Bridgeport Manual to CNC conversion...

[Clive S]

Very nice again Dave. How come you did not put some grad marks on the feed and speed

I have made a few for mine but cut them out just with the 60' V cutter. Saves changing tools.

Did you use Bold Arial

[Davek0974]

:)
Grad marks would be meaningless i thought as its based on the screen display not any real position so i didn't bother, i can always redo them i guess one day ;)

Yes it was Arial Bold and a v-carve path

[Davek0974]

Anyone have any views on what sort of speed and acceleration i should be aiming for?

Bearing in mind it has a relatively low spindle speed, even in aluminium, the feed rates are pretty low, I don't think it's worth going much above 2500mm/min?

I have read that there is a point in acceleration where Mach starts rounding corners etc, is this a known point or just something that can happen at some setting value?

Its currently set for 1000mm/min but that seems quite harsh when you do a rapid, it makes the machine shake a little at start/stop of the move.

[Boyan Silyavski]

Judging from power servo feeds made for that machine, ~900mm/min is the maximum. i think a machine like that could even reach a maximum of 5000mm/min but with slow acceleration. So if servo motors could do the trick of moving it fast, its up to you to decide the balance between speed and acceleration, depending on what you would be doing.

I have to ask Jeff who has a servo driven similar machine, but as far as i remember once he told me, he doesn't push it more than 500mm/min ever.

So no point of making it run away from your workshop if not needed. I would leave it like that / ~900mm/min / and with normal acceleration. Then with the time you know it better you could fine tune it.

Whats your acceleration set at?

[Davek0974]

It needs to be a bit faster, i have tool paths that run 1150mm/min, i think 2500 may be a good compromise. The servos themselves will easily push it to 7500mm/min if i let them but it is very scary.

I will try my usual 1/10 rule - 2500mm/min and 250 acceleration and see how it goes i think.

[Boyan Silyavski]

250 acceleration is not much, so even if scary at first, i think 2500mm/min will not be a problem. Dave, i have set 3000 acceleration on my machine, now that's scary, when you see 200kg gantry flying around with that speed.

[Davek0974]

Ok set speed for 2500 and acceleration for 400, moving right along - servo tuning.

Have done nothing on these apart from an auto-tune in CSMIO setup. I thought the results were ok, but having spent a few hours today scouring the 'net it seems they were pretty bad really. The first video here shows one axis after an auto-tune. Now, I have zero experience with servo's, being stepper builds up to this build, so I stand to be fully corrected but, i think the graph shows pretty bad over-shoot or oscillation?



So, throwing caution to the wind, i dived in and removed all of the "I" and "D" parameters as well as the "ff" or fudge-factor i think its called. That seemed to improve things so i started increasing the gain in steps of 1,000 and the graph seems better to my untrained eye?

The following error is lower, dead-band is reached faster and the dials on the machine no longer overshoot and slowly wind back to a stop - this was a concern as i could see it affecting cut quality etc.

This video was shot after my messing around...



Now, please feel free to rain on my parade, but does the last video look happier than the first?
Is there any issue running with zero "I". "D" & "ff" values?
I can't hear any grumbling from the motors, there is no visible 'hunting' at idle, following errors are down and the dials now stop on a dime as shown.

The Z axis would not tolerate as much gain and did go into permanent oscillation once so i backed off a fair bit but still no "I", "D" & "ff" values.

Suggestions?