Messages

61

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: June 03, 2016, 03:24:07 PM »

You do have the benefit of being able to move things manually, so you could probably manage without an override button.

I think it would probably be a good idea to wire up your control box to allow for the possibility of adding one later though. Have the limit switch loop come back to a terminal in the control box, before connecting to the E-stop loop, so if you do need to add one later, you've got a nice convenient point to wire one in, with minimal rewiring needed.

62

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: June 03, 2016, 10:42:37 AM »

Couple things from a quick look at the diagram, you'll need a limit override switch, and do you really need to have the power for each servo drive use a separate contact?
The same could be said about the ESR relay.

63

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 27, 2016, 07:17:19 AM »

There should be no need to kill power to the controller.

Under normal use, the E-stop circuit should always be live, as it should only be activated as a last resort. During normal use, Mach should only be disabling the drives when entering reset.
Continually cycling the power to drives/VFDs can damage them, but that should never happen under normal circumstances. If it is, then you have a problem.

64

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 27, 2016, 06:54:45 AM »

I've never had any issue with inrush currents, but you won't know until you try.

Drives/VFDs get powered up when the e-stop circuit is completed and power applied, which is when you're likely to have any surge problems as the internal capacitor banks get charged.
Drives shouldn't be activated until you hit reset, and the VFD should only get activated when you finally turn the spindle one, so everything after the initial power up should be fine.

65

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 27, 2016, 06:22:51 AM »

E-stops can be a pain to implement.

I opt for limits forming part of the physical E-stop circuit, so if that circuit gets broken, the main power to the drives/spindle/anything else mains powered i.e. coolant pump gets removed.
I then have the KFlop monitoring the e-stop, and should it get triggered, it activates inputs to the drives that trigger them to stop. However, the KFlop has the benefit of being programmed to do this within milliseconds, so it's not reliant on asking the computer/mach what to do.

I know Hood likes to use Safety Relays, that when triggered, will trigger the stop input on drives, then after a small time delay kill all power. This has the benefit the servo drives should remain powered long enough to do a fast controller stop, before power is removed.

I suspect the issue dude1 is trying to mention, is the feature of DC powered drives where they dump excess power back into the DC supply during heavy deceleration, which can cause a voltage spike resulting in over-voltage damage. This doesn't apply to the type of servo drives you're using (it would apply to regenerative drives), but it could cause the drive to trip out with a DC-bus overvoltage error, as they do dump power back into the internal capacitors. If the error did get triggered, all that should happen, is the drive will error out and let the servo freewheel to a stop.

66

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 26, 2016, 06:52:13 PM »

I used 6A type B circuit breakers for my servos, however I've got no idea where I got that spec from.

Just had a look in the manual, and it says 15A fuse for 750W motors, however the drive input current is listed as 5.5A (largest motor the drives will do is 750W). I'm guessing the fuse rating is for a quick blow (standard) fuse to give a bit surge tolerance, which normal circuit breakers will give anyway.

67

General Mach Discussion / Re: Mach3 Threading and Index Signal Problem

« on: May 24, 2016, 01:37:27 PM »

Does the leafboy card support threading?
When using external motion controllers, the motion controller has to support threading, and not all external motion controllers do.

68

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 24, 2016, 06:04:10 AM »

Is there setting software available for these servo drives?

I know with the Kinco drives fitted to my lathe, the software lets you flip the active high/low settings for inputs and output, which you couldn't do via the front panel. Or at least if you could, it wasn't mentioned anywhere...

69

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 22, 2016, 03:58:23 AM »

Have a search over on the home shop machinist forum, as I seem to remember John S(tevenson) posting about overhauling his POS Bridgeport varispeed head a while back.

70

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: May 21, 2016, 07:57:00 PM »

A simplistic generalisation is electric motors produce reasonably constant torque across their rated speed.

With varispeed, your 5Nm motor will result in a varied level of torque at the spindle. At say 145rpm spindle, and the motor running at 1450rpm, you have a 10:1 ratio giving you 50Nm torque at the spindle. Going the opposite way, and running the spindle at 4350rpm you have a 1:3 ratio, so you only have 1.67Nm torque at the spindle. With varispeed, you always have the full motor power available at the spindle.

Now if you go direct drive, you only ever have 5Nm available at the spindle. You will only get full power at full rated speed. Half the speed, you only get half the power, but still 5Nm. Quarter the rated speed, quarter the power but still 5Nm.
This is why most VMCs have such high power spindles. If they didn't, they simply wouldn't have enough torque for tapping, or large cutters/drills