Precision 3D Printer ... Revisited (Page 1 of 3)

Can the screw move as fast as the belt?

I don't know much about it, just wondering.

BTW, good look with the T slot frame.

Nice work! I have also some extra parts and been thinking about building another printer...

I made a few changes to the layout.  Specifically, I moved the Y-Drive screw on the outside of the frame, inline with the left side smooth rod, and then moved the X-Drive screw on top, and aligned with the forward smooth rod. 

As you can probably tell, the printhead block will only have the hot end on it, the extruder motor will be outside the frame, effectively a Bowden style extruder.

I mentioned earlier that I was working on a pulley system.  I remember from my old drafting days, that the drafting table used a pulley system to keep the arm parallel, so I replicated that here.  In theory, this should keep the X carriage nice and square, and prevent skewing.  It will use round groove idler pulleys, and steel wire.  The ends of the wire will be secured to, and tensioned on the back of the right X carriage block.

My only problem is finding small idler pulleys.  Right now al I can find that is under 12m OD, is made of plastic/nylon, and doesn't have any bearings.  I'll keep looking I guess.

A quick observation about Spectra line.  Sufix Brand is substantially better it is what they call a digital braided line.  I have used both on my SD3 and the Spectra just seemed to continually stretch.  It would be fine for about 10-15 hours of print time then needed to be re-tightened.  The Sufix brand which was all I could find locally I originally stayed away from because it seemed waxy.  I wish I had switched over sooner it has been running steady for a couple of months now and still looks like the day I installed it.

Ooh that's pretty. One of these? http://www.issoku.jp/product/pdf/z-006-d.pdf
Flex couplers are usually a pretty specific size, based on eBay D20 x 30mm is pretty standard, as long as you leave room for one then you can choose when constructing what type works the best!

This isn't exactly true, as you start to run into mechanical resonances that don't happen with belts (belts are natural dampers). Additionally, steppers have reduced torque as shaft speed increases. The inertial load from the carriage is basically the same since it is effectively "geared", but there's additional rotational inertia and friction.

tl;dr: belts are always faster.

Can you post what you've found, both the plastic and metal ones? I'm interested for a different (non-3D Printing) project.
I've been getting stuff lately from Misumi USA.  Their prices are good, and the product is good as well.  Here is the link to their idler pulleys.  You can work your way back through the catalog from there.

http://us.misumi-ec.com/vona2/detail/11 … 70/?Inch=0

The plastic pulleys I found on eBay.  Do a search for toy pulleys.  You'll find things like this:
http://www.ebay.com/itm/10pcs-20-4-1-9m … 5af1233a2c
http://www.ebay.com/itm/10pcs-Small-Ora … 416f5b442e

Additionally, steppers have reduced torque as shaft speed increases.
Yes, I'm aware the torque decreasing as RPM increase, but I'm not looking to break any speed limits.  I think that there's enough torque in a NEMA 17 motor to drive these screws at a pretty good clip.  For example a typical National Instruments NEMA 17 stepper is capable of 3000 RPM, while maintaining their rated holding torque.

My current SD3 belt setup has maximum feed rates of 500mm/sec in the X & Y axis.  (To drive the ball screw at 500mm/sec, I need to drive the motor at 100 RPM.  That's well within the capabilities of these motors.) 

Edit:
Oops, that was wrong, that would be 500m/min @ 100 RPM.  So to go 500mm/sec, I'd have to drive the motors @ 6000 RPM, so obviously the max speed with these motors would be about 250mm/sec @ 3000 RPM.  However, we never use those speeds for actual printing.  My max print speed is 75mm/sec for bridges, and 65mm/sec for non print moves, everything else is slower.  Those speeds translate into 900 RPM or less

You more or less have a H-bot here. Why not scrap the leadscrews and just drive the steel wire?
I've been thinking about doing an H-Bot, and I might still do, but I want to try my ball screws first.

That's the kind of thing I was thinking of! Having a browse myself, if you can stretch the brackets to fit 4x13x7mm (624UU) bearings then the price seems to drop a touch (50c/ea instead of $3.50/ea) - these look like a more common variety. The groove has some depth  (1.9mm), so with the 1.5mm diameter cable you're using that's cable centers of 10.7mm.

Update and some questions:

Here is a new rendering, a bit more fleshed out.  Most of the major mechanical components are in there.

The print bed platform is 12" x 12", the PCB heater and glass print surface are 10" x 10".  I'm still debating on the the "Z" lift design.  At the moment I have dual Z motors and m8 lead screws mounted on the back corners, while the front corners are supported by dual LMK8UU linear bearings.

The top of the lead screws are free floating, so the cantilevered surface is supported in part by the lead screws and by the front rods & bearings.

I was thinking of an alternate layout, where the lead screws are cross-corner from each other, rear left and front right, with the smooth rods & bearings in the opposite corners.

I could also go total overkill, and put 4 smooth rods in the corners, and the lead screws centered on the sides.

Also, if I go with the current design, or the cross-corner one, should I brace the top of the lead screws ?

What do you guys think ?

yeah, go all out, get four!

If you go 4 leadscrews for Z, you will have to constrain them up top. And they better be perfectly aligned, or else you will get horrible wobble for a slight misalignment.

But, my suggestion would be to have the screws cross-corner. That way you do not cantilever one end of the bed. It centers the 'push' along the middle of the bed. If you have the other two corners with smooth shafts constrained, you can leave the drive screws floating. It would be better if they were.

My only concern right now is your corner pieces. I hope you do not plan to print those that way. I have learned from experience corners on extruded aluminum have no rigidity, and the weight of the system makes the printed pieces split very easily before you get any tension on the frame with belts or whatever. In order to have printed parts, I made inside corners that were practically solid:

http://www.soliforum.com/post/46662/#p46662

You can see the part is printed in that orientation, thus giving some real strength to the two pieces being secured.