Re: Vacuum hold-down for 3D build surface. November 16, 2016 11:15AM |
Registered: 12 years ago Posts: 1,450 |
Working with very conservative values for everything I get a temperature drop of 53°C between the wire and the aluminium. I may look around for tough thermally conductive silicone or epoxy but if I don't find anything I will be happy with the FSC silicone.Quote
leadinglights
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the_digital_dentist
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leadinglights
I was going to use PTFE shrink sleeving over 0.71mm nichrome but when I tried it out I found that the resistance was too high - 4 Ohms for each half. I have sent for some constantan, also of 0.71mm, which should have a resistance of just under 2 Ohms per half. This is enameled but I will back that up but coating the inside of the grooves with a tough silicone elastomer (Electrolube FSC) and sealing the wire in with the same. silicone.
Mike
PTFE is thermal as well as electrical insulation, as is the silicone elastomer. Your controller is going to be measuring the plate temperature. It will take time for the applied heat to get through the thermal resistances and heat up the bed. During that time the insulated wire is heating to ever higher temperatures. Teflon decomposes at 350C. How do you guarantee that the wire won't get to 350C?
The wall thickness whether PTFE or silicone is 0.2mm or less, total area of the interface between the insulator and the aluminium is about 7800 mm² and a little over half of that at the wire. Long experience with heater elements tells me that 144 watts through an indifferent thermal insulator will be less than 100°C without even doing the maths - though I may look up the thermal resistances and formulae to allay any suspicions.
Mike
Re: Vacuum hold-down for 3D build surface. November 24, 2016 03:38AM |
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Re: Vacuum hold-down for 3D build surface. November 24, 2016 07:15AM |
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Re: Vacuum hold-down for 3D build surface. November 24, 2016 11:48AM |
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Re: Vacuum hold-down for 3D build surface. November 25, 2016 09:58AM |
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Re: Vacuum hold-down for 3D build surface. November 25, 2016 10:38AM |
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Re: Vacuum hold-down for 3D build surface. November 25, 2016 01:55PM |
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Re: Vacuum hold-down for 3D build surface. November 25, 2016 03:09PM |
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Re: Vacuum hold-down for 3D build surface. November 26, 2016 07:00AM |
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Re: Vacuum hold-down for 3D build surface. November 26, 2016 08:34AM |
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o_lampe
DD, I hear you, but high voltage on a modified bed heater is probably dangerous. The gap between the traces is probably to small ( especially the cuts must be done twice )
A rule of thumb is: 1mm per 100Volt
OTOH the vacuum pump could be switched by a pressure sensor and would only run occasionally.
Re: Vacuum hold-down for 3D build surface. November 28, 2016 02:49PM |
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o_lampe
I want to fuel up this discussion with an additional proposal:
I always wanted to add a "conveyor belt"-like foil on a heated bed to allow overnight production of multiple parts. Maybe adding a rectangular bed to a delta or the tripteron?
With such a vacuum bed, it would be much more likely to avoid warping.
When a print is done, switch off the pump and run the conveyor until the part reaches the turning point of the belt. It peels off the foil ( I hope ) and drops in a box for next day delivery
Re: Vacuum hold-down for 3D build surface. November 28, 2016 03:52PM |
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Re: Vacuum hold-down for 3D build surface. November 29, 2016 04:44AM |
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the_digital_dentist
.....
After rethinking the whole thing, I don't think electrostatic hold down will work. It can provide enough force to hold the film in place, but not if the print warps. I'm not sure a vacuum would help with that, either.
Re: Vacuum hold-down for 3D build surface. January 17, 2017 02:40PM |
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Re: Vacuum hold-down for 3D build surface. January 20, 2017 09:58AM |
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Re: Vacuum hold-down for 3D build surface. January 20, 2017 10:03AM |
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Re: Vacuum hold-down for 3D build surface. January 22, 2017 04:49PM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 05:04AM |
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JamesK
That's interesting. My test with OHP film and abs the adhesion was good enough to pull the sheet off the adhesive holding it to the glass (but the adhesive was poor, so that may not be saying all that much). I guess one of the problems with using OHP is that there is likely to be a lot of brand to brand variation. PETG works very well on my OHP film, but has very little warp so perhaps isn't a challenging enough test for your purpose.
What temperature do you print your ABS at? I print on the hot side and probably put the first layer down at 250C for my test.
Re: Vacuum hold-down for 3D build surface. January 23, 2017 05:07AM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 05:46AM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 07:47AM |
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leadinglights
Since it can be nearly £1 per sheet, what has worked best for you?
edit: The one that didn't work was Dataline transparency film for inkjet
Mike
Re: Vacuum hold-down for 3D build surface. January 23, 2017 07:49AM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 08:00AM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 09:08AM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 09:26AM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 01:37PM |
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leadinglights
Holes in an aluminium plate may work quite well and a small drill may be usable if fitted instead of the hot end in a 3D printer. You would still need to find a way to get the vacuum to all of the holes - which is why I used the pattern on the front face of the build plate.
I have attached a picture of the bottom of the build plate showing the manifold which connects to the suck holes (??) and the heater under a layer of thermosetting glass fabric.
[attachment 89434 20170116_1200001.jpg]
I know that it is complicated but if it works I will try to make it somewhat simpler
Mike
Re: Vacuum hold-down for 3D build surface. January 23, 2017 03:10PM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 03:18PM |
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Re: Vacuum hold-down for 3D build surface. January 23, 2017 04:02PM |
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Re: Vacuum hold-down for 3D build surface. January 24, 2017 02:45AM |
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