Getting close enough in my printer build to need to sort the print bed.

3D Printing
, , , ,
1

Getting close enough in my printer build to need to sort the print bed.

Frankly, I would rather just use something on the market, but since my bed is close to 400mm x 400mm, the stock solutions thin out awfully fast. Also, especially for larger heated beds, using AC rather than DC makes sense - which further limits easily sourced beds.

If I were designing an ideal bed, the bottom layer would be some insulating material (perhaps cork), next the heating pad (silicone embedded?), a somewhat-thick aluminum plate (to spread heat), and perhaps a magnetically attached thin steel plate with top-coating (as with the Prusa mk3).

The insulating bottom will prevent wasted heat, and improve heat-up times.

The lower thermal conduction of the steel top layer will tend to force a more even heat distribution through the higher conduction aluminum plate. (Yes, I want to hijack Prusa’s mk3 work, which I assume is excellent.)

There is still a problem with the ensuring the top surface is flat.

We can get milled or “tooling” aluminum plate … at much cost. We could hope that ordinary aluminum plate is sufficiently flat. Or we could accept multi-point “auto-leveling” as always required of an on-temperature bed (rather often).

We could use borosilicate glass as the top - an inexpensive flat surface, that does not distort with temperature. Thin glass is easily shattered if the print head descends a bit far, or other stress. The low conduction of glass means the bed would take longer to temperature, but should give more even heat distribution through the underlying aluminum plate … though if the aluminum plate is not as flat as the glass, uneven contact might mean uneven heat in the glass.

Right. Stacked trade-offs … just not what I want … :confused:

For reference, Sanladerer has some excellent videos:



If I could ensure sufficient volume, there are likely … with enough engineering … more economic solutions. But just now I want to get my printer built, not design a new print bed … so … trade-offs. :confused:

2

If you have any scrap metals dealers near, you might see if they have any mic6 aluminum in their collection. I got a bunch of chunks up to a half meter on a side for $2/kg. It’s ground flat on both sides. My thought when I do the 350x400mm bed on my big printer is to use a piece of mic6 thick enough to drill/tap some 4-40 holes in, then use silicone adhesive to stick an AC silicone heating pad on the bottom, then put a layer of blanket insulation under that, then a layer of plywood, with screws going from the plywood into the 4-40 holes, snugged just tight enough to keep the whole works together without distorting the mic6.

3

@John_Bump On a one-off basis, you are right. There was a local scrap metal dealer (near the massive aerospace research place) from which I bought stuff as a teenager.

But I want to source stuff on a repeatable basis.

4

$46 for 15.75" square at 1/4in thick.
https://www.midweststeelsupply.com/store/castaluminumplateatp5

5

@Stephanie_A Or $35.04 (today) for 19" square plate: https://www.midweststeelsupply.com/store/6061aluminumplate

Right. Again, trade-offs.

6

@Michael_Johnson Keenovo is in my bookmarks…

7

I bought a huge 10mm thick MIC-6 surplus disk for my big delta a while back. Paired it with a 450W 320mm diameter or so AC heater and that sucker heated up quite quickly. Cooling down was another story…

AC is the way to go if you are over 15A to me. I just think it’s a safer. Alirubber on Aliexpress has quite nice silicone heaters.

Something to also mention- buy a good name brand SSR. The Fotek ones are not reliable.

8

My only suggestion of to use an SSR from a reputable source such as digikey… I had a 40A Fotek SSR, such turned out to be a fake 12A SSR…

9

1000w heater is not firesafe you need to choose heater in the way that if the relay stuck or fet shorts your printer bed will not go on fire. You need to choose power that will not be sufficient to go above 150C degrees. 1000w i way too much I would try 200w or something like this.

10

If you need a custom milled MIC6 heat bed with AC Keenovo heater let me know. I can machine to specs and ship a ready to go heatbed.

Here is 400mm sq heatbed I did for my custom build: https://imgur.com/58oWOSX

11

@Kyle1 I would be interested in a heat bed with the size 328x328x5/6mm. I have ordered a Keenovo heater 300x300mm. How to contact you for details?

12

@George_Novtekov I will use a 750W heater with my 300x300 bed, but of course the bed is not connected straight with one SSR to the mains. I will have another relay in between that is switched of by the board on heat runaway alarms.

13

@Gerald_Dachs email me at Kyle@http://elitemachineworks.com

14

@Kyle1 Thanks. I am very much tempted to just buy a properly built, precise build plate. But … in my current exercise I am trying to build the sort of high performance printer I would like to use, at the lowest possible cost.

There are folk here who will say I have made a few dubious choices along the way. They are not wrong.

Having made enough dubious choices to present, adding more dubious choices is not high on my preferred list.

But … seems to stay in theme, I must.

So my print bed is going to be a largish square of 6061 plate (not cast or machined), with a Keenovo heater (a Chinese maker with an unusual reputation for quality), and underlaid insulation. Will see where we get with this minimum.

Going to go with something of an oversized aluminum plate (within my printer’s 500mm^3 space), so as to (much!) reduce printing times for the corner supports. There are some undesirable thermal characteristics to the larger plate … that might not matter.

15

Ha! Just throw throw in a monkey wrench…

A 400mm square 120v Keenovo heater pad is about $110. Larger would cost more, or course.

Bigger heater pads will give faster and more uniform heating. But most prints tend to be smaller.

Assume we are talking about an enclosed printer, where the print bed has an insulated bottom. For large / long-running prints, the chamber will reach equilibrium, and the heated bed need only offset heat loses through the sides of the printer.

The main challenge on the heater is to bring the print bed to temperature, from cold.

For smaller prints, waiting for the larger bed to heat is a waste. For larger prints, the time to heat the print bed becomes less significant compared to the time required for the print.

If an aluminum slab (the heat spreader) is topped by a glass or stainless steel plate, that will tend to force heat more uniformly to the edges of the aluminum.

All the above tends to argue that we could use a smaller heater pad.

For smaller prints, the center will reach temperature quickly., even with a smaller heater. For larger prints, the start time is much less significant (by roughly a cubic factor). This tends to argue for a smaller heater, with software correction to require larger start times for longer prints.

For a single money-is-no-object printer, you want the larger heater to reduce the individual design/print cycle. If you are building an entire print farm, smaller heaters might be more cost effective.

16

FYI, after a bit of dithering, ordered a 400mm x 400mm 120v Keenovo heater, and a 17.75" square x 0.25" thick 6061 Aluminum plate. (Ordering metric sizes in the United States is not practical.) Did not order “tooling” plate, so will see if flat enough.

That will give me a ~450mm plate, smaller plastic corner braces, and about an inch of space inside the frame for any intrusions … and a few weeks to wait.