Printrbot Metal Plus Z Axis screw rattling

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Printrbot Metal Plus Z Axis screw rattling

Postby barry1685 » 2016-Dec-Wed-13-Dec

Hi,

I am having some Z Axis screw rattling, I checked all the screws and everything is tight. It looks like it's loose at the top of the screw, it is housed in a black rectangular plastic looking box. It looks like there is some give in it. Does anyone have any information about this happening or solutions?
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Printrbot Metal Plus Z Axis screw rattling

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Re: Printrbot Metal Plus Z Axis screw rattling

Postby RetireeJay » 2016-Dec-Wed-13-Dec

By "rattling" do you mean it's making noise? Or do you just mean that the top of the screw moves around a bit? It's actually necessary for the top of the threaded rod to be "unconstrained," i.e. free to move around a bit. The rod is tightly constrained at its coupling to the motor, and its position is also constrained at the point where it goes through the nut that supports the carriage. If you added a third point of constraint, you would in fact create large forces internally that would cause problems. This is because it's essentially impossible to line up the three points of constraint exactly to the micron, and even if you could there's no guarantee that the threaded rod itself is perfectly straight to the micron tolerance.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
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Re: Printrbot Metal Plus Z Axis screw rattling

Postby barry1685 » 2016-Dec-Wed-17-Dec

Thanks, and I agree, I wouldn't want to constraint the top of the screw. I just hear a lot of rattle when printing and never heard rattle when I first got the printer. My guess is that over time the top of the z axis screw wore a larger area in the housing. The housing has a cylindrical cut out for the screw, and I think the vibrations over time has worn the space between the plastic and screw. I suppose the saying, "don't fix it if it ain't broke" applies to this.
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Re: Printrbot Metal Plus Z Axis screw rattling

Postby RetireeJay » 2016-Dec-Wed-17-Dec

If you are sure that's where the noise is coming from, OK. But in general, parts that are loose and rattling against each other is not a good sign. Ideally there should be enough room for things to move without rattling, or else they are held firmly enough not to rattle.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
User avatar
RetireeJay
My next printer is...
 
Posts: 4709
Joined: 2013-Jan-Wed-13-Jan
Location: Greenville, SC
Reputation: 477

Re: Printrbot Metal Plus Z Axis screw rattling

Postby barry1685 » 2016-Dec-Thu-11-Dec

I'm confident that's what is causing the rattling, by applying light pressure to the z screw (near the top of the screw) it doesn't rattle anymore. The higher the z axis rises the less rattling is heard. Which makes sense as the z screw's are supported at the top portion by the x axis.
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Re: Printrbot Metal Plus Z Axis screw rattling

Postby barry1685 » 2016-Dec-Thu-12-Dec

I found the term for the housing unit for the z acme screws. It's called a "z-block".
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Re: Printrbot Metal Plus Z Axis screw rattling

Postby barry1685 » 2016-Dec-Thu-13-Dec

I found a 3d cad model of the printrbot plus, I can extract the z block and 3d print another one to replace the z block I have currently.
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