Sagging MDF, the Q & D fix that anyone can do

From the thread:
[forums.reprap.org]

Quote

..and you will have to attach that to the the y-axis-rib and y-axis-cross rib - if you think about it (and if we for the sake of argument say the heat spreader is not needed) what's the difference between what you are trying to achieve compared and the Q & D fix?...beside a lot of added work of drilling holes and the cost of the extra aluminum?

The sagging corners of the mdf bed will hold the aluminum down and fixed on the 3 point T foundation of the supporting ribs, the corner of the mdf will arrest the aluminum in the horizontal direction

A fix that anyone can do, all you need to do is to drill a hole in the aluminum for the temp. probe
I moved the heat spreader down to support the bed (and the holes in the corners)



Make a hole for the probe:


Cut the corners of the MDF bed:


Back it goes:


Nice and tidy:


Not perfect, but it will do for now


Erik

nice lateral thinking Erik

Ray

Thats save me a lot of time looking for suitable material and also cutting into shape. Thanks for the great idea!

But are you now losing the heat spreader between bed and glass?
Will that degrade the temperature uniformity across the Kapton tape?
Greg

Edited 1 time(s). Last edit at 02/10/2014 03:10AM by GregL.

---

Ormerod #17

Hi Erik, nice solution which I thought I might try, but now have my aluminium sheet.......

Your pictures did make me think..... Do you need to cut the MDF? Would you not get the same result with a three point mount as you are now using?
Looking at my bed the corners both sag so I'm not sure they would have any impact if I only used the central heater mat screw as you are doing and ignore the others.

Just a thought as then at its simplest you just need to remove two screws and put one in the central position. I might just try it!

---

Ormerod #007 (shaken but not stirred!)

Quote
Treth
...Your pictures did make me think..... Do you need to cut the MDF? Would you not get the same result with a three point mount as you are now using?...

No you don't have to cut the front corners of the MDF at all, easier fix not to do it actually, just drill a hole for the probe and place the aluminum on top of the old bed and fix it with the four screws

I hold the front end down with a metal clip (picture do not show, sorry) because the aluminum can not reach the front screw (because of the out-cut for the PCB board) I just cut the corners to save weight and make it easier to access the wiring

yes I use three point adjustment, now only with a spring at the front and the two nearest the duet the old nut adjusting way, I want those two point to be solid as they have to carry the momentum of the bed, other wise the one solid screw could act as a hinge for the bed if the spring loaded one should slip (was very strong spring and not a problem, but just in case it would be)

Very easy fix, just a hand drill to make a hole, no material but the old aluminum plate and I don't find that it is needed as a heat spreader, my Ormerod seems to print just fine without it



Erik

Quote
GregL
But are you now losing the heat spreader between bed and glass?
Will that degrade the temperature uniformity across the Kapton tape?
Greg

I see no difference whatsoever, been printing without it for quite while now

Erik

Has anyone tried printing ABS without the heat spreader? I'm thinking that at the higher temperatures, the non-uniform heating might be more important. OTOH the bed takes so long to heat up anyway that perhaps it doesn't matter.

---

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].

dc42

I should be happy to do a test but that would be my very first ABS print ever so it would hardly prove anything, well maybe I'll go for it anyway

A 180x180mm low side single wall square or such would be a good test object

I did take the bed to ABS temperature and there was no problem with that of cause

..good point about heat spreading over time - comes to think of it - a slower heat distribution might provide greater heat loss at the edges due to the missing aluminum and could make it more important to seal those edges, should be easy to do though

And talk about heat loss, I'm not at all happy with the loose cardboard isolation thing, would prefer some better isolation material permanently fixed to the PCB, I would think science should be able to provide us with something better

Erik

Hi Erik

Neat idea! Most other repraps don't use a heat spreader. We've always found it very useful when printing full trays of parts - they stick much better towards the edges with it, otherwise the temperature fall-off towards the edge of the bed can be 5-10C. You may also find that, without the heat spreader, the bed warms up faster, and will get to a higher temperature, as there is less thermal mass. I'm really not sure what is more important...

Ian
RepRapPro tech support

PS I've been a bit quiet on here recently, as everyone is so much quicker coming up with answers than I am! And I haven't got anything new or exciting to tell people about... yet.

@ ormerod168

Hi I have some material for insulation I will be testing, its a ceramic blanket material designed for insulating furnaces. you have to carful what you buy as some of this stuff is carcinogenic.

I had some on hand from an earlier project and as you can see from the picture I can laser cut it to shape, its about 2mm thick and will handle up to about 1800 degrees c


regards

Mike

EDIT... so far this material isn't performing well at all and it may be that it only works well at really high temperatures so I wouldn't recommend it

Edited 1 time(s). Last edit at 02/11/2014 07:43AM by Mickyblueeyes.

Quote
droftarts
Most other repraps don't use a heat spreader. We've always found it very useful when printing full trays of parts - they stick much better towards the edges with it, otherwise the temperature fall-off towards the edge of the bed can be 5-10C.

Ian, could you not compensate for the temperature fall-off at the edges by using thinner PCB traces near the edges and thicker ones in the middle?

---

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].

Thank you Erik,
I followed your instructions and found this mod very easy to do. I am sure that bed instability has been the root cause of all my problems so I can't thank you enough for a good solution.
I have been thinking about the insulation problem, it strikes me that we need a material that can adjust itself to different thicknesses, my gap ranges from 8mm at the rear to 5mm at the front so something would be more compressed at the front.
I don't know anything about materials especially ones that can stand high temperatures.
I wonder if anybody else has any suggestions?

Thanks again
Paul

Quote
appjaws1
Thank you Erik,
I followed your instructions and found this mod very easy to do. I am sure that bed instability has been the root cause of all my problems so I can't thank you enough for a good solution.
I have been thinking about the insulation problem, it strikes me that we need a material that can adjust itself to different thicknesses, my gap ranges from 8mm at the rear to 5mm at the front so something would be more compressed at the front.
I don't know anything about materials especially ones that can stand high temperatures.
I wonder if anybody else has any suggestions?

Thanks again
Paul

How about loft insulation?

Dave
(#106)

The insulation doesn't need to be very good, so I think the corrugated cardboard supplied is quite adequate. To take up the gap between the heat spreader and bed support created by using bed levelling screws, I suggest putting some squashable plastic foam underneath it, such as the foam supplied with the kit. If that is too thin, either use thicker foam, or a second layer of cardboard as well.

Edited 1 time(s). Last edit at 02/12/2014 09:15AM by dc42.

---

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].

Quote
dc42
Has anyone tried printing ABS without the heat spreader? I'm thinking that at the higher temperatures, the non-uniform heating might be more important. OTOH the bed takes so long to heat up anyway that perhaps it doesn't matter.

Yes finally, and with no problems whatsoever, btw, heatup time was 12 minutes going from 19 to 110C - with 11,4 volt from the atx, 11,4 measured on the Duet's ingoing side

[forums.reprap.org]

Erik

Erik: I've added your mod to the Ormerod improvements page: [reprap.org]

Ian
RepRapPro tech support

Realy nice work.

Can't believe I only stumble upon this now.