New bed, from scratch.
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In process of making my own bed, it'll be aluminium and silicone heater wire.
Want to consider adding magnets for use with spring steel, but I only have one aluminium heatsink (very low profile) and that won't allow me to experiment with which side to make pockets for the magnets.
So do I embed magnets topside and epoxy them in, or can I embed them from under and leave the top surface intact?
If they can go under, how much stock should be left between magnet and top of the aluminium surface? I've tried looking at the Prusa Mk3 beds, but from pictures its not easy to tell, and not even sure if the Mk3 bed is aluminium or fiberglass as that might affect the magnets?
Any insight will be appreciated, if trial and error is the way, the so be it.
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I'd have thought it would depend very much on the size, and type of magnet you use. Rare earth magnets might work on the underside of the plate but I'd have thought that you'd still need to inset them as far as possible. Maybe do some experiments with offcuts of thin aluminium sheet?
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That's an interesting concept of making a heated bed. I am not sure I read the pic right, is that 52 degree the brightest color ? Would that be just a short test or max heat ? Would you embed the heater wire in some form of flexible resin or silicone ? What are the electrical parameters for the length of heater cable/wire you use on that bed ?
Jan
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Yes, I would probably buy rare earth magnets, unless I can wait for the summer when I can get someone to bring me back a high temperature magnetic sheet from McMaster. For rare earth N35UH i think is what is somewhat readily available, both in the "prusa" size, and a few other shapes and sizes. Problem is the offcuts are essentially just metal chips, I suppose I'll have to see if I can find some scrap somewhere. This country is impossible to get small quantities of anything unless ordering online sadly, which makes it slow or expensive.
Hehe, you get creative when you spent the budget on the electronics .. it was indeed just a short test before I started cutting the heatsink to size, and milling out some of the fins to keep the wire from protruding.
The wire was supposed to be 223 ohm/m, but I think it came out to 230ohm/m. Total resistance is about 660ohm, and it got to 100C in 8 minutes flat before bonding the silicone wire to the aluminium with more silicone, so I'm hoping to get closer to 5min with bonding and some insulation; more than acceptable for me.
edit: added link to the high temp sheet 250F/120C
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I can't say I got very scientific about this, but seems the magnet doesn't care very much if there is air, cardboard or aluminium between it and the steel sheet. And even at 1mm gap a handfull magnets provide ample holding force (or so I would think)
But I've been told I can have the 120C/250F magnet sheet "smuggled" to me in a couple of months, so I'll skip trying to mill out pockets for magnets this time around. Mostly because the larger magnets would end up having the heating wire pass directly over them and not sure they would enjoy that despite being rated for 150C.
Used "704" to tack down the heating wire, clamping each row down to try and get a good thermal bond, covered it all with high temperature silicone, a layer 2mm ceramic wool and a sandwich of silicone, fiberglass and aluminium foil. Will see how durable it ends up being. Also put a 120C thermostat, a 150C thermal fuse and PE bond on it, hopefully that takes care of the health and safety checkboxes:)
6 minutes and some change to 20 to 100C, phone died while recording so not quite sure.
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@bearer said in New bed, from scratch.:
I can't say I got very scientific about this, but seems the magnet doesn't care very much if there is air, cardboard or aluminium between it and the steel sheet. And even at 1mm gap a handfull magnets provide ample holding force (or so I would think)
But I've been told I can have the 120C/250F magnet sheet "smuggled" to me in a couple of months, so I'll skip trying to mill out pockets for magnets this time around. Mostly because the larger magnets would end up having the heating wire pass directly over them and not sure they would enjoy that despite being rated for 150C.
Used "704" to tack down the heating wire, clamping each row down to try and get a good thermal bond, covered it all with high temperature silicone, a layer 2mm ceramic wool and a sandwich of silicone, fiberglass and aluminium foil. Will see how durable it ends up being. Also put a 120C thermostat, a 150C thermal fuse and PE bond on it, hopefully that takes care of the health and safety checkboxes:)
6 minutes and some change to 20 to 100C, phone died while recording so not quite sure.
Did you check out our Kickstarter? We are offering 150º C magnet and PEI coated spring steel; might be a perfect fit for your bed!
https://www.kickstarter.com/projects/1536120962/pei-coated-flex-plate-system-for-3d-printers/
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@klcjr89 said in New bed, from scratch.:
Did you check out our Kickstarter? We are offering 150º C magnet and PEI coated spring steel; might be a perfect fit for your bed!
https://www.kickstarter.com/projects/1536120962/pei-coated-flex-plate-system-for-3d-printers/
Yeah, seen it, seems like a good product but two issues, the biggest is me being done with kickstarter and having deleted my account there, the second is at 120x120mm its not really cost effective to pay $60 and another $40 or so in fees and taxes for the import.
Kickstarter can ***********. Which is a shame.
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Maybe I didn't understand but if you don't use magnets the flexible magnet sheet isn't going to stick to aluminium. Unless the top of the bed is in steel. I tried using a 1 mm aluminium sheet but the problem was with the IR sensor not reading very well with the metal polished or dull. Went with a 5mm sheet of black glass on my 10mm aluminium bed works great don't have to use anything as it sticks as is. I had tried something like you did but changed ideas as it wasn't as nice as yours is. How many watts does it use?
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I'll put an adheisve magnetic sheet on top of the aluminium, the steel sheet will then stick to the magnet. Meanwhile ahesive PEI straight on the aluminium. Its good to 120C so hopefully it'll cover my needs for ABS and PETG for now.
With the bed being 120x120mm I only use about 70 watt or so, so I went with the small SSR modules with 2 channels, so I can add enclosure heater from the same heater wire. SSR only get up to 30C wihtout heatsink or active cooling at that load so it'll be fine as it is.
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Necrothreading a little as the magnets i had ordered for this project finally arrived and I'm looking for some input from those trained in the dark art of magnetic fields.
I've got a 3x3 grid, and I can't tell if it seems to make a difference if they're all aligned the same way or if aligning them in a pattern of sorts with respect to north and south. As seen in the picture I've stacked three on top of each other, such a stack can be turned 90 degrees as well as 180 degrees to orient the fields in any direction desirable.
Wikipedia has an article about planar hallback arrays
But I'm not sure if that translates into a 3x3 grid at all or if i'm just doing it wrong? Orientation is plain in the picture, and the hold is substantial even sideways, but if it can be improved..:)
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Does it stay flat when you heat it up? It looks like the borders are pretty wide/thick...
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@mrehorstdmd (edit: not) as far as I've tested, but can always stick it back on the router and take off more stock if needed.
(Started off with a cheap low profile heatsink, which is why the shape is as is)
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When you heat the center, which appears to be relatively thin, it will expand more than the edges which will be cooler and more rigid. I think that the center of the bed will bow.
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Iirc the ribs and center is 6mm, the valleys are 2.5mm and the outer edge is 6.5mm thick, magnet pockets are down to 0.8mm. If warped less than what can be seen with a traight edge in the first tests so i'm not worried it'll be any worse than the pcb heater it'll replaced. if the 0.5mm makes a difference i can mill down the edges. (And the temperature seems to be more even than the thermal camera can differentiate)
