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shiremog

A new bed for the UM2

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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:

Original bed

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:

New bed

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

New bed

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!

 

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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.

 

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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:

 

 

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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!

 

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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..

 

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