Difference between revisions of "Milling101"

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*Rubber-faced clamping surfaces are NOT stiff enough for metal.  Or even plastics sometimes, if the milling is aggressive  
 
*Rubber-faced clamping surfaces are NOT stiff enough for metal.  Or even plastics sometimes, if the milling is aggressive  
 
* If you need to cut or drill all the way to the bottom of your stock, you must use a piece of SPOIL BOARD.  MDF is very common for this.  We've got tons of plywood and acrylic scrap which would also suffice.  
 
* If you need to cut or drill all the way to the bottom of your stock, you must use a piece of SPOIL BOARD.  MDF is very common for this.  We've got tons of plywood and acrylic scrap which would also suffice.  
*Cuts which free an internal piece are a huge problem. Internal piece must be clamped before it goes free or it'll bang around like you won't believe, maybe go flying. Could break teeth on the bit, snap the bit, or bind it up and break a gear on the transmission. Most of the time we prefer to mill away internal pieces entirely if we don't need them.
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*Cuts which free an internal piece are a huge problem. Internal piece must be clamped before it goes free or it'll bang around like you won't believe, maybe go flying. Could break teeth on the bit, snap the bit, or bind it up and break a gear on the transmission. Most of the time we prefer to mill away internal pieces entirely if we don't need them.  
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*When it's a drill press- and ONLY a drill press, WITH A DRILL BIT- claming solutions are not critical.  Well, no more so than any drill press operation.  If you use a milling bit, EVEN IF you only intend to plunge, you MUST have a secure holddown solution in place
  
 
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Revision as of 08:39, 16 October 2011

 A subtractive process- this is sometimes expensive, if your stock is far from the final size

Can be a drill press-
Gib locks
Mills are far more accurate holes than large drill bits

The drill chuck is very poor for runout, and is only for drilling. Won't take the side forces

of milling.

Note that there's no protection against milling the table

Clamping solutions

  • Clamping MUST be very stiff, esp for aluminum.  Visualize a hyperactive 2-yr-old with a #2 screwdriver and an aggression problem going after it.  If you can picture it moving, it'll probably move during milling.  It can't be able to lift, drop, rotate, or shift in either direction.
  • Failure of a clamping solution can cause chatter, which will result in poor finish, can chip the bit, or even send the work flying across the room
  • 90% of milling work is the clamping solution.  This is hardly an exaggeration.  Much of the skill learned is in clamping properly.  You might spend an hour figuring out how to hold a part and 5 min actually milling it.
  • We have a clamping kit with T-nuts, step blocks, and top clamps, and two milling vices.
  • Top clamping simply won't provide access to  the entire top at once.  In some cases, clamps may be moved to an area you're done milling to expose the rest of it.  We don't have a side-holding solution other than the vices.
  • Your stock size is limited by the ability to clamp to the table, rather than the "work box" (travel range of the leadscrews).  However, it possible to clamp stock longer than the X-axis or Y-axis and only work on a part of it. 
  • The mill is NOT bolted down. If you put something heavy on it offset, it can TIP OVER. You might start with something heavy on-center, then drive the X-axis down until it's NOT.
  • Rubber-faced clamping surfaces are NOT stiff enough for metal.  Or even plastics sometimes, if the milling is aggressive
  •  If you need to cut or drill all the way to the bottom of your stock, you must use a piece of SPOIL BOARD.  MDF is very common for this.  We've got tons of plywood and acrylic scrap which would also suffice.
  • Cuts which free an internal piece are a huge problem. Internal piece must be clamped before it goes free or it'll bang around like you won't believe, maybe go flying. Could break teeth on the bit, snap the bit, or bind it up and break a gear on the transmission. Most of the time we prefer to mill away internal pieces entirely if we don't need them.
  • When it's a drill press- and ONLY a drill press, WITH A DRILL BIT- claming solutions are not critical.  Well, no more so than any drill press operation.  If you use a milling bit, EVEN IF you only intend to plunge, you MUST have a secure holddown solution in place


Fear of Fly cutter grabbies. Don't wear loose things or gloves.

Feed and speed issues

  • Larger bits are run proportionately slower, because the speed of the tooth is higher
  • More teeth should go faster to ensure the same chip size, but usually 2-flutes really are the best 
  • too slow and you can melt/burn materials
  • you can work-harden some materials, which stops the bit
  • too fast is bad
  • appropriate speed depends on feedrate
  • chip size should be chips. Not dust
  • Feed and speed recommendations may be found online, but we're kinda screwed because the Grizzly has no numbers on the mill to quantify the RPM anyways.
  • This head always turns the bit CLOCKWISE. Just like a regular drill. If you're feeding the stock material towards you, and the work is on the left, this is CONVENTIONAL milling. If it's on the right, it's CLIMB milling. Neither one is "prohibited". Here's a note of the differences:
  • http://en.wikipedia.org/wiki/Milling_cutter#Conventional_milling_versus_climb_milling
  • Cutting a deep channel is a chip-clearing problem.  Don't go deeply in a pass and clean out the chips between passes.  If you're cutting a channel say 1.5x the width of the bit, don't cut the whole depth of one then the other.  Cut one side, clean out chips, then the other, clean out chips, then step down.  The space to the side will provide a place for the chips to go.
  • Soft materials- plastic, copper, aluminum- can clog the bit and if the tooth isn't clear, it CANNOT cut with clogged teeth.


Bit Types

  • HSS is cheap, wears somewhat quickly.  
  • Carbide is now cheap.  It's super-stiff and works great in the superior 2-flute geometry.  Carbide does not wear easily, but chips easily on abuse like loose/chattering, dropping it out of the spindle when changing tools, dropping on concrete or tile, striking steel screws unexpectedly. 
  • Ball end mills can never flatten a surface without scallops
  • Endmills can flatten, but still scallop on a ramping surface
  • Ball end mills can scallop LESS on ramps, but it'll still be there
  • Bullnose is a combination of the two
  • Mostly, manual milling uses flat endmill. Smooth 3D shapes can't be made anyways.
  • Plunging is a major issue with many milling bits.  Some bits are not designed to plunge at all, many 4-flute bits cannot.  If there's any space in the middle not covered by teeth, it can't possibly plunge.  Some 4-tooth have 2 teeth which meet in the middle whereas the other 2 teeth don't- this allows plunging. If you can't plunge, you're limited to starting from the side, or using a drill bit to start the pocket. 
  • 1/4" is a common size. 1/8" is common. There's a ton of 1/8" carbide tooling with narrower flutes, but commonly flute length is 4x the diameter. So, "not very deep at all".


All internal box cuts are ALL limited by milling bit radius. It's physically impossible to

make an internal box WITHOUT rounded corners.



Don't break the gears
Don't stall the motor. Use low gear as opposed to turning down motor RPM If you can.

Motor starting procedure:

  • Plugged in
  • Turn RPM to zero (that's the trick)
  • lift yellow slam button
  • Flip toggle switch
  • Turn up RPM
  • Emergency stop: hit the slam button, or toggle switch


Condition to leave the tool in:

  • Slamswitch closed, toggle off, RPM at zero
  • Bits removed and stored
  • Drill bits back in on tool shelf
  • Chips cleaned up, incl floor
  • Milling tooling should NOT leave the proximity of the mill. Only drill bits and the green vices may be moved.


Drawbar usage
-you may have to bang... try to be gentle.
-do not let the tool drop
-there's a washer up top meant to be loose

don't drive the X axis off the nut

Tramming questions

Clothing

Metal chips

Cleaning.
Lubrication

Protection of bits

Be aware some videos online about milling omit coolant for visibility



If you break the tranny, fess up, it's no big deal, we've got 2 replacements