grex-mini mill question

[h_2_o]

a bunch of us were talking about different methods of retrofitting a mini and we came to a question nobody really new the answer to. as small as a mini mill is, would someone really benefit from using a grex over a parallel port? i can see the benefits in larger mills where the more fluid motion would benefit but the overall size of a mini would it?

anyway any comments are more than welcome

[pstockley]

The grex will allow you to run higher resolution and/or faster rapids (assuming your servos/steppers can cope). Plus you can use a lower spec PC or a labtop. I think in the long run the Grex is a way better solution than using the parallel port. I suspect eventually it will also achieve better results, especially for complex 3D toolpaths and 4 axis stuff.

If you need a solution today, there is no alternative to the parallel port option. However, 6 to 12 months from now go for the Grex. I am going to fit a Grex to my Tormach and Hardinge lathe (support for lathes is probably over a year away).

Plus, I will add that the smaller the parts you make, generally the accuracy needs to increase. My hobby is model engineering and from experience on a big part you cannot often spot 0.001" out of tolerance. However it becomes clearly visible on small parts.

[Chris D]

With a parallel port setup, you will be able to achieve speed well in excess of what you want on such a small machine. For example, 200 IPM would be more than fast enough when your longest travel is 12 inches or possibly less. You will be able to configure this for .0001" resolution which is also well within the machine's capabilities.

One advantage to the GREX device I see is that it no longer needs a parallel port on the computer - this makes it useful for use on laptops and such. However, you will need either a USB or network interface depending on which configuration you go with - both of which may have problems associated with them too.

As for being able to run your machine with an older, less powerful computer, that may be an advantage. However, you can purchase new computers for around $200.00 at Fry's that run machines just fine and dandy.

For the machines I have been doing (routers, small lathes, bench mills etc.), I don't think I would use the GREX as I have yet to reach the bounding limits of a parallel port configuration. My CNC router runs at 200 IPM with .0002 resolution 1/4 stepping and works just great. The mill and lathe will run slower, but then again, they don't have as long of travels and generally you don't cut metal as fast as you do wood.

Chris

[h_2_o]

I wonder if you could make a "breakout box" that is not optoisolated for the grex. no i'm not thinking breakout board but for those of us with small shops that do one thing on the mill then go over to a lathe and do something if a box could be rigged up similar to something like this



but instead of it being a video source, you can select if you want it to push your lathe or mill or whatever else you got going on. and i'm curious if any type of isolation would be needed.

[Chris D]

Don't see why not, nor why you couldn't do the same thing with a parallel port interface. You would need to have the computer near both machines for practical reasons.

There have been printer switch boxes for as long as there have been printers. As for the Grex thing, well, I believe there will be two different interfaces for it - network and USB. USB is hot swap capable and I believe the network cables are as well.

[h_2_o]

actually i was thinking more have it connected via network and that part would never be disconnected, but the output connections to the drives and any other inputs could be controlled by a switch box. that is why i was curious if it would need to be isolated.

[Chris D]

again, I suppose you could switch all the I/O after the Grex to the machines. I would power everything down between the switching and such though to make sure nothing is damaged. Stepper drives don't like things being plugged in / out, power on / off etc.

Chris

[dserratt1]

The GRex has some advantages first if you ignore the price it has 16 inputs and 16 outputs along with 6 axis support. but if you consider that printer ports are getting hard to get on new computers the cost of a good breakout board is $100.00 to $150.00 plus you will need microstepping drives which are not needed with the GRex because it will give you all the pulses you will ever need, if your talking gecko drives thats $34.00 per drive since you only need 201 instead of 210. next is performance I am converting a Dyna Myte 2400 with 3 gecko 210's and a Campbell Designs breakout board, I found out the performance is only as good as the printer port pulses which are hardly adaquit. after switching to the GRex I was saving for my BP conversion I discovered my motors ran so much better accell decell top speed noise every aspect, I am selling my Campbell board and getting another GRex. after some research i found that printer port pulse timing is not perfect or even good to give you an example lets say you send 5000 pps to a motor the variation in timing is the same as telling the motor so speed up and slow down as the pps change. The grex is almost perfect pulse timing. also dosent tax your cpu nearley as much.