Thinking about a 5i25 board only

Hi everyone. I have a fairly simple (I hope) question. I have a 4 axis router that is working pretty well with a parallel port. I am using LinuxCNC V2.8 in MM mode on a HP RP5700 computer. My max jitter is about 32000. I have it set for 35000 and it's performing reliably. Only the stepper speeds are really slow, about 40 - 45 or so. I would like better performance, but I can live with what I have.

I am thinking about getting a 5i25 card to simply replace the parallel port. It looks like the hardware will do it. Has anyone tried this? I could not find out very much about it and Mesa has not returned my email. Are there subtle problems that I have not found in googling the heck out of it? I basically just want to know if I can get away with just the 5i25 card, or do I need a 7i76 with it.

I would greatly appreciate your input.
Thanks,
Chuck Tilbury
whistlemaker.com

andypugh wrote:

Are you sure that it is step-rate and not hardware that is limiting your speeds?

No, I am not sure. I can set it up to step much faster, but it's not reliable at a higher speed. The stepper drivers are based on the TB6560 chip. It could very well be that the hardware is the limitation and increasing the step rate won't help. I don't know of a way to prove it one way or another. That's one of the reasons I am being a little cautious about just throwing money at it.

tommylight wrote:

Also 40 to 50 what

That's MM per minute. You see why I want to increase the speed....

Should I post screen shots of stepconfig? Is that the info that will help?

I misspoke earlier. The max speed is not 40 MM/minute it's 55 MM/second. That's very adequate to do simple stuff. The "fast move" times are not terrible, but could be much better, I think. That's what we are really talking about. The machine will move fast enough to break a 30 degree V bit in MDF.

I have several configs. This one is the simplest one.
configuration file for 3 axis

Here are some pics of my machine. Right now, it's set up to do flat work. I built a platform of MDF and then "leveled" it with an end mill.
front side
control box
back side

This is just a cheap 3040 type machine with the 4th axis. ( see it here ) The hardware is okay. I had to tighten things up a bit and adjust it to get it to actually work. The ball screw for the X axis to the stepper was grossly misaligned and the Y axis guides were loose. All told, I am pretty happy with the quality of the machine. The controller box is another story. I rewired it because it was terrible. Frayed wire terrible. I also replaced the power supply because it was under powered. The steppers are 2A each and the PS was a 6A supply. It would not power up the system if all of the motors were connected. I put a 15A supply in it and that works now. I am not happy with the spindle. It's a cable drive spindle and I really need a direct drive. It also has a crappy speed regulator. I will be changing those at some point.

Edits: tried several different ways to link the tar file. You can view it, but you may not be able to download.

I actually think your speed is limited more by your step drivers than by the controller

A 5I25 (or any fast external step generation hardware) will make the most difference with
higher end drives, (Gecko or Leadshine for example) higher ustep ratios, or step/dir driven servos

What leadscrew pitch and ustep ratio are you using?

PCW wrote:

I actually think your speed is limited more by your step drivers than by the controller

That may very well be true. Is there some way to definitively tell? For example, if I jog the X axis (the heaviest one) at too high a speed, it will start to move, but then when the steps ramp up to a certain point, with acceleration set pretty slow, it freezes and just hums as me.