13 replies to this topic

[darkapollo]

This started as a project about two years ago when I bought the venerable Celestron Astromaster 130EQ! Never trust amazon reviews... 

As so many already know, the EQ mount and tripod that it comes with is way too weak for the weight of the scope (all 5 pounds of it) plus the DEC has only a 90* 'swivel' rotation. 

My initial plan was to just rebuild the scope to be as light as possible to hopefully get the EQ mount to function just a bit better. 

Then it was tax return season. Then, suddenly, I had a few hundred dollars. Then, suddenly, I did not have a few hundred dollars but I had a new 10" dob and the 130 went to the basement.

 

I took my Z10 everywhere. I brought it to Star parties, to the eclipse, to the beach, every where I could. However, even with my haul-anything hatchback, it took up a great deal of room so if I was going anywhere with anyone else, it just wasnt coming along. Plus I enjoy doing AP and a push-to dob can be frustrating when trying to keep a target centered at a higher magnification. 

I was going to OnStep my Z10 but at the time my electronics skills weren't up to the task.

 

I did still have that 130 collecting dust in the basement. It was small, light, and could be brought along. However I did not like the shaky tripod or EQ mount. I also had recently purchased a large format 3D printer (my previous printers were 6x6x6 printable area or less. This was 12x12x15. Literally the sky was the limit) 

 

My next idea was to make an EQ fork.

The plan was to do a push-to and then use a simple clock drive to rotate the RA for easy tracking. 

I was never happy with that design.

 

I DID however, like the look of the hex-tube tri-truss

 

This version was less than half the weight of the 130EQ, however my mounting solution left a lot to be desired (nothing like the entire scope sliding around because the clamps on the tubes dont clamp enough)

It actually balanced with a single 4.8lb weight at the top of the counter weight shaft instead of both 4.8lb weights at the bottom. 

 

Then, I just went a bit crazy. The first and second prototypes used a shell around the mirror cell that I was going to fill with either sand, or lead shot, or BB's to help balance the scope. It was very much not needed. 

So I turned the shell into a lighter, single wall (.4mm) light shield and it is still a bit back heavy. My 5* self-locking fine adjustment helical focusor is also built and I was testing draw tube distances.

 

But I still wanted to make an EQ fork. I just loved the way they looked.

 

Do not do this. Do not do this unless you want to waste a lot of plastic. I over engineered it with 5mm thick walls too. It was so wobbly. Even breathing near it would send it into convulsions. Way too much weight for that poor crappy tripod to handle. 

 

I did have quite a bit of 20x60, 20x20, and 20x40 aluminum profile.. I had the telescope already done, but nothing to mount it to.

My first attempt was to make an EQ mount. It failed. It failed almost as hard as the printed fork mount. I didnt even bother to take a picture of that. Clearly I was under estimating the leveraging forces at work.

 

So I thought "What if" and measured the profiles I had. It seems odd that they were perfect lengths and no cutting was required. Almost like it was meant to be (the yellow bearing block is from the failed EQ..).

 

The design came together very quickly too. 

 

One thing thing that nagged me though was how to attach the RA. Well, I thought, I am using a 10mm aluminum pin for the DEC and I have plenty of that bar stock.

 

Success! Or.. Or not. The weight of the fork assembly caused my old nemesis to come back. Again I under estimated the forces at play at that joint. There was several degrees of sag and the assembly wobbled nearly as bad as the printed fork. 

 

I need something.. beefier. 

A quick trip to my local Lowes solved that. 3/4" x 6" rolled steel tube (which is actually 1.05" (~26mm for you metric users) because why call something 3/4" when it is 3/4"...) Apparently this stuff is for metal hand rails. What ever. It is perfect.

 

Unfortunately I was running too low on yellow (it happens when you rush to print something large and dont double check measurments... TWICE...) so I had to use... peach... 

 

SUCCESS! FINALLY! There is near-zero slop. I could eliminate it all together but that would make the axis too tight to rotate freely. As is there is less than a half millimeter of deflection and that is without the nylon gliders installed. 

Wobble? WHAT WOBBLE! I kicked the mount base and the scope settled in under a second! (not shown is the spline bushing which will help support the axle and keep it off of the rear foot.)

 

I still need to wire up the OnStep controller (Using one of my spare 3d printer boards since they support that now..) and position the motors, but after two years in the making it is finally close to completion. 

All in all it may have been cheaper to just buy a travel scope, but where is the fun in THAT?

 

Both the DEC and RA can be smoothly pushed to position with a single finger and the scope is so well balanced with the camera that it stays put.

 

Edited by darkapollo, 26 February 2019 - 09:37 AM.

[petert913]

That's a large printer.  Those parts are big !  Very cool project. 

[descott12]

Very cool!

[Stellar1]

You must have a printer the size of a refrigerator! awesome project there.

[Araguaia]

Cool!  What plastic is that?  How accurate does it come off the printer?  Do you need to file things down for a perfect fit?

[calypsob]

Wow great project and execution of an idea! This kind of work has me really wanting to upgrade to a cr10s pro.

[JoeInMN]

I know nothing about 3D printers... Can the plastic from the false starts be chipped/shredded and used again?

[darkapollo]

Wow great project and execution of an idea! This kind of work has me really wanting to upgrade to a cr10s pro.

I did all of this on a CR-10 so no real gain for the larger build of the S-Pro  

Just more bed to heat.. Of course, if I wanted to do this in say.. 8" or 10" (the scope is designed around a 6" mirror but I had the 5" on hand which is why I had to fiddle with focusor draw tube lengths) the CR-10S would be my go-to. 

[darkapollo]

Cool!  What plastic is that?  How accurate does it come off the printer?  Do you need to file things down for a perfect fit?

PLA. Eventually it will be Carbon Fiber - Nylon just because why not. 

I know the general tolerances from my printer so I build in accuracy. For example the parts that the RA axle attach to are printed at 26.5mm (roughly 1.05" is 26.6mm) and they are VERY tight purely friction fit. I had to hammer the axle in. The axle support is printed at 27mm and it is snug but just lose enough to allow rotation.

However for things like screw holes, if I want a clean fit +.25mm if I want to thread the hole +.1mm over the nominal. (IE an M5 would be 5.25mm or 5.1mm) 

 

The gear teeth will need cleaned up a bit only because they are thin and some first layers did not stick very well to the bed. 

Edited by darkapollo, 26 February 2019 - 12:31 PM.

[darkapollo]

I know nothing about 3D printers... Can the plastic from the false starts be chipped/shredded and used again?

It COULD, yes. I do not have an extruder to re-filament-ize the failed prints so in the trash they go! PLA is biodegradable so its ok. My ABS prints usually end up in an acetone bucket for use as glue or bed material. 

[calypsob]

It COULD, yes. I do not have an extruder to re-filament-ize the failed prints so in the trash they go! PLA is biodegradable so its ok. My ABS prints usually end up in an acetone bucket for use as glue or bed material. 

you may find petg is a bit more car heat friendly

[darkapollo]

I am pretty certain the scope wont see temps over 120f.. glass transition for this is over 170.

[Dale Eason]

I am pretty certain the scope wont see temps over 120f.. glass transition for this is over 170.

The PLA I know of has a glass transition temp much lower around 140 F.  The sun has deformed the PLA I have used before and I live in a moderate summer climate at 45N latitude.

I used PETG for my scope.

 

Have you found a better PLA?

 

Dale

[darkapollo]

Ive never had that happen and I have tons of PLA parts on my other scope. The solar cap is one big disk of black PLA and it still looks like the day I made it, and it was used heavily leading up to the eclipse in late august.
I can tell you that with this brand (MG Raptor), at bed temp of 70c (160f) it is just barely soft. I typically use eSun for most things and at 70c it is like gum, very soft and flexible. Raptor needs a higher print temp too. I think the lowest Ive ever gone is 225 (220 was too low), but for better layer bond I run it at 235. eSun I print no higher than 210.
That said, I do not recomend dealing with that company which is why I was hesitent to meantion the brand. They have ripped me off as well as countless others.

Edited by darkapollo, 27 February 2019 - 04:10 AM.