mrdovey
08-13-2005, 10:17 AM
Yesterday morning I fired up my Bot and got a message to the effect that SBCUT was unable to determine my CPU speed, that my SHOPBOT.INI file had been corrupted, and that I could try exiting and restarting SBCUT to cure the problem.
Easy enough - I terminated and restarted SBCUT and immediately discovered that my hand-tuned SHOPBOT.INI file had been discarded and a default file installed with a horribly wrong Z-axis steps-per-inch value. I restored the working value (helpfully provided by ShopBot two years ago) and was back in business.
But then I decided to do a bit of "belt and suspenders" checking to make sure that the value was, in fact, correct...
I zero'd the Z axis and did an "MZ 3" - then got out a 1-2-3 block (accurate to within 0.0002") and discovered that the block stood almost a quarter of an inch higher than the bottom of the bit.
I re-checked with moves to z = 1 and z = 2 and found that the errors seemed to be at least approximately proportional.
I fiddled around with the parameter until I arrived at what appeared to give me accurate z-axis movement, wrote the working parameter value in my Command Reference, and paused (nervously) to consider the implications of it all.
What, I wondered, if there are also problems with my x- and y-axis setup?
I ended up clamping a digital caliper to the end of my table, opening the jaws, lowering the bit between the jaws, closing the movable jaw until it contacted the bit, and pressing the "zero" button on the caliper to get a 0.000" reading. Then I issued a "MX %(1)+1" command to move exactly one inch from the current position in the positive x direction, followed by a "MX %(1)-0.5" to back away from the caliper jaw before issuing an "MZ 3" command to give me enough room to read the caliper. The caliper readout indicated that the Bot had actually moved 0.992"
I'm not sure where the discrepencies come from; but they're definitely there and weren't the result of lost steps. They aren't terribly difficult to correct - but I'd made the mistake of assuming that because the parameter values came from ShopBot, they'd be accurate to the precision of which the machine is capable. My bad - but I learned a worthwhile lesson that I'll pass along to the group:
Assume nothing - check your machine.
Easy enough - I terminated and restarted SBCUT and immediately discovered that my hand-tuned SHOPBOT.INI file had been discarded and a default file installed with a horribly wrong Z-axis steps-per-inch value. I restored the working value (helpfully provided by ShopBot two years ago) and was back in business.
But then I decided to do a bit of "belt and suspenders" checking to make sure that the value was, in fact, correct...
I zero'd the Z axis and did an "MZ 3" - then got out a 1-2-3 block (accurate to within 0.0002") and discovered that the block stood almost a quarter of an inch higher than the bottom of the bit.
I re-checked with moves to z = 1 and z = 2 and found that the errors seemed to be at least approximately proportional.
I fiddled around with the parameter until I arrived at what appeared to give me accurate z-axis movement, wrote the working parameter value in my Command Reference, and paused (nervously) to consider the implications of it all.
What, I wondered, if there are also problems with my x- and y-axis setup?
I ended up clamping a digital caliper to the end of my table, opening the jaws, lowering the bit between the jaws, closing the movable jaw until it contacted the bit, and pressing the "zero" button on the caliper to get a 0.000" reading. Then I issued a "MX %(1)+1" command to move exactly one inch from the current position in the positive x direction, followed by a "MX %(1)-0.5" to back away from the caliper jaw before issuing an "MZ 3" command to give me enough room to read the caliper. The caliper readout indicated that the Bot had actually moved 0.992"
I'm not sure where the discrepencies come from; but they're definitely there and weren't the result of lost steps. They aren't terribly difficult to correct - but I'd made the mistake of assuming that because the parameter values came from ShopBot, they'd be accurate to the precision of which the machine is capable. My bad - but I learned a worthwhile lesson that I'll pass along to the group:
Assume nothing - check your machine.