet, that has a screw to tighten and lock the cylinder in place. if one of these petals isn't enough, you can print 2-6!
Very smooth movement, very clever design!.
I had some trouble finding a tube with the right diameter. Then I saw that toothpaste dispenser idling in the bathroom... Ta-Da!
Neat part! I'm really excited to see more telescope parts on here.
I wonder, would this work better with small rubber wheels instead of bearings? I wonder if the metal bearings would slip on a smooth plastic tube.
Thanks!
I thought it might slide, but it doesn't seem to, at least with the piece of acrylic i'm using as a tube. maybe a harder material would be different, or with a heavy eyepiece. The zip tie keeps all the bearings in contact with the tube
It can "unscrew" with a heavy eyepiece, probably easier than it would slide. the Lock petal is a must if you have heavy eyepieces (and probably a good idea regardless), with a nylon M4 bolt if you are worried about scaring the tube..
Collections
License
More from Buback
which bearings are you using because i don't seem to be able to find that anywhere
it uses 624 bearings (6 of them). I seem to remember that thingiverse used to have a parts list functionality, and i probably had it listed on there, but that's over a year ago, which is like 10 years in 3d printing time.