A call for help/ideas to develop the Heated Bed

[jamesreprap.blogspot.com]

Here's my blog post on the subject, the photos aren't great because I tend to work on my printer at night when the light is terrible.

You didn't bloged yet as you promised, right? ;-)

psst. Next time, suggest they make a wiki page.

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

james glanville Wrote:
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> [jamesreprap.blogspot.com]
> -heated-bed.html
>
> Here's my blog post on the subject, the photos
> aren't great because I tend to work on my printer
> at night when the light is terrible.

Ok, thanks! And I added a link to that blog message, because your heated bed is almost near the one described on RepRap wiki.

I also added more links, like for MakerGear shop and prusjar.

I also removed a reference to NetFabb software, which is closed source. We have Open Source Skeinforge and so we don't need other closed source softwares.

My opinion is that closed source software my be good as a boot strap but as soon as possible we should use Free/Open Source, or we would not be here. Just Open Source gives us the knowledge and power to make our tools, and not like closed ones like the others printers, for example.

Aging of polyimide (Kapton) tape

Something not being discussed yet.

Edited 1 time(s). Last edit at 03/14/2010 07:05AM by casainho.

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james glanville Wrote:
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> and a STP55NF06
> I like to massively
> overspec mosfets so I can forget about overheating
> them)

that mostfet can only do 5A with no heatsink:


sqrt((175C - 25C) / 62C per watt / 0.018 ohms) = 4.99A

this math is best explained by Understanding FET current ratings

I'm using the IRL3803 which can do 7A with no heatsink on my extruder heater, haven't got to heated bed yet but one of these with a small heatsink, or two in parallel would work nicely I think. They're pretty cheap from futurlec here in australia.

I like to overspec my mosfets too- and I like to run with no heatsinks where possible.

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Wooden Mendel
Teacup Firmware

Eh?
(175 - 25) / 62 = 2.4W

sqrt(2.4 / 0.018) = 11.6A

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[www.hydraraptor.blogspot.com]

hm, apparently google's unit converter has some very strange ideas about celsius and kelvin. punch in 62 kelvin per watt instead and it works a lot better. I'll have to keep that in mind

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Wooden Mendel
Teacup Firmware

I thought that I would toss my plan into the ring here. All of my design is completely untested at this point. I am looking at a 1/2" thick piece of aluminum cut to the geometry of the Mendel table with water lines drilled in it and then hacking a coffee maker for heater parts. I'll insulate a container and I figured I could hook the schematic as shown previously to an SSR to control the heating mechanism on the boiler. When I was forming plastics we used aluminum temperature controlled tools and free coffee makers are everywhere (the first person I asked gladly gave me one).

Best Regards,

-J

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-J

True wisdom lies in knowing that you know nothing

Cefiar Wrote:
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> Has anyone thought of putting a lid over a heated
> bed during the initial heating? Could this help
> reduce the initial time to get it up to temp?

It works very well! It is much more quick on my 150x150x15mm aluminium heated bed :-) -- When I have it at 110ºC and ready to print with ABS, I remove the lead and I quick see a change on temperature, going lower about 5ºC... which means the lid really works :-)

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

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I guess the next thing to do is cut out (extrude) a bed that will wrap around the part(s) to be made and prevent heat loss in the otherwise exposed areas. Once the part(s) get to be several mm thick, the entire heated bed would be insulated, and should keep the power down, and the part more evenly heated.

Another task for the non-Google Summer of Code is writing an STL file or G_Code file to design the 'thermal blank' to cut or extrude to go with it.

Mike

Maybe the thermal blank could be some pieces on the sides of the bed sitting on rails than can be pulled over the section that won't be used. If there is a hole in each piece and the software knows where they are, the nozzle can pull the pieces into a precalculated position.

I'm thinking about four pieces all on one side that slide parallel to each other. If you need only 25% of the x axis, you would slide three of them all the way closed and then the forth one to close up as much of the y axis that you don't need.

All that is needed is some sort of locking mechanism so that they won't move when in position.

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]

casainho Wrote:
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> Cefiar Wrote:
> --------------------------------------------------
> > Has anyone thought of putting a lid over a
> > heated bed during the initial heating? Could
> > this help reduce the initial time to get it
> > up to temp?
>
> It works very well! It is much more quick on my
> 150x150x15mm aluminium heated bed :-) -- When I
> have it at 110ºC and ready to print with ABS, I
> remove the lead and I quick see a change on
> temperature, going lower about 5ºC... which means
> the lid really works :-)

Great to hear that it improves the heat-up times, and hopefully cuts down the need to throw lots of extra power in to gain a fast heat-up.

Any chance of doing some measurements over time with lid vs not? It'd be interesting to see the sort of difference it makes.

Also, what did you use for the lid? Size vs bed size, how was it held above/on the bed, how big is the air-gap between the bed/lid, etc, etc.

Re: A thermal blank

The only issue with a thermal blank like rocket_scientist suggests is the waste of plastic. If you can reuse the plastic it wouldn't be so bad. Either recycle the plastic - which is a whole thread in itself, and there is one in the general forum under the topic: Plastic recycler - or if possible for an identical/similar print.

If there is a different print between these identical/similar prints, then we have the issue of alignment to worry about. This could possibly be solved using a few indents in the surface of the bed, say near the corners of the bed, for extruded plastic to form into. This way the plastic laid down as the blank would have pre-made markers for alignment, allowing multiple re-uses.

The idea mccoyn has doesn't have these issues, but there will be the logistics around the blanking pieces (storage, movement, support, shape, etc) to deal with.

Got some tentative ideas around all this, but they're still fermenting in my head and haven't taken shape.

Cefiar Wrote:
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> Any chance of doing some measurements over time
> with lid vs not? It'd be interesting to see the
> sort of difference it makes.

Sorry, I have other much more important problems to resolve now, like non working extruder heater -- I am being printing my Mendel parts :-)


> Also, what did you use for the lid? Size vs bed
> size, how was it held above/on the bed, how big is
> the air-gap between the bed/lid, etc, etc.

I used a piece of acrylic a bit more the size of the table - that acrylic were to use on the table but then NopHead did discover about Kapton tape and acrylic is gets bended with high temperatures :-(

About 10mm the air-gap, but for now I am not worried to much since this is not my final printer... when I have the Mendel, then I will work for the best solution to it.

Heated Bed temperature for ABS

Yesterday I printed a relative big piece for Mendel Z axis. It was very hard to remove it from Kapton tape... and I used 110ºC on Heated Bed.

I remember to be more easy to remove the pieces when printing with PLA with 55ºC on Heated Bed...

Does anyone experimented lower temperature values for ABS? does it helps removing the final piece? What are yours experience about removing ABS VS PLA?

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

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I found out the hard way that the MOSFETs on the Extruder Controller (V2.2) cannot handle 3A @ 12V for more than about 20 seconds before they overheat and shut down. They work fine at 2A but with 6Ω of nichrome (two stretches of 12Ω in parallel) my heated bed is taking a LONG time to heat up to 110°C, even with a potholder over the top as insulator!

I guess I should use the MOSFET to control a relay or larger MOSFET. Then I could draw more power and heat the bed faster.

JohnWasser Wrote:
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> I found out the hard way that the MOSFETs on the
> Extruder Controller (V2.2) cannot handle 3A @ 12V
> for more than about 20 seconds before they
> overheat and shut down. They work fine at 2A but
> with 6Ω of nichrome (two stretches of 12Ω in
> parallel) my heated bed is taking a LONG time to
> heat up to 110°C, even with a potholder over the
> top as insulator!
>
> I guess I should use the MOSFET to control a relay
> or larger MOSFET. Then I could draw more power
> and heat the bed faster.

If it holds the temp fine once it has been reached, you could add a second element and drive that with a relay, and only use it to get it up to temp. How you control that is another thing entirely.

Are you using second extruder board just to control your bed? If so, you've got a plethora of outputs there you could use to drive a relay, or possibly even drive the second (or third?) elements directly.

JohnWasser Wrote:
-------------------------------------------------------
> I found out the hard way that the MOSFETs on the
> Extruder Controller (V2.2) cannot handle 3A @ 12V
> for more than about 20 seconds before they
> overheat and shut down. They work fine at 2A but
> with 6Ω of nichrome (two stretches of 12Ω in
> parallel) my heated bed is taking a LONG time to
> heat up to 110°C, even with a potholder over the
> top as insulator!
>
> I guess I should use the MOSFET to control a relay
> or larger MOSFET. Then I could draw more power
> and heat the bed faster.

See the solution on [objects.reprap.org]

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

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> Yesterday I printed a relative big piece for Mendel Z axis. It was very hard to remove it from Kapton tape... and I used 110ºC on Heated Bed.

Did you allow the part to completely cool before removing it? As I remember, Forest did this and the ABS shrinks as it cools, breaking it free from the kapton tape.

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]

mccoyn Wrote:
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> > Yesterday I printed a relative big piece for
> Mendel Z axis. It was very hard to remove it from
> Kapton tape... and I used 110ºC on Heated Bed.
>
> Did you allow the part to completely cool before
> removing it? As I remember, Forest did this and
> the ABS shrinks as it cools, breaking it free from
> the kapton tape.

Yes, I did. I left it on bed (turned off) during one night and removed the piece after.

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

[www.3dprinting-r2c2.com]

It can be hard to remove ABS from Kapton. That is why I mount the Kapton on a flexible steel sheet held down with magnets onto the aluminium. Before that I had to knock the parts off with a piece of wood and a hammer!

Lower bed temperatures make the object stick less well and warp more, so the corners start to lift during the build. That makes the object easy to get off, but is not aesthetically as nice.

IIRC, PLA sticks less well and is a bit easier to remove.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> It can be hard to remove ABS from Kapton. That is
> why I mount the Kapton on a flexible steel sheet
> held down with magnets onto the aluminium. Before
> that I had to knock the parts off with a piece of
> wood and a hammer!
>
> Lower bed temperatures make the object stick less
> well and warp more, so the corners start to lift
> during the build. That makes the object easy to
> get off, but is not aesthetically as nice.
>
> IIRC, PLA sticks less well and is a bit easier to
> remove.

Today I removed with easy another piece, but this time I let the heated bed to cool. Last time I had problems to remove, I didn't let it cool... maybe we need to let the heated bed cool before try removing the printed piece.

What experiences you guys have?

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

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> Today I removed with easy another piece, but this
> time I let the heated bed to cool. Last time I had
> problems to remove, I didn't let it cool... maybe
> we need to let the heated bed cool before try
> removing the printed piece.

And yesterday I let one big piece cooling during all nigh. This morning it was to much easy to remove it :-) -- I think that having a removable heated bed would be the best and simple for the ones that want to print continuously.

I just added this info to the wiki page, on the section: Operational considerations -> Removing the final printed piece.

Edited 1 time(s). Last edit at 03/24/2010 07:17AM by casainho.

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

[www.3dprinting-r2c2.com]

This could be a good idea to return to the idea of multiple heated zones. Print a part in zone 1, then let it cool while printing in zone 2. If you have a large part, it can cross multiple zones and use the entire bed, but you will have to wait for it to cool before you can print something else.

The other benefit is that if you are just printing one part, you don't have to heat the whole bed.

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]

mccoyn Wrote:
-------------------------------------------------------
> This could be a good idea to return to the idea of
> multiple heated zones. Print a part in zone 1,
> then let it cool while printing in zone 2. If you
> have a large part, it can cross multiple zones and
> use the entire bed, but you will have to wait for
> it to cool before you can print something else.
>
> The other benefit is that if you are just printing
> one part, you don't have to heat the whole bed.

Thats an idea, however everyone is going to aluminium and then the idea of heating just one zone is impossible, I think.

Makerbot Heated Bed V2 solution.

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

[www.3dprinting-r2c2.com]

casainho,
have you already forgotten my post on page 5 of the heated bed discussion?

16 x16 zone heated bed.

My idea was to attach large numbers of resistors in columns and rows to small blocks of aluminum. The use a high temperature glue to bond the whole lot to a thick sheet of stainless steel. SS is a very poor thermal conductor for a metal, but strong enough for keeping the build platform flat. Adding much glue to fill the gaps between blocks will make it stiffer still. Then bring out the column wires and the row wires. Power one row at a time and only drive the columns that should be heated in that row. The resistance of the heater resistors will change as they get hotter. By inserting a small, current sense resistor in series with each column MOSFET, you can measure the temperature of that square without having a separate temperature probe for every single square.\

This is far more complex than a single heater element for the whole bed with a single thermalcouple to read the temp. It will need a dedicated microcontroller all its own. But an Arduino Mega, a few analog multiplexers to read all 16 channels, and 32 power MOSFETs should be enough to take care of the whole thing. And only heating areas covered by raft of part should help provide insulation to reduce the power needed to keep just those zones warm. Although I seem to remember someone saying their bed temp dropped when they started extruding.

Mike

Mike

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

rocket_scientist Wrote:
-------------------------------------------------------
> casainho,
> have you already forgotten my post on page 5 of
> the heated bed discussion?
>
> 16 x16 zone heated bed.
>
> My idea was to attach large numbers of resistors
> in columns and rows to small blocks of aluminum.
> The use a high temperature glue to bond the whole
> lot to a thick sheet of stainless steel. SS is a
> very poor thermal conductor for a metal, but
> strong enough for keeping the build platform flat.
> Adding much glue to fill the gaps between blocks
> will make it stiffer still. Then bring out the
> column wires and the row wires. Power one row at a
> time and only drive the columns that should be
> heated in that row. The resistance of the heater
> resistors will change as they get hotter. By
> inserting a small, current sense resistor in
> series with each column MOSFET, you can measure
> the temperature of that square without having a
> separate temperature probe for every single
> square.\
>
> This is far more complex than a single heater
> element for the whole bed with a single
> thermalcouple to read the temp. It will need a
> dedicated microcontroller all its own. But an
> Arduino Mega, a few analog multiplexers to read
> all 16 channels, and 32 power MOSFETs should be
> enough to take care of the whole thing. And only
> heating areas covered by raft of part should help
> provide insulation to reduce the power needed to
> keep just those zones warm. Although I seem to
> remember someone saying their bed temp dropped
> when they started extruding.

Yes, I had forgotten. And that looks like much more complex to build... I think the best is you build it and then report. I am sure dealers like Makerbot and others prefer simple and cheap systems.

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

[www.3dprinting-r2c2.com]

I may start with an 8x8 zone system. It cuts the number of blocks on aluminum to cut and attach resistors to by 4, and still gives fairly good resolution. Also, a single large microcontroller usually has 8 analog inputs, eliminating the need for analog multiplexers to monitor each individual block.

I am still working my way through a McWire build. Heated bed will have to come later.

Mike

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

The heated extruder bed captured my interest enough that I've been thinking about various approaches. Specifically, I've wondering about the use of a PCB withlong etch traces as the heater.

Today, I ran across these two sites after a search and I thought they would be of interest here (I did a quick search of the forum and I don't think they were previously posted):

[www.raphnet.net]

[www.neufeld.newton.ks.us]

More generally, I can't help but wonder if an enclosed, heated, system would be better than a heated bed (the 3D printer where I work has a heated chamber). But it is pretty clear that a heated bed can be simpler. It could be that it is "good enough" and then "simple" clearly wins.

TC

TC,
Fascinating reading! The idea had completely slipped by me. You can regulate the final resistance by how thin and long the traces are, and also by what thickness copper you are using. And of course you place the control electronics on a tab sticking out the side of the board, too. That way only power needs to come in. Well, maybe an I2C connection to specify the temperature. It could also take out a LOT of the work of building, machining, connecting my 8x8 or even 16x16 zone heater. It might take a double sided board, but with fat traces going to each zone, and serpentine thin traces to make a small heater in each zone, then a thick line to bring the power back. You could mount the components on the bottom side, but the MOSFETs really should be on the top side where they can get a cooling breeze.

Mike

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

Mike,

Meeting of the minds! You described what I had in mind really well.

Using a 2-sided board would make it simple. Fat (low-resistance) etch on the bottom, serpentine etch for the heat zones on the top. However, this would require multiple vias to stitch the top and bottom traces together (to carry the current). But my hunch is that it is all workable as you described.

TC

I just finished a heated bed, converted from an electric skillet. I paid about $25 for the skillet and the built in controller heats up the "bed" from room temperature to 60C in less than a minute and to 125C in about a minute and keeps it constant. No extra electronics needed. Just another wall outlet. Good luck everyone with your ideas.

Edited 1 time(s). Last edit at 03/29/2010 08:07PM by Shayfir.

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[Shayfir.blogspot.com]