1 Topic by rickq

  • rickq
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Topic: Front bed support - stops aluminum bed wobble.

The aluminum bed on our SD3 would wobble during high frequency reciprocating x translations (like during thin wall infills).  If you push on the side of the front edge of the bed, it will flex the vertical rods that the bed slides on.  Adding glass to the bed exacerbated the issue due to the increased mass (lower frequency wobble but larger excursion, which is the real problem).

My fix was to use some 1 x 1 aluminum angle as a front cross bar, some fab'ed little wheels and blocks, and shoulder bolts for axles.    The wheels on cross bar the ride up and down on the front vertical steel angle that is part of the SD3 case.  The wheels have an o-ring "tire" on them to provide compliance.  The cross bar was notched to clear nut inserts on the bed and the 2 holes were drilled in the bed to attach the cross bar.

I have access to machine tools, so I did not print the parts, but they certainly could have been designed for that easily enough.

Wobble be gone.  The last pic is an Arduino Uno box I printed post mod at .3mm.  No Z axis lead screw mods yet on this machine, but pretty smooth none the less.

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2 Reply by jenninaj

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Re: Front bed support - stops aluminum bed wobble.

Interesting idea. I'd played with this approach on my SD2 as I could screw a crosspiece into the wood of the bed and then have a wheel on the end. I put a compression spring between the wheel and the crosspiece to allow for some flexibility and to ensure constant pressure.

I noticed with my solution that there was a problem when printing pieces that were long in the Y direction: as the bed was raised/lowered the max Y part of the bed moved slightly less than the min Y part and so my layers were slightly different across the piece. Not a big deal for 0.3mm layers but became a problem as I printed at 0.1mm layers.

As I was looking to prevent Z banding with this approach I trashed it and went with the helical beam coupling detailed elsewhere. It looks like your rig is addressing your problem - good work.

3 Reply by johnforeman

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Re: Front bed support - stops aluminum bed wobble.

Very clever.  How square are the side rails?  Does it bind as it goes down towards the z limit?

4 Reply by rickq

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Re: Front bed support - stops aluminum bed wobble.

My 1st thought was single sided (easier certainly) but I figured the side load would wear things and/or bind things.  Being double ended solved that. 

I forgot to mention that the blocks can slide in the X direction in slots in the cross bar.  This way the wheels are individually adjustable so the cross bar can be made with a hacksaw, drill and file (i.e. no special tools and you can print blocks and wheels if you choose).

1. Attach the wheels to the blocks
2. Loosely attach the blocks to crossbar
3. Attach the crossbar to the bed
4. Adjust blocks such that the wheels contact the SD3 case.

And ... Thanks

5 Reply by rickq

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Re: Front bed support - stops aluminum bed wobble.

johnforeman wrote:

Very clever.  How square are the side rails?  Does it bind as it goes down towards the z limit?

On my SD3 the rails are within 0.005" top to bottom inside the case.  So figure 0.001" or so for every 2" of vertical print.  The o-ring squish takes up this error.

6 Reply by agentsmith

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Re: Front bed support - stops aluminum bed wobble.

That's an interesting mod, I see indeed some vibrations on bed edges, this mod could be the next after the threaded rod upgrade!

7 Reply by Tomek

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Re: Front bed support - stops aluminum bed wobble.

Is there any particular reason you used a stiff right angle? I was hoping to get away with using some random aluminum parts, and making the joint holding the wheel to be from plastic with an oval slot to adjust. 

Also, I have a wooden SD2 part, so I haven't decided how to mount this. But I believe it will be beneficial.

8 Reply by iowajames

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Re: Front bed support - stops aluminum bed wobble.

I'm curious about whether this would work with the printable ball screw mod, or if it would put too much tension against the ball screw assembly.

No trees were harmed in the creation of this email, though some electrons were horribly inconvenienced.

9 Reply by Tomek

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Re: Front bed support - stops aluminum bed wobble.

Iowa< I'm not sure how this puts tension on the ball screw assembly.

Do you mean compression? I mean they come hand in hand on a rod (b/c bending involves both tension and compression), but are you worried about this mod "pressing" into the side of the ball screw assembly? I'm not sure what would make this particularly incompatible with the ballscrew smile

Thanks.

10 Reply by rickq

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Re: Front bed support - stops aluminum bed wobble.

Tomek wrote:

Is there any particular reason you used a stiff right angle?

The angle provides a convenient a plane transformation.  And it is cheap and stiff.

11 Reply by Tomek

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Re: Front bed support - stops aluminum bed wobble.

Cool smile. Thanks, i wasn't sure if there were particular reasons. I think I might do the same thing, but use a thin plate rectangle, because I have some. I am not sure how I will mount it to the solidoodle z platform, but I might just drill through the plate and tap a hole into the wooden Z-axis I have.