What a difference a computer makes

[jwatkins]

I'm new to the site, so I thought I would start by sharing something I discovered a couple of days ago;

I have been trying to get my machine to cut parts more accurately for over a year. It never dawned on me that the computer could be the problem because I figured the weak link would be the LPT port and they're all the same. Well, I was wrong....

I put a desktop machine on it instead of the laptop and the improvement is absolutely staggering. My fastest jog previously was maybe 180-200 in/min with occassional stalling and tons of position loss. Average jog/rapid speed was more like 40-60.

Yesterday I ran my machine for about a half hour using a little test loop at 806 in/min with any discernable loss of position (eyeballing it). Needless to say, I'm thrilled with it. The big test will be next week when I'm cutting Ebony 8 hours a day for several days.

Here's a shot of my machine;

[anoel]

Hey John, welcome over here... I know you from MIMF... ( You shoud post some of your work in the "Musical Instrument Construction" and "Rhino 3D" forums here... We could definitely use some more Musical CNC'ers here.)

Your machine still kicks butt. and it's such a nice departure from whatthe other guys here have homebrewed... I definitely shows that your was developed from Independant thought and not a copy cat.

[samualt]

jwatkins:
What were the specs on the laptop and desktop? I ask because I was going to use my laptop on my CNC. Maybe I'll re-think that...

[InventIt]

What control software are you running?

[jeffs555]

There usually are no specs which will indicate how well a given computer will work over the printer port. Some laptops may work better than some desktops. The only way to really know is to try it.

[jwatkins]

The laptop was 500mhz, 64mb. The desktop is 833mhz, 384mb.

The control software is CNC Pro.

[pminmo]

What controller are you using? Not all controllers are equal, and I suspect that is your problem. A laptop's parrallel port sometimes has a slightly lower output voltage in the high state. How this manifests itself is as you described, inaccuracy and slower. This is because it misses step pulses a percentage of the time. Even some desktops run on the marginal edge.

Phil

[ynneb]

That design is sure a departure from the conventional designs.
At first it looked fragile, but on looking at it closer I can see that it would be quite stable.

Did you ever consider stabilizing the 4 pillars at the top or is that unnecessary?

Welcome to the Zone.

[jwatkins]

Pminmo, I'm using CNC Pro, or did you mean the post processor?

Ynneb, the pillars are 4" square 1/4" wall steel and are welded to the table and shelf below. The frame weighs a little over 700 lbs. without the gantry. No, I never considered stabilizing it further.

[jwatkins]

Here's a pic that was cleaned up a little for web site use and shows the layout a little better.

[pminmo]

I meant stepper controller hardware? Xylotex, hobby cnc....

[TyRex]

What diameter rod are you using for the rails??? And how much flex over the whole distance is there using that type of rail setup?