How to Flat
Contents
Resources:
http://its.foxvalleytech.com/MachShop3/basicmill/squaring1.htm
http://www.hsmworks.com/docs/cncbook/en/#AppxA_Project03
http://rick.sparber.org/Articles/cb/cblock.htm
Squaring the Stock
In maching the raw metal is called “stock”. Usually the very first operation in making a new part is to cut your stock on some type of saw to rough approximation of the solid rectangle that with which you are going to start, but oversized so that you can cut it down to a perfectly flat, square block.
Once your raw stock has been cut, how do you make it into a “square” piece?
Pro Style
1st Side
Clamp your stock into the vise, possibly using parallels to extend the top surface above the vise jaws. You usually don't want more than ½ of the stock to be above the jaws, but you also don't want to cut to lower than about 1/4” - 1/2” above the top of the jaws.
Let's say your stock is roughly 1.5”x2.5”x4”. Place the large face up and support it with parallels so that about 3/4” is above the jaws. Clamp firmly, making sure your part is riding on the parallels with the deadblow hammer, tapping moderately.
Touch off your facing tool (let's use the shell cutter) to the highpoint of your stock, setting that height to User Z=0.
Figure out your feeds and speed for your cutter/metal combination and take small cuts, starting at z=0 and positioning the spindle with X and Y placing you off the part to the right. Spin up the cutter. Either manually jog the cutter right to left until completely off the left side or write a small gcode program (see the following) A Sample Program - Facing with G Code to go from OFF RIGHT to OFF LEFT, then raise the cutter, return to OFFRIGHT and lower the cutter to the original height.
Lower the cutter about .025 per cut until surface is completely cut. Then take a finish pass with about 005-.010 as a finish cut. Stop the machine and move the piece for access.
The top is now EXACTLY (to within our tolerances) FLAT on Side #1.
2nd Side
Remove the stock from the vise and flip it over so side#1 is BACK and use parallels on the back face if needed and a brass rod in front to keep the uneven front face from hitting the FLAT VERTICAL front jaws and causing the stock to skew, reclamp firmly.
Side #1 is now perpindicular to the plane of the cutter. If you repeat the above process you will produce a clean side, side#2 which is flat and square to side #1.
3rd/4th Side
Take the stock out of the vise and reposition the piece with the #1 on the back, #2 down on parallel if needed and a brass rod on the front. Use a parallel to keep about 3/4” above the vise. Flat this as before.
Now Side #3 will be flat and the #1/#3 edge and the #2/#3 edge will be 90 °. Flip the part over and place side #3 down, use parallels as needed and flat side #4.
Final Sides
Remove the stock and place the piece with side #1 UP and sides #3 and #4 touching jaw faces leaving unfinished side #5 extending about 1” over the right side of the bars. Use parallels to get the stock slightly above the top of the jaws. Use a normal end mill to face the SIDE of the stock, repeating until flat. Then flip and finish side#6.
You now have a piece of metal with flat, square sides which is slightly larger than your part.
DONE.
Quicker Style
1st Side
Just like Pro Style. Clamp your stock into the vise, possibly using parallels to extend the top surface above the vise jaws. You usually don't want more than ½ of the stock to be above the jaws, but you also don't want to cut to lower than about 1/4” - 1/2” above the top of the jaws.
Let's say your stock is roughly 1.5”x2.5”x4”. Place the large face up and support it with parallels so that about 3/4” is above the jaws. Clamp firmly, making sure your part is riding on the parallels with the deadblow hammer, tapping moderately.
Touch off your facing tool (let's use the shell cutter) to the highpoint of your stock, setting that height to User Z=0.
Figure out your feeds and speed for your cutter/metal combination and take small cuts, starting at z=0 and positioning the spindle with X and Y placing you off the part to the right. Spin up the cutter. Either manually jog the cutter right to left until completely off the left side or write a small gcode program to go from OFF RIGHT to OFF LEFT (see the following) A Sample Program - Facing with G Code, then raise the cutter, return to OFFRIGHT and lower the cutter to the original height.
Lower the cutter about .025 per cut until surface is completely cut. Then take a finish pass with about 005-.010 as a finish cut. Stop the machine and move the piece for access.
The top is now EXACTLY (to within our tolerances) FLAT on Side #1.
2nd Side
Flip the piece over and finish the opposite side. These two sides should be reasonably parallel now.
3rd/4th Side
Take the stock out of the vise and reposition the piece with the #1 on the back, #2 in front. Use a parallel to keep about 3/4” above the vise. Flat this as before. If your are doing plate stock that sticks more than about 1" above the vise capture it between 1-2-3 blocks so that only about 1" shows. This will stop the part from vibrating too much while cutting.
Now Side #3 will be flat and the #1/#3 edge and the #2/#3 edge will be 90 °. Flip the part over and place side #3 down, use parallels as needed and flat side #4.
Final Sides
Just like Pro Style. Remove the stock and place the piece with side #1 UP and sides #3 and #4 touching jaw faces leaving unfinished side #5 extending about 1” over the right side of the bars. Use parallels to get the stock slightly above the top of the jaws. Use a normal end mill to face the SIDE of the stock, repeating until flat. Then flip and finish side#6.
You now have a piece of metal with flat, square sides which is slightly larger than your part.
DONE.
