Chriske

The most important part in a tracker this accurate is the quality of the threaded rod. A standard threaded rod out of a 'normal' hardware shop is a no-go. Even with a integrated PEC system it would not be feasible imo. These threaded rods are good enough to track the stars if you don't mind the objects floating up and down constantly in the FOV. As my little lathe can't handle thread cutting I will use the threaded rods very often use in 3D printers for the Z-axis. They're available with different pitch. From 2 to 8mm if I'm not mistaken. The 2mm pitch would be the best choice. If I'd have a lathe capable of cutting threads I'd go for that option. These would be the perfect choice. My point : using 'everyday' threads in combination with Sven's software-solution would be a waste of time. Lead screw with T8 brass nut should do the job nicely.

Thanks Sven for joining in...!!!

Some tests have been performed if I recall correctly at CN forum years ago. These test were done side by side comparing two different spiders. There was no mentioning of loss of contrast at all. In our workshop we did the same test only a few years ago. During telescopemaking course exactly same telescope different spiders. No loss of contrast, Maybe there was some but not visible. To be clear all telescopes are identical. I asked course(I always do) members to switched mirrors every 10 minutes or so. They end up with exactly the same mirror/scope. So that is why we could compare these different spiders without any doubt at all.

Well first of all whether you would go for curved vanes depends. Installing classical vanes you end up with spikes in the field of view around bright stars. Diffraction you know. 4 spiders -->>four spikes in case of three spiders you end up with six spikes around stars. To get rid of these spikes you need to install curved spiders. To be completely correct. The diffraction of these curved spiders is not gone at all. It's diffraction is spread evenly all over the field of view, invisible of course. You need to bend these spiders correctly to achieve the correct result. Many curved spiders out there have the wrong curve, even commercial spiders. There's also another way to get rid of these spikes. The very old ATM-I book of Albert Ingalls also deals with this issue. He does mention a strange pattern is glued on top of the spiders. There's even a drawing of these patterns in his book. Never tried it. On the other hand many amateurs do love these spikes around bright stars, so up to you...😉

From time to time I do drink a beer, preferably a Belgian Leffe. It is a bitter/sweet beer. Anyway, I need to compensate (in my case that would be) for 875g (about 2 lbs) for both glass and bottle...😳 I was just curious....🤭

A fellow observer asked me to repair the alt-bearings of his 10" dob. The glue between the wooden bearings and Formica layers gave up after almost 40 years of intense use. I said : no, I will not repair them, I'll make you a brand new set instead. I started drawing and while at it was thinking of making these bearings multi-purpose. This is what I came up with. At the observers(eyepiece) side there are some holes in his new bearings, capable of storing 4 eyepieces. At the opposite side of his dob there's that second bearing with just one 8mm hole. Well in that hole I'll put a smooth rod + a couple of ball bearings. Hanging on these bearings, actually on top of these bearings, I will install him a platform on which he can put some refreshment, say a beer or so😋. To compensate for that beer sitting on top of that axis I'll add a counterweight at the lower side of the central axis. So where ever he's pointing his scope in the sky, ball bearings and counterweight will take care not spilling the goodies out of his glass of beer... These 250mm diameter bearings will be 3D-printed. They're 35mm thick. More images to come...

You could consider curved spiders.

I'll ask Sven whether it is do-able for a real barndoor capable of tracking one hour or even more. I mean, my Boxmount only tracks for about 20 minutes. For my goal it is more then enough as I explained higher up in this thread. So the differences in speed between centre position and highest/lowest point are very small. I suppose it will work for longer tracking, it's only a matter of extrapolating I guess.

Not yet, but I'll try it alongside with a cycloidal gearbox, that too looks promising.

Change of concept.... Because the mount has no constant speed over it's racking length I'll try another approach. The stepper will rotate very accurately at the same speed, but because the mount has a straight threaded driving rod it will not track the stars at the correct speed along the length of it's treaded rod. As a matter of fact it has the same tracking problem as the well known barn-door trackers. A friend of mine(electronics guru) said he could solve that problem. After some calculation he sent me a sketch to upload in my arduino in which he programmed the stepper's speed variations along the 20 minutes of tracking. I'm very happy with this solution. Needless to say this solution could be adapted for any 'barn-door-isch' mount.

In case it does not work, due to the heavy weight, you also could try a collapsible focuser. There's zero play and can hold a massive weight without sagging down. The only disadvantage is it's rather massiveness. But it does the job perfectly.

The list of parts and projects I've printed so far (during the 10 years I own printers) is long, very long. I can't even begin to tell how many things I've printed so far.. In my opinion every 3Dprinter owner should start learning drawing his own parts. Drawing your own parts, the possibilities are endless ....

The upper part will be printed in two separate parts. I cannot print higher then 210mm(yet). So 2x200mm = 2x 12hours printing time. They will be bolted together.

Painting all inner surfaces...

Assembling...

Some more corrections during filing and sanding...

After this first drawing I made a few corrections of course

I know 'a bit' about folded scopes...;-) In the past I've built lots of Kutter schiefs and bino-Newts. If you do not want to build a completely closed system then you need to pay attention about cutting the oblong hole in the tube. You need to cut it very precise and add a few baffles if needed. And btw I do not draw using lining paper anymore, I do it all on my computer these days. Far more accurate. 😉

The inner parts of an old mimo. I'll keep these for the endstops. Laser + batteries + holder Endstop + battery pack in place...

there's another lens waiting to be transformed into a scope. That second is a 140mm and a whopping 3500mm FL. Don't know yet what I will be doing with this one. it will be folded but I'm thinking of transforming it maybe into a drumscope.

Adding a laser-unit instead of a finder-scope. This the only location to add that laser-unit, (the rest of the refractor is 'filled' with optical path) between the lens and the secondary mirror. I did not want to mount the laser-unit externally. The complete unit can slide in and out and is blocked by the large knurled knob(left) The smaller knurled knob(right) is to activate the laser, by pushing the micro-endstop. That little endstop is cannibalised out of a old microsoft-mouse. They're just a few mm across. All the parts in the laserunit : * two AA batteries(mounted in a holder) * a green-laser unit(15mW) * small endstop * Collimation ring * on-off knob * Larger knob, at the side of the telescope, to lock the laser-unit in place * Cover, to protect the collimation bolts while handling the unit. In winter time a green laser will not work properly. In freezing environments it will even stop working completely. So I can remove the unit from the telescope and store it under my coat, close to my body, to keep it warm. Starting another observing session I slide the (warm)unit in the scope and find me another object in the sky. When done I remove it and tuck it away under my coat again. To be sure that every time again the unit is correctly inserted at the exact same location in the telescope, it is pressed against a V-shape wall

I use PLA printed bearings in combination with felt these days, not for very large and heavy scopes of course.

Again... nicely done..!!

Nicely done.. What process did you use to smooth up the surfaces of these Grado's..?