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Printrbot PLUS Precision Bed Leveler

by Jerrill, published

Printrbot PLUS Precision Bed Leveler by Jerrill Jan 18, 2013

Description

This is second bed leveling method that I've tried on my Printrbot PLUS. The first worked well down to a nozzle size of 0.35 mm but I wanted to go even smaller! So I needed a design with a little less slop.

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The plywood print bed was bowing a little under tension from the y-axis belt so I put aluminum ribbing in the x and y directions to make it more rigid. It would have cause any bed leveling I did to drift over time. I'm planning to upgrade to an all aluminum print bed so it looks nicer and I could eliminate this mod altogether with tapped holed for the heater PCB mounts. But this is working and I haven't gotten around to it.
What is the aluminum for on your print bed? Rigidity?

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Instructions

Tools required: 1) Phillips screw driver 2) 5/32" drill bit to drill out part holes, add new holes to the plywood print bed, and open up the mounting holes in the heated print bed 3) Hand drill 4) Exacto knife to clean up the first layers and clean out the holes for the hidden nut 5) Soldering iron to press the hidden captured nuts into their nut retainers so they are flush with the surface 6) Dremmel tool or saw to modify the front y-axis rod clamps

Additional parts you'll need: 1) 2 x #6-32 2" screws 2) 6 x #6-32 3/4" screws 3) 4 x #6-32 1-1/2" screws 4) 6 x #6 washers 5) 8 x #8 washers 6) 12 x #6-32 nuts 7) 4 x stiff springs (NOTE: I found that the long style springs from the "seats and springs" kits sold in the faucet repair / plumbing section of Lowe's are great!)

Print 8 copies of nut-retainer.stl. That's 2 nut retainers for each corner of the heated print bed- one on top of the plywood print bed and one on the bottom.

The center holes of the nut retainers are for the screws that attach to the heated print bed and line up with the existing holes in the plywood print bed. One of the holes in each of the front nut retainers lines up with the screws that attach the clamps for the y-axis rods. The front nut retainers are positioned so that the remaining hole is under the heated print bed for clearance with the y-axis bearings. The back nut retainers are mirrored across the x axis of the print bed.

You'll need to modify the clamps that attach the front of the plywood print bed to the y-axis rods by cutting off the neck of the part so that only the clamping portion remains. You'll have to drill a new hole closer to the gap in the clamp because the other screw hole will be removed when you cut off the neck of the part.

You'll additionally need to drill out the holes in the four corners of the heated print bed so a #6-32 screw turns freely in the hole.

Finally, you'll need 6 new holes in the plywood print bed so that three screws can go through each of the top nut retainers down through the plywood print bed to the bottom nut retainers.

You may need to use a soldering iron to press the hidden captured nuts into the nut retainers flush with the surface so the nut retainers sit flush on the plywood print bed. This will displace some plastic in the screw hole. Just drill out the squished plastic without damaging the nuts so that the through screws will turn freely.

The back nut retainers and the inside hole of the front retainers are cinched to the print bed with the following stack up: 1) #6-32 3/4" screw 2) top nut retainer 3) plywood print bed 4) #6-32 nut

The y-axis clamp is remounted through the front nut retainers with the following stack up: 1) #6-32 2" screw 2) top nut retainer 3) plywood print bed 4) #6-32 nut 5) modified y-axis clamp 6) #6 washers 7) #6-32 nut

The stack up of the parts (top to bottom) at each corner that mounts the heated print bed is as follows: 1) #6-32 1-1/2" screw 2) #6 washer 3) the heated print bed 4) #8 washer 5) stiff spring 6) #8 washer 7) top nut retainer 8) #6-32 nut captured between top nut retainer (center hole) and plywood print bed 9) plywood print bed 10) #6-32 nut captured between bottom nut retainer (center hole) and plywood print bed 11) bottom nut retainer

Once you tighten the screw down clamping the top and bottom nut retainers to the board you may have to adjust the screws a bit so that the center screw can turn freely as it is threaded through the assembly.

The height of the print bed is adjusted by turning the screws from the top of the heated print bed. You'll need to make sure that the 1-1/2" screws that attach the heated print bed turn freely enough to be able to adjust the height of the heated print bed with a Phillips screw driver, but not so freely that they'll come loose.

What is the aluminum for on your print bed? Rigidity?
The plywood print bed was bowing a little under tension from the y-axis belt so I put aluminum ribbing in the x and y directions to make it more rigid. It would have cause any bed leveling I did to drift over time. I'm planning to upgrade to an all aluminum print bed so it looks nicer and I could eliminate this mod altogether with tapped holed for the heater PCB mounts. But this is working and I haven't gotten around to it.
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