It's new to me

[ddmckee54]

Today was spent putting the Y axis leadnut assembly together. I started with your standard 3D printer anti-backlash leadnut, looks like this when assembled on the leadscrew.


This is just 2 modified leadnuts assembled back to back with a spring between them.. The spring keeps the 2 halves of the nut separated, removing the backlash, and a tab/slot arrangement keeps them in sync. This works fine for the minimal tool pressure of a 3D printer. BUT, and there's always a big butt, any tool pressure that opposes the travel will overpower that wimpy little spring and your backlash is back - don't think that'll do the surface finish any favors.

I remembered that Awesome CNC Freak had modified his 1310 machine to deal with backlash, so I did some digging - and then quite happily swiped his idea. This was the test rig I built.


It proved the concept. By using the nut to squeeze the 2 halves together you eliminate the thread backlash, and it's much more rigid. It does take careful adjustment though, you go from free falling to totally locked up in 1/4 turn of the nut. The bolts I used on the test rig weren't long enough though, the nylocks wouldn't lock - going from M3x35mm to M3x40mm bolts solved that problem. The bolts also keep the 2 halves in cync. This is what the business end of the Y axis anti-backlash leadnut assembly looks like.

That part will be buried between the Y axis bearing blocks though. This is all you'll see.


OK, OK, if you ignore the bit in the lower LH corner - THAT's what you'll see. Really shoulda cropped that picture.

[vtsteam]

Thanks greatly for pics! 

[ddmckee54]

Thanks greatly for pics! 

I had my old Blueberry flip-phone for so long, I keep forgetting that my new flip-phone has a camera.  It doesn't have the anti-blur capability of my camera so sometimes it takes several attempts to get a decent shot.

[ddmckee54]

I had a couple of 3D printing milestones recently, I started printing with something other than PLA and the P1S glitched on me.  Although in all honesty I probably made it worse than it should have been. 

I decided to try PETG, and I wanted to get the scaling dialed in to correct for shrinkage.  I decided that I might as well be printing something useful to do this testing.  My new spindle uses an ER11 collet, so I found an STL for a chip fan that presses onto the collet nut.  The friendly Google AI said the scaling factor should be 100.3-100.8%, so I scaled the fan to 100.5% and gave it a shot, way too tight.  I scaled it to 100.8% and printed it again. It takes less than 1/2 hour to print the fan - including the 7+ minutes the P1S uses for setup on every print.  It was still too tight, but I could force it on the nut.  I printed it again, this time scaled to 101.5%.  It presses onto the nut, not all the way, but since I didn't design the fan I can only guess the designers intentions.  I WAS going to print a fan scaled to 102%, but that's when the glitch occurred.  I started the print and left to do something else.  When I came back about 15 minutes later I had a bird's nest on the print bed.  It happens, so I did what I do when the D6 screws up late at night - I shut off the power and went to bed.

When I got up the next day and fired up the printer it was not happy with me, the AMS was making very unhappy noises.  I realized that I SHOULD have aborted the print, then shut off the power and gone to bed.  Ain't 20/20 hindsight just wondermus though?  I realized that the filament had frozen in the extruder and that I needed to get it out of the hot end so the AMS could retract it and be happy again.  But, I needed to do that before the AMS was powered up.  I decided to try unplugging the AMS, heat up the hot end, and see if I could pull the filament back by hand - to see if that would work.  I did, and it did - so I decided to try printing again.  All seemed to go well, until it tried starting to print about 50mm above the print bed.  All I could do was abort the print and hang my head in shame wondering "What the Hell did I do to this poor machine?"  Before I contacted Bambu Labs and confessed my sins, I wanted to run the initial calibration cycle again.  I wanted to see if that would let the printer find its' lost marbles. 

I'm proud to report that it worked and the plastic pooping robot is now about 7 hours into an 8 hour print.  That print will give me the Z axis rail holder, and the bearing block that will slide on those rails.

Don

[ddmckee54]

The Z axis carriage is starting to come together, literally.

The Z axis rail holder was usable, a little oversized but usable - the bearing block was not. Somewhere between the design notes and the cad operator, the understanding got lost that 20mm was the C-C spacing for the mounting holes, and that the remaining 28mm of the 48mm bearing block width was to be used to center the spindle mounting bracket. Somehow the 28mm became the C-C spaving, and the 20mm was split to center the spindle clamp. The 15mm bore for the bearings was over 15.1mm on the unusable part, not exactly a press fit. And NOBODY caught that boo-boo's before the files were cleared for production. When the assembly techs started screaming that the damned thing don't fit and went on break, THAT's when we found it. The rail holder was supposed to be 60mm wide, it measured 60.5mm. I had originally scaled the STL models to 101.5%, I dropped that back to 101.2% when I reprinted the bearing block. I kept the 6 perimeter walls and 80% infill though.

When I reprinted just the bearing block the print time dropped from 8 hours to 3 hours. I accidently ordered M5x70mm bolts, everything was designed around M6 bolts, but these will due for now.

[vtsteam]

Yipes, a string of bad luck! I'm sure you'll get it working soon.

This is what I hate about trying to program absolutely everything in advance, as opposed to measuring and cutting during fabrication. Not that fabrication isn't also subject to errors, but with work in hand, often times you can try pieces against each other, or mark from each other, or quickly measure a fastener and the drill bit you are planning to drill it with, etc.

Some people work better one way, others vary from that. I find I make fewer errors in manual work than I do in additive machining, because the latter demands advance perfect location of all features or a part is often ruined. One frequent problem in an imperfect initial rendering: since infill is usually partial to save material and time, relocating or even resizing a hole or other feature is often not feasible.

Nevertheless, I admire anybody who makes the effort by this or any other means and manages to create something in our hobby. I'm sure this mill project will provide rewards when it starts machining other parts!