Upgraded to a g4 love it, but...

[robtown]

I've finally been able to do a couple things with the table since my upgrade, other than just jog it from corner to corner at high speed (I love doing that...) Anyhoo, what I'm noticing now is some serious vibration in the Y axis when cutting. (it's a PRT 96 by the way).

It doesn't do it jogging only cutting, like I'm getting some flex in the gantry because my motor's torque is only being applied to one side. Does that make sense?

Would it behoove me to consider a second Y motor, or would my efforts be better spent trying to stiffen up the Gantry, or, as I suspect, should I consider both?

[paco]

Have you consider (or already have) moving the cutting head closer to the Y motor. Have you make a throughout check on the hold down rollers?

[robtown]

Hey Paco,
I'm not sure how I would accomplish this, and I don't think it would make any difference. I can stand there and watch it while cutting and see the gantry almost "lurch" when cutting the Y axis. It's hard to explain, but it you watch carefully, the vibration seems to be coming from the fact that the mototr is only pushing on one side of the gantry, and the other side has to "catch up" from time to time because of the inherent flex in the old PRT gantry design...

[paco]

At all of the speed range? My tool, an 7.2:1 Alpha, is shaking a bit more in the 1.5-2.5"/sec. range.

[waynec]

Rob,
I have an Ascension control box that uses Gecko 201 drivers, probably not dissimilar to your G4. I had a problem with that lurching. After breaking the motors loose from the rack and watching, one motor was not working at all. You might check to make sure that you are running on both motors.

If you are not, suspect first the connections, then the settings in Mach 3 software (if thats what you use) then the Gecko driver. I replaced the Gecko and the problem went away, but I'm not 100% sure it was the Gecko because I was also twiddling the Mach 3 motor settings at the same time. It could have been that Mach 3 loaded improperly or had some software glitch, or it could have been the Gecko.
Works fine now!

Good luck with it.
Wayne from White Salmon

[robtown]

Hey Wayne,
I'm currently only using one motor for Y, I suspect that another motor for the Y axis would make a big difference here.

Paco, the "lurching" (it sounds worse than it actually is...) only seems to happen when actually cutting, and it's across all speeds. Thus my assumption that it's caused by flex in the gantry due to the drive torque being applied to only one side of the gantry vs. the torque of running the bit through the material.

[gerald_martin]

Hello Rob: My previous 'bot was a PRT and I had upgraded to an additional Y motor...If you disengage the existing motor from the rack and the carriage rolls smoothly, and all the wheels, upper and lower, stay engaged with their respective tracks, then I would suspect you are right...my opinion, the design of the PRT pretty much merits dual y motors if you want equal torque on the y axis anyway.

Gerald

[srwtlc]

Rob,

The hold down rollers could be binding somewhere.

My previous bot was a PRT also and what I did (other than adding another motor) was to remove the original hold downs for the Y carriage and make a different hold down on the far end. I also made a plate to stiffen the Y car.


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