A new bed for the UM2

[shiremog 0]

I'm new to 3D printing. This has dis-advantages ( I don't know what I'm doing :???: ) and advantages ( no pre-conceived ideas of how things should be done ).

Having played with the new UM2 for a month or so, it seems a well thought out & put together machine which produces good results ( when you've worked out how to use it!)

The one weak point to my mind, is the bed. It's too flimsy. It narrows at the back edge where maximum leverage can be applied. This is made worse by two cut-outs at the weakest point. I'm sure we've all had prints which self-destruct when the bed judders as the nozzle crosses the fill...So I decided to play:

First I tried these two aluminium tee strips. They were fixed with double-sided tape, not ideal but it worked. Before fitting them, I measured the deflection on the outside edge of the table when a weight was added, then measured the deflection after fitting the strips. The deflection was reduced from 0.018" to 0.012". I found a significant improvement, with noticeably less judder. Encouraged, I decided to go for it & make a complete new bed:

Top face. Note the integral bearing brackets with strengthening buttresses.

Underside. Strengthening ribs all around. The deflection test showed a reduction to 0.004". So far I've not managed to get any judder, even at high speed. It might be my imagination, but the surface finish also seems better.

The new bed was cast in aluminium, using a pattern printed on the UM2. It had to be made in 6 pieces, which were glued together. This may be a bit extreme, but it shows that anything which stiffens the bed is an improvement!

 

[anon4321 16]

Cool, did you cast it yourself? Like with sand and a furnace?

Actually, the UM2 bed is considered to be pretty good. In fact, the UMO bed upgrade kit is very similar to the UM2 bed and is considered to be a worthy upgrade.

And when you say glued together, I assume you mean the pattern and not the bed itself.

 

[shiremog 0]

Yes, home cast, green sand. & yes, it was the pattern that was glued!

 

[anon4321 16]

That is very cool. You are obviously experienced at foundry work.

However, for others interested in foundry stuff, I found this guy on youtube that is a former metal shop teacher. He does a lot of machining but also foundry work. He's has a lot of lathes and mills in his workshop.

He has a series on casting a small steam engine. I believe in later videos, he does the machining for the steam engine.

Here is part one, you can find the other parts on his channel:

 

 

[anon4321 16]

Did you have to do any machining on the bearing holders?

 

[shiremog 0]

Yes. That's the trickiest bit as they have to be at exactly the right distance apart.

 

[drayson 74]

Great!!! If I had an UM2 I would order at you :-)

Like the nice metalwork...

[anon4321 16]

Yeah, I wish you had access to do this to a UM1. I'd send you money as soon as possible. I wish I had access to a mill.

 

[tinydancer 0]

How much heavier is the bed? Just wondering since a significant increase is going to put more stress on the z-axis rod. I'm not an engineer though.

Regardless, that's very cool.

 

[shiremog 0]

There's about a 50% increase in weight. The effect on the shafts & bearings should be minimal. The potential problem would be the end load on the stepper motor. I've not been able to find that value in the specifications for the motor, but if the worst happens & the bearings die, I'll fit a thrust bearing to take the load.

The increase in weight has an advantage: greater mass damps any vibration, result: better finish!

 

[visu-al 2]

i like that cause i hate it sometimes @ infill printing it starts wobble and that creates some peaks of material were it goes over next time and wobbles even harder and creates higher peaks until the whole thing souns terrible but most of the time this doesn't destroy my prints and creates a nice finish still at the end..

 

[donmilne 2]

How does this affect the heating of the bed? I would have thought you have effectively added a large heatsink. Temperatures will be more stable, but harder to reach. Also potential burnout of bed heater.

 

[visu-al 2]

is it possible to just add a stronger heatunit that uses its on power supply ?

(i mean obviously it is but without changing something else just plug in the allready existent cables/plugs)

 

[shiremog 0]

There's a large air gap between the bed & the heated plate, so no problem. It that respect, it's no different to the standard bed.

 

[chrisr 18]

Will you be making anymore.... maybe to sell? (hint hint) :-)

 

[visu-al 2]

i would buy one :-P

 

[shiremog 0]

Don't think so, much too time-consuming!

 

[chrisr 18]

Don't think so, much too time-consuming!

 

Shame - looks great! Well done :-)