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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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My Taig is Wearing Out - Upgrade Etc...
On 11/27/2010 05:48 PM, Bob La Londe wrote:
I think I have a design for a Z-axis retrofit for it all worked out, and I have a question or request for clarification from some of you guys who have built, retrofit, or modified your own machines. Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. I can't speak to the necessity of a brake, but how about counter-weighting it so there is no force required for it to stay put. It will increase the inertial load, but that is probably less of a problem on the Z axis. BobH |
#2
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My Taig is Wearing Out - Upgrade Etc...
My Taig is wearing out. I've had it for just over two years and I would
guess its seen well over 1000 hours of run time. Probably over 2000. I should probably save my time and energy and just jerk the spindle and steppers for a new machine, but I hate to waste it completely. Its biggest problem since day one has always been the quality of its Z-axis. I think I have a design for a Z-axis retrofit for it all worked out, and I have a question or request for clarification from some of you guys who have built, retrofit, or modified your own machines. Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. How much force does it take to back drive? I know the answer is probably "it depends", but I was looking for a more general answer. A. Next to nothing. (stop driving it and the weight of the ball nut alone will fall with no load) B. A gentle push. (it takes some force, but the weight of the ball nut isn't going to back drive. C. A firm push. (you can get it moving with the ball of your thumb and your carriage weight will definitely make it fall.) My other thought is that with a very light weight spindle and carriage would the power of a 380oz stepper motor be adequate to hold it in place? Then just apply a simple relay operated friction brake or even a manual one when the power shuts off for the motor. Ok, upon afterthought that last part kinda answers itself. If the motor can move the carriage adequately (steppers are rated in holding not moving force) with out stalling under cutting load then it should have no problem holding it while idling. Note: A 380 oz stepper motor is a very adequate drive for most applications. It takes real force with your hand against the table to stall one, and you can't do it by grabbing the shaft with your thumb and forefinger except maybe at speeds in excess of its rating. |
#3
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My Taig is Wearing Out - Upgrade Etc...
On Sat, 27 Nov 2010 10:48:24 -0700, "Bob La Londe"
wrote: My Taig is wearing out. I've had it for just over two years and I would guess its seen well over 1000 hours of run time. Probably over 2000. I should probably save my time and energy and just jerk the spindle and steppers for a new machine, but I hate to waste it completely. Its biggest problem since day one has always been the quality of its Z-axis. A thought, coming from a person interested in but not yet working with CNC mills, but coming from a mechanical background: Are you lubricating it sufficiently and frequently and is the interface adjusted firmly/properly? What's wearing? a) the leadscrew and nut b) the table and ways c) the column and ways d) all of the above Note: A 380 oz stepper motor is a very adequate drive for most applications. It takes real force with your hand against the table to stall I've seen kits made with 185 and 270oz motors, so 380 oughta work. one, and you can't do it by grabbing the shaft with your thumb and forefinger except maybe at speeds in excess of its rating. Caution Kids: Don't try this at home. (DUH!) -- Education should provide the tools for a widening and deepening of life, for increased appreciation of all one sees or experiences. It should equip a person to live life well, to understand what is happening around him, for to live life well one must live life with awareness. -- Louis L'Amour |
#4
Posted to rec.crafts.metalworking
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My Taig is Wearing Out - Upgrade Etc...
On Sat, 27 Nov 2010 10:48:24 -0700, "Bob La Londe"
wrote: My Taig is wearing out. I've had it for just over two years and I would guess its seen well over 1000 hours of run time. Probably over 2000. I should probably save my time and energy and just jerk the spindle and steppers for a new machine, but I hate to waste it completely. Its biggest problem since day one has always been the quality of its Z-axis. I think I have a design for a Z-axis retrofit for it all worked out, and I have a question or request for clarification from some of you guys who have built, retrofit, or modified your own machines. Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. How much force does it take to back drive? I know the answer is probably "it depends", but I was looking for a more general answer. A. Next to nothing. (stop driving it and the weight of the ball nut alone will fall with no load) B. A gentle push. (it takes some force, but the weight of the ball nut isn't going to back drive. C. A firm push. (you can get it moving with the ball of your thumb and your carriage weight will definitely make it fall.) My other thought is that with a very light weight spindle and carriage would the power of a 380oz stepper motor be adequate to hold it in place? Then just apply a simple relay operated friction brake or even a manual one when the power shuts off for the motor. Ok, upon afterthought that last part kinda answers itself. If the motor can move the carriage adequately (steppers are rated in holding not moving force) with out stalling under cutting load then it should have no problem holding it while idling. Note: A 380 oz stepper motor is a very adequate drive for most applications. It takes real force with your hand against the table to stall one, and you can't do it by grabbing the shaft with your thumb and forefinger except maybe at speeds in excess of its rating. There's not a Z brake on my knee mill machine. The Z axis is just a quill. Bob, if you've used the Taig this much; its time for you to move up to something like Iggy's mill. You'll be able to make the parts in 1/4 of the time and the machine will last 20 years. Just my two cents Karl |
#5
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My Taig is Wearing Out - Upgrade Etc...
Bob La Londe writes:
Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. That makes no sense. If you have a motor controlling the axis, then the motor provides the braking. If you are running free (manual control with a quill lever) then your hand or the spindle lock provides the braking. Stepper motors are neither economical or appropriate for motion control when significant force is required as is the case for CNC metalworking. Servomotors are the proper element. Steppers' only virtue is relative simplicity, but this is obviated by Geckodrive controllers and the like. |
#6
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My Taig is Wearing Out - Upgrade Etc...
On 2010-11-27, Karl Townsend wrote:
Bob, if you've used the Taig this much; its time for you to move up to something like Iggy's mill. You'll be able to make the parts in 1/4 of the time and the machine will last 20 years. Also may increase your general happiness!!! i |
#7
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My Taig is Wearing Out - Upgrade Etc...
Richard J Kinch wrote: Bob La Londe writes: Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. That makes no sense. If you have a motor controlling the axis, then the motor provides the braking. If you are running free (manual control with a quill lever) then your hand or the spindle lock provides the braking. It makes plenty of sense, and all the medium and larger machines incorporate a mechanical power-to-release brake on the Z axis. Without this, when the machine is powered off, the servo is no longer providing a braking effect and the pneumatic or hydraulic head counterbalance is no longer operating the head will drop down until it contacts something to stop it, such as expensive tooling, fixtures, etc. Stepper motors are neither economical or appropriate for motion control when significant force is required as is the case for CNC metalworking. Servomotors are the proper element. Steppers' only virtue is relative simplicity, but this is obviated by Geckodrive controllers and the like. This is simply not true. Steppers produce a lot more torque than you apparently think, with even small 23 size units producing over 600 oz-in. Coupled with any reasonable leadscrew / ballscrew pitch that translates into plenty of force for smaller machines. Since smaller machines also don't have high HP spindles, the stepper drive is well matched to the cutting rates that the spindle can handle. |
#8
Posted to rec.crafts.metalworking
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My Taig is Wearing Out - Upgrade Etc...
Stepper motors are neither economical or appropriate for motion control when significant force is required as is the case for CNC metalworking. Servomotors are the proper element. Steppers' only virtue is relative simplicity, but this is obviated by Geckodrive controllers and the like. This is simply not true. Steppers produce a lot more torque than you apparently think, with even small 23 size units producing over 600 oz-in. Coupled with any reasonable leadscrew / ballscrew pitch that translates into plenty of force for smaller machines. Since smaller machines also don't have high HP spindles, the stepper drive is well matched to the cutting rates that the spindle can handle. For all but the smallest machines, I also believe servos are far superior. That 600 oz-in is 3 ft-lb, most anyone turns manual handles harder than that. Exceed that for even a sec and the machine looses steps and ruins the part. Now my bias against steppers is based on bitter experience. When the bandit control died on my knee mill, I had to go to steppers as no cheap PC control using servos existed at that time. Even after upgrading to high performance 2000 oz-in steppers I continually lost steps and ruined parts. I had to make parts at 1/4 speed and watch it like a hawk. So, I watched eBay and bought a high dollar control for cheap. Then put those bandit servos back on with encoders. WHAT A DIFFERENCE! Don't know why I put up with steppers for two years. Now today, with EMC2 well developed, it makes no sense to go stepper. You get a free control with position feedback and a strong user base for support. Just my two cents. Karl |
#9
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My Taig is Wearing Out - Upgrade Etc...
"Bob La Londe" wrote:
I think I have a design for a Z-axis retrofit for it all worked out, and I have a question or request for clarification from some of you guys who have built, retrofit, or modified your own machines. Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. How much force does it take to back drive? I know the answer is probably "it depends", but I was looking for a more general answer. I've worked on VMC's that used brakes and one that used a chain with pig iron for a counter balance. See if a counter weight, simple as a pulley, cable and a balancing weight will do. Oh, I was responsible for a waterjet cell that used an air counter balance but it had a brake in case we lost air pressure. Air cylinder and pressure regulator might be the easiest way to go. This isn't a danger to life app like full sized machines. Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller |
#10
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My Taig is Wearing Out - Upgrade Etc...
Karl Townsend wrote: Stepper motors are neither economical or appropriate for motion control when significant force is required as is the case for CNC metalworking. Servomotors are the proper element. Steppers' only virtue is relative simplicity, but this is obviated by Geckodrive controllers and the like. This is simply not true. Steppers produce a lot more torque than you apparently think, with even small 23 size units producing over 600 oz-in. Coupled with any reasonable leadscrew / ballscrew pitch that translates into plenty of force for smaller machines. Since smaller machines also don't have high HP spindles, the stepper drive is well matched to the cutting rates that the spindle can handle. For all but the smallest machines, I also believe servos are far superior. That 600 oz-in is 3 ft-lb, most anyone turns manual handles harder than that. Exceed that for even a sec and the machine looses steps and ruins the part. Now my bias against steppers is based on bitter experience. When the bandit control died on my knee mill, I had to go to steppers as no cheap PC control using servos existed at that time. When was this? EMC and Mach3 have both been around for quite a while. Even after upgrading to high performance 2000 oz-in steppers I continually lost steps and ruined parts. I had to make parts at 1/4 speed and watch it like a hawk. It sounds like you had some tuning and/or drivetrain issues. So, I watched eBay and bought a high dollar control for cheap. Then put those bandit servos back on with encoders. WHAT A DIFFERENCE! Don't know why I put up with steppers for two years. Now today, with EMC2 well developed, it makes no sense to go stepper. You get a free control with position feedback and a strong user base for support. You can go servo with position feedback with Mach3, EMC or EMC2, and with any of them it still makes sense to use steppers for smaller machines and particularly machines with minimal force requirements such as plasma cutters. |
#11
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My Taig is Wearing Out - Upgrade Etc...
Wes wrote: "Bob La Londe" wrote: I think I have a design for a Z-axis retrofit for it all worked out, and I have a question or request for clarification from some of you guys who have built, retrofit, or modified your own machines. Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. How much force does it take to back drive? I know the answer is probably "it depends", but I was looking for a more general answer. I've worked on VMC's that used brakes and one that used a chain with pig iron for a counter balance. See if a counter weight, simple as a pulley, cable and a balancing weight will do. Oh, I was responsible for a waterjet cell that used an air counter balance but it had a brake in case we lost air pressure. Air cylinder and pressure regulator might be the easiest way to go. This isn't a danger to life app like full sized machines. Auto type gas-springs work pretty well on small machines. I use a pair of them with a cable and pulley 2:1 ratio setup to counterbalance the head on my cnc mini mill. |
#12
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My Taig is Wearing Out - Upgrade Etc...
Now my bias against steppers is based on bitter experience. When the bandit control died on my knee mill, I had to go to steppers as no cheap PC control using servos existed at that time. When was this? EMC and Mach3 have both been around for quite a while. My beloved Bandit, that I had upgraded to 300K memory died in early 97. The machine was down for a whole year before I got it running with steppers and a DOS control called AHHA. Good control for its time and I learned a lot about refitting machines. I bought a failed Camsoft refit of a Mazak M4 lathe in 2000 and was totally in over my head figuring out what was done wrong so I put the servos back on the Excello to learn Camsoft. Don't remember the exact time anymore, must have been about March 2001 when it finally ran with servos again. I got the M4 running in 2003 and upgraded in 2004. 2005 and 2006 and into 2007 were spent on a hardinge CHNC that started as a pile o' parts. 2008 I did another fella's knee mill. 2009 I started a plasma cutter and ran into tons of other stuff and didn't finish. This year,the kid bought a new place and asked me to get his Matsuura running. The times aren't perfect, but its a general summary of'my refit hobby. The hobby is active maybe two months a year,I still have to work for a living. And I have to fish with most of my free time. You got to have your priorities. Karl |
#13
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My Taig is Wearing Out - Upgrade Etc...
On 2010-11-27, Bob La Londe wrote:
My Taig is wearing out. I've had it for just over two years and I would guess its seen well over 1000 hours of run time. Probably over 2000. I should probably save my time and energy and just jerk the spindle and steppers for a new machine, but I hate to waste it completely. Its biggest problem since day one has always been the quality of its Z-axis. Since you are talking about a Z-axis -- I presume that you mean the Taig mill, not the Taig lathe (which is what I have).. I think I have a design for a Z-axis retrofit for it all worked out, and I have a question or request for clarification from some of you guys who have built, retrofit, or modified your own machines. Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. How much force does it take to back drive? I know the answer is probably "it depends", but I was looking for a more general answer. A. Next to nothing. (stop driving it and the weight of the ball nut alone will fall with no load) B. A gentle push. (it takes some force, but the weight of the ball nut isn't going to back drive. C. A firm push. (you can get it moving with the ball of your thumb and your carriage weight will definitely make it fall.) Yes -- "it depends". A ball nut on a vertical ball screw will move under its own weight -- and accelerate rapidly. However -- this is not counting the various frictions involved. How good are the ways -- and how tight are the gibs? What about how the stepper motor forces get to either the ball screw or the ball nut? (I know that the X-axis and Z-axis on the Bridgeport BOSS-3 rotate the ball nut around a stationary ball screw. And in the Z-axis, the ball screw is hollow around the quill so it pushes the quill centrally on axis. Depending on the size of the stepper motor -- it may have enough torque just from its internal magnetism to resist the falling weight of the Z-axis -- even with no power applied. Certainly power applied to one pole should be sufficient to prevent motion unless something else is seriously wrong. My other thought is that with a very light weight spindle and carriage would the power of a 380oz stepper motor be adequate to hold it in place? Then just apply a simple relay operated friction brake or even a manual one when the power shuts off for the motor. If there are no cutting forces, probably the internal magnetic fields will hold the motor stationary enough -- even without power. Ok, upon afterthought that last part kinda answers itself. If the motor can move the carriage adequately (steppers are rated in holding not moving force) with out stalling under cutting load then it should have no problem holding it while idling. Yes -- and as I said above -- likely with power off, the permanent magnet fields in at least some steppers may be sufficient to resist the force of gravity. First off -- with no Z-axis leadscrew and nut installed, does the weight of the head move it on the ways? If not, you should be fine with no power one. But once cutting forces come into play, things like the spiral of the flutes can affect how much feed is applied to the Z-axis by the spindle. (And, of course, a left-hand spiral would generate up forces instead of down.) Note: A 380 oz stepper motor is a very adequate drive for most applications. It takes real force with your hand against the table to stall one, and you can't do it by grabbing the shaft with your thumb and forefinger except maybe at speeds in excess of its rating. Then probably good enough to hold the ball screws. The usual reason for warnings about ball screws is for a manual machine where cutting forces can back-drive the ball screw unless you have a hand on the wheel for each axis. (Hmm ... three hands ... ??? :-) Enjoy, DoN. -- Remove oil spill source from e-mail Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#14
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My Taig is Wearing Out - Upgrade Etc...
"Karl Townsend" wrote in message
... On Sat, 27 Nov 2010 10:48:24 -0700, "Bob La Londe" wrote: Bob, if you've used the Taig this much; its time for you to move up to something like Iggy's mill. You'll be able to make the parts in 1/4 of the time and the machine will last 20 years. I'm working on that. http://www.yumabassman.com/bulletinb... 5b&mode=view Meet Metal Nibbler Three. Just my two cents 50,000¢ but close. |
#15
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My Taig is Wearing Out - Upgrade Etc...
Pete C. writes:
Steppers produce a lot more torque than you apparently think, with even small 23 size units producing over 600 oz-in. Coupled with any reasonable leadscrew / ballscrew pitch that translates into plenty of force for smaller machines. You confuse torque and linear force with power. Yes, you can gear up or down to any torque you like. But power is what counts: force times distance per time, which is to say the capacity to complete useful work when integrated over time. Steppers are inherently weak. Their dismal torque ratings are only delivered at very slow speeds, which is to say, at limited power. Some motion control tasks require little power, and steppers will do, but for metalworking, you need power: the ability to accelerate quickly and push rapidly against resistance. |
#16
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My Taig is Wearing Out - Upgrade Etc...
On Sun, 28 Nov 2010 00:39:27 -0700, "Bob La Londe"
wrote: "Karl Townsend" wrote in message .. . On Sat, 27 Nov 2010 10:48:24 -0700, "Bob La Londe" wrote: Bob, if you've used the Taig this much; its time for you to move up to something like Iggy's mill. You'll be able to make the parts in 1/4 of the time and the machine will last 20 years. I'm working on that. http://www.yumabassman.com/bulletinb... 5b&mode=view Meet Metal Nibbler Three. Just my two cents 50,000¢ but close. That's right, I remember your post. An old Hurco will be a FINE machine. Karl |
#17
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My Taig is Wearing Out - Upgrade Etc...
"Richard J Kinch" wrote in message
. .. Pete C. writes: Steppers produce a lot more torque than you apparently think, with even small 23 size units producing over 600 oz-in. Coupled with any reasonable leadscrew / ballscrew pitch that translates into plenty of force for smaller machines. You confuse torque and linear force with power. Yes, you can gear up or down to any torque you like. But power is what counts: force times distance per time, which is to say the capacity to complete useful work when integrated over time. Steppers are inherently weak. Their dismal torque ratings are only delivered at very slow speeds, which is to say, at limited power. Some motion control tasks require little power, and steppers will do, but for metalworking, you need power: the ability to accelerate quickly and push rapidly against resistance. Perhaps when hogging out with larger cutters, but for detail work with tiny cutters they generate more than enough speed and "force." The trick is to find an optimum feed, depth of cut, approach, and width of pass to get fairly decent material removal without breaking cutters. An 1/8" or larger cutter can crash the machine, but a 380oz stepper has enough force to break anything smaller in a heart beat when you go for too much. For some of what I am doing an 1/8 cutter is very large. The only time I really wish for more force and bigger cutters is when making larger parts to modify the machine itself like different spindle mounts or motor mounts. When I get the Hurco going it will get to do all those big parts. |
#18
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My Taig is Wearing Out - Upgrade Etc...
"Richard J Kinch" wrote in message . .. Bob La Londe writes: Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. That makes no sense. If you have a motor controlling the axis, then the motor provides the braking. If you are running free (manual control with a quill lever) then your hand or the spindle lock provides the braking. Stepper motors are neither economical or appropriate for motion control when significant force is required as is the case for CNC metalworking. Servomotors are the proper element. Steppers' only virtue is relative simplicity, but this is obviated by Geckodrive controllers and the like. I think that steppers have a place in CNC mills used for metalworking so long as an appropriate system design target and approach is used. They've been working fine for me during the past 3 years or so on an 1100-lb commercial mill. No lost steps that I'm aware of. |
#19
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My Taig is Wearing Out - Upgrade Etc...
On 11/27/2010 11:48 AM, Bob La Londe wrote:
My Taig is wearing out. I've had it for just over two years and I would guess its seen well over 1000 hours of run time. Probably over 2000. I should probably save my time and energy and just jerk the spindle and steppers for a new machine, but I hate to waste it completely. Its biggest problem since day one has always been the quality of its Z-axis. I think I have a design for a Z-axis retrofit for it all worked out, and I have a question or request for clarification from some of you guys who have built, retrofit, or modified your own machines. Everybody says you need a brake on the Z-axis if you use a ballscrew or it will backdrive. How much force does it take to back drive? I know the answer is probably "it depends", but I was looking for a more general answer. I have put a ballscrew on a minimill (I think equivalent to and X2) and have had no problems with it dropping when power is off. This is with a servo, even, not a stepper. So, I would not worry about this with a reasonably fine thread pitch. If you do it with a 2 TPI ballscrew, then it could be a problem. You can use springs to reduce the weight of the Z to help the motor. Jon |
#20
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My Taig is Wearing Out - Upgrade Etc...
On 11/27/2010 02:27 PM, Karl Townsend wrote:
Bob, if you've used the Taig this much; its time for you to move up to something like Iggy's mill. You'll be able to make the parts in 1/4 of the time and the machine will last 20 years. twenty years? Hmmm, MY Bridgeport was made in 1938, and was in a production shop for the aerospace industry until about 1982. So, that's 44 years of real production, and then 28 years of lighter use. Yes, it has detectable wear in the X and Z slides, but it is really not that bad, yet. One of these days I'd like to scrape the ways, but I can't afford to have it out of service for 9 months or more. So, I just use it. Jon |
#21
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My Taig is Wearing Out - Upgrade Etc...
"Karl Townsend" wrote in message
news The times aren't perfect, but its a general summary of'my refit hobby. The hobby is active maybe two months a year,I still have to work for a living. And I have to fish with most of my free time. You got to have your priorities. Missed that the first time. Fishing definitely cuts into my time for playing in the shop too. In fact I need to go re-spool a couple flipping sticks right now. |
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