Welcome! Log In Create A New Profile


Are newer printers better?

Posted by Diemex 
Are newer printers better?
August 23, 2019 04:58PM
I got the Mendel90 5 years ago and didn't really know what I was doing when I assembled it. I was only in my 2nd semester of my bachelors and didn't know what to do with the printer and also didn't get it to work properly. After the thermistor on the hotend somehow failed and it melted through a PEI sheet whilst heating up the hotend I had enough and it sat in the cupboard for 4 years.
Now I am in my masters and I have started using the printer again after reviving it by simply reconnecting the thermistor.

So far this year I managed to melt the J-Head hotend by not using the fan and setting it to 240C for PET-G. The brass nut on one side of the Z-axis got its threads stripped and I have switched to T8 nuts and leadscrews. I basically now have a 1.75mm bowden dual drive extruder Mendel90 with leadscrews, claw z couplings, replaced LMUU bearings (they rusted) and quite a few reprinted/modified parts in PET-G.

I have been thinking of getting a 2nd/new printer especially because they aren't that expensive and I have been sinking so much time into this printer. At this point it has reached the "project car" status. I have remodeled the x-motor-bracket and started on the z-motor-brackets to add those rubber vibration dampers. I am using onshape and have imported and assembled the parts I need to modify. I am positive I can get it to work, but I am afraid that I am investing time into an obsolete platform. I am learning quite a lot by improving my printer, so I am not really wasting my time.

I am eyeing the Ender-5 printer. Are the new printers which use aluminium profiles for the frame of the printer better or are they just easier to set up? Is there a difference between a properly calibrated and assembled Mendel90 and a newer printer? It seems like the aluminium profiles should be sturdier, will give me less troubles and provide easier modification. I am also afraid of leaving the Mendel90 to print on its own. This is mainly because it has melted through the PEI sheet a few years back. If one of the couplings gets loose on one side it could bend the whole axis, the thing can always start to somehow burn and it hasn't worked for more than 3 days at a time without something failing on it. This is probably not an issue with the printer or the design, but simply my lack of understanding which seems to at least get better with every accident/crash/failure.
Re: Are newer printers better?
August 24, 2019 06:12AM
The J-Head shouldn't melt at 240C, I run them up to 255C for the white ABS the kits are made from. I think you must not have the right thermistor if you replaced it. Thermistors don't normally fail when they are cemented in unless molten plastic gets into the cement. They then read high and the hot end temperature falls.

PEI melts at 217C so you can easily melt it if you crash the nozzle into it. If your Z axis is working properly that shouldn't happen though. I use glass to print on so that never melts!

I have one of the very first Mendel90 kits I built to make the manual photos and it still runs fine despite printing Mendel90 parts continuously for 3 years and being used regularly ever since . The Z nuts haven't worn out but I do keep them lubricated with car engine oil. I always leave it unattended while printing and never worry about it failing as it is very rare and never catastrophic. Nothing has ever burned.

The things I have replaced are extruder gears, x-carriage when it breaks at the back, and probably the Wade's block. I have replaced the hot end a few time but only when I got some bad ABS with black particles that blocked it. With good plastic they seem to last forever, which is just as well as I don't think I can still buy them.

Not sure why you would want vibration dampers on the Z-axis as it moves so infrequently. Since the weight of the X axis is carried by the Z-motors the height might get inconsistent if you mount them on rubber.

The DiBond frame is almost infinitely stiff in the directions the motion forces act so I don't think you gain anything with extrusions. The main advances since Mendel90 was designed are probably hotends, extruders, heatbeds, firmware and slicers. The Prusa I3 MK2 is probably the most advanced design at the moment.

Re: Are newer printers better?
August 28, 2019 04:59PM
I noticed that when I calibrate the bed height using a dial gauge that the frame isn't that sturdy. Just leaning on the table on which the printers sits has an effect. Pushing down on a corner of the base dibond sheet is visible on the dial gauge.

Isn't most of the weight of the x-axis resting on the base dibond sheet? The leadscrews are connected to the axle of the motors and that should press straight down onto the motors. My motors are mounted with their backs touching the base dibond sheet. So the weight of the axis should rest on the dibond sheet. I mainly want to add some felt between the motors of the z axis and the dibond sheet so the dibond sheet doesn't act as a huge resonating body. I noticed that the vibration dampers move the bracket up so much that I either have to increase the size of the mounting hole or get some idea on how to get the nuts into there. Maybe I'll scrap that idea as its not *that* important.

I wasn't able to find the J-Head anymore and especially not for 3mm filament, so I was forced to change to a 1.75mm E3D extruder...

If you are interested this is my current design: The axis can be moved around which is pretty cool. The z-motor brackets are highly WIP and the x-carriage needs some adjustments. As the hotend is mounted in the center there are 2 centimeters of printing space lost on the right side of the x axis. The x motor bracket and x idler are basically done.
Re: Are newer printers better?
August 29, 2019 04:50AM
Yes the frame can twist but if it is standing on a solid flat surface then it will be stable and braced against the forces generated by the axes moving.

I would imagine a frame built from extrusions would also conform to the surface it was standing on unless it had only three feet. If it was totally rigid it would rock but it would need to be extremely stiff to do that without being a box frame with diagonal bracing.

My next machine will be a box frame with sheet panels to brace it and form an enclosure. It will stand on three on three rubber feet to be independent of the surface it stands on.

Re: Are newer printers better?
August 31, 2019 11:13AM
While I stumbled upon the mechanical rigidity reprap wiki articles I have some questions.
I was wondering why the bearing traps on the x-axis-motor-bracket and x-idler don't use cable ties to lock them down? Are they supposed to flex a little bit?
The back follower bearing on the x carriage has these flex elements. I would assume these were designed to be printed in ABS and won't last that long or are too inflexible if printed in PLA? PET-G should work though, right?
Re: Are newer printers better?
August 31, 2019 12:04PM
The X bearings are a tight fit in the X ends so they are held rigidly once snapped in.

Yes the third bearing mount is designed to float in the Y direction, so that it won't bind if the X rod spacing is not exactly right. I have only printed the parts in ABS, so I don't know how they would last in other plastics. In theory it doesn't need to flex if everything is perfectly aligned.

Sorry, only registered users may post in this forum.

Click here to login