Heated bed issues.

[mrbi11]

Ok, I saw a post about someone who made a 1/4" aluminum bed cover, and i have spent 2 hours searching and googling and I cannot find it again.
>>>> Did I dream that or can someone point me to the post with the 1/4" bed plate build?
(NOT the 1/8" plate.
BTW, the forum thinks it unreasonable to search for 1/4 says "1 and 4 are too common"
NOT helpful in a build forum to treat fractions as 2 numbers.)

My onyx bed has the usual hotter in the middle problem, which I must solve to make large prints.
I'm leaning toward aluminum plate. My standard setup is 50 C on printable edge then center is 100 C.

Questions:
I also see aluminum foil as recommendation. How much benefit does that have?

Calibration:
The issue is that changing temp changes the surface curve. Edges HAVE to be cooler,
so hotter center must expand, and that must go somewhere. So the curve changes
depending on the bed temperature, so the calibration for ABS cant possibly work for PLA,
at least not over the whole print surface. I would expect the software to handle this,
such as giving it a "hot" and "cold" calibration, and making an interpolated Z axis adjustment
based on both the Z zero measurement and the Radius correction. In other words,
for a given bed temperature, it should be straight forward to calculate the correct
calibrations between the hot and cold settings.

I may fix the software myself, but this is such a large change, I'd like to know
my effort may be incorporated into the main product. Any way to submit bug fixes?

As it is now, if you have a big print, you had best recalibrate of you make any significant temperature changes.

Problem solved(not)
Hint, as a workaround, I set my first layer thickness to about double, instead of 0.35 I used 0.6
so while the surface calibration may be .3 mm off, a .6mm first layer will at least do SOMETHING
if it is too high or too low. I was getting parts of the bed with nothing printed because the head
was touching the glass. 0.6 is larger than recommended for 0.5 head, but its just to get the thing stuck down,
and has the added effect of "leveling" the virtual print surface slightly. This allowed me to print
a 138mm by 1mm circle. which came out decent. I will post the gcode if anyone wants it. Slicr3r can
generate bad code printing that big.

What Temp?
I have recommendations for ABS from 70C bed temp to 110C bed temp? What is the right answer?

[mrbi11]

fyi to anyone, aluminum foil does not appear to help a whole lot.
Edges were still 50C with center at 100.

[Flateric]

I'm running 1/4" aluminium heat dis. plate. Cut myself one and that was the only thickness I had handy at that time.

I have found that the thicker build plate results in a slightly longer heat time but a more even overall temp across the entire bed. I also do not seem to suffer from the extra hot central problem.

I can see alu foil acting far more as an insulator then a "spreader" Also the foil would be hard to get to adhear to the build plate and the printed piece without tearing issues and the foil itself does not really lend well to being a "sticky" surface.

Your ABS bed temp it's about right on the money with your stated range of temps. Color and source of filament can require variances in this temp.

I generally find the Polycarb and Nylon can be printed extremely well on a UHU glue stick prepped surface. This is against the generally believed to be popular temp and surface prep. But with nylon I don't get any real warping. Nylon 645 that is.

Let me know if I can help any further.

[Eaglezsoar]

I'm running 1/4" aluminium heat dis. plate. Cut myself one and that was the only thickness I had handy at that time.

I have found that the thicker build plate results in a slightly longer heat time but a more even overall temp across the entire bed. I also do not seem to suffer from the extra hot central problem.

I can see alu foil acting far more as an insulator then a "spreader" Also the foil would be hard to get to adhear to the build plate and the printed piece without tearing issues and the foil itself does not really lend well to being a "sticky" surface.

Your ABS bed temp it's about right on the money with your stated range of temps. Color and source of filament can require variances in this temp.

I generally find the Polycarb and Nylon can be printed extremely well on a UHU glue stick prepped surface. This is against the generally believed to be popular temp and surface prep. But with nylon I don't get any real warping. Nylon 645 that is.

Let me know if I can help any further.

Does the 1/4" plate eliminate the "doming" effect that a lot of users see with the heated bed?

[mrbi11]

I'm running 1/4" aluminium heat dis. plate. Cut myself one and that was the only thickness I had handy at that time.
....

May I ask how you cut the circle? Did you buy regular stock alum plate or cast?
I was going to make my own, but with "flatness" needing to be within about 0.1mm
I'm obsessing (possibly for no reason) about whether I will cause the surface to become uneven.
I see another forum thread where cutting 1/8" plate went way wrong. So its not entirely sky is falling concern.

I can get 1/4" 12x12 plate of course. probably 6061. I assume that is sheer cut, and wonder how flat it is.
To cut I have a hand held metal cutting band saw, works well for steel. I assume it would cut aluminum ok.
I have no experience regarding the effect of cutting on tiny warping.

[Eaglezsoar]

I'm running 1/4" aluminium heat dis. plate. Cut myself one and that was the only thickness I had handy at that time.
....

May I ask how you cut the circle? Did you buy regular stock alum plate or cast?
I was going to make my own, but with "flatness" needing to be within about 0.1mm
I'm obsessing (possibly for no reason) about whether I will cause the surface to become uneven.
I see another forum thread where cutting 1/8" plate went way wrong. So its not entirely sky is falling concern.

I can get 1/4" 12x12 plate of course. probably 6061. I assume that is sheer cut, and wonder how flat it is.
To cut I have a hand held metal cutting band saw, works well for steel. I assume it would cut aluminum ok.
I have no experience regarding the effect of cutting on tiny warping.

A lot of users have used this site for cast aluminum circles (Mic-6) but they will still need cut to size. I had a machine shop cut mine.
http://www.sandsmachine.com/alumweb.htm

[Fiddler2070]

fyi to anyone, aluminum foil does not appear to help a whole lot.
Edges were still 50C with center at 100.

I think you're using the really thin regular aluminum foil. I used heavy duty foil. After 4 minutes the center was 48C (bed set to 50C for autotune), edges were at 38C. So only 10 degree difference. better than plain glass, not as good as 1/16 inch aluminum plate.

[Flateric]

Very long in my reply to this thread, very sorry about that.

I cut mine on my own cnc mill with flood coolant. Alost taking much light cuts than I normally would have to minimize and heat buildup.

I imagine that the practice would be very similar with a bandsaw, use lots of coolant/lubricant and take it slow and easy.

God I do not remember now if I did a heat relief process or not to it before putting it to use. I remember wanting to....but not sure.

Wouldn't hurt I suppose.