How To Quick Heat A Bed

I got tired of waiting forty or more minutes for my PCB heated bed to get to 110, so I decided to do something about it.

I went to the home improvement store and got a 8mm x 300mm slab of granite and asked them to cut it to 200mm square. (I actually had to ask them to cut it to 7-7/8" because you say mm and they just give you a dumb look.) When I got home I put it on my smooth top stove (which has a burner big enough to accommodate this) and heated it to 150, using my IR thermometer to measure the temp. I removed it with a set of pliers, set it on a board for transport, gently laid it on my naked bed, and turned the bed on. I held my glass about an inch over the stone and slowly lowered it to the surface of the stone to give it time to heat up without busting. Within ten minutes my bed was at 110. I slid the glass back until it was offset from the stone about an inch, lifted one end of the stone with a knife, grabbed it with a pair of pliers, and slid it out from in between the stone and the glass being sure note let the glass crash down onto the bed. Clipped the clips and I was ready to go.

Well that would do it!

My PCB Prusa Mk2 bed takes about 15 minutes to reach the same 105-110°. Odd that there is so much variation?

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Yvan

Singularity Machine

That sounds like quite a process to begin each print. It seems that those PCB heatbeds do not perform consistantly. I have one and can heat to 110C in about 10 minutes with no insulation underneath it at 12 volts yet other people report taking much longer to heat.

The more wattage your bed uses, the faster it will heat. I finally got a hold of the rep from the place I am looking at for the beds for my printers. The good news is, he has the capacity to make whatever I need, with the exception of thermocouple only versus thermistor. The bad news, he really is not interested in selling only one. I told him I want a 3-5 minute time to 120C. I should have a price next week.( I was up front with him that the second machine will not be out by next month. )

For fast heating, I use a McMasterCarr 35765K31 heating pad. It takes a few minutes for the glass bed to get to temperature. It runs on 115AC, so you need to use a SSR to control it.
It the pad itself heats up in a few seconds and can go above 170C, so I installed a thermal fuse for safety. The setup from bottom to top: insulation, heating pad, 1/8" 6061, borosilicate glass topped with PET.

appdev, would you know how many ohms you get across the two contacts on your bed? Both of mine are 1.4 ohms. Can you check amperage while in use? That would be the real indicator. I get the feeling it must be well below 11 amps with yours.

Anyone else have those numbers for their PCB bed?

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Yvan

Singularity Machine

One way to heat up rapidly is to use an insulating cover for the bed. I use a 200mm square piece of 6mm mdf with two layers of metalised bubble fim glued to the surface.
You do have to make sure that you take the cover off before starting to print though.
Mike.

i am pretty satisfied with warm up time. for pla cca one minute.for abs(110 degrees) about five -10 minutes.

i turn on preheat, when i set up parts on board, slice them few minutes and it start to run..

i have few sheets of paper under heated, warmup time alot faster with some isolation under bed

Edited 1 time(s). Last edit at 07/27/2013 05:50PM by woo.

Maxx Mayhem Wrote:
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> The bad news,
> he really is not interested in selling only one. I
> told him I want a 3-5 minute time to 120C. I
> should have a price next week.( I was up front
> with him that the second machine will not be out
> by next month. )

So what is his minimum quantity?

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Yvan

Singularity Machine

I think there is one important thing to note about my setup, I built per the prusa mendel instructions at the beginning of the year. At the time these still had the double plate design, so my heat bed is sitting directly on a sheet of MDF. It has to heat that sheet to. I asked around at the time about pic I seen of the single plate bed with stand offs for the PCB and was advised to follow the current design.

I put an insulator on top of my bed while preheating too. Its a cloth diaper!

I will check my ohms, from the end of the wire, but I used large guague speaker wire and it will prob add a little bit of resistance.

Yvan, he mentioned 5, would be his preferred low number. If this machine pans out, I would like to produce it(with a lot fewer parts to be certain) and I told him this. So I'm waiting for a quote before I get too excited...

appdev, oh I see. I started my Prusa i1/2 about the same time you did, but it got shelved till a couple of months ago. So I ended up putting my PCB on standoffs. Same thing with my Prusa i3, I printed some of the first generation parts, and I'm assembling it now. I'm guessing this is part of why you're upgrading to an i3...

Maxx, wow, five units is a very low number. If the price is not crazy that is not bad at all. Maybe I should call this guy...

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Yvan

Singularity Machine

40 minutes, wow. I thought my gheto stripboard HBP was slow. I'm pretty sure it does better than 5 minutes. I'll have to time it. Fully customizable and only about $5 for materials.

OK I lied. I guess time just seems to pass quicker when I'm in the shop working on/with my 3d printers. Anyway, in real time it takes about 10 minutes to 100 C and 14 minutes to 110C. If I put a folded dishrag on top it cuts the time down to 6 and 8 respectively.

I wonder if appdev007 could get similar results with a hair dryer or hot air gun without the hassle/danger of carting a hot slab of granite around.

Or even better, a heat lamp, a hot air gun and a space heater all at once. Hmm, maybe a fresnel lens matched to the heat lamp. Perhaps just a second HBP board that you could lay on top to speed the heating and then take off for printing. Propane torch anyone?

Edited 2 time(s). Last edit at 07/29/2013 03:30PM by bryanandaimee.

bryanandaimee Wrote:
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> Or even better, a heat lamp, a hot air gun and a
> space heater all at once. Hmm, maybe a fresnel
> lens matched to the heat lamp. Perhaps just a
> second HBP board that you could lay on top to
> speed the heating and then take off for printing.
> Propane torch anyone?

Acetylene! Acetylene! That's what I use when I want lots of heat fast.

BTW, drilling a hole horizontally into the granite might make it easier to pick up.

Edited 1 time(s). Last edit at 07/29/2013 06:05PM by Yvan.

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Yvan

Singularity Machine

Tried the hair dryer, not enough heat. Don't got a heat gun or heat lamp, but considered both, might work. And don't think I didn't consider fire, but I don't think my normal glass or the PCB would hold up.

Like the second PCB idea, hadn't arrived there yet. They are rather cheap. Been considering witching to AC right out of the wall, but just don't like the idea. I might be willing to do it with the second one since it would be removed for printig and away from the printer.

I guess I will either have to switch my i2 to single plate bed with PCB standoffs or put up with it until I get around to implementing the i3 upgrade I have sitting in wait. But, I just fixed about four issues with one fix and my i2 is running pretty damn good now. I was upgrading to i3 to solve some of those issues.

Or you could just get another Prusa HBP and hopefully it is a better one than the one you have now. Maybe cut your time to 10 minutes. Swap out. Then you could use the old one to speed things up when you are really impatient. I still like the heat lamp and Fresnel lens though. I might have to try it some day. I have an 9x11 inch lens somewhere around here.

My heated bed takes less than 3 minutes to get up to temperature.
The heater pad is a mains powered silicon pad with the 100K thermistor built in.
The Mosfet that normally controls the power to a 12 volt pad is used to operate a solidstate relay. The solidstate relay switched the mains power on and off as needed.
Very simple upgrade, uses a lot less power from the 12 volt supply so there is ample power for all the other 12 volt items.