Gina's Mini Dome Observatory for Widefield Imaging Rig

[Gina]

Interesting idea but I think it would need a lot of redesign and re-printing.  I agree that it would be more elegant.  I don't think the hole for the string would work, I'm afraid, due to the curvature and the string needing support across the opening.

[Gina]

I'm looking into other ways of stopping the shutter parts falling off that may be simpler and more elegant.  I can hold the parts in place when closed and when fully open it's in between that's the problem.

[wimvb]

 

42 minutes ago, Gina said:

Interesting idea but I think it would need a lot of redesign and re-printing.  I agree that it would be more elegant.  I don't think the hole for the string would work, I'm afraid, due to the curvature and the string needing support across the opening.

Yes, very likely. one intermediate solution would be to print a similar guide rail and glue it onto the existing parts. But that may be a poor fit.

[Gina]

I don't think a full guide rail is necessary.  I've taken some scrap ABS heated it and bent it to form a couple of hooks cut to length and shape and glued to dome.  Seems to do the trick.  Will need a couple more but looking promising.

[Gina]

I've been looking into the whole imaging system including not only the imaging rig which will fit in the dome but also the mount and all the support structures.  I could end up with a small green pimple on a somewhat larger structure if I'm not careful!   My large 3D printer is out of action ATM due to print bed problems which will take a couple of days while waiting for replacement parts so looking into other parts of the micro observatory would be sensible. 

Even if this dome isn't suitable for the intended imaging rig, it might do for something a bit smaller and in any event I have enjoyed the exercise.  Also, if I decide I need a bigger dome this one can act as a scale model.  I really would like to make a working dome.  The mount is a DIY project too and by no means insignificant.

My current idea for the imaging rig includes ASI1600MM-Cool camera, filter wheel and vintage SLR lens with the whole thing in a framework providing rotation so that I can fit the image frame to the object.  The latter adds considerably to the size - a non-rotating rig should be quite a bit smaller.  I may be trying to do too much, as usual

[wimvb]

If you do put it to use, you should have a little plastic figurine right next to the open shutter, gazing up at the sky. Just for the fun of it. 

[Gina]

Been having a good look at my widefield imaging rig and I can simplify it considerably, particularly if I abandon the remote rotation.  This is a nice thing to have but only needs setting at the start of an imaging run or beforehand so hardly a problem.  The only thing with a dome might be getting at the rig but I think the slot is wide enough to get a hand in.  Doing away with the remote rotation means the fork mount can be smaller too.

[Gina]

Here are a couple of cross-section diagrams showing the earlier design and latest with the dome and mount etc.

[Gina]

The mount seems well over-engineered but this is no bad thing for stability and accuracy and I have all the main parts.  I might change the design a bit but it seems better to keep this main design rather than start again from scratch.

[Gina]

I've added more hooks/brackets and checked the shutter operation and it seems alright.  I have yet to work out the full route of the drive strings.  Over the dome is fine but they will have to run round the base to link up.  I plan to drive the strings with a pair of drums run off a stepper motor.   I shall also have to work out how to place endstop detectors.  Hall device switches and magnets are probably what I'll use as these cope fine with a damp environment.

I have also to sort out how to turn the dome, to stop it from blowing off in a storm and guide it in a circular path.  I have various ideas.  This will also be driven by a stepper motor.  It will also need detection of the HOME position.

Edited June 19, 2017 by Gina

[Gina]

I think this dome might be usable as the rig fits in it but the mount still looks big in comparison.  I shall have to sort out a casing to cover the mount and hold the dome.  The main supports for the dome and casing consists of four fence posts held in metal spikes in the ground.  The mount has a separate support in the form of a Skywatcher Pillar Mount sitting on three heavy concrete blocks.

[Gina]

Latest photos of the dome.

[Gina]

The dome needs a structure to support it and the mount needs covering and I have been looking into this in the fork mount thread.  But I've realised that this support and weather excluding casing probably ties in better with the dome than the mount so I'm continuing here.  I'm hoping I can 3D print a lot of the casing to match the dome in appearance.  Also I'm using WiFi to connect so aluminium is not an option between the two RPi boards and the router.

Here's a couple of screenshots of a SketchUp model I've been working on.  Didn't manage to make it perfect though and stil have gaps.

Edited June 23, 2017 by Gina

[Gina]

As can be seen, this will not fit in a 300m cube printing space so will need splitting up into workable sections.  There is still a possibility that I might build a bigger printer in the future but meanwhile I have 290mm x 290mm x 325mm in which to build what I want.  It might be possible to increase the X and Y ranges slightly as long as I limit the bed contact area to 290mm square.

I think I may be able to 3D print the mount cover part if I split into two.

 

[Chriske]

Gina,

I saw in one of the pictures you use 3mm filament.
you should try printing with 1.75mm  filament. Print quality will improve significantly.

[Gina]

Yes, I use 1.75mm filament in my smaller "Pilot" printer which gives very good results for smaller prints.  I've been thinking I might change over to 1.75mm on this bigger one too as that is reckoned to be easier to melt in the hotend.  It does mean buying some new parts though.  And I have a fair stock of 3mm filament.

[Chriske]

The smaller 1.75mm diameter filament and it's higher speed result in a flow that can be controlled far more accurate compared to 3mm filament.
I even use 1.75 mm filament with a 0.7mm nozzle, it gives me smooth prints with no issues(except for the layers itself of course). Layerheight 0.52mm..!
Lucky me (except for the nozzle) I make my hotends myself. I have a lathe and a milling machine.
I integrated a fast exchangeable hotend in my printers. (I do not believe in fast exchangeable nozzles) A few days ago I also bought a 1.0 and a 1.2 mm nozzle... And I read somewhere printing with a 2mm nozzle can be done with a 1.75(!)mm filament..

[Gina]

I'm using a 0.8mm nozzle on this machine (0.4mm on the Pilot) and 0.5mm layer height though I think it could probably take a bit more, I'm still experimenting.  I bought an E3D Volcano hotend which came with 5 nozzles of 0.4mm, 0.6mm, 0.8mm, 1.0mm and 1.2mm.  I'm also using E3D Titan extruders on both machines which I've found feed filament a lot better than anything else I've tried including ones I've made myself.  I have tried making my own hotends but had problems.  I have one of those cheapo Chinese mini lathes (for my sins) which I've done my best to improve.  I also have a micro mill - useful for small jobs.

Hotends are pretty quick to change with the E3D Titan extruder - just 4 bolts to take out.  More trouble would be swapping cables over, though the heater and thermistor could be taken out I guess.  I might have another go at making hotends.  Might be advantageous to use a bigger cartridge heater than the standard 40W RepRap type.  I'm finding the "bottleneck" in the extrusion process is the rate at which filament can be melted.  Yes, I know that would be better with smaller filament.

I can't really see how a 2mm nozzle could be used with 1.75mm filament - it would barely touch the sides!!  I suppose it might just work with a relatively small gap between nozzle and print bed.  Once it melted it would "back up" and help the following filament to melt.

[Gina]

Had a thought - with home made heater block you could have two 40W heater cartridges and connect them in parallel.  The power MOSFETs in the RAMPS are well capable of taking the current.  I've got lots of those 12v 40W cartridge heaters.

Edited June 23, 2017 by Gina

[Chriske]

9 hours ago, Gina said:

Had a thought - with home made heater block you could have two 40W heater cartridges and connect them in parallel.  The power MOSFETs in the RAMPS are well capable of taking the current.  I've got lots of those 12v 40W cartridge heaters.

I was planning to do that...

[Gina]

This might be an interim option :- 60W Ceramic Cartridge Heater – 24V Heating Element – 3D Printer – RepRap

50% more power in the same size heater.  Direct replacement just needs 24v instead of 12v.  I'll have to check how much spare current capacity I have in the 24v PSU.  24v 60W is only 2.5A.  As I recall the 24v bed heater takes 12.5A and I have a 15A PSU so 2.5A spare.

[Chriske]

9 hours ago, Gina said:

I'm using a 0.8mm nozzle on this machine (0.4mm on the Pilot) and 0.5mm layer height though I think it could probably take a bit more, I'm still experimenting.  I bought an E3D Volcano hotend which came with 5 nozzles of 0.4mm, 0.6mm, 0.8mm, 1.0mm and 1.2mm.  I'm also using E3D Titan extruders on both machines which I've found feed filament a lot better than anything else I've tried including ones I've made myself.  I have tried making my own hotends but had problems.  I have one of those cheapo Chinese mini lathes (for my sins) which I've done my best to improve.  I also have a micro mill - useful for small jobs.

Hotends are pretty quick to change with the E3D Titan extruder - just 4 bolts to take out.  More trouble would be swapping cables over, though the heater and thermistor could be taken out I guess.  I might have another go at making hotends.  Might be advantageous to use a bigger cartridge heater than the standard 40W RepRap type.  I'm finding the "bottleneck" in the extrusion process is the rate at which filament can be melted.  Yes, I know that would be better with smaller filament.

I can't really see how a 2mm nozzle could be used with 1.75mm filament - it would barely touch the sides!!  I suppose it might just work with a relatively small gap between nozzle and print bed.  Once it melted it would "back up" and help the following filament to melt.

While changing hotend I do not swap cables at all. I designed it to be as easy as possible. To swap hotends I only have to remove two screws. All stays in place as a unit. In both XY-carriage and hotend I have two littlt PCB's with contacts. The contactPCB in the XY-carriage has a little bit of play to avoid tension on these PCB's in case of little positioning errors. But as far as I can feel all works very smooth while inserting the hotends in it's carriage.
I also have to remove the partscooling nozzle(2 screws).

 

 

[Dr_Ju_ju]

Just check that the cartridge will actually fit the hot-end, I've had some where the diameter was greater than the hole...

[Chriske]

9 hours ago, Dr_Ju_ju said:

Just check that the cartridge will actually fit the hot-end, I've had some where the diameter was greater than the hole...

reamer...?

[Gina]

Decided to go for 1.75mm filament as an option for this printer and have ordered a couple of Volcano 1.75mm nozzles - 0.8mm and 1.2mm.  I have also decided I'm going to have a go at making a heater block to take two 6mmx20mm 40W 12v heater cartridges, one thermistor and M6 threaded hole for Volcano nozzle.  Like the Volcano heater block I shall use a pair of clamping screws for each heater.  Probably heat conducting grease too.

I think I'll also see if I can arrange to be able to change hotends.

Edited June 23, 2017 by Gina