Since I completed my second build, I was finding that I had quite a problem with missing steps. The usual solution of reducing speed and acceleration helped some but it did not solve the problem. I found that machine runs with curves made it worse. i.e. if the x and y axes were both working at the same time the problem was visible. It resulted typically in a position shift of about 1mm in x and 0.5mm in y over a 20 minute run. Enough to make any machine pretty useless. It got worse on longer runs. This made me suspect that there was noise or emf getting into the system. Then came a bit of an embarassing moment. When I built the second machine I reused the wiring loom from the first machine which was unshielded. I had intended to swap it out but simply forgot to. Anyway after a days hard work the entire wiring was swapped out with shielded cable. All of the shields connected back to a single earth which went nowhere else but the mains earth. I also covered my BoB housing with aluminium tape and earthed this too. I just ran a 1.5hr job hit the goto zero button and it returned precisely to where it started. Proper sorted!! Another thing I noticed is that my spindle rpm which used to wander up and down by a few hundred rpm now only varies by < 5 rpm.
Just thought I'd post this in case anyone else is puzzling over a similar problem. Electrical noise is your enemy and shielding is your friend.
Great to see you got it sorted Dave but problem with this blanket swap everything out approach is that you never actually found or know the source or the noise.? . . This means you may still have the noise and just masking it out.! . . For now.!!
If it happens again or if others have similair issue it's much better if you can track down the source of noise. Often noise comes from one area or component and can be sign of component starting to fail. Often it's poor quality components, Esp with Cheap Bob's cauisng the problem.
To be honest I've never understood why people try to take short cuts with wiring because it's no harder to do it correctly and saves so much headache and time further down the road.
I'm pretty sure the noise stemmed from just a rats nest of unshielded cable. The clue was that it was worse when the vacuum was on. It seemed to make sense to replace all the cabling in one go since that job had to be done anyway.
Whereas I would totally agree with the "do it right first time" school of thought, I think its right to keep in mind that not everybody has the same level of experience. For me on my initial build, it never even crossed my mind that unshielded cable would be a bad idea. I just wanted to get it up and running. I know now and in future I will not make that mistake again. To me, the real fool is the one who repeats a mistake.
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