Using a corner rounding mill?

I always take it all in one pass. Actually, I climb mill and then conventional mill at the same setting when using a manual mill. On the CNC I usually only make one pass and climb mill. If the machine is rigid enough climb milling is preferred. When routing you make conventional cuts. This type of cut tends to make the cutter deflect into the work so leaving enough material for a clean up pass will help insure a cut with no gouges. Climb milling deflects the cutter away from the work. If climb cutting is done with hand held tools things can get away from you in a hurry. ERS

Did you mean to write this? I virtually never climb mill on a manual machine, even for finishing. I find I never get a really great finish anyway, and if a good finish is required in die making, the surface is typically ground or stoned.

Regards,

Robin

Really? I'd bet most would say they can get a better finish climbing than conventional anytime. Do you machine dry?

-- Randy Replogle

My wife says I'm doing my Christian duty... annoying the hell out of her. Randall Replogle 2006

Randy, we've all been asked not to tease Robin about his hyperhidrosis, you are SO mean!

Good one, Tom! Wonder how many readers had to go to the dictionary?

Robin, I read what I wrote. And yes, it's accurate. I'm surprised you don't climb mill on manual machines. I almost always climb mill. Easier on cutters, better finish, the tool deflects away from the work so that parts aren't cut undersize when heavy cuts are being used. Actually, steel oftentimes will have a better finish after a conventional cut, but aluminum and brass look better after climb milling. So when milling steel I usually climb mill first and then conventional to get a good finish. This of course is when a relatively heavy cut is being taken. ERS

Maybe I've been spending too much time with a disc grinder and not enough time on a mill but I would never *ever* recommend that someone climb mill on a manual milling machine when taking a cut which could be described as "heavy."

This is an excellent way to break a cutter and ruin the work piece, not to mention making the whole table (assuming a Bridgeport-type machine) jump violently. Indeed I snapped a 1" roughing endmill and nearly toasted an O1 punch by carelessly approaching the work from the wrong direction (climbing) earlier this week.

I always run the machine to the point of the spindle audibly slowing down, assuming the cutter will take it. I've taken about a half a dozen full time machining courses through and before my apprenticeship, and we have never been taught to ever climb mill on a manual machine, although it has been suggested with a low voice (although never written!) that one can climb mill while taking a *light* finishing pass.

Climb milling is standard on CNC machines for the reasons above, but they are capable of safely climbing only because of their near zero-backlash ballscrews. Obviously manual machines do not have that option.

I suppose anyone is allowed to run their own machine however they want, but I can't imagine anyone consciously choosing to always climb. Other than perhaps rich adrenaline junkies...

Regards,

Robin

We had radio commercials in Southern Ontario about "hyperhidrosis" recently. I now understand it's treatable and that one doesn't need to be embarrassed...

I can't wait until August. They give out freezies on the shop floor when the temp goes over 35ºC. Even better when working in presses with no ventilation (don't want to blow dust onto the panels) and the 50+HP motors. Sometimes the presses get so hot they shut themselves down before they get damaged. If we could all be so lucky... We're supposed get water ever 20min, thirsty or not.

Regards,

Robin

Robin, I suppose I am ruining the mill. I mean it's only 25 years old and already there is a little more backlash in the center of travel. Perhaps you were never taught to climb mill on a bridgeport, or taught to never climb mill on a Bridgeport. But please don't assume I am ruining a machine. I've only been machining metal for 30 years or so and maybe you have more experience than me. Still, you should maybe watch me climb milling and see if it works well or not. ERS

I specified that one can break a cutter and ruin a work piece by climbing. The machine will jump but I'd be surprised if climbing could cause any irreversible damage to the mill, assuming the gibs are tight.

I've done it before and I that's why I cannot stress enough the danger involved with climbing. Can you give an example of the type of cuts you're taking?

For instance, I would run a 1" roughing endmill in O1 at about 200RPM (about

600RPM+ for aluminum), perhaps .3-.5" radial depth of cut, 1"+ axial depth of cut, feeding until the spindle bogs down a bit (may require two hands to apply adequate force on the crank to sustain the cut). As I said before, my accidental climb cut broke the cutter and made the table jump in a similar situation.

Do you never have issues with the table jumping and breaking cutters?

Regards,

Robin

Robin, Any screw with any clearance will make the table jump in a sort of stick/slip scenario. Unless the table has drag on it. Using a ballscrew will cause all kinds of problems unless it too is run with drag. On a CNC machine the servomotor provides this drag. It's not generally looked upon as drag, but it does prevent the pressure from making the screw turn enough to lose position within the parameters of the machine control. So if a climbing cutter pulls the table into the cut then the ballscrew will be rotated to move the work out of the cut. Then the direction reverses so the cutter is again climbing. Then the screw reverses, etc. If effect dragging. On the manual machine using acme screws the table locks are set to provide enough drag to prevent the cutter from taking up the backlash in the screw. As regards your method of milling it has been my experience that when hogging material it works better, and gives longer cutter life, if the cutter is fed into the work at almost the full cutter diameter. So instead of using a shallow radial, deep axial cut, I use a deep radial, shallow axial cut. This keeps more of the teeth cutting at one time and is easier on the machine. BTW, I believe the rotating cutter that removes the most material in the shortest time is a twist drill. That is if all the material in converted to chips. Obviously an annular cutter will remove more material, especially if the diameter is large. Eric

Are you sure the servo actively acounts for backlash? As I understand it, the ballscrew nuts are preloaded to virtually eliminate backlash. I know that in older worn machines, there are control paremeters that can account for backlash, but because there is give in the (worn) screw, the fix is not absolute. Interpolating arcs which cross 0º, 90º, 180º and 270º is impossible and results in a slight flat is left on the work piece as the axis reverses direction and the table is left floating.

Again, I'm no expert but I cannot imagine 3D machining would be possible if not for a mechanically rigid machine which would include preloaded nuts.

I am again interested in whether you have issues with the cutter grabbing you work. I suppose I'm beating this subject to death, but you're basically the only person I've ever heard specifying climbing on a manual machine.

I've always shared your observation (and have read articles which support it as well). I remember there were quite a few articles written about "plunge roughing" a couple of years ago. I don't do work which requires that type of roughing but I can imagine it would be very efficient if applied correctly.

Regards,

Robin

I wouldn't do it on either my B/port or my horiz mill except maybe for very light finish cuts, full depth, to remove tool marks.

I *have* broken cutters and ruined workpieces when trying this many, many years ago. With a heavy enough machine and enough drag on the table, I'm sure you could get away with it, but I don't care to try.

PDW

Greetings Robin, I guess I wasn't clear. When climb milling I use the table locks to put enough drag on the table to keep the cutter from pulling into the work. And I'm not alone. In all the shops I've worked in this is a common method of machining. Especially because of the increased cutter life. Now, let's talk about the active backlash compensation going on in a machine tool. Ballscrews can be set up with virtually zero backlash. Close but not quite zero. Thrust bearings are set up when the machine is new to have zero backlash. But everything wears in the machine and backlash will eventaully occur. So CNC controls have a parameter for backlash compensation. Even my 28 year old Fanuc 5T controls have this parameter. So whenever the the rotation of the ballscrew reverses the backlash amount is added to the move. But even in a machine with zero backlash the servo motor has to reverse direction when the cutter grabs. It then must go forward to advance the cut. This all happens very fast and so it looks like the motor is always going forward. If the machine has a brushed DC servo motor, and only two brushes, then the motor can only spin one way or the other. It can't just stay locked in one place. If a load is placed on the motor, and the current is adjusted to exactly match the load, then the motor can be locked in place. But if the load varies enough then the motor direction will need to reverse. First the load opposes the rotation, then it helps the rotation. If you don't want the motor spinning faster than the command the voltage must be reversed and the motor will reverse direction if there is any backlash. If you can, notice what the motor is doing on a cnc machine when it is stationary. It will be vibrating back and forth just a little. The machine has some kind of position feedback and usually the position sensor is not mounted directly to the motor shaft. So if the encoder is on the end of the ball screw then the very tiny amount of belt stretch will result in backlash that does not need to be programmed for, but will cause the motor to vibrate because it will spin one direction, stretch the belt a little, and then the ballscrew will rotate and the encoder will sense this. When the ballscrew rotation overshoots then the motor reverses. When it first reverses the tension on the belt is released and then it is stretched in the opposite direction. Finally the belt stops stretching and the ballscrew begins to turn. Eventually it will turn enough for the encoder to sense the rotation and the motor reverses again. This is where the vibration comes from. Now, my hands hurt from too much typing so I'm gonna quit. Cheers, Eric

I think you both are missing what Eric said. He typically cuts using almost the full diameter of the end mill. Do it that way and there is almost no difference between conventional and climb milling. Bury the full diameter of the cutter and there is no such thing as climb milling or conventional milling.

My initial thought was that, if he is setting the table locks so tight that the cutter won't move it, he's setting the table too tight, but again - if he's using the full cutter diameter there is less force needed to keep the table from jumping. Especially with four-flute and more cutters.

John Martin