The second kind of problem you may experience is more subtle. Your ShopBot is basically working -- but something is not working quite right. This problem can reveal itself in the tool having slight positioning problems or with cuts that are not of the quality you would like. Generally speaking, electronics and software usually work or they don't work. Thus positioning and quality problems are usually related to the mechanical function or 'tuning' of the tool. Listed below are areas of mechanical operation you should check (you might also check the maintenance section above).
Bits, bits, bits … You’ll probably get tired of hearing this, but bit quality and sharpness is
incredibly important to successful cutting with your ShopBot. Your tool is capable of
generating about 60 pounds of force as it moves the cutter. This is usually enough to plow through most material, or break a bit trying. However, you typically do not want to be cutting with this much force. The more force you put on the cutter, the more the cutter flexes and your ShopBot flexes. Such flex creates inaccuracies and increases the likelihood of uneven cutting and chatter. The best way to reduce this force is to use sharp cutters and to determine optimal cutting speeds and number of passes for the cutter. Plan to renew cutters frequently for quality cutting, and remember that with a CNC tool it is easy to accumulate mileage on a bit.
Ride. The ways in which the carriages of your tool ride the track are critical for good cuts.
Pull the X and Y motors away from the rack and evaluate the motion of the carriages. The carriages should move freely on the track. Look at the bearings, are they all exactly in their grooves. Is the pressure of the hold-down bearings on the Y axis appropriately tight to resist racking (all bearings should be engaged, you should be only just able to rotate them with your fingers). For the Z axis, is the carriage tight and resistant to flex and wobble in each direction.
Motor Engagement. Move the motors back into position with the pinion gear fully engaging
the rack. Grease the rack. Now start the software and activate the motors. With the motors on but stopped, try to wiggle the carriage. Are all elements of the drive train tight and locked in position? Be particularly attentive to a set-screw being potentially loose on a shaft and allowing the pinion to move on the shaft. If you have a PRS with gearbox motors there is a small amount of backlash in the gearbox, but this should be a fraction of a degree.
Positioning. PRSalpha motors are closed-loop so positioning problems should be minimal.
The information in this section is primarily for PRSstandard tools. If your tool seems to lose its location by a small amount, try to determine when and where this is happening. If happens only when you are cutting material, then it is probably a problem related to the forces of cutting at Move Speed. If it also happens when you are just air cutting, it probably has to do with positioning and tool action at Jog Speed. In either case, it is important to determine whether you are experiencing some sort of mechanical flex during the cutting, or whether the stepper motor is losing steps and thus losing track of its location. Go to the 0 point for each axis and mark or measure the carriage location on the track. Then run through the procedure that generates the location problem. Send the tool back to the 0 point and look at your marks. Assuming that you reproduced your cutting error, has the tool returned to its exact 0 location or is it now off position? If you are back in the right zero location, then the cutting errors must be a result of some sort of flex in the tool (assuming
that the tool moves the right distance when air-cutting … see above). If you are not back at the 0 location, then you tool has lost steps and lost position. If you lost steps and the problem happened while you were cutting material and not when you air cut, then you do not have enough power at the speed you are cutting to support that machining operation. The cutting may be too aggressive. (We are assuming that you previously eliminated the possibility of binding by confirming that your carriages are moving smoothly and the pinion position and pressure correct.) If you are cutting at a 1” per second or slower, your tool should have considerable force (say 60-75lb) ... if not, give us a call to help figure out what's going on. If you missed steps at Jog Speed, try giving your tool more margin by reducing the Jog Speed.
Position can also be lost as a result of electrical noise (voltage spikes) inadvertently
triggering stepper driver electronics. The effects of electrical noise can usually be observed as occasional erratic stepping during air-cutting of a part. Electrical noise is typically only seen in shops with considerable heavy electrical equipment and is usually eliminated by putting the computer and ShopBot Control Box on a separate circuit and running them through a UPS (Un-interruptible Power Supply) or line conditioner.
TIP: The Psychology of Troubleshooting. Problems with your tool never occur when you have lots of time to enjoy solving them ... When they happen, you will usually be stressed out by other things going wrong at the same time and you will, no doubt, be in the middle of a production crisis. It's easy to say 'be cool' but we know how hard that is to do when the 'gol darned thing just won't work ...!'
Practically speaking, to fix things efficiently, what we really need to figure out is whether we need to send you a part, or whether something just needs to be changed or tweaked on your tool or with your software. That's it. So kick the tool or kick us ... then let’s get down to effectively figuring things out. What we want to avoid is going off in the wrong diagnostic direction because we're not thinking clearly or understanding clearly what kind of a problem it really is.
Remember that when you e-mail, FAX, or call us that we are coming at the problem cold. We need to quickly know as much about the situation as possible to be most useful. We have found that first sending us an e-mail is the best way to handle problem. It can be especially efficient since you can lay out the problem and attach any relevant files as well as the PROBLEM.LOG file from your ShopBot folder; and we can look up the details of your tool. We continuously monitor e-mail during the workday, and regularly check it in the evenings and on the weekends. Go to the support section of our web site, or address the e- mail to: [email protected]