I’m blaming @Tom_Keidar for this one. I need a Direct drive testing platform to push the Drakon Extruder to the next stage. This was meant to be a build from parts I have in, but it’s turning into another one of those projects where I’m probably going to be spending more than I want. Meet the Railgun 3D Printer. I’m aiming for a high accuracy Direct drive, high-ish speed (80mm/s) platform, hence the MGN rails.
The offset Z Motors are to prevent torsion on the X axis, I’m not sure on the Y, yet. The main frame is 2040 Extrusion, using bracketry from the FB2020 to join it all together. It will, of course, use a Drakon Extruder with a Pancake stepper driving it.
I’m mot sure how the offset z will prevent torsion. Is it possible to find some left-handed lead screws and nuts? Then the z motors could counteract each other’s torque.
@Thomas_Cox - Torsion may be the wrong word, sorry, twisting is more appropriate. Basically my thinking is that it will twist if I have the motors on the same side. Although having said that, I have just worked out a better way of doing it to prevent that. Rails on one side, leadscrews on the other.
I have few advices for you:
- Move the Z motor down, do not mount it top as it will transfer the vibration to the frame. Keep as much mas lower near to the ground.
- You can think of adding second MGN rail for Z because cheap MGN bearing are not preloaded and you can expect some wobble in this design.
You can also think if you can afford it of course for Y axis to use something like THK KR33 auctiator. If you use large and thick aluminium build plate fast movements will cause ringing in the belt and you will need to lower the acceleration which will increase your build time. I had this issue with Printrbot Plus and I had to rebuild entire build plate to reduce the mass.
If you want real accuracy you can think to use ballscrew for Z or auctiator like THK KR33 but be aware THK KR actuators use very high quality ball screw and bearings and you may need to add brake for the stepper otherwise without current Z could unwind by its mass.
If you are interested in using industrial actuators you need to hunt in ebay for second hand deal. As new this items are super expensive, but often in ebay you can find pristine piece or “like new” for 100-300$ depending on the travel and condition. Usually auctiator with stroke 200-300mm cost less than 200$ for a good deal. Also some THK KR actuators come with Nema 17 mount build in. Also not only THK produce such actuators but also Rexroth, NSK, Parker, Festo and etc. You just need to hunt for a good deal.
@George_Novtekov - Thanks for advice. Things you are missing with this, though, are that it’s 2040 extrusion for the main frame, IE it’s built like a tank, so vibration issues on X/Z are pretty much moot, and I design with this in mind. There is a 2nd Z axis linear rail, but it’s on the back, this has since been moved (see attached image) in favour of running the rails on the front and the leadscrews on the back. I’m also looking at running a closed loop belt on Z as well to bring Z down to running only one motor, which will again cut back on any chance of vibrations. The way it is laid out now would negate the single motor at the bottom as well.
I’m fully aware of ringing issues that can present themselves with a heavy Y axis, having run acrylic framed Prusa i3 clones for a long while. You’re also missing the point that I need to keep costs down, I’m looking at spending a Maximum of £200 so actuators are way out of the budget. Also, Actuators will negate the required speed of 80mm/s as all they basically are are a leadscrew in a block, depending on the pitch, you’re not going to get much more than 60mm/s out of it. This will be in total my 9th printer (that is mine) and my 3rd design, I currently run 4, others have been sold, I’ve built a few others for customers as well, so I’m well aware of things that can happen.
Please don’t take my tone as “having a go”, just stating the background and discussing the flaws in what you have pointed out.
missing/deleted image from Google+
@Ax_Smith-Laffin Just to mention it is not true that auctiator will limit you to 60mm/s my cnc is capable of 160mm/s with such auctiator and it is silky smooth. The maximum permissible speed is 0.6m/s for them and they are often used for pick and place machines. But agree they do not fit in budget 200BP. And they are not lead screw but ball screw.
guilty as charged - taking full responsibility 
love how it’s turning out, actually pushed me to do some tests on a new x axis i`ve been thinking about.
