Update: I completely uninstalled Repetier host and all associated settings (including slic3r settings) from one of my PCs and reinstalled using the RH download from the solidoodle website. The printer seems to be working a lot better, so must have been down to conflicts in some settings somewhere.

Before I was using the very latest RH downloaded from RH website, which I had configured myself for solidoodle.

Wardjr: I have tried levelling the bed using a dial gauge and when it moves from front to back I can see the dial gauge change as it moves across the bed. I am trying your suggestion of using hairspray to hold it down. In my case hairspray didn't work, but spray-mount did.

Hairspray needs about 3 heat cool cycles to stick.

Before I was using the very latest RH downloaded from RH website, which I had configured myself for solidoodle.

Wardjr: I have tried levelling the bed using a dial gauge and when it moves from front to back I can see the dial gauge change as it moves across the bed. I am trying your suggestion of using hairspray to hold it down. In my case hairspray didn't work, but spray-mount did.

Now I understand. That makes sense I will try that.

However, I have now come to the conclusion that the first layer of the model (excluding brim and skirt) is being printed 1 layer height above the bed. That is, the brim and skirt print fine, then the bed lowers 1 layer height before the first layer of the actual part prints.

Try setting first layer height to the same as other layers in your profile.  I always thought brim and first layer were the same but maybe not.  Also set z-offset to zero I have always had mine set to zero.

However, I have now come to the conclusion that the first layer of the model (excluding brim and skirt) is being printed 1 layer height above the bed. That is, the brim and skirt print fine, then the bed lowers 1 layer height before the first layer of the actual part prints.

It is difficult to tell, but generally the outer parts (say 25%) are very high, and the centre is very low.

Also, i noticed yesterday when printing and in the gcode that the first layer of the gcode is split. That is the brim is layer 1, and the perimeter and infill are layer 2.

There is also a noticeable drop of the platform when it goes to layer 2. Obviously the brim is not a full layer height, but it's like the gcode is trying to print the perimeter and infil in thin air, which would explain the why things closer to the middle aren't sticking.

Also, I use clips to hold the glass on. I don't want to stick the plate on with tape as I like to be able to swap over the glass beds quickly if I damage the kapton on one, or they need a good clean.

Would only using 2 clips help? i.e. one centre rear, and one centre front

Just to be clear I never suggested you tape your glass to the bed.  Use hairspray to hold the glass to the tape ready on the bed.  This allows the glass to sit level and holds the glass in place.  The glass is still very much so removable.  As far a two clips or not I say any clips are too many as they just aren't needed.  Plus the added benefits of no warped glass an your extruder won't crash into clips.

If you look closely you can see in the front view that the second layer is above the print bed.

1. Front view of layer 1
2. Top view of layer 1
3. Front view of layer 2
4. Top View of layer 2

I am getting really fed up of slic3r.

Will start a new thread.

Also, i noticed yesterday when printing and in the gcode that the first layer of the gcode is split. That is the brim is layer 1, and the perimeter and infill are layer 2.

There is also a noticeable drop of the platform when it goes to layer 2. Obviously the brim is not a full layer height, but it's like the gcode is trying to print the perimeter and infil in thin air, which would explain the why things closer to the middle aren't sticking.

Also, I use clips to hold the glass on. I don't want to stick the plate on with tape as I like to be able to swap over the glass beds quickly if I damage the kapton on one, or they need a good clean.

Would only using 2 clips help? i.e. one centre rear, and one centre front

Glass will not warp, your post is not clear.

Something seems wrong in your report of the situation...If glass warps permanently, it has plastically deformed, in which case it would have shattered since it has almost no plastic deformation range when below its transition temp, and we def be below the transition temp.

Most glass sold is very flat, because of the process of making glass. perhaps your glass was not flat when starting, but that is also a bit fishy.

Hmm.. I'm puzzled.

EDIT: I would look at your rails? Maybe something is wrong with them? This is a stretch.

So you are certain the problem with edges pertains to *all* the edges? Because if it's biased in to one or more edges, that might tell us something.

+1 on the rods.
Go buy some cheap plate glass cut to size at any hardware store.  If your bed is truly warped you can add strips of kapton tape to the low areas.  I have an SD3 with a warped aluminum plate and to get my glass to sit flat I put an extra layer or two on the two sides that were low.  Then I just use hairspray to stick the glass to the bed (2 or 3 heat/cool cycles).  Clips on the glass can warp the glass very quickly to match your warped bed so avoid them.

Something seems wrong in your report of the situation...If glass warps permanently, it has plastically deformed, in which case it would have shattered since it has almost no plastic deformation range when below its transition temp, and we def be below the transition temp.

Most glass sold is very flat, because of the process of making glass. perhaps your glass was not flat when starting, but that is also a bit fishy.

Hmm.. I'm puzzled.

EDIT: I would look at your rails? Maybe something is wrong with them? This is a stretch.

So you are certain the problem with edges pertains to *all* the edges? Because if it's biased in to one or more edges, that might tell us something.

I am finding that after only a few prints, they seem to warp. Filament being printed at the outer edges is all blobby (bed too high), whilst at the same time filament at the centre barely sticks at at all (bed too low).

I have a reprap style pcb heated bed on one SD3 and the standard silicone heater on the other. Both usually running about 95 degrees, printing with natural ABS. Both have the same problem.

I bought 8 tiles in a pack, I'm wondering if they were like this from the beginning.

Anyone else find this? Can anyone recommend some better quality sources of glass (preferably UK)?

Printer 1 details:
SD3
solidoodle 0.35mm hot end
PCB heated bed
Lawsys Mk5 extruder
Lawsys carriages
Bubble wrap cover
M5 Z axis upgrade

Printer 2 details:
SD3
0.5mm J-head
Standard bed heater
Lawsy mk5 extruder
Standard carriages
Bubble wrap cover
M5 z axis upgrade