Retrofitting a 1986 Maho MH400E

Thanks for the detailed reply. I am currently PID tuning to get better performance. Your parameters made the machine extremely sluggish in comparison to my previous experience.

As an example: I've been cutting acrylic at the allowable Philips max feed of 1500. The changes in direction were rather abrupt (no lookahead), but never did I get the impression that the machine couldn't accelerate fast enough. You'd start seeing some kind of lag at G0 (3000/2500/2500 mm/min X/Y/Z), but if I could have tried cutting at those feeds (spindle speed permitting), I'd do so for sure. I just didn't see the limit in that area, I thought the speed issues were more related to the gear reduction and low initial motor speed, not acceleration.

Then again, the machine was originally tuned by guys who did only that all day for many years. I think they squeezed those drives for all they could (reasonably).

What Linux does that's annoying in comparison is arbitrarily (or more likely based on the parameters in the ini) creates a velocity ramp on rapid moves. You get a very pronounced speed up/slow down effect which wasn't present on the Philips at all.

I guess it's all related to the trajectory planner somehow but in that case it's our job when tuning to get it to work as best as we can. In all fairness though, once you have the machine up and running, this tuning process is about as fun as sanding wood with very fine grit sandpaper.

EDIT: within the given limitations, the drives should feel very responsive. When I used to control the machine with the original pendant in step mode, 1mm felt really fast and abrupt. The frustration was more down to rapids across the work envelope (600mm travel in X for example is when you see that 3m/min is slow).

What Linux does that's annoying in comparison is arbitrarily (or more likely based on the parameters in the ini) creates a velocity ramp on rapid moves. You get a very pronounced speed up/slow down effect which wasn't present on the Philips at all.

I guess it's all related to the trajectory planner somehow but in that case it's our job when tuning to get it to work as best as we can.

That is good to know, as that ramp is directly driven by the acceleration value set in the INI. There is nothing inherent to LinuxCNC limiting that performance. The trajectory planner helps to keep velocity high by avoid using the machines accel/decel where you don't need to slow down if the next line of code is in a similar direction. I didn't touch the Indramat's settings. I figured anything I could do would only screw up what MAHO did well. The Indramat knows nothing more than it's commanded velocity. If the Phillips had a much larger value for acceleration, and thus much steeper ramping it could mean:
A/ My tuning sucks, and a little sanding with that fine sandpaper will return the Maho it its former glory.
B/ The Maho engineers accepted significantly greater following errors, and we should too. They know way more about this stuff than we ever will.


My bet is on option A.

Here's what I came up with today, afer several merry hours. Note that it's still not the same as it was on the Philips, at least at the top rapid speeds.

MAX_ACCELERATION
X 90
Y 100
Z 65

These values allowed me to retain a following error of ca. 0,025mm at max speeds. They were tuned at a feedrate of 1000 to within ca. 0,015mm, using a move of 25mm. The latter error value represents the largest spike, which in my case happens close to the beginning; most of the way the error is below 0,01mm. Due to absolutely zero experience as a CNC service tech I have no idea if this is all good or bad.

I got very anal about the P and ferror values and didn't do anything with I or D. The machine still has perceptible speed up and slow down periods in rapid moves. I haven't really done anything with the G64 modes though, it was running default for tuning.

The drives sound more annoying in Linux than they did on the Philips. I assume this is the combined effect of wear with the faster rate the controller uses to communicate with the Indramat. You could probably replace the motors with modern ones with better parameters that would be silent, and maybe raise the rapid speed to 5m/min. There are two sources of noise in my drives: the hum of the DC motors, and the noise of the reductions, ways and ballscrews. The Z axis in particular has a length of noisy travel. Your Maho is probably much better in this regard due to its excellent mechanical condition.

Regarding your points, it may well be that the low limit of programmable feeds on the Philips controller was connected to the following error at higher speeds (among other factors, chiefly the controller itself). Rapids just need to get to point B quickly, and any overshoot is going to be corrected instantenously. Nobody would think of rapid moves in material. Then there's the issue of spindle speed, design purpose and available tooling, which meant that in the 1980s Maho engineers didn't care about higher speeds that much. Deckels were the more agile machines, but they didn't have the obscene torque of the Maho geared spindles.

If you think about it, a following error of 25µm lag in the linear direction of travel is next to nothing. Maybe we should try tuning for 200µm Ferrors at rapid speed and see what that means for the overall performance?

If there is someone reading here who has experience with the setting up this sort of thing, please jump in.

I and D are not used with velocity controlled drives. FF1 and FF2 have a significant effect on the initial accel and final decel behavior.

Deckel FP CNC's also have gearboxes. Do they not have a similar range of speeds to the MAHO?
Mark

Looking at a 1982 Maho sales catalogue

400 P and 600P ( non CNC but straight line or point to point or not 432 control )
Resolution = .005mm ,.0002inch ( may be non LS403 scales ? )
Rapid Traverse = X and Z axis 2.4 m/min , 94.5 inches/min - Y axis = 1.6m/min , 63 inches/min

MH500C using the 432 control
Resolution XYZ axis= .001mm ,.00004 inch ( may be just the LS403 scales and not the complete machine resolution )
Feed Range for all XYZ axis = 1 to3000mm/min, .04 - 118.1 inches/min
Rapid Traverse for all XYZ axis = 5 m/min , 197 inches/min

MH700C and MH900C using the 432 control
Resolution XYZ axis = .001mm ,.00004 inch - -B axis =.001 degree ( may be just the LS403 scales and not the complete machine resolution )
Feed Range for all XYZ axis = 1 to3000mm/min, .04 - 118.1 inches/min
Rapid Traverse for all XYZ axis = 6 m/min , 236 inches/min

Note : The this is from a March-1982 sales brochure , but in 1982 the Marketing Departments didn't drive the engineering as they do in today's world.

Mark Is this of any use to you? Noticed the use of a radius vers sharp tip on the engraver tool. Don't know if your cutter grinder has a radius attachment - yet .

Wish I had the electric power hooked up for my MAHOs !
Bob


p

Hi Bob,

I do have the Clarkson Mk1 radius grinding attachment, but that doesn't really help as long as I don't have a high speed engraving spindle. That is why I made the drag engraver, which does not spin, it is just a scriber which get pushed into the work and dragged through it. It needs that sharp point.

The resolution of the E series Mahos is also 1µm (although mine has only 5µm resolution on Y at present due to the replacement EXE used), and has max rapids of 2500mm/min, but those specs say nothing about how much following error Maho allowed. The high resolution allows the controller to know real position, verses commanded position (= following error).

What we don't know is what following error at rapid speed is considered normal and tolerable for a tool room mill in this class.