Hello all.
I'm slowly working my way through building a prusa.
I made a decision to use 6mm alluminium for the bottom plate and 6mm MDF for the top. I'm planning to put a square of gasket material, then MK1 heatbed, then a sheet of 3mm glass.

I have not purchased the glass yet and am at 943g so far.

Are there any motor torqe/speed issues with regards to print bed weight?

Yes, you want to be as light and rigid as possible.

Ditch the 6mm plate for the bottom, that's just way overkill.

You can use LM8uu holders or a full printed Y carriage.

Have a look at using Di-bond for the lower section and to support the heated bed - above the Y carriage.

Fit the heated bed PCB on top of the Di-bond supported by M3 metal Hex stand-offs, cardboard and foil thermal insulation under the PCB and 3mm Mirrorglass on the top, bulldog clipped front and back.

It's all very light-weight and can move very quickly with high acceleration.

Don't use any springs or anything that can move, Once you have it level, it will stay that way.

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[richrap.blogspot.com]

Ok. Will ditch the 6mm.
I like the sound of a printed y carriage but will save that for the next one.
I have a 3mm Aluminium at work so I think I'll use that and make it like swiss cheese.
No springs. I assume I level it with washers under top plate. Will stick with 6mm MDF as it's pretty light. Will look into di-bond if I get through this one ok.

Thanks.

Printed y carriages introduce a ton of issues. Go with the holders!

I have to say that I've had pretty good luck with TommyC's printed y-carriages (http://www.thingiverse.com/thing:23880). They print well and are pretty strong, even when printed with PLA. If you do choose, at some point, to use a printed y-carriage, make sure to measure your y-axis smooth rod spacing. Mine were nearly a half millimeter narrower than "spec", sure doesnt sound like much but can be an issue at the limits of bed travel. I've been using the following assembly with great success: printed y-carriage, printed spacers, 1/8" MDF, MKI heated build plate, 3/16" aluminum plate, kapton tape.

I just used 10mm ply for my bottom and top plate with cutouts in the top plate for the wires from my heated bed and thermistor.

I held these off with a screw head bolt recessed through the top ply, then nut under the top plate, then small spring, bottom plate and lock nut under the bottom plate.

The spring between the top and bottom plate has saved my setup a few times when the z stop micro switch moved and the print head tried to bury itself into my glass top plate.

I haven't had a problem with the top plate moving due to the spring setup yet.

Hi:

I second the weight issue. My Mendel uses a 6mm AL plate I had handy. It limits my feed/speed rate or the y axis misses steps. 30mm/sec is OK, but no more. I am planning on a lighter bed soon.

j

WildBill Wrote:
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> Printed y carriages introduce a ton of issues.

Like what?

I would like to use a printed y carriage, so I too am interested in hearing about its possible problems.

thx.

Printed y-carriages introduce no issues. I used one extensively on my Prusa Mendel. They are light weight too.

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I did some testing with a printed Y carriage of my own design, which I chose not to release due to the following issues:

1. It consumes a lot of plastic and takes 9 hours to print.

2. Despite the design being optimized for stiffness, it was still not as stiff as the thin steel plate that I was using before. It had noticeable vibration during movement, and a light touch could bend the bed out of alignment. Usually it would rebound to close to level.

3. I printed it in ABS, because PLA would have fallen apart when the heatbed PCB was used for ABS. Even in ABS and even with insulation it would sag when heated, and the bed would drop by 0.5mm or so.

For these reasons I judged it inferior to the galvanized steel plate I was using previously. In order to use it I had to carefully check the bed level and multiple locations before every print. With a steel carriage the level is extremely stable over time.

The best material I have found for the Y- carriage is 3mm dibond. It is light, stiff and stable. You can buy it cut to size online and doesn't const much but the postage is more if you only want one. It is also easy to cut and drill.

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[www.hydraraptor.blogspot.com]

I just poked around on the internet and found it offered in full 4'x8' sheets at $200+ for 1 sheet in 4mm thickness.

Nophead, where did you find it that had "reasonable" prices?

[www.cutplasticsheeting.co.uk]

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[www.hydraraptor.blogspot.com]

Try your local sign-writer. I purchased an offcut from a local sign-writer business. $10 gave me enough for 4 printers.

Also Dibond is a trade name, there are other companies that make the same sort of thing with different names: Reynobond, Alupanel, Alcom. I haven't looked at the specs of these to see if they are identical.

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[www.hydraraptor.blogspot.com]

Down to 530g minus glass.
top plate
How exactly do the springs help. I assume you have a mechanical stop for the z axis and set it up so springs don't bottom out before this?
What breaks if there are no springs?

crispy Wrote:
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> 1. It consumes a lot of plastic and takes 9 hours
> to print.

The one I'm using took 70 grams of plastic and 4.5 hours, which is not all that much.
Lm8uu Y Carriage for Prusa Mendel V2 printed in one piece with about 124x175 bolt pattern.

> 2. Despite the design being optimized for
> stiffness, it was still not as stiff as the thin
> steel plate that I was using before. It had
> noticeable vibration during movement, and a light
> touch could bend the bed out of alignment.
> Usually it would rebound to close to level.

I'm not seeing any vibration and the stiffness in the directions that are needed during printing is more than adequate.

> 3. I printed it in ABS, because PLA would have
> fallen apart when the heatbed PCB was used for
> ABS. Even in ABS and even with insulation it
> would sag when heated, and the bed would drop by
> 0.5mm or so.

Only an issue if you need to run the printer with both a cold and hot build platform. Otherwise you can level it while hot and just not worry about it.