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Dremel CNC Plans

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punxrus:

--- Quote from: SithMaster on September 19, 2008, 06:07:27 pm ---How does the software account for differences in motors?

So who's going to use these to build cabinets.   ;)

--- End quote ---

I'm going to make the worlds smallest arcade and then....TAKE OVER THE WORLD!  >:D

Ed_McCarron:

--- Quote from: SithMaster on September 19, 2008, 06:07:27 pm ---How does the software account for differences in motors?

--- End quote ---

Typically, the program draws (cuts?) a line.  You measure it and tell the software how long it is.  It can then calibrate its pulses to equal a real world measurement, ie, 894 steps = 1 inch.

Just remember, with a stepper based table, theres no position feedback like in a servo table.  You miss a step, or bind, and everything gets thrown off - but its a load cheaper and simpler.

Franco B:

--- Quote from: facesmiths on September 19, 2008, 04:14:44 pm --- mine is accurate to with in a few 10,000ths of an inch and repeatability with in 6 to 7 10,000ths

--- End quote ---

Fair play :applaud:  Have you got any pictures of yours?

I would be tempted to build one myself if I didn't have these at my disposal.  :P





facesmiths:
1. bom (ballpark) for mine was: $400 for 150oz in motors x 4 plus a control board that will allow me to go up to 7 amps per phase. this is good for my mid size project (the one I have will cut single player CPO's as it stands and will move my rotozip up and down and even move a decent size router but I assist mine with a pulley to keep from wearing out the lead nut as I used a thick piece of polyethylene (part cut out of the top of a 55 gal plastic barrel) and to be honest my table could be bigger with these motors. as for the mill it's self I dumpster dived all my parts from computer racks (the "C" channel rails that the plates you don't see inside the rack mount cabinet) that were being thrown away by a local pipeline company. and MDF for a lot of the body from a local company that distributes tile and so they use it to make signs with bunches of tiles on them as displays. the only things I spent money on were scrap block and plate aluminum for the base insides as well as the ends of the table axes, and my various nuts and bolts and 1/4 inch threaded rod for the lead screws. so I would say I have spent on parts and motors and a control board (all in one) about 500 bucks. I mean even the wire I am using to connect the board to the motors and cable to run the board from the parallel port and the finally the old computer (pentium 75 mhz) was dumpster dived and the euro screw terminals (I have seen some one use them for a keyboard hack here) was a gimme from OKE I belive is the name I just wrote them for some other samples, noticed they made them, added the terminals, and they sent all of it free. I image buying everything from radio shack and various suppliers would only run up another 150 to 200 though cause the old computer you can get from a thrift store for like 3 to 5 bucks and it is really all you need.

2. if I built something for some one else I would probably ask about 2 grand for some thing like mine just a better design to utilize the knowledge I gained from building mine and would include something to address the lack of feed back issue Ed_McCarron mentioned and include some optical sensors to account for this. I have designed and tested a concept that uses an old mouse and pinch wheel to track movement down to 1/4 of 1,000th of an inch which is my movement per step. a larger change over would up this ratio if need be, and to be able to buy extra boards and such to assure I could replace anything that did not make to the 6 month date as a sort of warranty back up. I can get them replaced but I would not want to have to wait to be able to ship a replacement. also I would have to include all the cables and a cheap computer to assure everything worked out of the box if that was what some one was looking for. cutting area 1 foot by 2 foot by 6 inches and a cutting depth of 2 inches with 1/4 inch extra long end mills. materials workable are really only limited to your imagination and the bits you use and the time you allow the end mills to do their job but I have done hardened steel work on it with tungsten carbide bits oh and I could not send one out with out a 4th axis. you would not belive how much more you can do with a mill with one of these on it. at the very least you can do lathe work on the mill with out having to have the extra machine sitting taking up space, though it is much slower and really more usefull for doing various cuts and gear making work  not huge but much more than a PCB maker would need.

last thing I need to say about the feedback issue addressed by Ed_McCarron

stepper motors or any other sort of motor gives a quick jolt of power it creates and this is called feed back. you probably already know this but what you may not know is there is a company that makes a chip that instead of being damaged by this and needed to be protected from it, this chip actually needs it to one of the inputs for that axis as it used this to know the motor moved! I so want a board utilizing these and will build one some day.

as for pics I will post some once I have it reassembled unless I stumble across my old pics from my last place and maybe some of the work I did on it

facesmiths:

--- Quote from: SithMaster on September 19, 2008, 06:07:27 pm ---How does the software account for differences in motors?

So who's going to use these to build cabinets.   ;)

--- End quote ---

the software I have allows for differnces on all 8 axes that can be hooked up to it so differning size motors that have to have differnt size threaded rod can be calibrated accordingly same with rotary axes.

mine is basicly this formula

200 steps per revolution of the shaft times 1/20 or 1/4 inch rod 20 thread (per inch) so 200 x 20 =4000 steps per inch
they make motors that do other amounts of steps per revolution but the popular ones seem to be 200 and 180 (180 works well if you like to work in degrees for a rotary axis) I dont but instead work in radians and this works out perfectly for the 200 step units since there are exactly 400 radians to a rotation and that is half. I will eventually be making some odd ball stuff that requires division of 3 instead of 2 or 4 and will have to have a 180 step motor but for now I am set just fine. with a 4 axis system and some decent sized cut off discs you can even make carbide tooling for your mill. I know because I have done it. you do of course have to do a bit of testing and account for breakdown of the discs but it worked really well and I don't think the bits I have bought were much better really though I don't do productions work  so I don't know if the commercial ones would have a longer life. probably.

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