what is the useful upper rpm limit

Velocity, accel, torque, rpm are all related thus each has a bearing on each other and is system related.
It all depends on the motor and other parts of the system. In the end  reliability / consistancy for what your doing is
just as important as.

Just want you to uderstand the whole picture.

RICH

Gerr & Rich

Gerr,
The specs on the steppers remain top-secret.  The seller/builder can’t seem to get me the information nor can he provide a tracking number.  Gotta love eBay!  It is rumored that the machine will arrive Tuesday.  Hopefully the mystery will end there.  The picture of what I believe I bought shows rack and pinion on all three axis. No specs on their ratios either.  Arguably, it will have larger steppers than what we are messing with.  The power supply is 36V.

Rich,
You are correct we will do both, live with what we have or will soon have and define what we require then seek it out.  Remember the goal is to learn motion control to prep for a re-control.  I don’t really need a plasma table but it looked fun.

I have made a few attempts to re-control a router but bailed out from the frustration.  The last attempt was in 2002 with a brand name control that never worked.  In follow-up with the manufacturer a week ago I learned that:

1) The system was incomplete and therefore will never work

2) It was registered to a company that is not mine

3) The person who it is registered to is an employee of manufacturer that I bought it from

How’s that for a scam?  It also explains why support (the same employee) blamed us for its failure and, well, wasn't very supportive.

If I really have a need for a machine I just buy it.  In this case, while banging about the net, I saw a plasma table sans its control for sale.  I bought it.  May as well learn to control it, right?  I have a zippity-doo-dah-whiz-bang plasma cutter that has 5 minutes use on it. The cutter even has a machine torch and switch gear of some sort.  It all seemed like a marriage made in paradise.  All we need is some motion.

Rich,

Thanks, I believe I get the larger picture.  I understand that there are numerous variables including ambient temperature.  I can see the top of the mountain from here I just need a little help finding the trailhead.  I think now we slap together what we have on the shelf and see what it’ll do.  From there we can throw some science and money at it.

The specs on the steppers remain top-secret.  The seller/builder can’t seem to get me the information nor can he provide a tracking number.  Gotta love eBay!  It is rumored that the machine will arrive Tuesday.  Hopefully the mystery will end there.  The picture of what I believe I bought shows rack and pinion on all three axis. No specs on their ratios either.  Arguably, it will have larger steppers than what we are messing with.  The power supply is 36V.

In a lot of cases, changing to larger steppers can actually result in even lower speeds. Generally, as steppers get larger, their maximum speed decreases. That's why it's important to know everything about the drive system. Without knowing all the information, it's hard to determine where the problem lies. It could be the steppers, the drives, or the drive system (poor gearing). It could even be caused by misalignment, which can cause friction and binding.

SHees I gave you  the important numbers target Vel and accel model numbers. Just apply those numbers against the weight the WEIGHT of your gantry.

To get best results you gear the axis for the ratios that give the best responce for accel/speed. It does no good to be able to rapid at 1000 if your accel never lets you get there cutting.

Acell in plasma IS the most important so you juggle gearing to get teh best torque at teh rpm range you plan to run in without stalling the motors

Next teh Z HAS to be fast accel/speed wise in order for the THC to keep up responce wise  to slow and you drag the tip a lot, too fast and you get into oscilations from the axis outrunning the thc and overshooting.