PCB Heatbed curved

while z-homing with a papersheet i recognized that the middle of the bed is higher then the edges (in x-direction).

after disassembling the bed for daveks mod i can see that:
o the glass is flat
o the pcb heatbed is curved (pls see the picture)

it seems that the pcb heatbed forces the glass the be also curved

any suggestions?

When I looked into this a few months ago, I discovered there were two causes of this issue:

1. A very slight doming of the glass, because it is clamped at the corners. This effect is small, perhaps 0.05 to 0.1mm. Using 4mm glass instead of 3mm instead should reduce it by more than half.

2. The main contribution is the hot end angle varying along the x-axis. One cause of this is the varying sideways force exerted by the Bowden tube on the hot end, which pushes the hot end sideways and the nozzle down harder in the middle of the x-axis than at the ends. Another cause can be a wave in the acrylic x-plate.

I've been wondering whether it would be worth implementing 5-point bed compensation (i.e. 4 corners + the middle) or 9-point (4 corners, 4 edges + middle) in the firmware, which is a possibility when using a z-probe that works anywhere on the bed, such as my differential IR board.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I think the actual doming of the glass (from clamping it down) is even less than that. But on the other hand, both the bowden tube as well as the weight of the hotend (causing the X axis to "sag" a bit) actually cause the hotend to move in an arc (as opposed to a straight line) which makes the glass seem curved when measuring.
In the Y direction, having the two rods not exactly parallel makes the whole bed "twist" a little bit as it moves, which has a similar effect.

so, the curved PCB should be not that problem.

my next steps will be:

o upgrade the bed, x rib and x plate (davek aluminium mod´s)
o check the whole printer for "parallelism"
o change to swiss clips - maybe more than 4 pieces for better force distribution
o if the doming is not better i will change to 4mm glass
o upgrade to dc42 differential IR board - sure a accordant bed compensation would be cool!!!

You might like to check the bed heights in the middle of each edge, as well as at the corners and the centre. That should give you an idea of how much is caused by doming of the glass, and how much by the x-axis.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

When I first leveled my bed after giving up running it in compensation mode, I found that the jacking screws looked crazy. My bed was level, but one end there was about 3mm of free screw thread showing, and the other only 1mm.
The following morning I looked in to this more, and found that the Main Bed Support Beam (that bolts to the bearings) was not level, but had a slope of about 2mm.
So I stripped the bed off, leveled the Main Beam, and replaced everything. That cured that problem.
As far as the curved Heat Plate is concerned, I'd rest it upside so the doming was pointing upwards resting on blocks at the edges, and place a few old paper back books (to use as weights) on top, and leave it over night.
If you really wanted to speed things up, you could connect the Heated Bed up, and power it up, and heat it up, cool it down, repeating 5 ot 6 times, and that should straighten it.
When they etch the Heated Bed, the Gaps between the Heater Rails is eaten away by acid, and can cause the Bed to curve. It can happen to any PCB, but isn't a show stopper.

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Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete

like that :-) :

Quote
FastFlyingFox
so, the curved PCB should be not that problem.

my next steps will be:

o upgrade the bed, x rib and x plate (davek aluminium mod´s)
o check the whole printer for "parallelism"
o change to swiss clips - maybe more than 4 pieces for better force distribution
o if the doming is not better i will change to 4mm glass
o upgrade to dc42 differential IR board - sure a accordant bed compensation would be cool!!!

Hi
Points 1-2 are sound, since fitting my own aluminium upgrades, my ormerod is running better than ever, I have been running some parts for use in my day job as well as printing a large filament spool holder which used practically all the bed on the printer. I was most impressed in that I could warm the bed, home all axes, wipe it with IPA and start printing immediately, all prints have worked perfectly.

I am not using any bed compensation but have also fitted the 10mm bearing in the x runner which also helped a lot, having the head at 90deg to the bed seems very important and is worth checking, this bearing should be a 10mm one in the kit and not a 9mm as supplied.

I'm still using the standard bed clips and standard glass with Kapton on top, I also have DC42's first IR probe board with the fan switch which is brilliant and I find the modulated sensor works well too.

The issue I have with bed comp is that it knackers the z screw so any way of getting rid of using it can only be good, in all I have probably spent 2-3 days levelling and tweaking my bed but it's worth it.

Edited 1 time(s). Last edit at 06/20/2014 02:35PM by Davek0974.

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Another RS Ormerod Mk1 meets the world

Retired now but I used to make....
CNC Machined Mk1 aluminium bed support plates for the Ormerod
CNC machined X-plates and ribs for Mk1 & Mk2 Ormerods
CNC machined bed support arms for the Mk2 Ormerod.
Dual Hot-End heatsink blocks.