Which Kit? Railcore? SecKit? Other? March 06, 2020 04:46PM |
Registered: 4 years ago Posts: 17 |
Re: Which Kit? Railcore? SecKit? Other? March 06, 2020 05:55PM |
Registered: 12 years ago Posts: 5,794 |
Re: Which Kit? Railcore? SecKit? Other? March 06, 2020 09:34PM |
Registered: 4 years ago Posts: 17 |
Re: Which Kit? Railcore? SecKit? Other? March 07, 2020 12:30AM |
Registered: 12 years ago Posts: 5,794 |
Re: Which Kit? Railcore? SecKit? Other? March 07, 2020 02:10AM |
Registered: 4 years ago Posts: 17 |
Quote
the_digital_dentist
I posted a CAD model of UMMD and a lot of information about problems and fixes for them. That's what open source is about. I'm surprised anyone tried to commercialize it because it isn't the cheapest way to build a printer, and cheapness seems to be the main driver of printer sales.
Most of the non corexy cartesian mechanisms move the X axis motor along the Y axis. A lot of people worry about the mass that motor adds, but I'm more concerned about having to run a cable to it. It's bad enough you have to run one to the extruder, but running two multiconductor cables to two moving motors is asking for trouble. I'm sure it can be done reliably if you apply enough effort, but it isn't my preference. My older printer, SoM, uses a flex ribbon cable to take all the signals and power to the extruder carriage. It has been working with 100% reliability for about 6 years now. If I could find a cheap source of that type cable and tools to terminate it I'd probably go into business selling it to 3D printer builders. I hate running cables to moving stuff and finally took the X axis endstop switch off the extruder carriage in SoM.
Back to your question. The short answer is no, I don't think there's any special advantage of corexy over any other cartesian (except maybe H-bot) when it comes to print quality when you're printing at "normal" speeds. Just about any mechanism will work fine. Corexy is pretty easy to build well, once you understand how it works.
I don't think much of the mechanical complication that something like a remote-motor extruder adds. The whole point of moving the motor off the extruder is to reduce moving mass so you can theoretically print faster, but in order to make it work they have to gear it down 20:1 and that may limit extrusion speed which will limit print speed anyway. What is the benefit that justifies the added cost and complication?
The Duet people are working on a design that runs power and a serial wire to the extruder and that's it. It'll have a board on the extruder carriage that drives the motor and controls the heater and fans. That will be a real advance over the multipin cabling and connectors that are needed now.
Re: Which Kit? Railcore? SecKit? Other? June 06, 2020 01:44PM |
Registered: 6 years ago Posts: 9 |
Quote
I'm not a big fan of the Railcore design. Too many printed parts that extend beyond the frame, making it hard to enclose.
Quote
The motor mounts look flexible, the pulley mounts don't look very good either. Standing a post with two pulleys up in a piece of printed plastic and putting tension on the belts is likely to cause the plastic to flex and tilt the post.
Quote
I'm also not a fan of using multiple Z axis motors. They get out of sync when you cycle power and that tilts the bed so you have to have some sort of scheme to relevel the bed frequently. It looks like the design could easily be modified to use a single Z axis motor.
Quote
It's hard to be sure from the CAD model that doesn't show the belts, but it looks like the A and G belt segments will not be parallel to the Y axis guide rails.
Re: Which Kit? Railcore? SecKit? Other? June 06, 2020 04:57PM |
Registered: 9 years ago Posts: 123 |
Quote
the_digital_dentist
I'm not a big fan of the Railcore design. Too many printed parts that extend beyond the frame, making it hard to enclose. The motor mounts look flexible, the pulley mounts don't look very good either. Standing a post with two pulleys up in a piece of printed plastic and putting tension on the belts is likely to cause the plastic to flex and tilt the post. I'm also not a fan of using multiple Z axis motors. They get out of sync when you cycle power and that tilts the bed so you have to have some sort of scheme to relevel the bed frequently. It looks like the design could easily be modified to use a single Z axis motor. It's hard to be sure from the CAD model that doesn't show the belts, but it looks like the A and G belt segments will not be parallel to the Y axis guide rails.
Re: Which Kit? Railcore? SecKit? Other? June 06, 2020 05:41PM |
Registered: 6 years ago Posts: 9 |
Re: Which Kit? Railcore? SecKit? Other? June 07, 2020 10:12AM |
Registered: 7 years ago Posts: 1,007 |
Quote
Wescherry
A lot of misinfo on the Railcore from the Dentist.
...
Quote
I'm also not a fan of using multiple Z axis motors. They get out of sync when you cycle power and that tilts the bed so you have to have some sort of scheme to relevel the bed frequently. It looks like the design could easily be modified to use a single Z axis motor.
This re-tramming of the bed happens automatically, doesn't take more than a few seconds and levels the bed better than most can do with manual screws. It also accounts for different thickness springsteel build plates automatically.
.....
Re: Which Kit? Railcore? SecKit? Other? June 07, 2020 02:57PM |
Registered: 6 years ago Posts: 9 |
Re: Which Kit? Railcore? SecKit? Other? June 07, 2020 03:08PM |
Registered: 10 years ago Posts: 14,685 |
Re: Which Kit? Railcore? SecKit? Other? September 03, 2023 11:57PM |
Registered: 9 years ago Posts: 75 |
Re: Which Kit? Railcore? SecKit? Other? September 04, 2023 11:25AM |
Registered: 12 years ago Posts: 5,794 |
Re: Which Kit? Railcore? SecKit? Other? September 05, 2023 06:53PM |
Registered: 9 years ago Posts: 75 |
Re: Which Kit? Railcore? SecKit? Other? February 09, 2024 07:27PM |
Registered: 9 years ago Posts: 75 |
Quote
the_digital_dentist
You won't need training on a lathe to build a UMMD copy. It's not entirely necessary to use a milling machine, either, though it can be very useful. Simple cuts and accurate, square drilling are the main uses for the mill- square up the ends and matching lengths of the frame pieces so that they bolt together squarely, and milling the perimeter of bed plate. You will want to drill holes squarely in the tubes for mounting pulleys, and drilling the holes to mount the Y axis linear guides and milling the t-slot flat where the Z axis guides will mount. Access to a fly cutter can be handy for cutting the large holes in the motor mounts, but a hole saw can be used instead. If you buy frame pieces from Misumi, they'll be cut squarely and accurately, so you might be able to get away with just a drill press instead of a mill. The mill can be useful for making cuts in the bed plate for the kinematic mount, though it's not entirely necessary. I invested in a 3 flute tungsten carbide mill (about $30) that's 1/2" diameter and has 2" cutting length for quickly squaring ends of t-slot in a single pass. I use it on an old Bridgeport mill at the makerspace.
Whatever you do, don't use 20 mm or 1" t-slot for the frame. It's cheaper and more rigid to use larger t-slot and just bolt it together than to use small t-slot and dozens of braces and corner plates and all the hardware that goes with them.
If you build it like UMMD- a single motor driving the Z axis- you won't really need auto tramming, but if you want it, use it. I wouldn't try to use a 3 mm plate for a bed that's 350 x350 mm. It's going to be too flexible. 6 mm or 8 mm cast tooling plate should work fine. Whatever you do, get a bed heater that's the same size as the bed plate. I see a lot of designs where the plate is a lot bigger than the heater- that's asking for it to warp when heated because the heated center of the plate will expand more than the unheated edges. Use ears for bed support screws like UMMD. If you use 3 screws or belts to lift the bed, put the reference and pitch support screws at corners of the plate and the roll screw at the middle of the edge opposite the the other two screws. Even if you use auto tramming, use the kinematic mount for the plate. That allows it to expand when heated without pushing laterally on anything.
I still use the original piece of 0.7 mm PEI (6+ years old) glued to the aluminum plate for the print surface. Everything sticks, though some materials stick a little better than I would like. I find that putting a few drops of IPA at the base of the print helps release prints from the PEI. PEI coated flexible steel sheets are OK, too, but thickness may vary so you may need auto tramming/zeroing to accommodate multiple steel sheets.
If you're mostly going to print with PLA (ugh!) or PETG you don't need to heat the enclosure (but enclosure is still a good idea) and you can put the motors inside the enclosure. If you ever intend to print with ABS, you'll need an enclosure and a heater for it. You need to get to 50C as a minimum to ensure reliable ABS printing, though even higher temperatures would be better, especially if you want to make large prints. Be sure the design you choose can be easily enclosed. You might want to move the motors outside the enclosure, depending on how hot you want it to get. The X and Y motors get about 10C above room temperature, so it would probably have been OK to put them inside the enclosure. The Z motor
Your printer is going to have a big footprint, maybe too big for most desks. If it will end up standing on the floor or on a cart, consider just making the machine taller, and then you can also expand the Z axis for taller prints. Make sure you can fit the printer through standard doorways (or your own doorways), and consider putting the electronics on top of the machine- that keeps everything accessible and cables short.
Re: Which Kit? Railcore? SecKit? Other? February 10, 2024 10:10AM |
Registered: 12 years ago Posts: 5,794 |
Re: Which Kit? Railcore? SecKit? Other? February 10, 2024 02:24PM |
Registered: 9 years ago Posts: 75 |
Re: Which Kit? Railcore? SecKit? Other? February 10, 2024 08:19PM |
Registered: 12 years ago Posts: 5,794 |
Re: Which Kit? Railcore? SecKit? Other? April 18, 2024 05:16PM |
Registered: 9 years ago Posts: 75 |