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To "which is better" question Forrest Addy replied-
I run endmills in my R-8 collets all the time. That's what they're for.
A collet wears more or less concentric whereas an endmill holder wears away from the setscrew.
Collets are cheap. When they wear out you throw them away.
When the spindle collet taper wears out you regrind it right in the machine.
The only time I use my end mill adapters is when I need a little extra reach past an obstruction.
When people tell you running endmills in collets is bad, smile politely but think "BS". If they persist with specious justification employ the "To each his own" or "Go piss up a rope" option as the situation dictates.
How end mill holders wear posted by Forrest-
Nearly all endmills these days have the familair Weldon shanks - a sraight shank with one or two flats for a setscrew.
The Weldon shank is a compromise. While it's a vast improvement over the Brown and Sharpe taper shank (1/2 per foot) in retention (taper wedging action Vs set screw), the Weldon shank also requires a few tenths clearance with the holder merely to insert the cutter.
The Weldon shank essentially a cantilevered shaft held by a set screw. The cutter in the work deflects under load to a rainbow shape concentrating its force on the edge or the tool adaptor bore. Grip a new pencil in your left fist and move the end of the pencil in a circle. Feel the stirring action in your hand. This stirring action is a rough analog of the Weldon shank in a set screw style tool adaptor.
Bell mouth wear progresses from the mouth of the adaptor bore to the opposite side from the set screw. Here the nearly circular stirring is modified by the clamping action of the setscrew to a back and forth motion causing the mouth of the adapter to wear elliptically and the bore opposite the setscrew to wear as well.
As wear progresses, the cutter moves eccentrically and to a small angle away from the setscrew until the tool adapter cuts on one side for light cuts and drags at a significant angle limited by elastic deflection of the cutter itself and the increased and non-circular wear clearance in the adaptor.
Most anyone using a setscrew adaptor has noticed a brown smear on the endmill shank after a session of heavy milling. This smear may be powdery or greasy depending if the work was cut dry or with coolant. It's a vivid reddish brown if dry and dark brown if oily. The brown stuff is fretting corrosion products - hard steel worn by heavy cyclic pressure into the finest powder and oxidized in the adaptor's clearance space. You also see the same products in ball bearing bores and around failed ball bearings.
So setscrew milling adaptors do wear. The wear is slow at first but progressive with heavy cuts and time.
I was issued four new 2" shank Sonnet bull nose adaptors for a special close tolerence job on a Gray 4 head planer mill. There was a lot of stock to rough off using "corncob" roughing endmills then finishing with extension straight flute and some formed cutters. I checked the endmills when we started and they ran within 0.0005 on all teeth. Within two weeks of round the clock operation, the freshly resharpened cutters were running out 0.003" on the exposed shank and 0.007 4" out. You could watch the bead of coolant at the mouth of the Sonnet adapter pump in and out with the forces on the cutter and the action of the bead indicated the influence of the set screw.
The endmill shanks were Rc 55 (pretty damn hard) and the Sonnet bullnose adaptor was Rc 50 (damn hard) but still the adaptors wore out in only 2 weeks of heavy but not abusive use. This lead to an examination of the 2000 or so 50 MMT Weldon shank adptors in the tool room. Over 90% were shot. Not a little bit shot but a lot shot - some having 0.020" bellmouth.
Collective recollection over past unaccountable errors by good machinists and very expensive work spoiled lead to speculation on the role of all these years old and worn out endmill adaptors in the shop reject rate. $70,000 of emergency funding spent on new adaptors lead to a reduction of several hundred thousand dollars in the shop reject rate over the next year. The rate slowly increased as the adaptors wore.
Therefore: set screw milling adaptors for Weldon shank endmills do wear.
Moving on to collets. They wear as well. A collet bore in endmill service wears bell mouth at both ends but more at the mouth that the other end. Collets have a fixed bore length. Larger sized collets have a shorter diameter to length therefore larger Weldon shanks have a shorter grip to resist proportionately greater cantilever loads. Thus, larger collets wear far quicker.
Collets wear bellmouth on both ends something like an hourglass until there's only line grip near the center of the bore instead of a full cylindrical grip. Futher use exacerbates the wear until the stirring action and the pull of the flute helix slowly drags the cutter from the collet no matter how tight you wrench the draw bolt.
Because the wear is distributed by a collet's circumferential grip, the cutters run more concentrically compared to a setscrew holder where the wear is concentrated eccentrically by the setscrew forcing the cutter off center as it follows the wear.
One only has to compare the stiffness of the grip of a new 3/4" collet with a worn 3/4" collet. Grip an 8" long piece of 3/4" drill rod so 6 3/4" sticks out. Torque the drawbolt for consistancy. Set an indicator near the end of the drill rod and apply a known force with a spring scale - say, 100 lb. Compare the deflections of worn Vs new. Note the magnitude.
I suspect this is the basis of Jeff Park's bad experience with endmills in collets working their axially. Maybe he will comment.
Most older machining centers using straight shank tooling use spindle collets with an annular relieved bore. The relieved center gives the collet longer life.
Erikson and other makers of high quality spindle tooling are all very well aware of the dynamics of gripping endmills. They've provided ingenious counter measures against the effects of wear in their excellent but expensive tooling.
Unfortunately the R-8 tooling most of us are stuck with is designed for much lighter service and smaller overhung loads. An R-8 spindle with its small, short taper and clearanced upper fit is not a good choice for modern machine shop envirnment imposing relatively large overhung loads like milling with large long milling cutters or worse, the 4" carbide face mills touted (I love them) for turret mills.
The R-8 taper soon becomes hour-glassed and the upper bore suffers from countless tool changes. There's no cure for the problem of spindle wear short of a 30 or 40 MMT retrofit or vigilence and an occasional regrind or upper bore sleeving.
I run endmills in my R-8 collets all the time. That's what they're for.
A collet wears more or less concentric whereas an endmill holder wears away from the setscrew.
Collets are cheap. When they wear out you throw them away.
When the spindle collet taper wears out you regrind it right in the machine.
The only time I use my end mill adapters is when I need a little extra reach past an obstruction.
When people tell you running endmills in collets is bad, smile politely but think "BS". If they persist with specious justification employ the "To each his own" or "Go piss up a rope" option as the situation dictates.
How end mill holders wear posted by Forrest-
Nearly all endmills these days have the familair Weldon shanks - a sraight shank with one or two flats for a setscrew.
The Weldon shank is a compromise. While it's a vast improvement over the Brown and Sharpe taper shank (1/2 per foot) in retention (taper wedging action Vs set screw), the Weldon shank also requires a few tenths clearance with the holder merely to insert the cutter.
The Weldon shank essentially a cantilevered shaft held by a set screw. The cutter in the work deflects under load to a rainbow shape concentrating its force on the edge or the tool adaptor bore. Grip a new pencil in your left fist and move the end of the pencil in a circle. Feel the stirring action in your hand. This stirring action is a rough analog of the Weldon shank in a set screw style tool adaptor.
Bell mouth wear progresses from the mouth of the adaptor bore to the opposite side from the set screw. Here the nearly circular stirring is modified by the clamping action of the setscrew to a back and forth motion causing the mouth of the adapter to wear elliptically and the bore opposite the setscrew to wear as well.
As wear progresses, the cutter moves eccentrically and to a small angle away from the setscrew until the tool adapter cuts on one side for light cuts and drags at a significant angle limited by elastic deflection of the cutter itself and the increased and non-circular wear clearance in the adaptor.
Most anyone using a setscrew adaptor has noticed a brown smear on the endmill shank after a session of heavy milling. This smear may be powdery or greasy depending if the work was cut dry or with coolant. It's a vivid reddish brown if dry and dark brown if oily. The brown stuff is fretting corrosion products - hard steel worn by heavy cyclic pressure into the finest powder and oxidized in the adaptor's clearance space. You also see the same products in ball bearing bores and around failed ball bearings.
So setscrew milling adaptors do wear. The wear is slow at first but progressive with heavy cuts and time.
I was issued four new 2" shank Sonnet bull nose adaptors for a special close tolerence job on a Gray 4 head planer mill. There was a lot of stock to rough off using "corncob" roughing endmills then finishing with extension straight flute and some formed cutters. I checked the endmills when we started and they ran within 0.0005 on all teeth. Within two weeks of round the clock operation, the freshly resharpened cutters were running out 0.003" on the exposed shank and 0.007 4" out. You could watch the bead of coolant at the mouth of the Sonnet adapter pump in and out with the forces on the cutter and the action of the bead indicated the influence of the set screw.
The endmill shanks were Rc 55 (pretty damn hard) and the Sonnet bullnose adaptor was Rc 50 (damn hard) but still the adaptors wore out in only 2 weeks of heavy but not abusive use. This lead to an examination of the 2000 or so 50 MMT Weldon shank adptors in the tool room. Over 90% were shot. Not a little bit shot but a lot shot - some having 0.020" bellmouth.
Collective recollection over past unaccountable errors by good machinists and very expensive work spoiled lead to speculation on the role of all these years old and worn out endmill adaptors in the shop reject rate. $70,000 of emergency funding spent on new adaptors lead to a reduction of several hundred thousand dollars in the shop reject rate over the next year. The rate slowly increased as the adaptors wore.
Therefore: set screw milling adaptors for Weldon shank endmills do wear.
Moving on to collets. They wear as well. A collet bore in endmill service wears bell mouth at both ends but more at the mouth that the other end. Collets have a fixed bore length. Larger sized collets have a shorter diameter to length therefore larger Weldon shanks have a shorter grip to resist proportionately greater cantilever loads. Thus, larger collets wear far quicker.
Collets wear bellmouth on both ends something like an hourglass until there's only line grip near the center of the bore instead of a full cylindrical grip. Futher use exacerbates the wear until the stirring action and the pull of the flute helix slowly drags the cutter from the collet no matter how tight you wrench the draw bolt.
Because the wear is distributed by a collet's circumferential grip, the cutters run more concentrically compared to a setscrew holder where the wear is concentrated eccentrically by the setscrew forcing the cutter off center as it follows the wear.
One only has to compare the stiffness of the grip of a new 3/4" collet with a worn 3/4" collet. Grip an 8" long piece of 3/4" drill rod so 6 3/4" sticks out. Torque the drawbolt for consistancy. Set an indicator near the end of the drill rod and apply a known force with a spring scale - say, 100 lb. Compare the deflections of worn Vs new. Note the magnitude.
I suspect this is the basis of Jeff Park's bad experience with endmills in collets working their axially. Maybe he will comment.
Most older machining centers using straight shank tooling use spindle collets with an annular relieved bore. The relieved center gives the collet longer life.
Erikson and other makers of high quality spindle tooling are all very well aware of the dynamics of gripping endmills. They've provided ingenious counter measures against the effects of wear in their excellent but expensive tooling.
Unfortunately the R-8 tooling most of us are stuck with is designed for much lighter service and smaller overhung loads. An R-8 spindle with its small, short taper and clearanced upper fit is not a good choice for modern machine shop envirnment imposing relatively large overhung loads like milling with large long milling cutters or worse, the 4" carbide face mills touted (I love them) for turret mills.
The R-8 taper soon becomes hour-glassed and the upper bore suffers from countless tool changes. There's no cure for the problem of spindle wear short of a 30 or 40 MMT retrofit or vigilence and an occasional regrind or upper bore sleeving.
