There is a verified version that is almost exactly like my next version here. (I made small changes so that I could make it completely parametric. Give me the rod lengths and I should be able to output the design.)by nicholas.seward - Developers
Quoteggherbaz I agreed with 691175002, one of the biggest issue you will have to deal with in a 4 or 5 axis printer would be the hotend, you would have to shrink it to needle size and make it long to work without crashing issues, also some geometries will be difficult to work with (selecting best axis to be printed on). I wouldn't underestimate what can be done with standard hotends. It reallyby nicholas.seward - Developers
Quotekrakadu Isn't the Delta style basically a perfected CoreXYZ type? The CoreXY utilises 2 motors working simultaneously to cover a plane. Similarly Delta utilises 3 motors working simultaneously to cover a volume. I would say the point would be to cover a rectangular prism volume while still being natively Cartesian. I love deltas but there are many reasons you might not want to use one.by nicholas.seward - CoreXY Machines
@polyglot: Gravity has nothing to do (or very little to do) with FFF printing. I regularly print upside down and sideways just to prove that point. Check the CoreXZ video in my signature if you want proof. Great News! I have a student that has made a generalized nonplanar slicer. I wouldn't say that is ready for prime time but it is a good proof of concept. Right now we used a 3DOF but noby nicholas.seward - Developers
Quoterobomaster Thanks for the answer. I teach a high school physics class, so I think I will test these fibers as an example science project next year. I just need to find some good suppliers that have genuine materials for cheep. Does anyone know what brands/suppliers of Spectra are most commonly used for 3D printers? Any place that has fishing supplies will have UHMWPE braided fishing line.by nicholas.seward - Developers
I can't speak about the others but I have use spectra. I had to tension/move-through-range-of-motion/tension/move/tension/move/... at first. It quickly hit a point where the tension didn't decrease after an iteration. I have let the 100lb test line sit under 5lbs of tension for months at a time (under heavy use) with no noticeable lose of tension. If it is creeping now, it is on the time scalby nicholas.seward - Developers
I can't give you a specific recommendation with out much more time and more detailed specification. The natural frequency and amplitude of that frequency is a function of... modulus of elasticity, diameter of cord, length of cord, moving mass in the system, max jerk setting, and max acceleration setting. I use 100lb test fishing line but I have seen 300+lb lines. The modulus is a function ofby nicholas.seward - Developers
@SydneyDesigner: VDX gets at the core of the issues. That said you have to look at the design requirements. As I said, I think I could hit the requirements with either a belt or a string. The problem is that it becomes harder and harder to solve the problem with string as the size of the working envelope increases. Before I go through the though exercise of designing a printer of your size wby nicholas.seward - Developers
QuoteSydneyDesigner Thanks to everyone for their contributions to this fascinating and informative topic. I'm particularly interested to hear what seems to be very successful uses of spectra/fishing line. My basic question is this. Is the consensus that (with good design) spectra/fishing line for X, Y and Z gives similar (or perhaps even better?) print precision and speed as GT2 belts? I'm notby nicholas.seward - Developers
QuoteCptanPanic Looks great. What are the bass guitar tuners for? Tensioning of the string and leveling of the gantry. (That is why you need 2.)by nicholas.seward - Developers
Quoteekaggrat There is no firmware for core xz just a gcode post processor . This was not meant to be a new printer but a retrofit for the prusa i2 . I have a hacked version of marlin that works for me. (No endstop code) No gcode manipulation required. PM me if you would like what I have.by nicholas.seward - Developers
QuoteMindRealm Wow! Really great idea. This should enable much quicker movement and it certainly stabilizes the printer by lowering the mass of the steppers to the base. I believe this one deserves a new variant name... Does CoreXZ not work for the name? In my signature below is a link to a working CoreXZ. (Box frame instead of thread frame but that is a minor detail.)by nicholas.seward - Developers
@DennyP: I have used printed spools with no truing on GUS Simpson. It is not hard for the error to exceed 250 microns. For a standard serial bot this would be much of a problem because the period of this error is spread over 60mm. With correct tolerances on parts, that would never be a problem. The problem you will run into with the CoreXZ is that the error will keep the prints from being lby nicholas.seward - Developers
Quotetulindo * In order to reduce the width of the X (having the same printable area) do you think it is possibile to bring bearings close to each other? (like in my attached file)... I don't se any drawbacks in doing this, do you? There are lots of ways to reduce width but as DaveGadgeteer mentioned you want to keep the lines vertical. Imagine doing a 90 degree fold along the z axis. I kept itby nicholas.seward - Developers
@ruggb: I have found the fishing line in no way to be deficient. I have been operating mine for 6+ months at high tension and have not had to retension or restring. The wire you have sited seems to be braided(?) stainless steel with a nylon coating. I suspect that to be a great choice for an application such as this. It the wire isn't braided then I would expect it to suffer from fatigue iby nicholas.seward - Developers
QuoteDedeHai Another off-topic question: You are using M8 bolts to hold the bearings. M8 is just below 8mm (like 7.8mm usually) but the bearings are exactly 8.0mm. Is this no a problem (play, off-center rotation, tilt)? After you tighten the bolts there is no play or tilt. The worst problem would be off-center rotation. In theory, this would remain constant and could be calibrated away.by nicholas.seward - Polar Machines, SCARA, Robot Arms
@DedeHai: You would be right if the motors were mounted between the shoulders and the elbows. As it is, the motors are static on the backboard. Therefore, you have to rotate to match the arm angle plus the rotation to change the elbow angle. stepper_1=constant(mechanical_advantage*c-g) stepper_2=-constant(mechanical_advantage*d-h) I was challenging myself to build the bot with all staticby nicholas.seward - Polar Machines, SCARA, Robot Arms
@DedeHai: You are right that there are no differential equations involved. You are also right that a 2D lookup table would be a decent approach for this. One slight problem would be that a change in calibration will be a complete change in the table. (On second thought, it might be possible to have a generic table but I will have to think on it.) You might be able to generate a new table atby nicholas.seward - Polar Machines, SCARA, Robot Arms
I never followed up on the forward kinematics. I have no doubt that it could be done without iteration but it would be some fun math.by nicholas.seward - Polar Machines, SCARA, Robot Arms
The math is bad but not intractable. It has been solved. (inverse kinematics) The real problem is calibration. The non-linear z is probably the biggest roadblock to calibration. That is why this thread exists. For the record, I have abandoned development on Wally. That doesn't mean that someone else can't pick it up and work on it. I am personally targeting a 1-arm SCARA as a Wally replacemby nicholas.seward - Polar Machines, SCARA, Robot Arms
Springs are good if you don't have a perfect system and want to maintain tension. Tuners are good for retensioning when the string starts to relax. Both solve different problems. I personally rely only on the compliance of the string to maintain tension. It has been many months since I tensioned it last and when plucked makes a high pitched note.by nicholas.seward - Developers
pi*d*wraps should be greater than x_travel + 3* z_travel. What is the length of travel? There are three ways to fix this. Larger diameter but that hurts resolution. Longer pulley but that adds to the triangulation error. Thinner string. Depending on how close you are it might be worth it to try lighter test string. (40lb test with 5-10 lbs of tension should do the trick. The 60-100 lb testby nicholas.seward - Developers
Fill the spool up with string. This will give you plenty of travel and the string will help track itself. Additionally, when you tension it will just rotate the spool a bit. As you have it now, tensioning both tuners will tension the system. Tensioning one will tilt the gantry. No change in your system is required. Also, I wouldn't worry about the string rubbing against itself. Low force,by nicholas.seward - Developers
Sweet! I can help you with the spool. You aren't using it quite right. Basically, you put the string through the off axis hole and then wrap the two free ends in opposite directions until you meet in the middle.by nicholas.seward - Developers
I will be doing a limited test run. Are you interested?by nicholas.seward - Repetier
PM me your email if you want me to share my MarlinXZ. It is a hack and has no endstop support. It also has the 3:1 reduction for the Z.by nicholas.seward - Repetier
My suggestion based on those pieces would be to get the cheapest SLS printer you can find. It will be slow but you could print many items at the same time. You also will be limited to materials you can get nice powder for and possibly only the material that the printer supports if it is a more commercial printer. Nylon is the standard material. I am not aware of any reason you couldn't printby nicholas.seward - Developers
@dursi: What surface quality do you need? A machine may have positional accuracy of 20 microns but the surface won't have that accuracy. You will see ridges for every layer. I am guessing that no 3D printer will do what you need unless you get one with an incredibly small nozzle and a very very small layer height but then it will take forever to make each part. You would probably need 40 $20by nicholas.seward - Developers