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eBay cnc machines

PostPosted: 19 Jul 2015, 16:50
by chicago_mike
Anybody has used one of those eBay cmc machines? ... 2ed6d8b36b

Been thinking of getting one of these. Also that pcbs mask paint that eBay sells. They have various colors. Blue purple and white would be cool.

Or am I just asking for trouble? :twisted:

Re: eBay cnc machines

PostPosted: 19 Jul 2015, 18:03
by Ice-9
In that link it looks like that model uses a parallel port which you don't find on many new computers anymore. a usb version would be better, I am not sure if a parallel to usb converter will work with this :(

I still use an old laptop with my labtool48 programmer as it needs a parallel port to work. That is the only reason I keep the old win98 laptop. It is something worth looking into if you can get it to work on usb or buy a usb cnc.

Re: eBay cnc machines

PostPosted: 19 Jul 2015, 18:19
by chicago_mike
I found a few usb controllers that are pic/atmel based and they claim to work. A regular usb to parallel cable won't do it.

If the machine itself is cool, I might pick one up. I visited a board house close to me and was inspired to really do my own stuff full on. :horsey: :slap:

Re: eBay cnc machines

PostPosted: 21 Jul 2015, 15:17
by R.G.
I have one. They work.

Be prepared to do some serious work on getting things set up straight, rectilinear and level if you're trying to hold tight tolerances on XY positions, repeatability, and accuracy. Go read about accuracy in machining; the UK "model engineering" literature from the 50s through the 70s is particularly good for this kind of thing.

They do want a parallel port. A USB to parallel is not a good solution. The way these machines get good accuracy is to do lots of real time computing in the PC and output step instructions to the XYZ motor drivers at critically important times. USB as a signalling protocol has built in delays and response times that degrade this. Worse yet, USB latency issues are not constant, which would mean they could be adjusted out. They are erratic, so USB to parallel adapters result in erratic missed steps and not-quite-repeatable positioning. A native parallel port is really the best solution.

Some modern motherboards have a parallel port connector on the motherboard, but no connector on the output. This would be fine. So -probably- would a PCIe parallel adapter card. Both solutions get mentioned in the CNC machine niche. So would an old laptop with a parallel port. This has the advantage of giving you the display and keyboard you need to drive the machine.

Re: eBay cnc machines

PostPosted: 21 Jul 2015, 19:20
by apollomusicservice
A few years ago, I made my cnc router from the control electronics to mechanical installations.
For that purpose I bought a used laptop with a parallel port and use it only for the controlling CNC.
I tried the USB / parallel interface but I find this solution more practical to have a laptop for router.

Re: eBay cnc machines

PostPosted: 21 Jul 2015, 20:18
by chicago_mike
I figure I can find a cheap ass happy to work the cnc machine.

I want to make pub's that way. :D Plus I can mill nice faceplates too.