Building Core XY dual extruder from scratch
Posted by ______BlackCat13
|
Re: Building Core XY dual extruder from scratch July 25, 2018 07:50AM |
Using 3 or 4 guide rails can be made to work, but aligning them will be difficult. If they aren't aligned perfectly, the bed will walk (tilt back and forth) as it moves up and down. As I said, the rails aren't there to prevent tilting, they are there to guide the vertical motion and prevent lateral motion. The lifters are what prevents tilting. The most stable lifting is done using 3 lifters- think of it like a 3 legged stool. The bed sitting on 3 lifters is stable at every position, which is also why you should use 3 leveling screws, not 4.
You're planning to use 20 mm t-slot for the 500x500 mm frame. I think it's going to be much too flexible. I wouldn't attempt to make anything that large with less than 40x40 mm t-slot. You're going to be throwing two extruders and the entire X axis back and forth at print speed at the top of the machine. The whole thing is going to wobble unless you attach rigid side panels or print very slowly.
A warning about thingiverse- there's a lot of poor designs that are essentially unprintable. The printed extruder mount design you linked doesn't look very good to me. I can't relate the photos to the printed part design, and the design looks typically thin and flexible. Look at the thin little discs that protrude from the design. What are those for and how are you going to print them, and how strong will they be if you manage to break away the support material they will need without breaking them off? If you want a printed part that is going to work/last, you have to design it like it's plastic, not steel. Plastic gets strength and rigidity from bulk.
Here are a couple parts I recently printed for a project- it's for a sand table using a cable driven coreXY mechanism. There will be tension on the cables, so the parts are designed with that in mind, and printed in an orientation that provides greatest strength - i.e. the tension on the cables is parallel to the print layers, and isn't trying to pull them apart. I don't want the parts to break or distort, so I bulk them up. They don't look like folded sheet steel or cast metal because they're made of plastic.
PLA is a toy material. It's fine for Yoda heads and tugboats and not much else. If you anticipate ever trying to print ABS in your printer, or ever transporting the printer in a car, don't put PLA in it. PLA softens and distorts at low temperatures, like in a hot car or a warm, enclosed 3D printer. PLA filament absorbs moisture from the air if you leave it sitting out, and becomes brittle. So do PLA prints. It is best to avoid printed parts altogether, but if you have to use printed parts, ABS or PC are much better choices than PLA, and it's best to limit their use to situations where the applied forces compress or are parallel to the print layers.
I'm not sure what you mean about a long rod and gears and a NEMA-17 motor. A NEMA-17 motor should have sufficient torque to lift a 400x400 bed and support structure if it is geared down sufficiently. If you take a look at the link in my previous post about the DIY printed worm drive you'll see that a 40 mm long NEMA-17 motor had no problems lifting the bed in my printer. The thing that was a problem was the quality of the gears. Imperfections in the worm gear show up in the Z axis of the prints and repeat every time the worm makes one revolution, 2 mm in Z in my case. The reason for using a worm gear over other gear reduction mechanisms is that a worm gear can be irreversible. The Rino is not guaranteed to be irreversible by the manufacturer under all loads (this is because of the pitch of the gears, the friction, and the maximum load the part is designed to handle), but under the relatively light load of lifting a print bed and print, it is irreversible. That means the weight of the load won't cause the motor to turn, so when power is cut, the bed stays put.
The motor voltage rating has nothing to do with the power supply voltage used in the printer. In general, you want low voltage rated motors- look for steppers rated for 2-3V, 1-2A. It is normal to operate stepper motors from power supplies that are rated up to about 10x the rated voltage of the motor. Also, in general, you will get best performance if you use low voltage motors and use a 24V power supply for the printer.
Edited 3 time(s). Last edit at 07/25/2018 09:43AM by the_digital_dentist.
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
You're planning to use 20 mm t-slot for the 500x500 mm frame. I think it's going to be much too flexible. I wouldn't attempt to make anything that large with less than 40x40 mm t-slot. You're going to be throwing two extruders and the entire X axis back and forth at print speed at the top of the machine. The whole thing is going to wobble unless you attach rigid side panels or print very slowly.
A warning about thingiverse- there's a lot of poor designs that are essentially unprintable. The printed extruder mount design you linked doesn't look very good to me. I can't relate the photos to the printed part design, and the design looks typically thin and flexible. Look at the thin little discs that protrude from the design. What are those for and how are you going to print them, and how strong will they be if you manage to break away the support material they will need without breaking them off? If you want a printed part that is going to work/last, you have to design it like it's plastic, not steel. Plastic gets strength and rigidity from bulk.
Here are a couple parts I recently printed for a project- it's for a sand table using a cable driven coreXY mechanism. There will be tension on the cables, so the parts are designed with that in mind, and printed in an orientation that provides greatest strength - i.e. the tension on the cables is parallel to the print layers, and isn't trying to pull them apart. I don't want the parts to break or distort, so I bulk them up. They don't look like folded sheet steel or cast metal because they're made of plastic.
PLA is a toy material. It's fine for Yoda heads and tugboats and not much else. If you anticipate ever trying to print ABS in your printer, or ever transporting the printer in a car, don't put PLA in it. PLA softens and distorts at low temperatures, like in a hot car or a warm, enclosed 3D printer. PLA filament absorbs moisture from the air if you leave it sitting out, and becomes brittle. So do PLA prints. It is best to avoid printed parts altogether, but if you have to use printed parts, ABS or PC are much better choices than PLA, and it's best to limit their use to situations where the applied forces compress or are parallel to the print layers.
I'm not sure what you mean about a long rod and gears and a NEMA-17 motor. A NEMA-17 motor should have sufficient torque to lift a 400x400 bed and support structure if it is geared down sufficiently. If you take a look at the link in my previous post about the DIY printed worm drive you'll see that a 40 mm long NEMA-17 motor had no problems lifting the bed in my printer. The thing that was a problem was the quality of the gears. Imperfections in the worm gear show up in the Z axis of the prints and repeat every time the worm makes one revolution, 2 mm in Z in my case. The reason for using a worm gear over other gear reduction mechanisms is that a worm gear can be irreversible. The Rino is not guaranteed to be irreversible by the manufacturer under all loads (this is because of the pitch of the gears, the friction, and the maximum load the part is designed to handle), but under the relatively light load of lifting a print bed and print, it is irreversible. That means the weight of the load won't cause the motor to turn, so when power is cut, the bed stays put.
The motor voltage rating has nothing to do with the power supply voltage used in the printer. In general, you want low voltage rated motors- look for steppers rated for 2-3V, 1-2A. It is normal to operate stepper motors from power supplies that are rated up to about 10x the rated voltage of the motor. Also, in general, you will get best performance if you use low voltage motors and use a 24V power supply for the printer.
Edited 3 time(s). Last edit at 07/25/2018 09:43AM by the_digital_dentist.
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
|
Re: Building Core XY dual extruder from scratch July 26, 2018 02:07AM |
Thanks a lot you for sharing a lot of your experience about building a 3d printer. If I'd seen your blog earlier, I might not have a department store at home today 
I agree that thingiverse has very good, but very bad designs also. To value it, I often check the Makes and Comments of the thing and whether the author has designed other things also.
I agree that thingiverse has very good, but very bad designs also. To value it, I often check the Makes and Comments of the thing and whether the author has designed other things also.
|
Re: Building Core XY dual extruder from scratch July 26, 2018 08:15AM |
Quote
JoergS5
Thanks a lot you for sharing a lot of your experience about building a 3d printer. If I'd seen your blog earlier, I might not have a department store at home today
I agree that thingiverse has very good, but very bad designs also. To value it, I often check the Makes and Comments of the thing and whether the author has designed other things also.
I know about that. Its just been a little hard to find a dual titan aero mount that will work on an mgn 12 rail.
|
Re: Building Core XY dual extruder from scratch July 27, 2018 08:18AM |
Quote
JoergS5
Thanks a lot you for sharing a lot of your experience about building a 3d printer. If I'd seen your blog earlier, I might not have a department store at home today
Yeah, but now you have parts for other projects....
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Sorry, only registered users may post in this forum.