CNC Noob Has Questions
January 1, 2021 10:24 AM Subscribe
Today I checked and the Onefinity CNC I ordered months ago is scheduled to arrive sooner than expected... like, gulp, next week. Little help?
Assembly seems to be pretty easy, so the first order of business will be building a platform and table, potentially with a piano hinge so that work pieces can be clamped vertically, e.g., for cool joinery. CNC veterans, what are your tips and tricks? How does your work flow go? Software preferences assuming that I'm already pretty proficient at FreeCAD and SketchUp and so not afraid to take on other design programs, e.g., Fusion 360, V-Carve, Carveco, or whatever is best? Accessories that are worth the money (I sprung for the 3 axis touch probe but not the gamer style controller)? Info sources you find useful? Project ideas for a beginner? Lay it on me, and thanks!
Assembly seems to be pretty easy, so the first order of business will be building a platform and table, potentially with a piano hinge so that work pieces can be clamped vertically, e.g., for cool joinery. CNC veterans, what are your tips and tricks? How does your work flow go? Software preferences assuming that I'm already pretty proficient at FreeCAD and SketchUp and so not afraid to take on other design programs, e.g., Fusion 360, V-Carve, Carveco, or whatever is best? Accessories that are worth the money (I sprung for the 3 axis touch probe but not the gamer style controller)? Info sources you find useful? Project ideas for a beginner? Lay it on me, and thanks!
I do not use that specific machine, but do have something similar with a 37" bed, so a few thoughts...
My workflow is:
Fusion360 for design
-> Fusion360 CAM for toolpaths
-> customized Fusion360 postprocessor for the actual gcode
-> CAMotics gcode simulator to double-check the toolpaths (your machine is based on the Buildbotics controller, which also recommends CAMotics.
-> I use UGS to send the gcode to my controller, even though CAMotics can do it
I use a customized postprocessor in Fusion360 to generate my gcode because I want to make EXTREMELY SURE that my feed rates are under control -- my machine is capable of scary speeds (well over 900ipm), so I have a post that keeps everything under control no matter what Fusion360 thinks is wise (Fusion360 likes to do some unrestricted speed movements, which will command your machine to make moves at the maximum possible rate, which can be .... not so great ... on hobby-scale machines). The other way to do this is to put limits in the controller itself, but I prefer to do it in post because that way it's easier to do those crazy moves if I decide it's a good idea, without having to reconfigure the controller settings.
If you're going to use a spoilboard (I use a T-slot bed, with a spoilboard on top) then you'll want a surfacing bit to flatten the spoilboard relative to the machine. I use a Whiteside bit for that.
Make sure you mount the machine to the most stable table you can, with plenty of bracing so that it doesn't vibrate too much in use. Since I'm using an old dining room table, I reinforced the table with cable bracing.
When attaching things like clamps and fixtures, I'm paranoid (again) and do most of my attaching using nylon screws and nuts -- this way if I fuck up a toolpath the bit can go straight through my "hardware" without even blinking. Nylon is of course not as strong as steel, but for my uses I can adjust for that easily by just using a larger fastener or else more of them. Brass hardware is the traditional approach, but I prefer nylon to attach my clamps and rails.
For certain operations with thinner pieces where I don't care about repeatability, the painters tape + superglue approach works well (put blue painters tape on bed, put blue painters tape on entire bottom of part, put superglue on bed tape, stick down part. When done, pull up tape from both parts and discard)
If you go for the piano-hinge bed, consider also adding some method of "locking" the two halves of the bed such that they vibrate as a single unit when the hinge is not being used (having two parts of your bed behave differently under load makes it really hard to troubleshoot, IME).
Consider your dust collection; if you're going to use a Shopvac style setup you will definitely definitely want a dust separator (link goes to a video explaining how to make a very cheap and surprisingly effective separator).
posted by aramaic at 11:29 AM on January 1, 2021 [3 favorites]
My workflow is:
Fusion360 for design
-> Fusion360 CAM for toolpaths
-> customized Fusion360 postprocessor for the actual gcode
-> CAMotics gcode simulator to double-check the toolpaths (your machine is based on the Buildbotics controller, which also recommends CAMotics.
-> I use UGS to send the gcode to my controller, even though CAMotics can do it
I use a customized postprocessor in Fusion360 to generate my gcode because I want to make EXTREMELY SURE that my feed rates are under control -- my machine is capable of scary speeds (well over 900ipm), so I have a post that keeps everything under control no matter what Fusion360 thinks is wise (Fusion360 likes to do some unrestricted speed movements, which will command your machine to make moves at the maximum possible rate, which can be .... not so great ... on hobby-scale machines). The other way to do this is to put limits in the controller itself, but I prefer to do it in post because that way it's easier to do those crazy moves if I decide it's a good idea, without having to reconfigure the controller settings.
If you're going to use a spoilboard (I use a T-slot bed, with a spoilboard on top) then you'll want a surfacing bit to flatten the spoilboard relative to the machine. I use a Whiteside bit for that.
Make sure you mount the machine to the most stable table you can, with plenty of bracing so that it doesn't vibrate too much in use. Since I'm using an old dining room table, I reinforced the table with cable bracing.
When attaching things like clamps and fixtures, I'm paranoid (again) and do most of my attaching using nylon screws and nuts -- this way if I fuck up a toolpath the bit can go straight through my "hardware" without even blinking. Nylon is of course not as strong as steel, but for my uses I can adjust for that easily by just using a larger fastener or else more of them. Brass hardware is the traditional approach, but I prefer nylon to attach my clamps and rails.
For certain operations with thinner pieces where I don't care about repeatability, the painters tape + superglue approach works well (put blue painters tape on bed, put blue painters tape on entire bottom of part, put superglue on bed tape, stick down part. When done, pull up tape from both parts and discard)
If you go for the piano-hinge bed, consider also adding some method of "locking" the two halves of the bed such that they vibrate as a single unit when the hinge is not being used (having two parts of your bed behave differently under load makes it really hard to troubleshoot, IME).
Consider your dust collection; if you're going to use a Shopvac style setup you will definitely definitely want a dust separator (link goes to a video explaining how to make a very cheap and surprisingly effective separator).
posted by aramaic at 11:29 AM on January 1, 2021 [3 favorites]
Oh, one handy trick to align a part to the machine prior to cutting is to put a rod in the spindle. Loosely screw down one corner of the part, jog the machine until the rod is in contact with that corner of the part, then command it to run along the long axis of the part -- this will cause the rod to push the part into alignment with that axis (rotating about the one screwed corner), so then you can just screw it the rest of the way down. Much simpler than messing about with edge finders, and plenty good for working in wood and the like.
posted by aramaic at 11:37 AM on January 1, 2021 [1 favorite]
posted by aramaic at 11:37 AM on January 1, 2021 [1 favorite]
Response by poster: This is all really helpful! Not to threadsit, but I also bought a dust collector shoe that I can hook up to a shop vac, so I should be all set in that department.
posted by carmicha at 2:37 PM on January 1, 2021
posted by carmicha at 2:37 PM on January 1, 2021
I don't have experience with hobbyist CNC machines, but I spent a decade operating massive industrial milling and turning centers before spending several more years supporting them as an engineer. Over the years, I trained a lot of new machinists, and I wouldn't let them begin supervised operation of the machines until they had a good grasp of the following:
1. Know what your origin is, where you have it set, and which direction the tool will move relative to the origin, given a positive or negative incremental move.
2. Understand the difference between absolute and incremental modes. How do you tell which one you are in? How do you change between them? When would an incremental move and an absolute move to an identical numerical value result in movements in opposite directions?
3. Understand tool length and diameter compensations. What would happen if your tool length comp value was set 2" shorter than actual length and your program's first move was a rapid travel to a point 1" above the work surface?
4. Have a decent grasp of the most commonly-used G-codes and M-codes, and have a reference sheet available. Why would a move of G00 Z -100.; concern you?
5. Understand the use of rapid override dial, the feed hold button, and the e-stop. When you're running a new program for the first time, you want one finger on the feed hold, and the other hand on the rapid override. Start at zero, slowly dial up and ensure the program is doing what you expect at all times.
There is, of course, much more to it than that, but these are the things I wanted people to understand before I let them push buttons during their training in an industrial setting. Ignorance of the above could result in somebody crashing a machine or throwing a workpiece out of a fixture.
Like most modern CNC programmers, it looks like you're going to be using CAM software, but I would really encourage you to familiarize yourself with Gcode enough that you can write some simple programs from scratch and try them out.
posted by TrialByMedia at 8:12 AM on January 2, 2021
1. Know what your origin is, where you have it set, and which direction the tool will move relative to the origin, given a positive or negative incremental move.
2. Understand the difference between absolute and incremental modes. How do you tell which one you are in? How do you change between them? When would an incremental move and an absolute move to an identical numerical value result in movements in opposite directions?
3. Understand tool length and diameter compensations. What would happen if your tool length comp value was set 2" shorter than actual length and your program's first move was a rapid travel to a point 1" above the work surface?
4. Have a decent grasp of the most commonly-used G-codes and M-codes, and have a reference sheet available. Why would a move of G00 Z -100.; concern you?
5. Understand the use of rapid override dial, the feed hold button, and the e-stop. When you're running a new program for the first time, you want one finger on the feed hold, and the other hand on the rapid override. Start at zero, slowly dial up and ensure the program is doing what you expect at all times.
There is, of course, much more to it than that, but these are the things I wanted people to understand before I let them push buttons during their training in an industrial setting. Ignorance of the above could result in somebody crashing a machine or throwing a workpiece out of a fixture.
Like most modern CNC programmers, it looks like you're going to be using CAM software, but I would really encourage you to familiarize yourself with Gcode enough that you can write some simple programs from scratch and try them out.
posted by TrialByMedia at 8:12 AM on January 2, 2021
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Depending on the types of cuts you're hoping to make (2D/2.5D/3D) you might have varying levels of success with varying workflows, but I've found that Fusion 360 is the best bang for the buck in that you can do everything - (design, sculpt, and toolpaths - within one program. I've also had good experiences with Rhino and RhinoCam (I really love Rhino), but it's a Windows-only process.
There are kind of endless directions you can go, depending on what you're making (furniture! relief sculpture! mechanical parts!). I found myself getting pretty hung up on feeds and speeds, and wish I hadn't worried too much about that, though I'm just cutting wood and not metal.. You can get something like G-Wizard if you want to go deep, but you can also probably just Google around for some basic charts.
For YouTube, I particularly like Winston Moy and NYC CNC. Reddit has a few pretty good communities for this as well - r/CNC and r/diycnc, and probably others too.
My advice for beginner projects would be to start simple with a basic 2D profile, or like a sign of some sort. Then you can work on something more 3D, and finally something that involves flip milling (which might be more than you want, but is pretty satisfying).
I don't know much about the onefinity, but the touch probe should be useful. I also have a pair of digital calipers which are helpful (I got whatever they had at HomeDepot). A video game controller seems kinda weird, but everyone does things their own way. Depending on how easily you can get the machine square, you may also want things like dial gauges, 1-2-3 blocks, or other machinist measurement tools, but hopefully you can avoid that initially.
If you're planning on cutting wood, you'll also want to make sure you have dust collection. Building a dust boot of some sort might be a really great early project, though if you're able to, buying one will be easiest.
Feel free to MeMail me. I am absolutely no expert, but I've been muddling my way through things for a couple of years, so I know some stuff.
posted by taltalim at 11:24 AM on January 1, 2021