Communication issue? Grind noise, then position loss

[Brett1970]

So, i've had this gremlin for 2+ years. My machine will be running, i'll hear a grinding noise, and i've lost X, Y, or Z position, and my sheet is ruined. Sometimes it happens once every 20 sheets, sometimes every 3 sheets. The problem is definately NOT physical, i've had every stepper off, gears are tight, teeth are good, all the V rails and teeth are good. Verified all the grounds, no issue there.

I am running a laptop, no internet, no other software. Automatic updates, etc every non essential service is turned off, i followed the guide on the forums i found to do this. Using the USB hub that came with my shopbot. In speedtest i get 74.9 I am cutting at 4 inches a second, and my jog speed is 6 inches a second (i think, whatever the factory setting is) I have no idea what to do. My machine had two other issues since day one, it's more or less been a lemon since i bought it new. It leaves a nub on every single part, and my proximity switches never worked right since day one.. it could be out in the middle of the table cutting away and it will say "stop hit" constantly, so it's disabled.

I thought 74.9 would be fine. I have a prs standard 48X96 with a 2.2 hp yaskawa spindle. Has anyone tried a desktop with USB 3.0 with a USB 3.0 hub, and what kind of speeds are you getting? seems to me a serial port would have been a better way to go than USB.

[gc3]

lemon......don't think so

you need to trouble shoot your machine...laptop issues?

a old VW saying, "be kind to your ass for it bears you"

[bruce_taylor]

Your speed seems a bit fast for a standard, what are you cutting? I think your loosing steps because your pushing to hard. Just my humble opinion. I'm sure some more knowledgeable guys will have some opinions. I've never heard a shopbot called a lemon before.

[adrianm]

Have you contacted ShopBot support directly over this? If you've had the machine from new it would seem to be the thing to do.

A USB 3 port defaults to USB 2 speeds when connected to a USB 2 device so it won't make any difference. A serial port is far, far slower than USB 1 let alone 2. With the speed test ratings you're getting it's not the transfer speed that will be causing your issues I wouldn't think.

Much more likely to be a build up of static or you're just pushing it too hard I have an Alpha rather than a standard but there's quite a few things I can't cut at 4ips. What are you trying to cut, pass depths, etc?

Given the issues you've had with the proximity switches my money would be on static or some other problem with interference on the electrical side.

[Brett1970]

oh beleive me, i've talked to the guys at shopbot plenty, and the proximities and the nub it leaves on the part have them baffled. Nothing fixes it. I cut 3/4 birch, and also 3/4 melamine. The melamine i cut at .405 per pass with a compression bit 1/4" and i cut the ply at .375 per pass with a double flute straight bit. My system is grounded, starting at the breaker box in the house. From there, it goes to the back of the control box, to the nearest machine rail. From that rail, one wire runs up the machine wiring to the X car, then up the chain wire guard, and directly to the side of the spindle. Back at the first rail, it runs to the second rail, and on to the dust collector base. then, it goes to stranded wire/no cover, and it goes inside the dust collection skirt, and attaches to the dust collection boot.

The entire system is properly grounded. All my cords to everything are 3 prong, so it's a total mystery. Frank at shopbot is telling me it's a communication issue. 74.9 is the best i can get with a laptop. I'm hoping a desktop with usb 3.0 and a powered usb 3.0 hub gets the numbers up into the 80% range.

[garyc]

David...
I have tested a number of computers with native USB 3.0. In fact I have 2, one with XP Pro-32 and one with Win7-64 on my test bench here. Both machines have USB 2.0 & 3.0 ports. I have seen nothing that would cause me to believe that a USB 3.0 system as you describe it would increase the comm rate to a ShopBot.

[richards]

I think that Bruce identified your problem. Try cutting at 2.5" or 3" per second and see what happens.

A stepper motor loses torque as its speed increases. If you are running the motors too close to the fall-off part of the torque curve, a very slight difference in materials can overload the motor.

A "grinding" noise indicates that a motor is loosing steps. Slowing down the speed puts the motor on a different part of its torque curve which may allow it to handle those slight differences in the material.

If you go to Oriental Motor's website and look at the torque curves for your motor (or a similar motor), you will see that a stepper motor has maximum torque at low speed and progressively less torque at higher speeds. As the speed continues to increase, the motor will reach the "knee" portion of the torque curve. The knee portion is where a minor increase in speed causes a major decrease in torque.

Sometimes there are ways to get more speed and more torque out of a motor, but it may require different stepper drivers, different wiring of the motors, a different power supply and sometimes a gearbox or belt-drive. None of those options are particularly easy; however, identifying the problem by reducing the cutting speed is easy.

[ken_rychlik]

It could be as simple as an incorrect bit for the job. If you are cutting full depth in one pass, slowing down like Bruce said will help.

For the proxy's not working, it's probably not grounded well.

There are so many things that will cause this and thus the many different suggestions. It may be a machine problem, but most likely not.

[khaos]

About the false proxy warnings. Two things come to my mind assuming your ground system is perfect as described. Line noise: This could be from a power line running parallel to your motor or proxy lines. Magnetism from the power line creates electricity in the other lines that could be read as a positive proxy hit.

The second issue could be a spike or drop in line voltage. This could be a surge amperage(current) from an aggressive ramp value. Or some appliance in the shop like a compressor, grinder, or saw starting. Or a surge from the grid. I have my bot on a quality UPS from APC.

Another piece of data is that resistance increases with heat. So if ANY of your power lines get warm with use longer use means more resistance in the wire which equals a voltage drop at the device and often noticeable current increase which raises temps more in a cycle.

The SB tech boys are really good at what they do but electricity is a fickle beast.

HTH,

[bruce_taylor]

I gave up on proximity switches long ago really not a big deal for me I cut 3/4 plywood alot at 3 passes .375 bit at 2.5ips 11000 rpm onsrud 60-121 or 60-123 compression, This is on my alpha, I know I could push it a little harder but it sits idle a fair amount and I don't like to push my tools to hard. I would slow down and see what happens.