bwnichols
09-08-2009, 02:03 AM
As my CW (with brand-new smooth-as-silk RockChuck installed) finished a recent pass, I asked myself "What could possibly be going, 'thunka thunka thunka thunk' at about 1 or 2 cycles per second, on a tool that's spinning upwards of 300 revolutions per second?"
Well I shortly received a clue in the form of a "Z-axis stall" error message, and a broken 1/8" end mill (i.e. CW 1/8" straight bit). Figured that I'd neglected to tighten the bit or RockChuck collet sufficiently, but a quick check confirmed all was secure.
After replacing the broken end mill with a cheap steel bit to troubleshoot, darned if that one didn't stall and bend to the point of uselessness when the x-axis started moving. Third time's a charm...after a trip to Home Depot for a couple of Diablo DR04100 1/8"x3/8" carbide router bits (most of my material is 1/4" or less), at last I notice the tool chuck is barely turning.
Turns out the flex shaft was spinning a groove into the top of the spindle instead of turning the tool. So of course I jammed it into the spindle as best I could and kept on carving, but every now and again after a pass I would hear that ominous 'thunka thunka thunka thunk'. While I was evaluating the performance of the Diablo bit and RockChuck combination for cutting 1/4" HDPE (like butter!), I might've saved myself the cost of a flex shaft had I realized the root cause of the spindle stalls, and re-squared the keyway as described below before continuing to carve.
But I didn't really connect the two problems (spindle stall and 'thunka thunk') until the carve was almost done. When the light bulb finally went on, I grabbed the flex shaft cover next time I heard a thunk. Sure enough, that 'thunka thunk' vibration was coming directly from the drive system. In my professional estimation, it was due to the flex shaft 'skipping' around the keyway in the top of the spindle. By dumb luck I finished that carve without a spindle stall, but upon examination afterward I discovered the spindle end of the flex shaft had become snub-shaped and the flex-shaft wire was beginning to unwind.
If this happens to you, stop right there! The flex shaft is symmetric, in that it can be installed in either direction. So take the presumably good, motor-end of the flex shaft and check the spindle keyway. It should slide down to the hilt without interference. If the top of the keyway has become grooved, as mine had, there will be interference and it is simply not an option to skip re-squaring it.
Purchase or borrow a 5/32" or 7/32" tapered (either will work, due to the taper) machinist's smooth-cut square file (not found at Lowe's or HD (http://www.pferdusa.com/products/201/20103/2010304P.html)) and gently re-square each corner of the keyway, until the undamaged end of the flex shaft seats smoothly without interference. Do not use a triangular file for this else more damage may easily be done to the opposite edge of the keyway than can be repaired at the corners!
Now try the spindle end. If you've caught this problem early enough, you may be able to reshape the end of the shaft in a vise such that it drops into the keyway as effortlessly as the undamaged end. But options are few if the flex wire has started to unwind -- someone good with silver solder may be able to repair it (but I was not), and trimming it off irrevocably shortens the working length, which will exacerbate the spindle stall problem. So if the damaged end of the flex shaft can't simply be reshaped to drop into the re-squared keyway without interference, then its time for a new flex shaft.
And before this or any flex shaft installation, always be sure to check and re-square if necessary the keyway in the top of the spindle!
Can post photos, if there is interest...
Regards
Brando
Well I shortly received a clue in the form of a "Z-axis stall" error message, and a broken 1/8" end mill (i.e. CW 1/8" straight bit). Figured that I'd neglected to tighten the bit or RockChuck collet sufficiently, but a quick check confirmed all was secure.
After replacing the broken end mill with a cheap steel bit to troubleshoot, darned if that one didn't stall and bend to the point of uselessness when the x-axis started moving. Third time's a charm...after a trip to Home Depot for a couple of Diablo DR04100 1/8"x3/8" carbide router bits (most of my material is 1/4" or less), at last I notice the tool chuck is barely turning.
Turns out the flex shaft was spinning a groove into the top of the spindle instead of turning the tool. So of course I jammed it into the spindle as best I could and kept on carving, but every now and again after a pass I would hear that ominous 'thunka thunka thunka thunk'. While I was evaluating the performance of the Diablo bit and RockChuck combination for cutting 1/4" HDPE (like butter!), I might've saved myself the cost of a flex shaft had I realized the root cause of the spindle stalls, and re-squared the keyway as described below before continuing to carve.
But I didn't really connect the two problems (spindle stall and 'thunka thunk') until the carve was almost done. When the light bulb finally went on, I grabbed the flex shaft cover next time I heard a thunk. Sure enough, that 'thunka thunk' vibration was coming directly from the drive system. In my professional estimation, it was due to the flex shaft 'skipping' around the keyway in the top of the spindle. By dumb luck I finished that carve without a spindle stall, but upon examination afterward I discovered the spindle end of the flex shaft had become snub-shaped and the flex-shaft wire was beginning to unwind.
If this happens to you, stop right there! The flex shaft is symmetric, in that it can be installed in either direction. So take the presumably good, motor-end of the flex shaft and check the spindle keyway. It should slide down to the hilt without interference. If the top of the keyway has become grooved, as mine had, there will be interference and it is simply not an option to skip re-squaring it.
Purchase or borrow a 5/32" or 7/32" tapered (either will work, due to the taper) machinist's smooth-cut square file (not found at Lowe's or HD (http://www.pferdusa.com/products/201/20103/2010304P.html)) and gently re-square each corner of the keyway, until the undamaged end of the flex shaft seats smoothly without interference. Do not use a triangular file for this else more damage may easily be done to the opposite edge of the keyway than can be repaired at the corners!
Now try the spindle end. If you've caught this problem early enough, you may be able to reshape the end of the shaft in a vise such that it drops into the keyway as effortlessly as the undamaged end. But options are few if the flex wire has started to unwind -- someone good with silver solder may be able to repair it (but I was not), and trimming it off irrevocably shortens the working length, which will exacerbate the spindle stall problem. So if the damaged end of the flex shaft can't simply be reshaped to drop into the re-squared keyway without interference, then its time for a new flex shaft.
And before this or any flex shaft installation, always be sure to check and re-square if necessary the keyway in the top of the spindle!
Can post photos, if there is interest...
Regards
Brando