Yeah, I think a dual Volcano nozzle with a combination of 0.4 and 0.8 nozzles may do nicely.

Two nozzles gives me access to the entire bed on the Y axis, and about 410+ mm on the X axis for both nozzles.

Also gives me some space to put cooling fans on the back of the carriage...


Plus, I can also switch back to a Chimera configuration with the dual v6 nozzles if I want smaller nozzles for detail pieces.

 

The X/Y motors will be mounted to the top front rail, one with its pulley above the bar and the other upside down, pulley below the bar.

Should be plenty of clearance for the belts.

 

Yeah, good point.

I'll make it fit, I only need about 10-15mm of clearance width for the belts to pass through.

 

I like these KFL08 Pillow Block mounts - I was going to use a printed part to hold a 608 bearing, but I think these will be better.

Now to find the dimensions so I can make a model of one...

Bingo:

 

And here we are, the finished model:



I've included the Sketchup file if you'd like to use it.

 

Rotated the bearing blocks by 33.226 degrees to have the two holes line up for a 20mm distance, and set them to the middle of the 20x40 vertical beams.

The top and bottom bearings are rotated in this way to give the Z axis wheels more vertical room to travel.

With an E3D Chimera w/v6 hot ends, it makes for just over 440 mm of vertical room - 430 mm if I use the longer Volcano hot ends (they're 10mm longer).


Plus, there's enough room on the back of the hotend carriage for a 5015 blower fan.

I'm also going to squeeze in an inductive proximity sensor for the Z-probe/Endstop.

 

So the giant sheet of PEI arrived today - 24" x 24", with one side slightly textured, and the other side smooth with a peel-off protector.

It's only about 1mm thick, but relatively stiff by itself.

I'll see if the aluminum plate is flat enough (on order), and if so I'll apply it smooth side up with adhesion tape.





The springs also arrived - pretty strong!

 

My bed will be heavier, with all that aluminum - 8 pounds for the 1/4" thick MIC6 aluminum, and 4 pounds for the 20x40 carriage assembly.

12 pounds worth...

However, with 4 x 3.5 pound springs, I should have about 14 pounds of lift, resulting in a positive balance - the bed will want to go to the top when power is removed.


So my belts will be tensioned against the upwards pull of about 2 pounds, possibly less..

I'm also using a combination of more powerful 60mm motors and a 2:1 belt drive reduction to increase the torque.


The one issue I'm working on resolving now is the belts - at the center distances I have, the next available endless belt is about 1140mm - 30mm too long:

http://www.robotdigg.com/product/270/1140-2gt-6-2gt-endless-belt

So I would have to take up about 30mm of slack for the belts to be at the right length.


Also I would rather use an endless belt rather than a cut length of belt because the endless belt would be stronger - no breaks in the belt to clamp together.

At least, in theory...

 

I've found this timing belt calculator to be really useful:

http://www.bbman.com/catalog/belt-length-calculator.html


However, since RobotDigg doesn't have belt lengths in every conceivable configuration I'm running into situations where the desired belt may be too long, or too short...


Edit:

A center distance of 523.0 mm gets me a belt that needs to be 1110mm long - and SDP/SI has them:

http://www.sdp-si.com/eStore/Catalog/PartNumber/A 6R51M555060

About $10 each, so they're not cheap... but they're bound to be well made.

 

I'm not sure which SparkFun part you're referring to - got a direct link?

 

Ah, got it.

Yeah, I had heard about the piezo sensors - and this may be something I'll see if I can incorporate.

Also: The Piezo element is similar to a load cell device, which reports voltage changes on pressures applied.

I wonder if I can get a more accurate, but not much more expensive load cell instead.

 

Modeled a dimensionally-accurate GT2 Belt Loop with a center distance of 523mm.

I used a rather nice OpenSCAD library that could generate belt lengths and circles.

 

Designed a simple 2-piece block clamp for bolting the belt to the side of the Z gantry.

The thinner block on the inside of the belt has a GT2 tooth pattern to interface with the belt.

The thicker block have raised wedges that fit into the V-Slots, with through-holes for clamping with bolts and t-nuts.

 

The MIC 6 cast and ground aluminum plate arrived!

The top and bottom surfaces are ground flat - this is the stuff that they make tooling plates for in CNC machinery, so the plates are cast and ground so that they're stress relieved and they won't warp.

The flatness tolerance on this thickness (1/4") is 0.015", or about 0.38mm - however when you consider that tolerance is over an area as large as this one is (20x16") it's still pretty darn flat.

You can see the grinding pattern in the pictures - but it's smooth and shiny to the touch.

The plate was CNC saw cut to 20"x16", and I can say that it's exactly on the mark.

 

I gotta say - this PEI sheet is the best build surface I've ever printed on.

I printed out this tall and thin lithograph with ABS, and a 3mm brim - and it stayed on for the entire 4-hour print.

Popped off very easily, used a plastic card to get under the brim.

I set the bed temp to 115, and it was about 100 on the surface of the PEI.

This printed in an open enclosure, and it came out great!

 

Yes, when I cut the large piece of PEI for the big 16*20 plate, I had a strip that's 8" wide x 24" long, so I cut a piece 8"x8" to fit my current printer.

The printer is an i3, with a MK2 heat bed and a piece of 4mm borosilicate glass.

I used a roll of 10mm wide 3M phone -repair tape I had and covered the glass in strips. It's not the super strength tape that's mentioned in the wiki, but it seems to work well.

 

Picked up this metric drill tap set today at Harbor Freight for about $11.

If it looks identical to the one that OB sells, it's because it is...



Also found the best way to measure V-Slot - stick the ruler in the slot!

That makes sure it's parallel to the length of the rail for better accuracy.

This yardstick/meterstick is aluminum and only about 2mm thick, so it fits in there at an angle perfectly.