jTr
04-10-2015, 11:41 AM
Have experienced a variation in squareness of cuts with my PRS Alpha 9660. Not fatal, but puzzling for a number of reasons. Decided to run Gary Campbell's gantry squaring routine again this week.
Puzzle Pieces:
1> Gary's routine came out perfect. I mean super- tight on square.:cool:
2> Next day I fired up and made cuts, I was out of square roughly .028. Precisely the same variable on each piece cut, regardless the size or location of cut on the table.
3> Parked gantry @ 96/60 that night in anticipation of running dovetails the next day- I use the negative symbol in front of X/Y Unit values to invert 0,0 home for processes run on the far end of the machine.
4> Very similar measure of .03 ish out, but in the opposite direction from the previous day. :confused:
5> Fully check legs, rails for level/true and all is very good - the concrete floor it rests upon has been quite stable for the 3 yrs it's been there, and I've not needed to adjust at all.
Questions pondered:
- Is gantry twisting somehow depending on where it's parked? Leveling checks indicate this is not the case.
- Is there something loose in the carrier systems? -all is snug and good there.
Then I realized:
- The day I ran Gary's squaring routine, It had been parked at 24,24.
- The day it was measuring long diagonally from 0,0 towards 96,60, it had been parked @ 0,0
- Each time I experience the opposite problem for end-work routines such as dovetails, it had been parked/reset at 96,60
Sounds like someone's pulling one end of the gantry towards center of the machine....
Could it be the cables tethered to that end of the gantry?
Dropped motors to disengage gears from rack and began free-wheeling. Sure enough- when parked at 0, had a friend hold up the cables to alleviate their weight from the gantry. When gently released, weight of cables pulled the gantry towards center of table by an inch or so. Even greater movement when applying this procedure to the 96" end. When clamping a block to the opposite side of the gantry, the cables appear to pull the gantry approximately .020 - .030 .
Theory: Cables are introducing enough tension to pull gantry out of square prior to resetting drivers at start up. Once reset, motors are locked into this mode for duration of the day, and cable weight is not enough to affect normal operation. Dust collection hose is centered above table, and incidentally contributes to the issue as well, most acutely on the far end of machine where things are pulled most out of square. Furthermore, if this theory holds true, the extra-wide gantry for a 60" machine is more likely to display this phenomenon than a 48" machine.
Short term remedy/test of theory: always park roughly centered on table. Diligently monitor parts for squareness. If proven true, long term solution would be to purchase e-chain to alleviate the variable pull caused by the hank of cable currently swinging on that side of the machine. At very least, allow more slack, but concerned about entanglement issues if too slack...
Thank you for any guidance as I seek enlightenment.:o
jeff
Puzzle Pieces:
1> Gary's routine came out perfect. I mean super- tight on square.:cool:
2> Next day I fired up and made cuts, I was out of square roughly .028. Precisely the same variable on each piece cut, regardless the size or location of cut on the table.
3> Parked gantry @ 96/60 that night in anticipation of running dovetails the next day- I use the negative symbol in front of X/Y Unit values to invert 0,0 home for processes run on the far end of the machine.
4> Very similar measure of .03 ish out, but in the opposite direction from the previous day. :confused:
5> Fully check legs, rails for level/true and all is very good - the concrete floor it rests upon has been quite stable for the 3 yrs it's been there, and I've not needed to adjust at all.
Questions pondered:
- Is gantry twisting somehow depending on where it's parked? Leveling checks indicate this is not the case.
- Is there something loose in the carrier systems? -all is snug and good there.
Then I realized:
- The day I ran Gary's squaring routine, It had been parked at 24,24.
- The day it was measuring long diagonally from 0,0 towards 96,60, it had been parked @ 0,0
- Each time I experience the opposite problem for end-work routines such as dovetails, it had been parked/reset at 96,60
Sounds like someone's pulling one end of the gantry towards center of the machine....
Could it be the cables tethered to that end of the gantry?
Dropped motors to disengage gears from rack and began free-wheeling. Sure enough- when parked at 0, had a friend hold up the cables to alleviate their weight from the gantry. When gently released, weight of cables pulled the gantry towards center of table by an inch or so. Even greater movement when applying this procedure to the 96" end. When clamping a block to the opposite side of the gantry, the cables appear to pull the gantry approximately .020 - .030 .
Theory: Cables are introducing enough tension to pull gantry out of square prior to resetting drivers at start up. Once reset, motors are locked into this mode for duration of the day, and cable weight is not enough to affect normal operation. Dust collection hose is centered above table, and incidentally contributes to the issue as well, most acutely on the far end of machine where things are pulled most out of square. Furthermore, if this theory holds true, the extra-wide gantry for a 60" machine is more likely to display this phenomenon than a 48" machine.
Short term remedy/test of theory: always park roughly centered on table. Diligently monitor parts for squareness. If proven true, long term solution would be to purchase e-chain to alleviate the variable pull caused by the hank of cable currently swinging on that side of the machine. At very least, allow more slack, but concerned about entanglement issues if too slack...
Thank you for any guidance as I seek enlightenment.:o
jeff