Topic: HBOT printer (or YAHP?)
Hey everyone. When I was waiting for my SD3 to ship, I was busy purchasing all the fun stuff to modify it with. GT2 belts and pulleys, DRV8825 drivers and motherboard/LCD, LM8UU bearings and hardened shafts, you know.
So what does one do when they get their SD3 and the biggest fluke happens? (This fluke being that the unit actually prints without banding, perfect circles, etc). I have all these parts that will maybe marginally improve my print experience. So instead of ripping a good printer apart, I build a new one.
So I purchased $55 in extruded 10 series and went to town.
I have used HBOTs at work for pick-and-place projects, and I like them. The idea that your motor is not attached to the moving parts is so invaluable. I also did some things that most people try to fix on their Solidoodles. For instance, removing weight and backlash from the X and Y axis for more precise movement and cooler stepper motors. I even switched to a Bowden setup. One of the main design goals is to get a really fast machine put together. For instance, here is the first test print at 180mm (3 times faster than stock SD3 speeds):
Here is the untouched output:
I have been finding that Bowden setups take alot more attention to get right. The Octi I printed at 60mm/s I had tuned the retraction to get rid of hairs and perimeter blobs, but any changes (especially speed) to other settings needs a re-tune of retraction. I am sure I will be able to get this dialed in better as time goes by. Of course, it means even more slicer profiles (uggh).
So far, here are the pros and cons of this printer:
PROS
-Perfect circles, there is a single belt tension and it is not that picky about how tight to get it.
-Stepper mounts are 'oval'ed, making belt tensioning really easy.
-Bowden setup has steppers running at 0.8 Amps and corners look decent since there is not alot of inertia to overcome for fast turns.
-The total X carriage weight including hotend is less than 40 grams. Its less than the E3D without fan.
-MK2A heatbed and 40W cartridge heater - very fast heating times.
-GT2 belts and 6MM Z axis screw: Steps in firmware are super easy. Everything falls on whole numbers.
-I got a 0.35mm nozzle hotend, and due to that I adjusted standard extrusion width down to 0.37mm and 0.25mm layer height. Its nice to see 4 layers per mm.
-LM8UU and LM12UU bearings are nice.
-I modified a Wades geared extruder assembly for 1.75mm filament and a NEMA23 stepper motor that has alot of low voltage torque. Its a heavier motor, but since it is a Bowden setup I dont care. This gives 39:11 gearing on the extruder so I can keep 1/16 stepping and I dont have the slightest moire effects.
-X axis has LM8UU on one rod, and uses 623ZZ bearings on the other rod as followers (wish SD did that instead of delrin blocks).
CONS
-Wades extruder uses the infamous hobbed bolt. Its temperamental. Combined with a cheap (less than $30) hotend, it leads to increased torque which leads to occasional stripping. I would like to either design a dual toothed extruder or something.
-Bowden setup has its issues getting just the right retraction. You can move the filament upto 2mm before it begins building pressure, or I should say that you need to retract 2mm to relieve the pressure. This number is not static. Changing speed and sometimes the type of print job you have means changing the retraction value. And it has to be fast (40-60mm/s).
-While the HBOT is super cool, there is a problem with the X gantry remaining square to the Y gantry. Even with the linear bearings, you can 'twist' the gantry. So far, I have not seen a problem as the single tension in the single belt holds it in place. Really what this type of printer design needs is linear blocks for the Y axis (super expensive) to hold it true. Or, a COREXY where you have 2 belts, but I dont want to go back to a 2 belt system.
-I tried a 4-screw Z axis system where a closed belt turned 4 screws to move the bed platform. While this was great when it came to leveling the bed, I found out that this created a Z-wobble on steroids. I printed out a cylinder and it looked like a screw. I trashed the whole thing and installed your basic Z axis (with all of its problems). I still need to work on this.
-Extruded T-slot does not play nice with printed plastic corners. No matter which direction I put the layers, any stress will begin tearing the layers apart. The entire machine actually shifts (as in, looking form the top you can push on the corners and bend it into a diamond shape). I think I will be getting some metal corners to hold the frame together better.
Conclusions: End goal is to get 0.1mm layer prints at 300+mm/s speeds. Retraction is constantly a problem. I know I need a quality hotend, but I dont want the weight of the E3D. I already have plans of making my own hotend, but not right now.
I am also planning a modification to the LISA SIMPSON delta robot. I may work on this more than tweeking the HBOT over the next month.
Opinions?
Sign Chuck Bittners petition