• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.
  • PLEASE: Read the FORUM RULES BEFORE registering!

80mm long focal length refractor

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#61
It came out parallel ok which now let me mark it out for the next three sides so back onto the tool post to remove the waste.
fb4.jpg

I must have listened to you guys too much and thought I could do no wrong. I got a tad impatient and attempted to speed it up a bit.
ARGHHHHHHHHHHHHHHHHHHHHHHHH disaster
fb5.jpg
It started chattering and pulled the tool out of the chuck and I took a huge divot out before I could stop. I will have to place one on the other side and call it a feature.
fb6.jpg
I think that part of the problem was not just the extra speed but the tool bit wasnt quite right so I ground the back of a drill bit so I could turn the cutting edge to the correct orientation (as I saw it) to hopefully not do the same muck up again. This cut very smoothly.
fb7.jpg
Now all 5 sides are cut I can drill the holes for the bearings and bolts.
Clamped at 45', first holes at 3.3 mm then 10mm clearance for the 9mm dia bearings.

Then back onto the lathe to bore the 53mm dia hole for the focusser tube.
fb8.jpg
Once that was bored I could cut the apex of the triangle off
fb9.jpg
The design is not my idea its from this clever gentleman http://jimshomeplanet.com/CrayFocus/CrayFocus.html so credit where it is due.
Thats it for a couple of days as I have to lay a heap of pavers in the back yard. (a large honey do)
 
Last edited:

prasad

Active User
Active Member
Joined
Jul 4, 2014
Messages
156
Likes
37
#62
Charles

I was looking at your bino-dobsonian project. I would suggest adding two controls for collimating the mirrors. one mirror moves around virtical axis and second moves on horizontal axis. The movement needed is very miute but without this adjustment your eyes will see different views which becomes confusing to the brain. I have viewed through similar bino and I have seen the problem.

-Prasad

Hmmm Tony, then I guess you want to see how this one is going eh?
View attachment 97244
The truss tubes are 12mm square steel tube. They are made but I still have to weld the diagonals in.
I have the two lazy susan bearings for the top cages.
I have the glass for the two mirrors plus the grinding and polishing machine ready.
They will be two f6 12" mirrors where the back face will be ground to the same radius of curvature as the fronts.
They will be polished to a sphere then flexed to the parabolic shape required. I have made one 8" f3.7 spherical mirror flexed to a perfect mirror to check the process.
When I finish the refractor I will be starting on these again and will start a project blog.
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#63
Its already in the plan but not on that drawing. However, when I was discussing this with the Bolton group who had a similar project they said they never had a problem with that and that the mirrors remained collimated. We will see. My thoughts are to ensure they can be co-collimated, better safe than sorry.
Also as they will be flexed then they wont slide around in the mirror cells so that may help.
 
Last edited:

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#64
Wow! time flies.
At last the focusser unit is finished.
all-parts.jpg
Moving downwards:- main block, 4 bearings-screws-spacers, then plastic washers from milk bottle, brass plungers that hold the shaft, then bolts with pressure springs to hold the shaft against the focus tube, brass pusher with spring and adjustment knob for tension and locking, large knurled knob with smaller knob bolted to it, smaller knurled knob for other side.

I wound the springs on this mandrel but a lot shorter than the test in the photo.
The first two coils were wound with no travel, then the threading was engaged at 3mm pitch, then stopped to wind the last two coils with no travel.
spring-winding.jpg

The four bearings are held in the block and just protrude into the bore for the focus tube to ride upon. Yes, thats two spacers on that bolt, my drill wobbled a tad out of alignment and it needs a tad more clearance.
I still have to make the dust shield to cover the top 3 faces of the block. I cant decide upon ally or brass, guess it will be whatever I find first.

bearing-closeup.jpg
The shaft then bears against the other side of the tube, friction alone moves the tube in and out as the shaft is turned.

The small knobs are for coarse feed with the large knob for fine feed/focus.
The brass knob is an extra pressure point onto the centre of the shaft as a lock.

assembled.jpg

I am most pleased as it moves very smoothly with no grabbing or jerking. Just as a focusser should.
Its bolted to the brass ring that screws onto the last tube of the telescope.
Tomorrow is testing time to check how short the focus tube really needs to be (or longer if my calcs are way out)
 

Bill Gruby

Global Moderator
Staff member
H-M Supporter-Premium Member
Joined
Jul 13, 2012
Messages
5,430
Likes
1,900
#65
Charles, fantastic work as always.

"Billy G"
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#68
Thanks Matthew.
I just realised I never showed the bearing holes
bearing-side.jpg
Pretty ugly and 4 large holes for dirt etc to enter so I covered them with a thin plate
bs-cover.jpg
That funny twisted loop is actually a length of cotton reflected in the polished cover.
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#69
The scope is finished and assembled. It took long enough.
finished-scope.jpg
The end cap has a small brass loop for some stainless chain that will be bolted to the bottom of the flange so as not to loose the cap.
Its held in the cell via an "O" ring.
I wont collimate the lens until its in the cradle on the mount as it will be easier then.
Now started on polishing all the cradle parts.
I cant look through it yet as its too cumbersome to hold still and I dont want to scratch the tubes by resting it on the fence.
 

Bill Gruby

Global Moderator
Staff member
H-M Supporter-Premium Member
Joined
Jul 13, 2012
Messages
5,430
Likes
1,900
#70
Very nice Savarin. You are a craftsman at his best.

"Billy G"
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#71
Thanks Bill but I wish I worked faster.
I'm desperate to start on the binos.
 

Bill Gruby

Global Moderator
Staff member
H-M Supporter-Premium Member
Joined
Jul 13, 2012
Messages
5,430
Likes
1,900
#73
Savarin:

Faster is not in the cards for a craftsman such as yourself. It's done when it's done.

"Billy G"
 

Franko

Active User
H-M Supporter-Premium Member
Joined
Feb 24, 2015
Messages
1,286
Likes
1,056
#74
What the world needs is more craftsmen such as yourself, Savarin, who take the time required to do a job worth doing.
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#75
Gorgeous. How much does the assembly weigh?
best guess (bathroom scales, notoriously inaccurate) is around 4Kg (8 lb) it feels around there as well.
What the world needs is more craftsmen such as yourself, Savarin, who take the time required to do a job worth doing.
Thanks Franco much appreciated.
 

ch2co

Grumpy Old Man
H-M Supporter-Premium Member
Joined
Jan 9, 2013
Messages
752
Likes
461
#76
Sir, your craftsmanship and attention to detail are above and beyond anything that I have ever seen. You have a great little lens there, I have a mid '50's Jagers 4" f15 lens that I turned into a scope. For planetary and double star work, this is my go to scope, harder to get around than my C8 cassegrain, but well with the extra effort. Long refractors rule.
What does the interior of your scope look like, baffles, type of antireflective interior tube coating etc?

AMAZING work

CHuck the grumpy old guy
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#77
Thanks Chuck,
The first baffle is the internal edge of the tube where it screws into the first brass joiner.
This is why the front of the scope has that large black casting to bring the diameters down so the tubes would not cause any vignetting, the second baffle is a thin internal edge in the middle of the second brass joiner, the third baffle is the internal edge of the focusser tube.
Everything inside is painted with a spray can matte black then top coated with thinned Artists carbon black acrylic.
I taped the ends of the tubes, poured the artists paint in and swirled it around to coat every surface, drained it and stood the tubes on end to drain fully and dry.
Of all the matte black paints I experimented with the "Atelier Artists Acrylic" Carbon Black was the flattest and blackest paint I could find.
The paint
paint.jpg
Shots where the camera is just sitting pointing down the full length of the scope.
Unpainted inside
bare-tube-at-outside.jpg

Spray can matte only
spray-can-matt-at-outside.jpg

overcoated with the artists matte
spray-and-artists-rolled2.jpg
Those two grey dots at 7 oclock were popped bubbles since been smoothed down and re-touched to remove them.
Simple test but looks "black hole" ish to me.
 

ch2co

Grumpy Old Man
H-M Supporter-Premium Member
Joined
Jan 9, 2013
Messages
752
Likes
461
#78
I almost just sent you a series of 3 photos of my latest little refractor tube during blackening, and they look identical to yours. Thanks for the recommendation of the Atelier Artists Acrylic Carbon Black, never came across it before, but I'll have to get a bottle and try it out. John Dobson, of Dobsonian telescope fame, used flat black paint that he mixed sawdust into to get a very black and rough non reflective finish, a real mess, but it works great! Keep up the great work. Let me know how it works when you get around to actually observing with it.

CHuck the grumpy old guy
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#79
My experiments were very interesting.
Some paints were very black when dead on but turned shiny grey at a glancing angle.
What was very surprising was the ones that looked a shiny grey dead on turned very black at glancing angles.
What paint did you use?
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#80
I had a re-think regarding the end cap, prising it off by inserting your fingernails into the gap just didnt seem right so I made a knob.
end-cap-1.jpg

end-cap-2.jpg
Hmm, large finger print.
Easy to pop off now.
Now searching for some small stainless clips and chain so it wont get lost.
 

rwm

Active User
H-M Supporter-Premium Member
Joined
Mar 25, 2013
Messages
1,048
Likes
1,131
#81
Really impressive work! Looks beautiful and very professional.
If you have the capability, I would love to see some planetary images.
BTW stainless chain is super easy to make if you have any stiff wire or welding rod laying around. Also a great source is chain from a toilet tank!
R
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#82
The only way I could take pictures is just by sticking my camera in the end of the tube and hoping I can reach focus. Ok for the moon but not for the planets.
I'm not really into astro photography, its seems a lot of time and angst for not much pleasure. (just my take on the subject)
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#83
After much soul searching and attempts I have at last got the clutch and slow motion drive working.
I cant believe how difficult this was to work out. This is all the parts.
The bottom casting could have been re made and the shaft screwed into it but by doing it this way I can alter the tension of the two taper rollers for a smooth but firm movement and set it with a lock nut (to be added later)
clutch-parts-1.jpg

The curly keyway is where the bit flexed but as it works I didnt re-do it. The other one cut ok.
The lock screw stops the shaft from rotating when manually moving the aximuth plate (not shown)
The main part of the shaft is steel (old car drive shaft) and the top bit is stainless
clutch-parts-2.jpg

The azimuth plate bolts on to the top of the unit via the 6 threaded holes.
clutch-parts-3.jpg

The first ally spacer has a groove for an "O" ring to prevent dew and dirt from entering the bearing and seals against the hole in the azimuth plate (not shown)
plus a keyway and key that locks into the shaft preventing it from turning around the shaft.
There will be another "O" ring groove or I may use a thin gasket for the azimuth plate to seal against the top unit.
The next spacer is plastic and is machined to fit into the worm gear.
clutch-parts-4.jpg

then comes the worm gear, another plastic spacer, the stainless spacer with the internal tongue so it cant rotate around the shaft then the knurled pressure knob.
Approx 1/4 turn from free to fully locked.
The large gap is where the 10mm thick azimuth plate will be bolted on. There is approx 0.3mm clearance between the azimuth plate and the first keyed spacer.
clutch-parts-5.jpg

Now back to polishing.
 

brino

Active User
H-M Supporter-Premium Member
Joined
Jan 2, 2014
Messages
2,842
Likes
2,617
#84
Complicated mechanism.....I am still trying to understand how it works.......

Great close-up pictures, thanks!
On the piece with the locking screw is that pitting from a home casting?

-brino
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#85
More like porosity from a home casting, there's also some tearing in the middle of the casting which is why I bored it out and locktighted a section from a real ally bar in there.
Ha ha, I feel better now knowing someone else has a problem with this. Its my fourth attempt to get it working.
The worm is bolted to the plate that's bolted to the top circular part.
The worm gear (above) is only held in place on the shaft by the plastic pressure shims/washers.
The bottom large spacer and the stainless washer with the tongue are fixed to the shaft with keys so they can move up and down a small amount depending upon the pressure of the large knurled knob.
When that knob is screwed down tight the worm gear is locked solidly to the shaft via friction and becomes a solid part of the peir and that bottom casting, so as the worm is turned it screws itself around the gear dragging the azimuth plate with it. The telescope is fixed to the azimuth plate.
It doesn't help that the plate and worm aren't in the picture yet so its difficult to visualise.
The previous version didnt have the keys and when the azimuth plate was moved manually it unscrewed the knurled knob releasing all the pressure.
 

ch2co

Grumpy Old Man
H-M Supporter-Premium Member
Joined
Jan 9, 2013
Messages
752
Likes
461
#86
OK, I'm confused (which is really my normal state anyway), but are you currently building an equatorial mount for your 80mm scope? and is this just one axis of the mount?
or is this some sort of alt/azm mount??? or is this something completely different?

CHuck the confused grumpy old guy
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#87
Hi Chuck,
Its an alt/az mount but not like a dob.
Have a look at the first pic on page one how it goes together.
The cast part sits into a vertical tube, the scope sits in the alt bearings at one end of the plate and the whole top unit with the plat spins round.
Near the top of page 2 has some pics of the test assembly showing how it should go together.
I used the table saw yesterday to cut down the azimuth plate from the large rectangle it was to something a little more streamlined.
No work today as its party time in 2 hours.
 

ch2co

Grumpy Old Man
H-M Supporter-Premium Member
Joined
Jan 9, 2013
Messages
752
Likes
461
#88
So the worm gear if for hand control of the azimuth? Are you planning to put a flexible control cable onto the worm gear?

CHuck the grumpy old guy
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#89
yes, already to use but I may end up adding a rod in a bearing as an extension because I cant find any flex couplings longer than those currently used on cheap dept store gems.
Theres also a slow motion control for the altitude bearings.
These are probably overkill but they add to the impressive look :grin:
 

savarin

Active User
H-M Supporter-Premium Member
Joined
Aug 22, 2012
Messages
1,562
Likes
1,974
#90
Still have these to polish then lacquer.
Too much, I'm fed up with polishing, you start to get a bit ocd about removing every little micro scratch.
Most of these have gone through the tripoli but still have the polish to do, some still need a bit more sanding.
polishing-bits.jpg
Argh!!!!!!!!!!!!!! when will it end.
 
Container Above bottom breadcrumb