Bridgeport Manual to CNC conversion...

[Davek0974]

Was playing around with PID tuning today, reading the manual on how to do it manually (ooh-err) It was not happy and no amount of fiddling got it better, long positioning time, not sitting at position etc. That was until i stuck my finger on the end of the shaft and gave it a tiny amount of resistance - instant improvement rapid stopping on position etc. Lesson learnt, seems unloaded motors don't like tuning ;)

I have ramped it up to 3000rpm, been deliberately messing about with rapids for several metres each way plus millimetres each way, then put mach into reset and jerked the motor around, reset and did a go-to-zero and the damn thing snapped straight back to my zero mark - I was most impressed with this feat ;)

JAZZ - how did you wire the enable line to the drive - there is a signal mis-match here as CSMIO puts out 24v but the drive needs to be pulled low - I stuck a relay in which works but....

Also, what size fuse would be good for a drive and 750W servo?? Thinking 5A slow-blow?

[JAZZCNC]

JAZZ - how did you wire the enable line to the drive - there is a signal mis-match here as CSMIO puts out 24v but the drive needs to be pulled low - I stuck a relay in which works but....

I do it with a relay tied to the HV option on IP-A that enables all the drives.

[Davek0974]

Thanks, if it really is relays then thats fine, I have that working on the bench setup, just wondering if that was the only option here :)

[Davek0974]

Ok, where did I slip up...

Previously had the motor tuning set as book, 2000 steps per (10,000 / 5mm pitch)

When I fit this on the machine it will be at 2:1 ratio so i set steps per to 4000 (10,000 * 2 / 5mm pitch) and set velocity to 7500 (3000rpm / 2 * 5mm pitch) acceleration is at 750mm/s/s

Works ok in jog mode, works ok in code mode at speeds up to 7500mm/min

If i do a "Goto zero" it runs for a while then stops with ePid fault.

It also allows me to set feed higher than it can handle and then goes into ePid fault.

Is there a reason here?

[Davek0974]

Ok, found it - it seems it does not like running right at the limit of max speed - if kept just below max it all works perfect.


If I set the max at 7500 and command a feed at 7500 it faults, if I set 7400 it works perfectly in all modes.

Won't get t hat high in real life as the bed is not really big enough i think for a 7500mm rapid ;)

[lucan07]

Just to throw a spanner in the works may be completely irrelevant but on my travels today saw a bridgeport (couldn't tell you the model) converted to CNC, that used original and a 24k spindle slightly different setup to your plan.

The 24k spindle was mounted literally beneath the original in a frame so when changing between spinles he just had a Z offset to consider but apparently with Knee or second Z thats not a problem, frame actually locked into a collet then connected to frame, his spindle was shorter than mine and he lost a fair bit of Z travel but this still left a good amount of travel on Z for what he used the 24k for.

Just thought I would share unfortunately I was out on the road bike (lycra man) to escape idiots for a while so no phonewith me to grab a picture.

[Davek0974]

Should these collars just slide off, it feels like they are hitting a hard stop?



Probably surplus on a CNC machine anyway but don't know yet.