Design consideration  

RE: Design consideration

Threaded drive system are very slow generally and still have as much if not more backlash as belts which takes quite an effort to remove. Speed on z doesn’t need to be fast but imagine trying to move the extruder back and forth with threaded rods. 

RE: Design consideration

The Z axis action seems to be very quick with retraction. It's just inconceivable that rubber belts would be the best option. Motor technology can certainly compensate in windings to accomplish the task on the same voltage.

RE: Design consideration

Just because it’s inconceivable to you doesn’t make it not true. Yes you can build printers using lead screws, unfortunately they are Very expensive. Basically the printers are the best blend of price to engineering that meets the needed capabilities. Do some research on just what it costs to put together a machine using lead screws. Google is full of links. 
Could different choices lead to better quality, certainly. The price would be much more and let’s face it there are printers that utilise those other options and have the price to match. 

RE: Design consideration

The price for the latest printer seems to be high enough to include the hardware and software. Is this your opinion or are you responding on behalf of Prusa?

RE: Design consideration

There are projects out there that have replaced belts with screws. There are projects out there that have replaced screws with belts. Everything comes down to a balance of cost and complexity.

For a business selling 3D printers, if you can get good results at low cost with a reliable belt system, why change it? Would any benefits be offset by cost and complexity?

FWIW - Retraction is the E axis, not the Z. It uses a motor directly connected to the extruder gears in the case of the Prusa, or a geared extruder in other designs. Z-lift isn't particularly fast.

RE: Design consideration

It’s my opinion, why would I be responding on behalf of Prusa ? Like 99.9% of the people here including most of the moderators we don’t work for Prusa. 
Can I ask you a question ?  Have you ever actually sourced the parts and built a machine tool ? It’s not half as cheap as people imagine it to be. Even sourcing cheap parts from China. When you go for name brand parts from US or German manufacturers for example the price jumps up significantly.  That’s for a one off too. Once you factor in business cost like premises, wages, taxes etc then it’s another factor higher still. 

I’m not going to get into a discussion on if Prusa printers are ‘worth’ it. I’ll leave that to others if they feel like it. I own one so my opinion on that should be obvious. It’s purely a personal decision anyway. The simple answer is if you don’t think it’s worth it then don’t buy one. If you think you can successfully build and market one that’s better for less money, great go ahead. You could be the next Prusa. 

RE: Design consideration

If I had a spare printer, I would build my own prototype as a test. I have actually been tinkering with designs for plastic parts to make the conversion. I asked the question to see if I could garner some response from a factory rep but if they don't monitor the postings in any way I will have to pursue it by another avenue. I am very happy with my Prusa printer and my goal was to ascertain if there might be a plan to make that conversion. That was all.

RE: Design consideration

Is this a hobby project or are you trying to address a specific issue? I think the biggest improvement to the Prusa i3 design would be improved access to and replacement of the extruder assembly. The mechanics are pretty good. Nothing wrong with going down the wormhole with a pet project, of course.

My non-professional understanding is that CoreXY is all the hotness for balancing speed with mechanical XY stability. I don't think you can do CoreXY without belts, though I could easily be wrong.

RE: Design consideration

Posted by: @richardgondeckgmail-com

I'm sure this has been suggested before but I have to ask. Why are we using belts when two more threaded actuators would be trouble free and more accurate? I can't imagine it would be a cost issue. Inquiring minds want to know.

the extruder weight does not justify it .there is no point as there wont be any improvement .

unlike cnc machines ,3d printer extruders dont need high torque . if for some crazy reason your extruder head weight few kg , then maybe its a good idea to move to lead screws (or ballscrews) .

for current machines , belts are doing pretty good job , then whats the point . you wont get more accuracy by moving to a leadscrew .

if your heatbed is very large and heavy , then yes , moving to a leadscrew or ballscrew will improve things . but moving such a large bed in the first place is a bad idea . thats why next generation printers use coreXY system , or any other combination where the bed is stationary. 

also i dont think you can find a leadscrew that will move the axis same amount as a belt system for a given motor speed .if you do , then the accuracy and backlash of the screw will be much worse then the belt system .i also dont thing its possible to use the same acceleration and speed setting with a leadscrew . just imagine the extruder move back and forth in a narrow infill extrusion at crazy speed and acceleration. the leadscrew will overheat . 

RE: Design consideration

Posted by: @bobstro

I think the biggest improvement to the Prusa i3 design would be improved access to and replacement of the extruder assembly.

 

I second that opinion.

I've thought of making a different extruder mounting assembly but is there any out there that don't require modifying firmware?

RE: Design consideration

Bobstro and Nighthawk, not to hijack the thread but have you seen this gentleman's project? PitStop Bill of Materials 🛠️ — MihaiDesigns

It is pretty intriguing and I am thinking about building it for grins.

Steve

RE: Design consideration

@steve-17

Nice! I like that there's no firmware changes.

RE: Design consideration

Posted by: @steve-17

Bobstro and Nighthawk, not to hijack the thread but have you seen this gentleman's project? PitStop Bill of Materials 🛠️ — MihaiDesigns

Yes, I've seen it. Part of my hesitation is that I won't have a normal Mk3 to help others with. Since I'm not upgrading it, I'm already "non-standard", so perhaps it's time. Thanks.