Loosing home zero after a file run?

[knight_toolworks]

I noticed once in awhile if I stopped a file running that when I started it again it would not start from home.
This is with a prt alpha. I figured hitting quit threw something off, but since I updated to the newest software it happens more. I had a file to cut out demo text samples that had several paths saved as one. When it went to cut the second one it started off the table and when I stopped it and sent it home it was off by a few inches. This happened twice in a row.
I have run files where after done and the machine goes to home it is not always home. Any idea’s on this? It can be an issue and parts lost if it keeps up. The machine shows 0,0 but it is not where it is supposed to be.

[myxpykalix]

That used to happen to me but it was traced to a static problem that played havoc with the settings. Do you have a dust collection system? Do you have it grounded?

[knight_toolworks]

No it is not grounded. I am trying to remember if I ahd it even running when this was the worst. I think I was not using the dc though.
but it is easy enough to ground the collector on the machine.

[walksonwater]

Steve,

I had a very similar problem. Are you running the 7.2 motors? Look in the troubleshooting area, "loosing zero on all three axis".

Randy

[knight_toolworks]

I am running what the machine came with. I read that post but I don't knwo what I have. I have not gotten itn oteh details of the machine very closly. it was bought in december.
I do notice that my jog speed is far slower to get up to speed.

[walksonwater]

take a look at the end of the stepper motors...mine are vexta asm98aa-t72. I bought mine in November when Shopbot was first offering the 7.2 gear.

[knight_toolworks]

will do I bought mine the end of november.

[myxpykalix]

What happened with me is whether i was running a file or just jogging the carriage, it would just stop. Different times/places and i would lose my home and all settings. If i was in the middle of a cut i would have to start over. One tip I was told was to take your bit and make a small hole at your 0,0 point so you can "re-register" your bit to exactly the 0.0 point in case you lose your settings.
To ground your DC take a length of braided bare copper wire. Attach it to the carriage and run it up thru your DC hose all the way thru to the dust collector head. Run the wire out of the hose and attach it to the body of the unit.
Since i did that, i have not had one short. That i believe is your problem. I could be wrong.

[fleinbach]

Steve,

Jack is right the most likely cause is an ungrounded dust collection hose. When I first got my Shopbot several years ago I experienced the same symptoms. After grounding the vacuum hose I did not have the problem again.

[steve4460]

HI guys

What version of the control software are you running ?. There has been a problem with stoping and starting files with the stop command in some versions prior to 3.5.3 . I talked to SB and that is what they said .
Hope this helps .
bot on

[knight_toolworks]

I played with it today without turning on the dc and nothing but problems. I reset to default settings and that turned on both limit switches fixed that but never got it so it would home back to normal. I had printed out the threads and followed the recommendations on settings. Found or my motors are asm911aa’s
I finally uninstalled the newest software and went back to the version the bot came with. Not sure what version but I bet it is the one right before this last one.
It works fine and has been pretty reliable.

[myxpykalix]

Just because you don't turn on DC doesn't mean static electricity isn't being produced. Take the time to run the fix i described above. I did the same thing of not running the DC thinking that if i didn't run it, it wouldn't produce the problem. This would happen to me 2-3 times per file run. I got so tired of it happening I went and got the wire and fixed it as Brady suggested. I thought, how could such a simple thing cause me all this grief, but it hasn't happened since then. If you have already done this then I have no idea whats going on.

[butch]

Check your ground. Make certain that all of the equipment is connected to an 'earth' ground. Usually this is through the breaker box and is connected a copper post driven about 6 to 8 feet into the ground just outside the building. Another thing, is if this problem seems intermittent, soak the ground with water around the ground post. (Usually back east this doesn't happen, but here in Montana; the dirt around the grounding rod can actually get too dry to conduct electricity.)
I don't like running the ground through the hose, but I wrap the ground wire around the outside the hose with a wrap every 2-3 feet. Just make certain that the braded wire touches the plastic pipe. I use tape every 3 to 4 feet to assure I am making contact with the plastic. (I am of the belief and training that the static is generated by the air flowing against the plastic, thus the static buildup must get to the ground wire, and will arc between the plastic and the wire. Thus in my theory you could have a spark inside the hose with combustible dust. Plus any restriction in the hose can cause blockage.)
Next make certain that the grounding strap is connected to your equipment frame, which is the common ground in most equipment, and then the other end MUST be connected to the ground. I use the ground (bare copper wire or green wire) in the outlet box. You can usually do this by connecting the braided wire to the screw in the outlet box. If you have questions about the ground, do an Ohm check from the equipment to the ground on the outlet plug to make certain you have continuance. Some people believe that you only need one end of a ground strap connected to the ground. Electricity even in the form of static needs a circuit, thus both ends need to be connected. If you don’t you can see it arc trying to find the connection. I have seen static voltage in the 10 to 12KV range, which was the limit of the testing equipment we had. Thus it would arc an inch gap without too much problem. If your equipment is not frame grounded, static can destroy circuit boards trying to find a ground route.
The next source of static or interference is your power lines. This will cause a surge of voltage similar to static surges. Induction is the voltage generated by running a wire across magnetic lines. AC generates magnetic lines, thus keeping the wires criss crossing keeps the induction from generating enough power to cause problems. Separate the power cables from the data cables. Even a few inches help. If this is not possible, make certain that the data line and power lines do not lie parallel to each other. What I do is cross the data lines back and forth, across the AC lines, similar to braiding. The magnetic field generated by any AC power wire will cause induction into the data line. Usually you must use shielded wire when you have a data line in vicinity of an AC wire. This will cause a surge of voltage similar to static surges. I have had this actually blow up an IC board. If you can separate the data and power wires by even a few inches it lessens the likely hood of induction.
Remember ALL data lines should never run parallel to each other. Just criss-cross them every so often to assure they do not pickup data or interference from another wire. Note that even low voltage can jump across the plastic shield. We often saw data jump where ever the wires were flexed – the wires on the ShopBot are constantly being flexed and twisted. The plastic shield can become cracked to worn at stress points, so you can lessen the likelihood of picking up stray data spikes by criss crossing the wires rather than making nice neat parallel runs.
Next source that most people do not think of is florescent lights. If you must run data lines next to florescent lights you must use a shielded cable and make certain that both ends are connected to ground. Florescent lights generate magnetic waves and I have seen it so bad that I couldn’t run a simple RS232 line 40 feet through the ceiling. As soon as I ran the wire on the outside of the ceiling away from the lights, it ran fine and probably still does.
I know I went on, but these are the sources of induced interference I am aware of. I have been listening to people recommending running grounding wires through the dust collection hoses, and thought I would put in my two bits. Because of past experiences I just don’t feel comfortable with that, so I wanted to put my input in.
PS: Shielded wire is just a wire with wire braid on the outside called a shield. By grounding both ends, the unwanted induction, be it static or magnetic is grounded before it can interfere with the data in the wire. We have run data lines several hundred feet through these with little or no noise from outside sources.

Butch

[butch]

One more thing -
I believe that the ShopBot stops if it does not recogize the data. That is why static causes the ShopBot to stop. I have not been told this, but it is common practice to assure that the equipment doesn't do something 'stupid'. That is why static or induction will cause problems with the ShopBot.
Butch

[knight_toolworks]

I keep forggetting to buy some ground white for the dc. my building is an industrial one with good power so thats not an issue. but going back to the eariler version of the software I pretty much don't have problems. once in awhile if I stop a running file zero is lost but thats a known bug.

[ernie_balch]

I know an electical engineer that specializes in high voltage high current applications at GE and he told me that grounding both ends of a shield wire will cause problems with ground loops. With that in mind I googled ground loops and shielding wire and found the following:

SHIELDING
In general, it is good practice to shield all wires carrying low level signals. This is especially important if the signal level wires are
run near power level wiring such as motor wires or relay wires.
When shielding wires, connect only one end of the shield, preferably the source end. Connecting both ends of a shield will result in ground loops. It is recommended that the unconnected end of the shield be insulated to prevent accidental connection.

ernie

[jsfrost]

As an engineer that deals with grounding problems and low level signals from time to time, I agree that grounding one end of a shield is usually the best answer. But, more important, imho, is the axium, "if it aint broke, don't fix it" Each installation is different. If (when?) you have problems, start out following the recommended guidelines; if they don't work, experiment. What's right is what works in your specific aplication.