Gina's Mini Dome Observatory for Widefield Imaging Rig

[Chriske]

9 hours ago, Gina said:

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.

I was planning also to make a volcano for my 1.0 and 1.2.
I would have started here and modify it.
Maybe we can work this out together..?

[Gina]

Glad you found that E3D Volcano engineering drawing   Yes, I was planning to copy the Volcano but double up on the heaters.  Here's a rough model.  Not sure where to put the little hole for the thermistor.

Edited June 23, 2017 by Gina

[Gina]

Alternatively :-

[Gina]

From studying the Volcano drawing it looks like they just have a shallow hole for the thermistor and likewise for the threaded hole for the screw than holds the thermistor wires.

Edited June 23, 2017 by Gina

[Gina]

I've ordered a piece of aluminium 10mm x 20mm x 100mm from which I can cut about 35mm for the block.

[Gina]

I've been having another look at the casing that supports the dome and covers the mount.  The part that covers the mount can be a fair bit smaller so I've produced a new model.  The mount cover intersects the dome support much better now.

[Gina]

Curved end added.

[Gina]

Mount cover and dome support separated.  After printing these will fit together with the mount cover inside the dome support.  Each part will be divided into parts for printing as the biggest printer I have won't take them whole.

Edited June 23, 2017 by Gina

[Chriske]

On 6/23/2017 at 10:29, Gina said:

Glad you found that E3D Volcano engineering drawing   Yes, I was planning to copy the Volcano but double up on the heaters.  Here's a rough model.  Not sure where to put the little hole for the thermistor.

I'm planning to use a PT100, not a classical thermistor. It needs an additional amplifier board to be connected to the RAMPS.
more info

[Gina]

I presume you are dissatisfied with the standard thermistor then.

[Chriske]

dissatisfied ...no not at all,  I used them aal the time on all my printers in the past, but a regular NTC 100k thermistor becomes unstable and unreliable  above 250°C.
Some filament I'm using now (PETG - HT) requires higher temp than 250°C and a  PT100 will go far beyond that temp and is far more accurate to.

[Gina]

I use 260°C on my Pilot and 280°C on this one and the thermistors seem alright.  What are the symptoms of the problem at these temperatures?

[Chriske]

First of all  I don't trust it to work near the edge of the specs, especially with this chinese rubbish. I would buy somewhere else, but I can't determine anymore  whether parts are made in China or not.
but most of all when working near the edge results will become unpredictable, especially visible  in the perimeters. A well tuned hotend, having ran a PID will help improve quality, no doubt about that. It's not the only reason of course, but it helps.
I have no problem printing with 'fat' nozzles, but the layers should always be perfect,  no irregularities are allowed.

[Gina]

I see.  Mostly I'm getting clean layers and can see no reason to change temperature sensor.  Of course, I don't go by absolute temperature but by results.  Experience shows if the extrusion temperature wants increasing or reducing.  I say I'm using 280°C but that is the reading from the thermistor and the actual value may well be different.  I have always considered recommended temperatures as just a starting point and then adjusted according to results.

[Gina]

Lower half of mount cover printed.  Struts across the bottom of the print hold the shape and will be removed after assembly with other parts.  Last photo shows orientation of part when in use.

[Gina]

Now printing the other half of the mount cover.

[Gina]

That went fine  

[Gina]

The support for the dome (which is right on the maximum size this printer can take), had to be aborted due to severe lifting of the ends off the bed that made the print totally unusable.  I have been experimenting with PLA and I'm finding that sticks to the bed better than ABS even at a much lower temperature so I'm wondering if I can arrange for the larger parts that don't need solvent welding, to be bolted together with hidden internal brackets.  It would seem that modern PLA is fine outdoors, at least in lighter colours that don't absorb as much heat in hot weather.

Another possibility for the parts that do need solvent welding due to their shape is to make them in smaller sections.  More parts to glue together but at least possible.

Edited June 26, 2017 by Gina

[Dr_Ju_ju]

Try PetG, it has the strength of ABS but prints easily @ 80 bed with 240 hot end....

[Gina]

I have a reel of PETG on order to try.  From reading about it, it seems a great type of filament - very strong and not suffering from some of the problems of ABS.  Costs a bit more but you often get what you pay for and it pays to go for the better stuff.  I think this could well be the best printing material for my astronomy builds.

[Gina]

I've been looking at the design of the dome support and rotation and how the support connects to the mount cover.  Here is a cross-section.  The cylindrical dome support that goes down to the wooden framework has been reduced to fit on the print bed of my Titan 3D printer.  Just above that a section of a sphere will connect the running ring of the dome to the smaller cylinder and to the mount cover.

Edited June 28, 2017 by Gina

[Dr_Ju_ju]

I use E3D's version, they call edge http://e3d-online.com/Edge  Yes it is expensive, especially as the reels are smaller, but as you say, you get what you pay for... 

 

[Gina]

That certainly looks very interesting - particularly the ability to print with an overhang.  That aspect looks particularly impressive and would save on support material thereby saving on cost and making their cost price more advantageous.  I like that!   I think I may try it.

[Gina]

Gone for it   Ordered a reel of British Racing Green which looks like just what I want to match my main observatory.  I really must stop buying filament to try though   I'm enjoying it though so...

[Stu]

8 minutes ago, Gina said:

Gone for it   Ordered a reel of British Racing Green which looks like just what I want to match my main observatory.  I really must stop buying filament to try though   I'm enjoying it though so...

Does that mean completely reprinting the whole lot Gina?