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jonnybischof

My custom heated bed

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Hi community

I want to make a heated bed for my UM.

I started drawing a "common" PCB with heating coils, then I realised I'd have to calculate a lot and probably won't get accurate final results because of the usual manufacturing tolerances for PCBs.

Also, I ran across a theoretical problem: If you fix a "heater PCB" to an aluminum plate and heat both up, then both objects will expand. As the materials are (very) different, they will expand unevenly and create tension across the bed. I don't know whether this would lead to the bed bending (probably not), or the PCB bending and losing contact to the aluminum plate, or if the effect is too small and nothing at all happens. Anyways, it seems like a flawed principle.

So I searched for a different approach to create my heated bed, and I found one. I won't be using a PCB heater coil, but power resistors in TO-220 package. There are many benefits:

+ Have multiple resistors distributed all over (or under in this case) the heated bed to get a uniform heating.

+ Have less current per heater unit which makes things easier.

+ Be very flexible with heating power by just using the resistor values that you want to.

+ Add multiple temperature sensors distributed between the resistors and create different "sectors" that are heated individually to keep them all at the same temperature.

+ Construction is simple. You only need the aluminum heated bed and just glue all the stuff on the back (with thermally conductive 2K-glue)

+ Less power draw fluctuation by creating a smart PWM (not all resistors are active at the same time, instead stack them one after another)

Sadly, this won't be cheaper than the PCB variant, as the power resistors can get very pricey and you also need a custom heater controller (I'll get to that). But the price should stay manageable, I'm calculating around 150 Euros for the complete package inculding power supply.

So, I already started drawing the schematics for the controller, but I have one basic question first:

What would be the highest temperature I (or anyone using my design) want to reach?

There would be a hard limit at about 150°C, because that's the absolute maximum temperature allowed for the resistors.

Also, this will define the kind of temperature sensor that I'll use...

/edit

One more thing:

Does anyone know the dimensions of the printer bed and most importantly, the mounting holes?

The lasercut-parts files on thingiverse are of no use for me - can't use eps (no clue what to do with that...) and there are no dimensioned drawings...

 

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For the heater I'm going to use a silicon heater, you can search " Reprap 215*215mm 12V 100W Silicone Heater 3D Printer Prusa Mendel Self-adhesive" in ebay to find it.

And for the dimensions of the bed, I have done a DXF to ask for a quotation on how much does it cost to laser-cut it in a 5mm aluminium plate. You can find my drawings in

http://db.tt/VQJO1a00

The acrylic bed is a bit bigger than in my drawing (maybe 1.5mm bigger) but the mounting holes dimensions are accurate (I hope!).

 

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lately I finished my heated bed.

Used mirror on top of heating PCB (5mm, 220x220).

I simple mirrored acrylic bed wholes on aluminum sheet (4mm, 250x250) then printed holders for glass+heating PCB with mounting for aluminum.

Max would be 120 I think (ABS 110 around)...

 

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Wow!!

suddenly the heating element I bought for 46GBP it's now listed as 737GBP!!! :eek:

I hope that's a mistake, because it can't be so expensive! Well, it definitely has to be a mistake, because they have a bigger heater which is about the same price that the one I bought...

 

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...

Max would be 120 I think (ABS 110 around)...

 

Thanks for the info.

I don't know about the thermal adhesive yet, but I should be able to go up to 150°C, although that's the maximum rating for the resistors. So it would probably be safer to set the maximum to 140°C. If that's enough for every printing material, then I'm happy :)

These silicone heaters look interesting, but they're expensive. So maybe my solution may still be of value to someone else (IF it works....).

 

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These silicone heaters look interesting, but they're expensive. So maybe my solution may still be of value to someone else (IF it works....).

 

Seriously, there has to be a mistake in that price, ask the vendor. I only paid 54€ (including shipping) for mine, now it's 860€ that's just impossible!

 

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Hello,

I asked the ebay vendor yesterday : The price is set like this because he is actually out of stock. Price will return to "normal" in approx 1 month when he'll get stock again.

++

Gaël

 

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Lol, that's some way of making sure nobody buys the stuff o.O

I'll see how well the resistors perform. I like the idea of having multiple heater channels, that gives me the chance to eliminate power fluctuations on the PSU (stacked PWM).

The Silicone Heater could be a really good alternatice though, as you don't need another PSU for it, making it the cheapest overall solution...

 

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Just realised it took me 5 months until I got my heated bed working o.O

I finally ditched the idea about using power resistors and went with a silicone heater and Basalt bed from qu-bd (shipped around the world for about the same price as the parts...).

The HBP is heating up to 80°C as I'm typing this. Takes quite some time because the thermistor reading is way off the actual platform surface temperature (it shows 72°C but I can still touch the surface). However I hope that if I just wait some more minutes, the plate will be evenly heated up.

So far I'm just going to test the heating up and cooling down processes. I guess it will take at least half an hour for the plate to cool down from 80°C to 30°C.

I'm not yet ready to print on the thing as I'm still building the clamps to hold the bed in place and haven't adjusted the endstops yet. But so far, it's looking really good.

Guess I'm gonna have to get an infrared thermometer - I can still briefly touch the plate (though it's really hot by now) with the thermistor having shown 80°C for about 3 minutes.

/edit:

Cooldown-update:

Cooldown from 80°C to 46°C takes 22 minutes... without any active cooling measures.

 

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If you can tap the build platform without burning yourself, but not touch it for any longer than that, it is probably close to 90 C. 72 C isn't actually that hot (just 161 F). You could probably pick up and hold something that is 72 C for a little while. At least that was my experience from several years of working in a laboratory.

 

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Got myself an infrared thermometer, but of course I left it at home and can't take a measurement today. I'll report back as soon as I have some measurements.

I've heard that about 50°C is the point where it starts to hurt your fingers. But actually I have never given it much thought myself...

 

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Got myself an infrared thermometer, but of course I left it at home and can't take a measurement today. I'll report back as soon as I have some measurements.

I've heard that about 50°C is the point where it starts to hurt your fingers. But actually I have never given it much thought myself...

 

I calibrated my heated bed some days ago with a multimeter and thermocouple and worked great. I think it's the most accurate way if you stick the thermocouple to the bed with some kapton tape

 

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There's one advantage the IR thermometer will have versus a TC: With the IR I can measure any point on the HBP and determine whether the temperature is even across the bed.

I suspect there will be a significant temperature drop on my 2kg Basalt bed from the center to the edges. But I hope that if I heat it up longer than just what it takes for the thermistor to reach target temperature, it will eventually even out.

By the way: I'm doing the first test prints with my HBP right now. Don't get it to stick yet, but I guess I'm just doing it wrong for the moment. Doing some experiments...

 

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The thing is, I specifically bought the Basalt plate because there is no need to use any interface material (Kapton, Glue, whatever) with it.

The Basalt material is not exactly like glass, it's porous and not 100% mirror flat. That's what the seller says anyways.

I have a huge stock of Kapton tape (like 3 or 4 Rolls) but found it nearly impossible to get it on the platform cleanly. It's really hard to put a string of it on the plate exactly in parallel to the other, without them overlapping or having a gap.

And gluestick is no option in my opinion, I don't want to waste tons of gluestick while printing. I'm planning on making a little 3D printing factory with 3-4 printers which will be running almost all day. Depends on whether the things I'll design will be sellable or not (I'm still in the planning phase).

If you say you heat the platform to 70°C, does that mean that your thermistor says it's 70°C or did you measure the actual surface temperature of the platform to be 70°C (meaning the temperature set in software is probably higher)?

I think the cooling fan significantly drops the surface temperature on my bed. But I didn't complete my experiments yesterday so I'm not sure about that yet.

I will probably be using ABS for any "commercial" prints because they have to be long time stable (30 years and more service time -> storage products like specialised boxes and holders / stands). I hope ABS will stick better because there must be absolutely no warping.

I'll do more testing (with ABS mostly, and with the IR thermometer) tomorrow - today is a busy day :(

 

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I think you will probably find ABS more of a challenge than PLA. I've only printed smallish prints (85 x 85mm) so far but you can control warping to a great extent. It seems to be a careful balancing act with ABS to get the bed temperature high enough to maintain adhesion, but not too high so that it causes massive crystalline contraction. I've found somewhere around 96-97 seems to work with Ultimaker White ABS, but I start at 105 and use TweakAtZ to bring it down to 97 after the first layer. I've just started using Illuminarti's technique of applying glue stick and wiping with a wet cloth to dissolve the glue, then letting it re-dry with the heated bed. It's early days for me, but so far I'm getting more hits than misses. You can print directly onto glass, but I've found you have to keep the bed temperature higher which causes more contraction issues. Also smaller parts will probably be fine when printing directly on to glass without glue. There's always brim which works well. I use a very thin first layer, 0.15mm and really squish it into the bed. I think that's important for good adhesion. You need a really flat and level bed for this though.

 

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The thing is, I specifically bought the Basalt plate because there is no need to use any interface material (Kapton, Glue, whatever) with it.

The Basalt material is not exactly like glass, it's porous and not 100% mirror flat. That's what the seller says anyways.

I have a huge stock of Kapton tape (like 3 or 4 Rolls) but found it nearly impossible to get it on the platform cleanly. It's really hard to put a string of it on the plate exactly in parallel to the other, without them overlapping or having a gap.

And gluestick is no option in my opinion, I don't want to waste tons of gluestick while printing. I'm planning on making a little 3D printing factory with 3-4 printers which will be running almost all day. Depends on whether the things I'll design will be sellable or not (I'm still in the planning phase).

If you say you heat the platform to 70°C, does that mean that your thermistor says it's 70°C or did you measure the actual surface temperature of the platform to be 70°C (meaning the temperature set in software is probably higher)?

I think the cooling fan significantly drops the surface temperature on my bed. But I didn't complete my experiments yesterday so I'm not sure about that yet.

I will probably be using ABS for any "commercial" prints because they have to be long time stable (30 years and more service time -> storage products like specialised boxes and holders / stands). I hope ABS will stick better because there must be absolutely no warping.

I'll do more testing (with ABS mostly, and with the IR thermometer) tomorrow - today is a busy day :(

 

I used a 47K NTC thermistor that I had around and for which I didn't know it's exact specifications, so I calibrated it myself. For this, I measured the actual temperature in the top of the bed with a thermocouple and a multimeter. Of course, this won't be very accurate. With the fan on, the temperature difference between the top and the bottom of the bed will be greater than in my calibration.

In my case I have found that having the temperature in the 65~80ºC doesn't make much difference... In fact, right now I don't have any temperature control for my bed, I just adjusted the voltage in the additional power supply so the bed heats up to about 80ºC if I don't have the fan on, and with it the temperature drops to about 70~73ºC so it's working very well without any MOSFET or relay switching the power by software.

Of course, in the near future I will change this so I can run the entire printer with a single power supply. I'm just commenting it because I think the temperature hasn't have to be perfect. An error of 5ºC won't be a real problem.

But in your case... I'm sure that the thermal conductivity of the basalt is very low compared with aluminum. So the temperature gradient between the top and the bottom of the stone will be much greater. Also the thermal mass will be very high, so the temperature you are measuring can be very different... For example, when the fan turns on, the temperature at the top of the bed will decrease quickly, but the sensor at the bottom won't notice it until much later, possibly minutes, so during this time the temperature can decrease a lot at the top. This is just a guess, of course you should measure it and try to compensate for this errors.

You are right about the kapton tape, right now I have one roll of 10mm wide and it's very difficult to place properly, and the pattern of the kapton will show in the bottom of the prints, but I have bought a couple of rectangular kapton sheets of 20x20cm so this should solve the problem. Also, there are rolls of kapton of 20cm wide and even more but I think the sheets will be easier to place and will be more durable.

 

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My first stage of heat bed is finished. I bought a 200x200 basalt bed, 10 mm thick, and a 12V silicone heater.

The only thing I'm waiting for is a 0.5 mm copper sheet to put in between the silicon heater and the basalt bed. I have done som test printing (PLA) having the bed set at 60 degrees. I have measured the temperature difference at different positions of the bed and they are SIGNIFICANT. (Used a laser thermometer)

Center: 58C

Corners: 27, 35, 37 and 42C.

I definitely need a heat spreader!

My setup is quite simple.

I measued the thickness of the cable from the silicone pad and it was approx. 7 mm. Took 4 nuts that were a little bit thicker. Placed an old mirror on a table (I had one to spare.. but anything flat will do). I placed my silicone heater with the flat side down onto the mirror. Then I placed a sheet of PE-foil (GLAD-PACK, kitchen foil) over it. Then I placed the four nuts a bit away from the silicon heater in each corner. I covered the silicone heater with silicone (air curing - not the best, but I had it at home.). It took a whole tube. After that I put another layer of PE-foil on top of the wet silicone. Then I found something flat stif and heavy (in my case a 20 mm POM-board) and pressed it to the silicone until it layed flat on all four nuts. Then it got to dry..

Not the best of designs.. but well functioning..

Heat Bed v1

 

So, I will probably change the leveling to three-point, but for now it will do.

 

A fun part is that since the friction is high between the silicone and the surrounding materials the bed lies still. No need for extra fasterners.... allthough I will put some in place eventually..

Easy to get around doing to much modifications as the old bed still is the base. Of course I loose some height..but...

 

And, of course.. I had to fit a tube onto toe finger in the back so that the z-homing switch can operate.

 

In total I will loose approximately 18 mm in bulid height doing this but I think I can cope with that..

 

To power the thing I have used a 12V, 12.5A switching power supply, and to this I have coupled a solid state MOSFET relay (3-32 VDC input, 1-50V VDC output, 30A - Crouzet GN 84134870) with no need for cooling flange.

 

 

 

The prints come of just as the store promised, well not all the time, but most of. The rest you just have to put a little force to the piece and it snaps of.. Great!!.

 

One thing I noticed though... The stone should not be completely clean. I rubbed it with my hands to get a wee bit of grease onto it and into the pores of it.... and it worked much better... Can't promiss it will work as smothely using ABS as the temperature will be slightly higher though...

 

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By now I'm not really satisfied with my Basalt bed. The parts always warp off the platform (ABS very badly, PLA just enough to ruin my high precision prints).

The temperature is also not equal across the whole bed, but the maximum deviation is usually below 10K for me. I used RTV106 silicone glue to glue the heater to the Basalt bed. I think that works pretty well and a heatspreader wouldn't make any difference.

Imho the reason for the uneven heat distribution is the stone itself - the Basalt bed is massive in volume, and the "petty" 180W heater just can't heat it up before it's already cooled down on top, especially if the fan is running.

It also makes a huge difference whether you have the bed heated to 50°C or 100°C: 50°C heats up very quickly (about as fast as the nozzle heats up to 220°C) and the surface temperature evens out pretty well after 5-10 minutes. But for 100°C it takes 10-15 minutes to even reach target temperature, and there are bigger drops from center to the corners of the surface.

Also, it takes AGES for the Basalt bed to cool down. From 100°C to 25°C takes much more than an hour. This is especially bad if you want to change the bed temperature during the print - it takes extremely long to adjust even for just 5-10K downwards.

I have ordered some MK3 aluminum heaters, they seem more promising to me than the Basalt bed.

Atm I'm running a 30 microns print, even though it's almost 10pm (I'm still at work) I just can't leave that one, must see how it turns out :D

 

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By now I'm not really satisfied with my Basalt bed. The parts always warp off the platform (ABS very badly, PLA just enough to ruin my high precision prints).

The temperature is also not equal across the whole bed, but the maximum deviation is usually below 10K for me. I used RTV106 silicone glue to glue the heater to the Basalt bed. I think that works pretty well and a heatspreader wouldn't make any difference.

Imho the reason for the uneven heat distribution is the stone itself - the Basalt bed is massive in volume, and the "petty" 180W heater just can't heat it up before it's already cooled down on top, especially if the fan is running.

It also makes a huge difference whether you have the bed heated to 50°C or 100°C: 50°C heats up very quickly (about as fast as the nozzle heats up to 220°C) and the surface temperature evens out pretty well after 5-10 minutes. But for 100°C it takes 10-15 minutes to even reach target temperature, and there are bigger drops from center to the corners of the surface.

Also, it takes AGES for the Basalt bed to cool down. From 100°C to 25°C takes much more than an hour. This is especially bad if you want to change the bed temperature during the print - it takes extremely long to adjust even for just 5-10K downwards.

I have ordered some MK3 aluminum heaters, they seem more promising to me than the Basalt bed.

Atm I'm running a 30 microns print, even though it's almost 10pm (I'm still at work) I just can't leave that one, must see how it turns out :D

 

Of course the warping is dependent of mechanical structure, but considering a square box (or something like it) it should not warp that heavily. The warping may thus stem from uneven temperature distribution in the basalt. 10 degrees will give sufficient residual forces in the part to yield warping. IMHO I think it is important to find a setup were the temperature is as even as possible over the surface.

What I will do if the heat spreader doesn't take care of the temperature differences is to see too that I shield the edges of the plate so that I will only have one radiating surface, and then also change the fan setup to a cross flow fan in a more of closed box.

Maybe the basalt has a to low heat conductivity to be used but that we have to see.. Maybe I will run some thermal simulations to reveal what happens. As it takes long time for the plate to cool it more or less states that the heat capacity is very good - thus yielding a bed that is very little affected of what is going on on top of it. has to be investigated :-)..

 

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The Basalt bed is definetly not "bad". Yesterday I did a print with Faberdashery PLA. It sticked like crazy. No glue or anything, just on the bare bed at 70°C. It only came off after the bed had cooled down below 39°C. The other materials I used came off much earlier, including the Ultimaker blue filament.

I'll be able to make direct comparisons to the MK3 HBP soon, we'll see what happens...

Thermal simulations sounds really good! Few people have access (and skill) to do this, it would be very helpful!

 

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When I get more time I will do some simulations..

In the long run I would like to obtain a very stable, temperature controllable environment in UM. Especially considering the cracking of ABS due to difference in temperature for the printed part..

 

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[..]

Also, it takes AGES for the Basalt bed to cool down. From 100°C to 25°C takes much more than an hour. This is especially bad if you want to change the bed temperature during the print - it takes extremely long to adjust even for just 5-10K downwards.

[...]

 

Did you switch on the fan? Also with just a tiny airflow you can raise the heat transfer rate easily by a factor of something like 6 compared to air in rest.

 

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I have updated the heat bed with a copper sheet under the basalt bed. By doing this I have decreased the temperature spread. I Now have a max 5 degrees difference to the center of the platform. Nice - will lead to much less warping.

However, the thermal difference to the center of the platform varies over the surface - not being a constant drop of as a function of distance from the center of the plate. This implies that the thermal conductivity varies quite significantly over the plate. Measuring the temperature I find that in one corner I have a temperature 1 degree below the center of the platform. In another corner I have a drop of 5 degrees. Turning the plate does not change the behavior for that specific corner so it does not have anything to do with the heating materials under the basalt block.

Moreover, I have done a lot of testing for adhesion and what I can conclude that some filaments stick much better to the basalt than others. Golden PLA (UM) sticks very good. White ABS, at 255C ok, but not sufficient. Silver PLA not at all. But, I have found a nice system that for PLA works fine. I use pink TESA tape ("the tape that does not stick to wall paper"), tape it to the platform and then clean it with alcohol until it feels to start to get sticky. Finishing the printing the tape comes of easily of the platform and the part. Nice..

But, I now will consider changing the heat platform to aluminium in order to increase the uniformity of the temperature and to speed up heating and cooling.

One thing I will test, and I don't know if has been tested, is to use anodized aluminum - and not use tape.

 

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