Building my CNC

[Atomic_Sheep]

Hi guys, I've finally run out of excuses to start building my CNC machine. I've read some of the sites that have been suggested by other threads on this forum and other forums and I've got a general idea about the sort of issues that are important but I'm certainly not a pro so I need some advice along the way.

I'm thinking building something in the order of 1-2m x 1m with 1-2m preferably being as close to 2m as possible (in fact, I'm probably thinking something in the order of 1.5m-2m x 1m.

Since I'm not a factory, it's at least for now going to be only producing what I need which is not a lot and not very often.

I don't really care about speed so much, I'm more worried about accuracy. I'm not doing anything that requires amazing precision but I want more precision and less speed than more speed and less precision if you know what I mean.

Not 100% about where it's going to stand so something with adjustable legs would be nice and something that is somewhat not impossible to move would be a distinct advantage although I suppose it might be possible to retrofit retractable wheels on it or something but I haven't really thought that far ahead just yet, I just know that I don't have a guaranteed place for it for the next 10 years so it's gotta be relatively mobile if that's even possible for CNC machines.

Price, well... as cheap as humanly possible - I'm building it myself for a reason after all. However, when I say as cheap as humanly possible I'm also aware that I've said I'm after precision which means that I basically want the best bang for the buck and I won't necessarily go for the cheapest option all the time... if at all. I certainly prefer best of the best but then I shop around to find the super cheapest price. I think that's the best way of describing what I mean by cheap.

In terms of materials I want to cut with it... well since this is the metal section i think that it should be obvious that's what I'm aiming at. Not sure about stuff like steel... would be nice for sure, but definitely at the very least something in the order of 6mm aluminium? So I'll say 6mm aluminium and assume that it'll be able to cut steel of I dunno 3mm or so by the very virtue of being able to cut aluminium. Like I said, I'm not making lots of parts at the moment, so really, I don't mind having to go over the same cut over and over again - deeper each time to go through thicker metals. The only parts that come to mind at the moment made of aluminium that I'll need to cut would be around 1.6mm or so but I'm leaving some headroom in all my minimum requirements. The thickest material that I have planned for it at this stage would be 9mm wood, but as I said, I'm looking for some headroom with this.

I'm presently mainly planning on cutting just sheets of materials so a 3dof is all I'm after. I'm not sure how dependent curved cuts are when it comes to designing CNC machines but I need a machine that will be able to cut really nice curved cuts also.

Basically, I need help in finding as many plans as possible that would resemble the monster that I have in my mind. Would really appreciate all your input!

Regards

[pinjas]

Hah, this sounds more like a blog than a call for information. Were in the same boat, but I feel like my boat is a tiny bit ahead of yours. Get your reading eyeballs out and put your butt in a comfy chair, you'll need them. You didn't say how you wanted to cut these metals you speak of, I'd assume it was either plasma or router. Either way, there are two forums I'd suggest reading over. Plasma, EDM and other similar machine Project Log - CNCzone.com-The Largest Machinist Community on the net! and Open Source CNC Machine Designs - CNCzone.com-The Largest Machinist Community on the net! . You can get a lot of great ideas from threads in these sections. You could possibly even just completely copy something here.

Software is a pretty big component here, I am still so unsure of everything, but right now I feel like I've got a decent idea on the software end. A lot of people use mach3, it's cheap enough and it's well used. Mach3 is the cnc software, it's the stuff that runs the 'g-code'. G-code is the language used to tell your steppers/servos what directions to move.
Then theres cad and cam software. There is a pretty massive selection out there, pretty overwhelming, you'd think every guy and his grandpa was writing software based on the selection. CAD is the drawing portion of this process, computer aided design. CAM is the tooling direction portion, computer aided manufacturing. I am using software that I think combines both CAD and CAM together, I don't have a CNC plasma table, yet, but I know that I can draw things very well in the software I am using. I am using google sketchup with an addon called phlatscript. From what I can tell right now, it is super simple to use and I believe it's free. Those are two extremely important details there. I don't know if there is any downside to the quality of the drawings or something, but I can't imagine there is, I suppose only time will tell.
I've been reading and thinking and drawing for a while. Making a decision on this can be pretty tough as there is so many options and it is so difficult to know anything for certain.
Right now I am leaning towards a G540 for the driver, a lot of people seem to love gecko drivers. The driver is a piece of hardware that translates the G-code into electric signals and sends them to the steppers. I asked someone today who is just about done making their CNC table for woodworking, using a router as the cutting method. He got 387 oz nema 23 4 wire steppers for his table. This seems like good news to me, they are fairly cheap and have enough torque to do the job. I was worried about having enough speed and torque to be able to do both plasma cutting and router cutting, I think I should be fine if I grab something in the 300-400 range. From what I have read, accuracy and repeatability is dependent on two things, the drivers and the tables design. So long as everything is 'true' or another way of saying it is if the gantry of the table runs straight and your drivers do the 'right' things, than you should have precision, or so the tale goes.

[Atomic_Sheep]

Hi, thanks for your reply, you're right, that's just the sort of information that I was looking for. I was actually quite confused by the fact that there was no DIY section in the metalworking part so I just decided to post my thread here.

As for router vs plasma... definitely looking for router CNC machines.

Not 100% sure whether I'll buy pretty much a completed one/kit or start from scratch but I'll definitely post my project if it's going to be a scratch project! So it if the mods want to move this thread to that section of the board, then that would be fine.

EDIT: I've had a look at a few build threads and I'm really liking what Ernie has accomplished so far with his build...

http://www.cnczone.com/forums/diy-cn...ter_build.html

I've got a few questions though...

1.) Just wondering how one might weld the top 4 pieces into the rectangle in such a way that there is no warp? How would you find a surface flat enough for this?

2.) How do you know if the 4 steel tubes that he used are not bent in anyway i.e. they aren't sagging from the get go?

3.) How important would the straightness of the tubes be in terms of being a base for a perfectly flat top? Would you sand it somehow to ensure that they are perfectly flat?

4.) Lastly, how do you ensure that the side rails... if drilled with a basic hand drill, are installed horizontally with the guide rail not having any wavelike motion? Sure there's a lot of bolts holding the side rails but I dunno.

Like overall, it seems like a really cool looking project but I'm just not sure about hard it would be to create something that is perfectly straight and true if you know what I mean with these sorts of dimensions (and also how would you go about selecting your vendors for materials to ensure that you get straight bits of a high quality for this sort of job??)

Obviously all this depends on how accurate you want this thing to be and although I said I'm not looking to build anything ridiculously accurate, I'm starting to think I want something that's pretty damn accurate after all. I read that most hobby CNC machines range in accuracy from 0.01" to 0.001" in accuracy. I think I want to go for the 0.001" accuracy and better if possible but at this stage I'm totally in the dark in terms of understanding how one would derive such accuracy i.e. how you can design in a particular accuracy.

[pinjas]

1. Judging by your question, is it safe to assume you have little to no experience in welding? The most sure way to prevent heat warping is to not use heat. Plenty of people seem to bolt most of the pieces together. What that means is you'd use a drill press to match up holes and use nuts and bolts to hold the pieces together. This is an acceptable option if your table isn't holding fluid of any kind. How would you tackle this? - WeldingWeb™ - Welding forum for pros and enthusiasts I also suggest reading this thread.

2. You have a few pretty simple options as far as testing the trueness of a piece of metal. The first one is to place the metal on a flat surface, try and give each side a slight bop, if it wobbles, you know something isn't right, you'd do this for all 4 sides. The next is an eye test, I always use this for lumber. Line the piece up with your eye and light down range, you'll see any lack of straightness without doubt. The third option is to use a piece of string, wrap it against each edge, if the metal isn't touching the string all the way across, you know you've got warping, this would probably be true on only one or two sides.

3. I've got no real world experience with CNC, so your guess is as good as mine. I'd assume that it's pretty freakin important though. If your CNC is cutting a straight line and the machine shifts ever so slightly, it would be as clear as day in the line, I don't know how sensitive a CNC is to this type of thing, but I am sure it is something to consider important.

4. What are the side rails? Are you referring to the X axis? I don't understand this question at all, maybe another can answer it or perhaps you could re-word it.

As far as accuracy goes, I've come to some assumptions or conclusions on many details as aforementioned. Drivers and the tables design. So long as the table is ridged and true, and the drivers are great, than you should, in theory, get great accuracy.

I guess something I didn't mention earlier is what the AXIS system means literally. Each axis is a form of direction, they are always labled the same. X is the back and forth, it is what the table is directly attached to, the gantry rides upon it. Y is the side to side, this is within the gantry, it would hold the Z axis and back it go side to side or back and forth. The Z axis is the up and down, the part that holds the the router and makes it go up and down. There can also be two more axis, I believe they are usually called A and B, they aren't always the same things, sometimes one is a turn table, sometimes one is a type of motion for the z axis, YouTube - 5-axis milling demo with EMC2 here is a video of some example. I don't know anything of your ideal applications, it doesn't really matter. I suggest you go and read those threads, there is a lot of hidden information in them.

[Atomic_Sheep]

Hi, yep, I meant the X-axis... in the thread you can see the x-axis side rails bolted to the frame... I suppose you would do the same test for it as in 2.).

[pinjas]

Originally Posted by Atomic_Sheep Hi, yep, I meant the X-axis... in the thread you can see the x-axis side rails bolted to the frame... I suppose you would do the same test for it as in 2.).

I don't know if there is a universal answer to that question, it really depends on how you go about attaching the X axis to the table and what the X axis is made out of. I've been imagining making the X axis the 'top' of the table and running the gantry with 4 bearings on the legs of the gantry itself.

If you look at the photo I've attached, imagine it without the angle steel on the left side, now imagine bearings just running along the top, of the 'x axis'. The x axis or the tables frame would be made out of 14 ga 4x2 steel rectangle. I haven't figured out why a lot of tables seem to have upper and lower bearings, or bearings that would be on the top and bottom of the x axis, nor do I understand the benefits of many of these complex axis systems.

I feel that if the bearings are at 90 degrees, true and straight, it won't really matter how it is guided beyond that. I suppose that some designs are a bit less likely to get shifted around or pushed over due to enhanced stability, but honestly, I am hardly concerned about someone knocking over something that weighs as much as a CNC table.

[Atomic_Sheep]

Not 100% sure what bearings are but based on what I've read, what you're talking about i.e. the complex setups is probably to do with the centre of gravity of the gantry (assuming bearings are what the gantry move along). If bearings are what I think they are i.e. the linear motion system of the table, then they don't just need to account for linear forces but also other forces with the gantry moving about in the other axis which basically warrants the need for more complex designs.

EDIT: Possibly a stupid question but you can use a CNC machine to engrave to quite fine tolerances right? e.g. engrave writing just past the thickness of paint? Like into the material but no more than saaaay 1/3 - 1/5 of a mm?

[pinjas]

Originally Posted by Atomic_Sheep Not 100% sure what bearings are but based on what I've read, what you're talking about i.e. the complex setups is probably to do with the centre of gravity of the gantry (assuming bearings are what the gantry move along). If bearings are what I think they are i.e. the linear motion system of the table, then they don't just need to account for linear forces but also other forces with the gantry moving about in the other axis which basically warrants the need for more complex designs.

It's a surprise that you don't know what a bearing is, if someone wanted to learn how to drive and you said, step on the pedal and they replied, whats a pedal, would you still drive with them? Google bearing. The bearings are basically the wheels that the gantry glides upon, I suppose linear motion system is a fancy way of putting it.
I don't know about the 'center of gravity' thing, if there was balance involved I could see need for heavy levels of sophistication I suppose, but so long as everything is 'level' the balance should come naturally.

I've got no idea on the shallow engravings, but I bet you could do it.

[Atomic_Sheep]

Thats the site where I got the whole centre of gravity thing.

Do it yourself CNC router: Design Considerations, the Gantry

I only breezed over it so didn't quite figure everything out so was only hypothesizing.

I recently bumped into Joe's Design. I'm not sure how good it is in terms of accuracy (perhaps someone could fill me in on estimates of what to expect), but I've got a feeling that I'm going to build it since I don't want to spend the next 10 years building a machine. Will probably modify the design a little to accommodate a specific router though.

I was however wondering... it's designed to be built from MDF? Is it possible to make it from better materials like Baltic Plywood? I just read a forum thread which discussed material selection and I think I'd prefer to make it from ply.

EDIT: Forgot to ask... would this router be capable of cutting the materials that I outlined earlier?