New Hobbyist working on a retrofit mill

[Bigbluemill]

Hey guys, This is a pretty cool site! I'm new to this whole thing, and it all started with a senior project for college. I'm an electrical power student, and I decided to finish the CNC retrofit on an old Bridgeport mill. I'm not sure what model, but I will find out soon. It uses servos for the 3 axis. It has a Campbell designs Breakout Board, and then it has Rutex R90H drives. It is capable of running at 170v DC, but for now I have it stepped down for test purposes to 38 V DC. I'm having some trouble with my Z axis running away as soon as you apply power to the machine. I've swapped the motor leads at the drive, and it runs away in the opposite direction. I replaced the US digital single ended encoder. I'm not sure what path to run down next?? Any ideas on that one??

[NC Cams]

Make sure the encoders are PROPERLY providing feedback to the drive.

To do this, you have to verify that power is being fed to where it is supposed to go (you did plug things in properly???) and coming back in the proper polarity to the proper feed back ports (you did VERIFY the wiring???). Parts swapping is NOT the "magic bullet" solution until you find root cause!!!!

I"d be inclined to re-read the instructions (you did read them, didn't you????) and then look to make sure electrical signals are where they area supposed to be. Servo runaway is typically caused by electrical feed back deficiencies (Scope and/or voltmeer are MANDATORY tools, and much more important to diagnosis than anything else).

This sort of problem is where your electrical backround combined with the "scientific method of problem solving and root cause analysis" that your college SHOULD have taught you, will come in REAL handy.

Let us know what you do and don't find - we'll be able to help more at that point.

[Bigbluemill]

Thanks for the info, I know where you're coming from on what you said. I will have the portable O-scope here today so I can hook it up and check my feedback signals. I have verified the wiring on the encoder though and I know that is correct. I will soon see what the O-scope shows on the matter. Thanks again!!

Andrew