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= Knee Mill =
= Knee Mill =


Alex says this knee mill is a "drill and mill".
This knee mill is a "drill and mill".
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This is called a mill, colloquially called a "knee mill".  I've heard one story that "knee" comes from the knee-height crank handles that you use to adjust the position of the XY table.  I've also seen a reference to a typical mill design as a "knee and column" design, the knee being the huge casting that the XY table sits on.  I suspect the latter is why it's called a knee mill.
This is called a mill, colloquially called a "knee mill".  The "knee" is the big cast metal piece on the bottom that the table is mounted toThe table has hardware to lower or raise the table, bringing the work piece mounted on the table into contact with the end mill (the cutting head).


A mill is similar to a drill press with three big differences:
A mill is similar to a drill press with three big differences:

Revision as of 15:56, 28 November 2020

Note, this is a rough draft.

Knee Mill

This knee mill is a "drill and mill".

Mill2.jpg

Owner/Loaner:
Make/Model/Serial Number:
Arrival Date:
Current Status:
Primary Contact:
Training Required?:
Owner's Manual:

MillQR.png

This is called a mill, colloquially called a "knee mill". The "knee" is the big cast metal piece on the bottom that the table is mounted to. The table has hardware to lower or raise the table, bringing the work piece mounted on the table into contact with the end mill (the cutting head).

A mill is similar to a drill press with three big differences:

1) Similar to the difference between a wood router and a drill, a mill's motor and spindle is designed to take lateral force, force perpendicular to the plunge or the end mill.

Note: The end mill is the cutting head, i.e. the equivalent to what on a drll press would be called the drill bit. There is also a type of cutting head called a fly cutter, mostly used for flattening stock.

2) A mill has an XY table, a surface that you can move in the horizontal dimensions (left and right, forward and back) by turning handles.

The Z dimension is handled by a crank on the head of the mill.

3) Generally, much of the mill's basic design is about getting accuracy. For example, the knee is a large casting with a lot of mass to provide stability and vibration damping, not just a table bolted to the column.

MILL SPECIFIC WARNINGS

DO NOT crank the table inward past the edge of the ways.

ALWAYS raise the tool away from the stock BEFORE stopping the knee mill.

ALWAYS start the knee mill BEFORE moving the tool into contact with the stock.

Anatomy of A Knee Mill

  • head
  • spindles
    • little lever handle on back of head to release spindles
  • quill
    • big quill handle on side for gross height adjustment
    • note that when loosened, the head can rotate on the circular column and throw off zeroing
  • draw bar
  • collet
  • end mill or fly cutter
  • vise
    • bolt head on front of vise to open/close vise
  • XY table
  • cranks
    • on front of quill for Z axis (vertical)
      • metal handle on left side of quill locks the Z axis
    • on front of XY table for Y axis (front to back)
    • on either side of XY table for X axis (side to side)
  • XY table ways
  • XY table screw
  • XYZ Axis LCD displays, to left of mill

Also note: Stock, aka the material you're going to work with.

Also see: https://i.pinimg.com/originals/84/52/d8/8452d8ded4b03783df6db440da677164.jpg


General Usage

You will have to determine appropriate settings.

The larger the end mill, the slower the speed you should use.

If the mill is loud and chattery, SLOW DOWN.

The Quill, Draw Bar and Collet

The quill is the part of the head that moves up and down.

The collet is a separate piece that fits into the bottom of the quill and holds the end mill in place.

The draw bar is a long bar with a hex head at the top, which sits in a tube that goes down the center of the front spindle, into the quill.

The draw bar holds the collet in place and draws the collet up into the quill, which tightens the collet, which holds the end mill in place.

Choose a collet close to the size of the shank size of the end mill or fly cutter.

Most of the collets HackPgh has are English sized.

Before you use the mill, there should be no end mill in the collet, and the draw bar should be loose.

NEVER leave and end mill in the collet when done. It's okay to leave a collet in the knee mill when done using the knee mill. But leave the draw bar loose, don't tighten it when not in use.

Removing the End Mill

NEVER leave an end mill in the collet when done, but it's okay to leave the collet in the knee mill.

  • ALWAYS unplug the machine before doing any tool changes, speed adjustments, etc.
  • loosen draw bar (on top of the front spindle of the machine)
    • hold the rubber belt to keep spindle & draw bar from rotating
    • use a socket wrench on the top end of the draw bar to loosen the draw bar
    • just loosen it, don't unscrew it completely
  • hold your palm under the end mill to catch it
  • with your other hand, tap the top of the draw bar with the dead blow hammer to loosen the end mill
  • catch the end mill when it falls out

Removing the Collet

  • first remove the end mill (see above)
  • then remove the collet
    • hold your palm under the collet to catch it
    • unscrew draw bar the entire way
    • catch collet

Dial In the Vise

This is called "tramming" or "indicating" the vise.

Note: On this mill, the table is fixed, not adjustable. Only the vise is adjustable.

  • use small dial indicator
    • in tan case in top draw of file cabinet next to knee mill
    • note, indicator pin moves, is friction fitted
  • put dial in chuck
    • rotate dial indicator and point the indicator pin towards the back jaw of the vice
    • the back jaw doesn't move, so we'll dial in to that.
  • crank side handle until dial tip is at left edge of back jaw
  • crank the front handle of the XY table to move the table forward
  • stop when back jaw touches dial pin and dial needle moves
  • zero dial by rotating rim of dial face
  • zeroing X*axis
    • crank side handle to move pin from left edge of back jaw to right edge
    • if dial indicator is still zero, then vise does not need adjustment
    • if dial indicator is non*zero, right edge of back jaw is not even with left edge.
    • adjust vise location
      • vise is held to table with a bolt one either side
      • loosen ONE bolt slightly
        • it's easier to only adjust one side rather than loosen both bolts at once
      • watch dial and tap vise with dead blow hammer to adjust vise position
      • repeat left/right X*axis check
      • if still off, repeat adjustment process
      • once X-axis check shows zero difference:
        • tighten bolts
        • check X-axis one last time

This Old Tony

"This Old Tony" on Youtube is recommended, particularly his video on squaring stock:

https://www.youtube.com/watch?v=tW8HNAlUXxU "Stock? Mill? Square!"

Using the Edge Finder aka the Wiggler to Zero the X and Y Axis

[1]

[2]

Two videos showing using an edge finder.

[3]

This one is interesting but he advises you to touch a spinning edge finder and I'm a paranoid about that.

For the purpose of this tutorial, we're zeroing the X and Y axis for flattening stock.

This means we will be setting the zero position to be below the level of the top surface of the stock.

  • The edge finder aka the wiggler is kept:
    • in the file cabinet to the right of the knee mill
    • in the top drawer
    • in a small red, soft plastic case
    • in the large case of donated end mills at the front of the drawer

The edge finder has a body and a tip that can be offset from the body.

The tip has a wide part and a thin part.

The thin part of the edge finder is exactly 2/10" diameter (this wil be important later).

Put the stock in the vise.

Use the large handle on the side of the quill to adjust the gross height of the quill to something reasonable for the stock you'll be working on. Do this before zeroing the axes.

If the stock does not project above the vise, use a parallel (in the red plastic case) to adjust the spacing.

Parallels are pieces of metal that is very precisely machined so both edges are parallel to each other. They are used for spacing.

  • Take the stock out of the vise.
  • Place a parallel against the back jaw.
  • Place the stock in the vise, back edge resting on the parallel.
  • Hold stock flat against back jaw.
  • Tighten vise to hold stock in place.

Note: Make sure the stock is positioned left/right in the vise so that there is enough table travel for the end mill or fly cutter to reach the entire stock. The vise is usually installed off-center in the XY table.

There is also a circular vise that is seldom used. This adds a fourth direction of movement, rotational. This requires separate training.

Using the edge finder

  • insert edge finder / wiggler in collet
  • tighten draw bar to hold edge finder in place.
  • make sure the knee mill speed is less than 750 for edge finding, or centrifical force will throw things off.
  • zero the Y axis (front to back)
    • Position the edge finder over the back jaw, behind the stock.
    • Crank the Z axis until the edge finder tip is just above the surface of the back jaw
      • make sure the edge finder is NOT touching the vise or the stock
      • make sure the edge finder IS below the top edge of the stock
    • Make sure the edge finder's tip is offset, i.e. not lined up wtih the body or shaft of the edge fidner
    • start the knee mill
    • crank the Y axis handle (front of vise) to move the stock into the edge finder
    • as the thin end touches the stock, the edge finder will go from offset to centered
    • keep cranking until the edge finder goes to offset again, then STOP
    • press the black "origin" button on the Y axis display to the left of the knee mill
      • the display will take half a second and then will read "0.000"
    • raise edge finder away from stock
    • adjust the edge finder to compensate for the radius of the edge finder
      • move vise forward until Y axis reads "0.100" (half the 2/10" radius of the thin end)
      • press the black "origin" button on the Y axis again.
  • zero the X axis (left to right)
    • same steps as above, only start with the edge finder to one side of the stock

Oiling the Ways

"Ways" are the track/groove that the table slides in.

It's good practice to oil the ways, screws and oil ports of the XY table every time you use it.

TODO: Oil before or after using?

Especially if the table movement is stiff, i.e. cranking the table handles to move it is too hard,

There is an old-fashioned style oil can, a black cylinder with a squeeze crank and a modern looking flexible tube. It should be near the knee mill, or possibly on the lathe. This oil can contains hydraulic oil. There is a large can of hydraulic oil in the flammables cabinet if it needs to be refilled.

TODO: Insert photo of oil can.

Also get some paper towels to wipe up excess oil. There WILL be excess oil if you oil it correctly, i.e. copiously.

Crank the table from one side to the other to spray oil onto the ways.

Look at the table from the underside and spray the large screw liberally with oil.

Each crank has an oil port on top of the socket that the crank is mounted in. It's a small, circular, silver metal nub about 1/8" across with a raised dot in the middle. Press the oil spout against the dot to open the port and pump some oil into it.

Flattening with a Fly Cutter

Fly cutters are in the top drawer of the file cabinet to the right of the knee mill.

Select a collet that is near the size of the fly cutter's shank.

When using the fly cutter to flatten stock, crank slowly.

Start at about 1 full rotation per second.

Listen for chatter or other odd sounds, if you hear any, slow down.

Shutdown Procedure

  • remove mill
  • leave collet in place
  • leave draw bar loose
  • use shop vac to clean up metal dust & chips
  • use chip brushes (normally kept on the lathe) to move metal dust and chips to where shop vac can get to them
  • use hex head on front of vise to open vise so you can get at chips
  • ALWAYS center table when done
    • make sure front edge of table does not overhang the base
    • make sure the bulk of the mass of the table and vise is centered over the base
  • unplug ring light from back wall outlet to turn it off

Adjusting Mill Speed

You adjust mill speed by changing the levels that the two belts are on, on the spindles.

This is similar to how you adjust the speed on the drill press.

To adjust the belts you will first need to loosen the small paddle lever on the right side of the knee mill, towards the back. This will allow the back portion of the knee mill to move, although it is spring-loaded so you will have to pull that portion of the mill forward to loosen up the belt.

When you have the belts where you need them to be, push back on the body of the back portion of the knee mill to tighten the belts, then turn the paddle lever to fasten it in place.

There are 3 spindles, each with 4 levels.

The front spindle levels are numbered 1 at the top to 4 at the bottom.

The back spindle levels are numbered 5 at the top to 8 at the bottom.

The middle spindle will have two belts attached to it:

The belt from the front spindle to the middle spindle will be on the same level as it is on the front spindle. The belt from the back spindle to the middle spindle will be one the same level as it is on the back spindle.

There is a chart taped to the top, right side of the head that gives the belt positions needed for each speed.

For example:

The slowest speed, 120, is belts "4 - 5". That means that:

The front-to-middle belt will be on the lowest level of both the front and middle spindle.

The back-to-middle belt will be on the highest level of both the back and middle spindle.

The highest speed, 2500, is belts "1 - 8". That means that:

The front-to-middle belt will be on the highest level of both the front and middle spindle.

The back-to-middle belt will be on the lowest level of both the front and middle spindle.


Safety Information

Usage Instructions

Startup

Operation

Shutdown

Maintenance Info

FAQ

To Do

Things that need to be done for this machine.

Wishlist

Things you would like to changed/added to this tool.