Problem leveling hot bed

Hi,

I built a Prusa Mendel II and I´m getting crazy trying to level the hot-bed. I spent a lot of time level it fine to 0.1mm but after some printings it loss the calibration and the hot-end touch the glass.

I though the problem were the springs of the bed but I removed them and the problem remains. I also tried to level the bed when it's hot and more of the same.

I don´t think it´s the bed, may be the Z Axis? But, I checked and tigh everything twice and it seems OK. Also I checked the Z axis endstop and it is fine.

This is my configuration:

- Ball bearings in all axis
- Hot-bed MKII only with screws, no springs.
- 4mm glass
- Z axis nut springs
- Ramps + Pololu drivers

I will apreciate any help.

Victor

What is the Y carriage made from?

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[www.hydraraptor.blogspot.com]

Hi,

Thanks for your interest.

It´s made of 8mm steel rods, LM8UU ball bearings, the standard Mendel V2 bearing supports atached with plastic clamps and a piece of aeronautic grade 5mm plywood. I use a T2.5 belt , an aluminium pulley and a 42BYGHW811 Wantai 2.5A motor.

Victor.-

When I used wood, any type of wood, in combination with a heated bed, the heated bed would deform. Maybe without a heated bed, it might even deform by the heat of the thing you are printing.

If you are printing PLA, I think the solution might be printing on a glass plate, or a mirror, mirrors are usually more exactly flat compared to glass plates.

If you have a heatbed, my own solution has been making it out of two sheets of 2mm thick aluminum. One plate is connected onto the smooth rods, there are four holes in the bottom plate on the same place where they are in the heatbed (MKII). Then, I have made a second identical plate of aluminum, with the same holes, and I connect them together by putting in screws with springs in between, so the top plate is lifted on the screws (M3 inbus bolts). I sandwiched the heatplate underneath the top aluminum plate so it is tightly pushed against the top plate.

Ever since I started with this bed configuration one week ago, I only had minor adjustments. The corners all stay in the same orientation, all I have to adjust from time to time is the Z-height, which I adjust by an added piece of printed part that connects to the side of the right X-end. It's a screw that you can adjust so it defines when the Z-endstop is being pushed in.

Good idea.

I will try it!

Thanks,

Victor

Here's three pictures of how the heatbed is put together. I hope it's clear.

Thanks for the pictures.

I coul'nt find the alu sheet this weekend so I did a test with a piece of 5mm plastic kitchen board (I think it´s made of HDPE which support max. 110 °C) and you are right: the problem is that the MKII deforms with temperature. As you recomended I sandwiched the heatplate underneath the plastic board and the glass and I can level the plate easily.

A secondary effect is that the hot bed temperature rises very very slow and has difficulties to reach 70°C.

¿How fast rises the temperature of your bed with the alu sheets?

I am having no trouble with the heating, the current version I'm using heats up faster than any other heatbed I've used.

But, I'm using a Budaschnozzle with a ceramic heater cartridge, so that heats up like turbo compared to the resistor-based heaters I used before. Because the hotend reaches target temperature, I think (*I don't know for sure) that there is a bit more current when the hotend stops heating up so theres more power available for the heatbed.

The heatbed I use is connected through a relais (/relay), so it isn't powered through the Sanguino, it pulls the power from the PSU directly and only uses the connection of the Sanguino to switch the relais on.

Does this make sense? Anyway, I think the 2mm alu also might heat up quicker than a glass plate that is thicker because it has good heat conductivity and is a bit thinner.

I think Flashmanblack is a bot, the links in the signature are all normal, but the last one is a shop. They are keywords that are looked for a lot in google and all the comments are gibberish.

Admins, fix this account! Ban it or something, at least see if it is a real user?