A call for help/ideas to develop the Heated Bed

At $35 I don't think Rick at Makergear is getting rich. His kit includes a custom y stage, ceramic plate, nichrome, niobium magnets, 3 different epoxies, precut wires, and a pot holder. I don't know how he sells it at a profit honestly (I priced all the parts individual and I came up with $50 using a local laser cutter machine shop and the internet).

If you want no warp, Heat is the only way to go.

PLA has very limited warp, but still warps a little.

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repraplogphase.blogspot.com

i know at that price i am thinking about getting one, for me that would work, and the price is about right, it will save me some trouble that is for sure

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[mike-mack.blogspot.com]

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It's using a ceramic platform and kapton tape. And 60 or 70ºC...

That is not hot enough to get ABS to stick to Kapton in my experience and too hot for PLA??

The use of ceramic puzzles me. It's neither a very good conductor or a very good insulator.

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[www.hydraraptor.blogspot.com]

in that regard it is allot like cast iron cook wear, it is not the best conductor has well, that is why it has nice even cooking. with aluminum you can still end up with hot spots, being a good conductor can be a bad thing has well.

i do not see why the tile could not get hotter for abs, ceramic should be able to take just has much heat in this regard has any metal, i would also like to find out if it would be less likely to warp too.

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[mike-mack.blogspot.com]

I put 20Ω (about 900mm) of MakerBot nichrome on the bottom of a 100x100x13mm slab of aluminum using Kapton tape. Hooked up to 12v it only got to 40°C. Looks like I'll have to shorten the nichrome.

JohnWasser Wrote:
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> I put 20Ω (about 900mm) of MakerBot nichrome on
> the bottom of a 100x100x13mm slab of aluminum
> using Kapton tape. Hooked up to 12v it only got
> to 40°C. Looks like I'll have to shorten the
> nichrome.

P = U² / R <=> 12*12 / 20 = 7.2W.

Try to use at least 50W, by using a different wire, with lower ohms - about 3Ω.

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New cutting edge RepRap electronics, ARM 32 bits @ 100MHz runs RepRap @ 725mm/s:

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John - why are you using a 13mm slab...that seems awfully thick/heavy.

To make a heater mat you could thread nichrome wire around a piece of fiber glass mat. The woven stuff might be a bit thick but CSM (Chopped Strand Mat) should be doable.

I would go this route if I were casting a heater bed. to get the spacing on the wires and be sure it didn't move or short out as the concrete (or ceramic if you wish) cured.

It may also be worth going for thicker nichrome (less resistance per metre) and putting as much length as you can whilst keeping the resistance you want into the heating mat/bed.

The nichrome distributes the heat better.

I think Nophead had some useful figures on the required wattage, length of nichrome can be calculated once you know what wattage you want to achieve and at what voltage. (Same deal as the extruder heads)

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Necessity hopefully becomes the absentee parent of successfully invented children.

JohnWasser Wrote:
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> I put 20Ω (about 900mm) of MakerBot nichrome on
> the bottom of a 100x100x13mm slab of aluminum
> using Kapton tape. Hooked up to 12v it only got
> to 40°C. Looks like I'll have to shorten the
> nichrome.


Tap the runs if possible (depends on your layout) and convert them to parallel to lower the resistance.

The temperature for the ceramic platform can be regulated. The temp for printing ABS on Kapton film is 80C-90C but some people are using higher temps. You can see some photos of raftless ABS/kapton printing on the MakerGear homepage.

Rick Pollack Wrote:
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> The temperature for the ceramic platform can be
> regulated. The temp for printing ABS on Kapton
> film is 80C-90C but some people are using higher
> temps. You can see some photos of raftless
> ABS/kapton printing on the MakerGear homepage.

Rick, are you the men behind MakerGear?

If so, could you tell us if you tested aluminium and if is better or not compared to that ceramic?

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New cutting edge RepRap electronics, ARM 32 bits @ 100MHz runs RepRap @ 725mm/s:

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MakerGear has a basic aluminum HBP pack ($17.50) available - alu plate, power resistors, connectors and thermistor. I'm thinking about doing an aluminum version of the ceramic kit...here are a couple of the prototype laser cut 1/8" aluminum plates.



And, some other materials I tested - glass, stainless, and corian.



For this application ceramic makes for a very nice heated platform...better or worse really depends on what you are trying to accomplish.

Rick

Rick Pollack Wrote:
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> MakerGear has a basic aluminum HBP pack ($17.50)
> available - alu plate, power resistors, connectors
> and thermistor. I'm thinking about doing an
> aluminum version of the ceramic kit...here are a
> couple of the prototype laser cut 1/8" aluminum
> plates.

Ok, nice to know. Would be possible for you produce and sell also for RepRap (I guess Mendel as priority)?


> For this application ceramic makes for a very nice
> heated platform...better or worse really depends
> on what you are trying to accomplish.

Well, I guess we all want the same thing, better prints! and at the same time spend less power heating and lower price.

Could you tell us the main differences of power usage between ALU and ceramic table? what is quick to get hot and cold?

And why use different heater elements on ceramic and ALU?

And are the back of the heated table well insulated?

You know, we are looking for someone produce and sell to us the heated bed.

Edited 1 time(s). Last edit at 03/03/2010 11:28AM by casainho.

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New cutting edge RepRap electronics, ARM 32 bits @ 100MHz runs RepRap @ 725mm/s:

[www.3dprinting-r2c2.com]

This is a little off-topic, but I thought I'd mention it anyway. Nophead earlier was musing about the difference between Kapton tape and Kapton sheet. I just read in Scientific American that adhesive tapes are actually composed of four layers: adhesive, primer, plastic, and release agent. So the surface of the Kapton tape probably is indeed different than the kind available in sheets.

@casainho - join the MakerGear Google Group for detailed discussions about heating times and such...

Rick Pollack Wrote:
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> @casainho - join the MakerGear Google Group for
> detailed discussions about heating times and
> such...

Rick, I am just interested on RepRap Mendel. If you want to make and sell an Heated Bed for Mendel, than this is the correct forum for discuss it and not any other.

I do not want to discuss your solution but instead I would like that you could sell a solution for Mendel.

I would like that you provide the answers to my questions, but even you can ignore if you do not plan to build and sell it to Mendel.

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New cutting edge RepRap electronics, ARM 32 bits @ 100MHz runs RepRap @ 725mm/s:

[www.3dprinting-r2c2.com]

On the heated bed, a great deal of effort seems needed to get a perfectly flat surface. I'm getting the impression that this is because we're not printing a raft, and great flatness is needed to make sure the first layer of the object is of uniform thickness.

Plate glass is cheap, available everywhere, and has a very flat surface. But it doesn't conduct heat well. Might it be worthwhile to couple it with a liquid to spread the heat evenly?

I'm thinking of a shallow plastic dish with a thermistor and some nichrome in it, filled with motor oil and with a glass plate on top. Convection in the oil will keep the entire surface of the plate glass at approximately the same temp. Either seal it or have a small riser to let bubbles out. Maybe a combination of both. Printing it would have to be done in sections, since you can't print something larger than the bed on the bed.

This would be very messy if it failed. And dangerous, even a small quantity of very hot oil on your skin would leave a nasty burn.

But the real question that bothers me here is: Would the plastic melt/creep at the preferred temp for the heated bed?

A bit of googling later: 220C for ABS. ABS would definately creep at that temperature. Which is probably the point: keep the plastic above its glass transition temperature. Therefore, the bed itself cannot ever be printed from the same plastic that's printed on it.

So nevermind, I guess.

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I'm building it with Baling Wire

Just a silly idea I had, but how about using simple household aluminum foil sandwiched between a glass plate and the kaptonsheet.

The aluminum sheet(s) should be slightly larger than the kapton sheet, and power resistors aligned on top of the aluminum foil, right besides the kapton sheet.

The idea/hope is that the aluminum foil will conduct the heat from the power resistors sufficiently for the kapton to be reasonably isothermic, but thin enough to remain as flat as the glass plate.

(fixed a typo)

Edited 1 time(s). Last edit at 03/04/2010 05:41AM by anton.

I don't think it will be anywhere near thick enough to spread the heat. I don't have any figures to back that up, but look how thick the central members of a heatsink are.

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[www.hydraraptor.blogspot.com]

Many years ago I worked on a fdm 2000, it had a build platform made of polyurethane foam,( or something like it) similar to the stuff that lags hot water tanks, it is a poor conductor so did not remove heat from the polymer bead and had the advantage that the nozzle tip could be embedded into the foam a little to eliminate errors and get good adhesion, (very necessary when building tall parts),
of course the whole chamber was heated rather than just the build platform, this was probably a major factor in reducing warping etc.

The new machines use what looks like clear acetate sheet, but it may be more exotic stuff.

dissidence,
I must disagree with you on that one. Cast Iron pots will always have worse hot spots than aluminum of the same thickness. If you look at modern cookware, the aluminum pots and pans are thick, but not quite as thick as the cast iron. And anyone who has rounded the corner of a piece of aluminum on a grinder or sander knows just how good a heat conductor, in _every_ direction, aluminum is. This is simple thermodynamics. In a highly conductive material, like copper and aluminum, the heat spreads rapidly in all directions, and it is hard to maintain a hot spot for welding or brazing, without melting every other joint near by.





dissidence Wrote:
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> in that regard it is allot like cast iron cook
> wear, it is not the best conductor has well, that
> is why it has nice even cooking. with aluminum you
> can still end up with hot spots, being a good
> conductor can be a bad thing has well.
>



I also agree that aluminum foil will not be thick enough to handle/distribute the heat. My plan was to make an array of 16 by 16 small aluminum blocks, silver solder them onto a sheet of stainless steel (poor thermal conductor), and put a power resistor of 10 ohms on each one. I would wire the high sides in rows, and the low side in columns, so that I could selectively heat each square. This is where the poor thermal conductivity of the stainless steel comes in. To easily carries the heat from the aluminum to the surface right above it, but does not move to adjacent squares. If you only heat the squares with plastic being layered on top of them, the plastic will insulate the hot squares from the cold air and the heat will be concentrated just where it is needed, keeping total power consumption down. I have not yet built such a table, but I will start one as soon as I can.

Side note. Is Kapton film or tape the best thing to put on top of our very flat, well heated bed? I was Googling, and there are places that will add a PTFE/Teflon coating to virtually any surface, just like they do for aluminum cookware. You can also buy PTFE tape with the same high temperature silicone adhesive that is used in Kapton tape. It seems to me that it will be even easier to pull parts off of a Teflon covered bed than a Kapton covered bed.


Mike

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Team Open Air
Blog Team Open Air
rocket scientists think LIGHTYEARS outside the box!

rocket_scientist Wrote:
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> Side note. Is Kapton film or tape the best
> thing to put on top of our very flat, well heated
> bed? I was Googling, and there are places that
> will add a PTFE/Teflon coating to virtually any
> surface, just like they do for aluminum cookware.
> You can also buy PTFE tape with the same high
> temperature silicone adhesive that is used in
> Kapton tape. It seems to me that it will be even
> easier to pull parts off of a Teflon covered bed
> than a Kapton covered bed.

Ahhh... But the question really is - WILL IT STICK TO THE TEFLON?

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Sounds like a call for _immediate_ testing! Pity I don't have a machine yet, just piles of boxes of parts! You might try this from Amazon.com to start with.

Mike

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Team Open Air
Blog Team Open Air
rocket scientists think LIGHTYEARS outside the box!

I can't imagine anything sticking to Teflon. That is what it is famous for, non-stick and HDPE seems to come a close second.

With regard to heating just a small area: I think I got better results from my oversized bed. The reason being that, as it is a moving table machine you want the object to always be moving through hot air. With a small object on a large bed that is the case, but with a large object on a small bed it is moving into cold air.

As johnrpm pointed out, and something I found recently, if you have a tall object with a small base you need good adhesion as any force at the top has great leverage. I will try again with a raft.

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[www.hydraraptor.blogspot.com]

nophead,
quite true. I was thinking more of an enclosed machine, or like what I am planning for Open Air 1, a stationary table and moving gantry head. However, it is also possible to heat the outer most squares hotter than the inner ones to partially make up for the plastic there being more exposed.

I was also thinking that using cheap, carbon resistors on each square of the heater, then placing precision wire-wound current sense resistors between the power resistors and the column selecting power MOSFETs. This way, as the squares heat up, the resistors change resistance, and reading each current sense resistor will say how hot the aluminum block is in that square. This would mean running 256 PIDs, or simple bang-bang heater controls, but would greatly limit wasted heat.

Mike

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Team Open Air
Blog Team Open Air
rocket scientists think LIGHTYEARS outside the box!

I was looking at a glass heating plate on a serving trolley at my in laws place.

It had an all over heating element arranged in a serpentine pattern. In fact other than a thin insulating gap between the tracing the glass underside was completely covered by the heating element (sandwiched between two glass plates).

I think it worked a little like a rear windscreen heater.

Thinking about this I couldn't help but wonder if something similar couldn't be made by gluing a nichrome ribbon onto the back of a glass plate and then laying this on top of an insulating layer.

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Necessity hopefully becomes the absentee parent of successfully invented children.

rocket_scientist Wrote:
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> It seems to me that it will be even
> easier to pull parts off of a Teflon covered bed
> than a Kapton covered bed.

You need the extrudate to have excellent adhesion to the bed, otherwise your object will be pulled around by the extruder and end up looking more like a drip castle, or maybe adhering to the extruder itself and turning into a blob of death.

This is a delicate balance- excellent adhesion during printing, but with relatively easy removal when printing is finished.

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Wooden Mendel
Teacup Firmware

Thats good because the Kapton tape, expensive as it is, is still cheaper than Teflon tape with adhesive!

OK, I give. First project will use Kapton sheet on the bed. If I ever get there! Still have to finish helping the High School team in First Robotics Challenge Regionals, then there is the under water robotics challenge in June . . .

Mike

Rick Pollack Wrote:
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> John - why are you using a 13mm slab...that seems
> awfully thick/heavy.

I would have preferred using 1/4" aluminum plate (6mm?) but I could not get a 100x100mm square out of the scrap pieces of 1/4" aluminum I had in my shop. The 1/2" stuff (13mm) was the only scrap I had from which I could cut a full 100x10mm build platform.

JohnWasser Wrote:
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> Rick Pollack Wrote:
> --------------------------------------------------
> -----
> > John - why are you using a 13mm slab...that
> seems
> > awfully thick/heavy.
>
> I would have preferred using 1/4" aluminum plate
> (6mm?) but I could not get a 100x100mm square out
> of the scrap pieces of 1/4" aluminum I had in my
> shop. The 1/2" stuff (13mm) was the only scrap I
> had from which I could cut a full 100x10mm build
> platform.

I am using 15mm thick aluminium plate. On that way the guys on the shop sell it flat while the 6mm one I bought were bended :-(

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New cutting edge RepRap electronics, ARM 32 bits @ 100MHz runs RepRap @ 725mm/s:

[www.3dprinting-r2c2.com]