Milling top and bottom?

[bigvinney]

Sorry I'm new, but what is the easiest way to machine the top and bottom of a piece of aluminum bar without a 4th axis? Is there any tricks to this?

Another question I have is when your material is larger than the work that is going to be made, what is the best way to cut the object out of the material without damaging the works with it moving around after its cut?

(i.e. I have a 12"x6"x1" block of aluminum and in the center I am going to cut out a box that is 6"x3"x1". After you cut out the perimeter the part can move around and get damaged, so how do you eliminate this problem?)

Thanks Vince

[miljnor]

lots of ways to do it. All of them varying in complexity and accuracy, depending on what you looking for.

You didn't give a lot of info. so this is what i would do (with so little to go on). Get a smaller peice of material (or cut that one down with a band saw). Then since you said it was to be a box, Mill the inside of the box to the right dimension in a vice, then take the part out flip it over clamp on the inside of the box by expanding the vice. and cut the outside to shape.

This is a simplistic description, and its only one way to do it.

Another way is to mill the whole thing from the top but, on the outside of the box mill down to .875" (leaving an 1/8" for the vice to hold on to) and then flip the part over and mill off the excess.

And if your indexing skills are shaky or non-existant then make an 1/8 in round over on the bottom side to blend the two operations.

Well, My job is done here! These explanations are probably clear as thick mud! Enjoy!

[bigvinney]

here is a rough sample work that may help you figure out what I am trying to do.

[championp]

you can do a "paper doll" you can cut all the way down except for .020" or so at the bottom. then you you just whack it with a mallet and it falls out with a little work. this leaves a burr around the bottom edge for you to clean up with a file or buffer. you may have to experiment to find the right amount to leave at the bottom. the bigger the cutter you use, the more you have to leave to keep a little strength there.

you can always make your square to size before machining it.

you can machine it a little past half way down, then flip the part over and cut the rest from the back. This is good practice to see how well you set your x,y zeroes.

from the looks of the dwg you posted. I would machine the large rectangle first, as far down as you can with out hitting the vise or clamps etc. then flip it to cut the boss second. for the second op, touch off on the four sides you just cut and mathematically find the center of the part. unless you put a hole in the center, then you can dial in the hole.

Chris

[bigvinney]

I was thinking of milling the outer perimeter almost all the way through and then flipping it over and after cutting the pockets, finish the perimeter, but I was not sure if the x,y zeros would be the same since the edge I started on (ie lower left) is now the upper left corner when you flip it over.

[championp]

just touch off of the same corner (top left in the 2nd setup) that you used for the first op. if you're using an edge finder you are bound to have a slight difference from one op to the next. when flipping parts like this, You will get a much better match up if you touch off all four sides and use the center of the part for zero, instead of a corner. I use a dial indicator in the spindle and sweep against each side, and then do the math to get center of the part.

Chris

[StephenD]

Drill your 3/16 through holes first setting 1 hole at X0Y0.Machine 1st side, flip and dowel pin holes,X0Y0 remain the same ,machine second side.
Steve

[bigvinney]

Thats a good idea thanks