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ballanux

Aluminium heated bed questions

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Hi all!

I would like to add a heated build platform to my ultimaker. For this purpose I have bought a 215x215mm silicone heater in ebay and I'm thinking of using an aluminium heated bed instead of a glass one.

To get a rigid bed I think I should use a thickness of 4 mm at least. A sheet of 240x*240x4mm would weight about 620gr. Is this too much? It seems like a lot of weight to me, but as the platform seems very sturdy, it may handle the weight just well.

As the aluminium can be drilled without problems, I would use the current leveling screws to support it. But this may be a problem, do you think the transfered heat to the screws can be high enough to melt the plastic inserts in the wood? would be a good idea to replace them?

The silicone heater can be driven up to 18V 12A, does anyone know a good power supply with this characteristics?

Does anyone use this type of heaters? how well they work? (maybe I should have asked this before buying it! :mrgreen: :mrgreen: )

Thanks

 

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The plastic that holds the screws will be fine. It won't get too hot. I have 6mm aluminum plate and it isn't too heavy but I wish I got the 4mm. Make sure you get MIC6 aluminum.

Because of the weight my wooden ultimaker support arms droop from day to day so I have to relevel often. But they are very solid and the weight is not a problem at all.

 

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That's a special aluminum for tooling plate right?

I asked lasermaster.co.uk price for laser cutting a plate and for their flatness tolerance. They say the material tolerance for flatness is +- 0.2mm over the face of a whole 1250x2500 sheet. would that be right?

Anyway I will also ask them about the mic6 aluminum.

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I got mine in USA from here:

http://www.metalsupermarkets.com/catalog/ALUMINUM/PLATE/MIC-6

The tolerance is much better than +/- .1mm. Other types of aluminum will warp over time and will warp when heated and won't be as flat unless the last step they do is to machine it flat on a milling machine which I would expect to cost something like $100 just for that step.

Look harder for mic6. It's great stuff. I rechecked and I was wrong about the thickness. I got .5 inch (about 12mm) which was much too thick. I think 6mm would be about right. The worst thing about 12mm thick plate is it takes so long to heat up - maybe 20 minutes with an 80W heater. If I did this as a business I would both buy a more powerful heater and a thinner sheet of aluminum but I rarely use the heater lately anyway.

 

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I didn't cut the slots. You will need MUCH stronger springs if you do it this way. Instead I support the plate from below. All I had to do was drill shallow holes (aka blind holes) in the bottom at the correct positions. I just used a hand drill. And I took out the 4 screws and put in them through from the bottom instead. No extra parts needed.

If the head crashes into the plate, the wooden arms holding the bed bend enough to keep from damaging the nozzle so that's not an issue.

The other advantage of slots is you can remove the plate but if it's a heated bed and you don't have a connector this won't work so who needs slots?

 

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Finally I'm going to use standard 5mm aluminium plate and hope it won't warp

 

If it does just buy some glass and put on top of the aluminum with clips that let the glass expand. Ideally you want pyrex but many people use cheap standard glass (you can probably get 10 cut and edges smoothed for a few dollars each) and mount it with clips so it can expand and they only break occasionally. The advantage of lots of pieces of glass is you can remove one finished part and let it cool while starting the next.

 

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If it does just buy some glass and put on top of the aluminum with clips that let the glass expand. Ideally you want pyrex but many people use cheap standard glass (you can probably get 10 cut and edges smoothed for a few dollars each) and mount it with clips so it can expand and they only break occasionally. The advantage of lots of pieces of glass is you can remove one finished part and let it cool while starting the next.

 

I will do that! well... better if I don't need to :mrgreen:

but it's a good idea

 

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I was trying to minimize the heated mass so I tried 3/16 (~5mm) sheared aluminum (I think 5052 alloy) for the substrate on my HBP. I didn't even try it as it wasn't as flat as the stock acrylic bed. The supplier I had chosen did not publish a flatness tolerance, and the piece was warped in the process of shearing so I went to the MIC6 which is very flat. For me, the best advantage in my opinion to upgrading to the HBP is the added flatness. The inherent flatness of the MIC6 and/or 3/32 window glass greatly reduces the need to re-level. I can now confidently start a plate of parts and don't need to be present for the start of every part.

The heater I chose is an adhesive silicone type like sold by Omega in the US. Mine is 7x7" 120vac, and approx 250watts. To heat the whole thing up including an 1/4"x9x9.5" MIC6 plate, and the glass takes 4-5 minutes.

MIC6 is also known as cast aluminum tool(ing) plate.

Don't forget to leave enough area around the print area to fasten the glass to the aluminum with printing clearance. If I do it again, I would make my aluminum plate a bit larger.

I would also strongly recommend changing to a 3 point leveling system

If interested, I am controlling mine with a SSR wire to the UM HBP output and powered by a separately fused 120vac main. I used a thermistor in the usual way. There is more specifics on the google group

good discussion here, more specific to my chosen solution nearer to the end

https://groups.google.com/forum/#!searchin/ultimaker/hbp/ultimaker/8xjR_npZACw/QhmUO3jaWNcJ

and here

https://groups.google.com/forum/#!searchin/ultimaker/hbp/ultimaker/lqqVzodLcwU/Wzgop__xu44J

Matt

 

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Some updates! :mrgreen:

I have received the silicone heater and looks great!

I'm still waiting for the aluminium plate to come... the guys at lasermaster are taking their time to cut it... I don't know if they have a ton of orders or if they just don't care about a small order like this...

I have bought a switched power supply in eBay, should be enough to power all ultimaker stock electronics and the heated bed. It's 18V 22A, so just under 400W.

The silicone heater will take 12A and of course I will need to regulate the power either with a MOSFET or a relay. Provably to use the current MOSFET it will be necessary to put a heatsink, but this would be the best solution. Also, I don't know if the PCB traces are wide enough, I will check the PCB desing

Ideally it would be great to control the heated bed with the Marlin firmware... but this is not currently supported right? I will try to take a look at it, after all I'm a firmware developer for temperature controls at my job :mrgreen: :mrgreen:

If this is too much trouble I may end up just using one of the temperature controllers that we make at my job:

http://www.keld-electronics.com/en/product-category/keld-control-product-line/temperature/

 

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Ideally it would be great to control the heated bed with the Marlin firmware... but this is not currently supported right?

 

It is supported. It's just not built into the versions of Marlin that come prebuilt for you with Cura. You can built your own Marlin which I recommend since you are familiar with software and embedded software. In fact maybe you can contribute some day:

So download the source files here:

https://github.com/ErikZalm/Marlin

Then edit Configuration.h – that’s probably the only file you need to edit.

Then build Marlin yourself. It’s not hard. If you google “build marlin” you should find a few good websites that explain it including this one which does it the command line way (I prefer the GUI way) but is still excellent set of instructions:

http://www.extrudable.me/2013/05/03/building-marlin-from-scratch/

WHATEVER YOU DO, make sure you:

Save the resulting Congifuration.h file and the resulting hex file in a permanent location that you never ever change and date it and explain why you built it so that when you need to build another Marlin a year from now you can do a diff of Configuration.h to see what you did differently from the "norm". And if your arduino dies and you need to reload marlin you will have the hex file ready to go.

 

THERE IS ALSO a super easy marlin builder here which you should look at first and I recommend you use it to create a configuration.h file to start with if nothing else (when you build it creates both the hex file and the configuration file).

http://marlinbuilder.robotfuzz.com/

 

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WHATEVER YOU DO, make sure you:

Save the resulting Congifuration.h file and the resulting hex file in a permanent location that you never ever change and date it and explain why you built it so that when you need to build another Marlin a year from now you can do a diff of Configuration.h to see what you did differently from the "norm". And if your arduino dies and you need to reload marlin you will have the hex file ready to go.

 

Great advice! will do that :mrgreen:

I hope I can contribute with something... but the time is sooe scarce!!

 

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So, finally I have everything I need for the heated platform build! Well, I still don't have all the cabling, but at least now I can see how everything fits together.

First, this is the aluminium plate that came from lasermaster... I really expected something much better... they took 3 weeks to send my order and the plate was completely scratched on one side... the other side isn't that bad, but if this is the service they provide, I won't be buying anything from them, nor recommending it to anybody.

This is the scratched side, I will put it in the bottom:

g28r.jpg

This is the "good" side. You still can see some scratches:

n2jb.jpg

This is the silicone heating pad I got from Ebay, it fits very nicely over the aluminium plate. Also you can see a small NTC I got from work, it's 47K and I don't know the exact temperature table from the manufacturer, but I think it will be good enough, my main concern is that it was small enough. Usually we have only encapsulated NTC which are at least 4mm diameter. If this isn't good enough I will switch to a thermocouple, but I think a couple of degrees of error won't matter much.

pbxl.jpg

Finally, this is the power supply I got from Ebay, I plan to run the entire printer form it, not only the heated platform... but I will have to see how stable is the voltage when the controller starts switching to regulate the heated platform...

7r76.jpg

I still have to see If I can run the heating pad directly from the MOSFET if I can mount a small heatsink with good airflow I think it will be OK. The conduction losses will be about 1.8W, I still need to see about the switching losses.

I see that most people are using a relay to be sure they don't damage the board (and it's a good precaution to take) but it would be neat to use the MOSFET. Does somebody have done this before with the ultimaker electronics?

And of course, I still have to take a look at the marlin source to build the firmware with heated platform support.

Still a lot of work to do!

 

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Hi Ballanux,

You are taking a very simlar route to me, and mine has been working fine off the standard mosfet, no relay, for well over a year now.

You need to mypass the 5A DC connector by soldering to the PCB directly with your power leads but other than that no problem, the tracks have held up fine.

I used a reprap PCB heater rather than a silicone one but I don't think it matters. The only problem I had was when the aluminium wore through the insulation whilst removing a stuck part and shorted the PCB heater solder joints, which you won't encounter with your heater.

I chose a 24v version of the same power supply, but it adjusted down to 19v, as I am sure your 18v will adjust up if you want.

If you use the mosfet directly, you can enable PWM control of the heater plate in the formware which is a lot more stable than the slow on-off control. Be sure to run a M303 to establish your PID constants if you enable this.

Andrew

 

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Hi Ballanux,

You are taking a very simlar route to me, and mine has been working fine off the standard mosfet, no relay, for well over a year now.

You need to mypass the 5A DC connector by soldering to the PCB directly with your power leads but other than that no problem, the tracks have held up fine.

I used a reprap PCB heater rather than a silicone one but I don't think it matters. The only problem I had was when the aluminium wore through the insulation whilst removing a stuck part and shorted the PCB heater solder joints, which you won't encounter with your heater.

I chose a 24v version of the same power supply, but it adjusted down to 19v, as I am sure your 18v will adjust up if you want.

If you use the mosfet directly, you can enable PWM control of the heater plate in the formware which is a lot more stable than the slow on-off control. Be sure to run a M303 to establish your PID constants if you enable this.

Andrew

 

Thanks for the tips! You are right about the connector, maybe 10 amps is too much for it. How much current does your heater need?

 

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The machine is connected to a UPS which displays the power on the front, so:

The whole machine draws about 350Watts of mains when the bed and hotend are on full at warm up, and 70W with bed off. Assuming the PSU at 19volts is about 85% efficient, the machine is drawing 15.5Amps of which 10.5A is the bed.

Definitely more than the DC conenctor can handle.

 

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