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Discussion Starter · #1 ·
As a part of a business idea I am looking into CNC machines for working wood and plastic. They are totally foreign to me since my experience is mainly with hand tools. Other than size of the table what are the main factors contributing to the cost? What would I be expected to pay for a respectable setup with a 20 inch or so table? What brands should I look at and what should I avoid? Any suggestions or places to find info will be helpfull.
 

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Are you talking about a CNC router or a CNC milling machine? Features effecting cost are the work cube (X, Y, Z axis travel) spindle HP, spindle speed, controller and features, and lots lots more. CNC CAD/CAM software can be VERY expensive, stay away from BobCad don't say I didn't warn you! If a CNC mill would meet your needs you can get a used 'real' CNC mill for about or a little more than you would pay for a lot of pretend CNC router machines and hobby CNC machines. It would help to know more about what you plan to build to advise you. Also recommend you speak with some local CNC shops, they may be able to do the work for you on their machines for a reasonable price, jumping into CNC can get expensive fast, machine, maintenance, software (the software vendors are forever trying to pick your pocket for annual maintenance and upgrades and you can't jump from version 2 to version 5 they make you buy all the in-between upgrades you skipped. Another way to spend a lot of money is to crash your machine e.g. you make an ooops and the thing takes off and tries to cut a steel vise in half. THAT can get expensive really fast.
 

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Discussion Starter · #3 · (Edited)
My sister runs a letter press business. Her printer uses plastic and wooden plates as the negative for the printer and it occurred to me that a CNC could make the plates. With my limited knowledge It would be obvious that the Z travel wouldn't have to be significant but it would have to be able to do a 3rd dimension to some degree and have to be produce some extremely detailed results.

I am a cartographer by trade so I am very familiar with vector, raster, and cad data. But I'm not sure what software would be best for this usage. My sister would be the one designing the plates, she would then pass on an image to me.
 

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I own a CNC Shark Pro bought from Rockler.com. I also teach college students how to use their HD 2.0 version that resides in the college furniture design shop. The software they come with is VCarve Pro from Vectric.com, and in my opinion it is currently the easiest to learn and excellent for turning vector drawings or bitmaps into projects or project parts. Great potential for sign making (although I don't do much of that). Capable of doing just about any kind of project that fits within the 24.5x24.5 work area. Cut3D is also included for turning 3D work into tool paths for cutting out on the Sharks. Not a 3D editor though. We cut furniture parts, jigs to help make furniture parts, shop jigs, etc.. Right now Rockler has a Black Diamond special bundle that includes router and touchplate and dust brush, as well as some other extras.

cncsharktalk.com is the forum for Shark users. You can download free trail versions of VCarve Pro and other products at vectric.com. They also have a forum.
 

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How thick is the stock? Less than 1/4 inch? I saw a demonstration of a CNC laser at the Portland Woodworking show this past weekend you want detailed that machine can do extremely fine detail and I mean extremely fine no CNC mill or router could come close to that level of detail. I took some pictures I'll have to post them here later.
 

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Discussion Starter · #7 ·
From what I've been able to see the accuracy of standard CNC routers is about 0.004" which will probably be enough for me. Also after taking a closer look at the ebay special the hardware seems to be outdated pretty significantly, parallel port vs usb 2.0. Would this offer any problems?
 

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From what I've been able to see the accuracy of standard CNC routers is about 0.004" which will probably be enough for me. Also after taking a closer look at the ebay special the hardware seems to be outdated pretty significantly, parallel port vs usb 2.0. Would this offer any problems?
It will if you don't have a PC with a parallel port. The work-around is usually a USB>parallel adapter. Added expense.

The Sharks work over USB. Their smallest model is $2900, software included.

http://www.rockler.com/cnc-shark-routing-system-with-new-7-0-software
 

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.004 is okay IF the machine actually delivers the accuracy they advertise. I'm speaking from experience here :furious: Remember you are restricted by cutter size in terms level of detail and tool path best practices. For example you can't just go hogging into an inside corner with a 1/4 inch bit and expect to cut a 1/4 radius corner the bit will chatter, you would need say a 3/16 bit for that.

Then there's fixturing, how you will hold the stock while cutting which can eat into your work cube and present you with head scratching opportunities. A lot of times the rest is simple compared to fixturing.

I love CNC I don't want to discourage you its a blast but there's much to learn and it can be expensive and frustrating if you go into it ill informed.
 

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I appreciate the input there's a good bit to consider. Speaking of added cost that one does not come with a router and is $1,000 more than the general cnc sold at Woodcraft.

http://www.woodcraft.com/Product/20...rver-CNC-Carving-Machine-Model-40-913-M1.aspx
I see it uses stepper motors, recommend you educate yourself on steppers vs servo motors. Stepper motors can lose steps and if its losing steps each time it performs a movement and it performs that movement a number of times pretty soon it no longer knows where the cutter head is within the work cube and bad things happen. Servo motors while more expensive are more reliable, though a hard crash could knock them out of whack also. But steppers can lose steps simply due to load.

I had a CNC hobby mill once, it used servo's on X and Y which were quite reliable, it had a stepper on Z however and even with the head counter weighted the stepper motor lost position with each up/down movement on Z, within a few movements it would be off .050 inch which ultimately limited the machine. Never was able to resolve that issue and the manufacture left me hanging. For the thousands of dollars I poured into that machine I could have purchased my brothers use Haas mill. (face palm). I spent a couple years running large industrial CNC lathes and mills, there is a world of difference between them and the hobby class stuff that's out there.
 

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Discussion Starter · #12 ·
Very helpful thanks, I see even the more pricey machines ive looked at use stepper motors. Are all steppers equally unreliable or are some better than others. Would smaller steps be better?
 

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Its not always the stepper motors fault, they can be reliable. If the manufacturer uses an undersized stepper or some cheap stepper or their stepper controller is junk or their software is junk or their mechanicals are junk or a combination of the above well you get the picture.

Servo motors have an encoder disk that spins with the motor, in the better systems (because it is a system of mechanical components, motors, electronics and software) it will tell the servo to move say 4 inches on Y and confirm that it actually did move exactly 4 inches on Y or fault out. With lesser stepper systems the system will tell the stepper to move say 400 steps in Y and assume/pray that it actually moved 400 steps and not 375 or 430 steps then keep right on trucking. I'm exaggerating a bit but its the accumulated errors over multiple moves that gradually get the machine out of whack. That .004 advertised accuracy becomes .020 then .040.

You can easily see a .001 error in accuracy in a machined surface, it may just be cosmetic and not matter, but .004 will be quite noticeable usually when the ball screws reverse direction.

Take backlash (slop) for example, if you tell a CNC machine to machine a 6 inch circle your ball screws will move the router 6 inches on both axis then reverse and move back 6 inches on both axis. What happens if you have .004 backlash or slop in the system when the screws reverse? With mechanical slop plus stepper slop you may end up with a circle that looks like two halves of a circle that are not quite aligned.

There are mechanical and software based methods of reducing backlash to zero, even $250,000 CNC machines have slop, it may only be .0002 but its there. But you need a 'system' that is stable and consistent not a moving target due to stepper errors.
 

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I own a CNC Shark Pro bought from Rockler.com. I also teach college students how to use their HD 2.0 version that resides in the college furniture design shop. The software they come with is VCarve Pro from Vectric.com, and in my opinion it is currently the easiest to learn and excellent for turning vector drawings or bitmaps into projects or project parts. Great potential for sign making (although I don't do much of that). Capable of doing just about any kind of project that fits within the 24.5x24.5 work area. Cut3D is also included for turning 3D work into tool paths for cutting out on the Sharks. Not a 3D editor though. We cut furniture parts, jigs to help make furniture parts, shop jigs, etc.. Right now Rockler has a Black Diamond special bundle that includes router and touchplate and dust brush, as well as some other extras.
Where can I sign up for your class? ;)
 

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