Milling slots

[wawoodman]

I have to make some 1/4 wide x 3/4 long slots, all the way through the end of 3/4 x 3/4 CR steel. I have a Rockwell vertical mill.

Should I do this with a 1/4 inch, 4-flute mill, and cut them from the top, or should I get a 1/4" side milling cutter and work horizontally? I already have the arbor.

If the recommendation of the group is to go with the side mill, what diameter would be best, and what speed would you suggest?

Thanks from a newbie!

(As a side question: when I make a cut, must I raise the cutter clear of the work before returning to my start point, and then recalculate my depth of cut and move in, again? Or can I just back out, go deeper, and cut? Does backing up damage or dull the cutter?)

 

[November X-ray]

If I understand you correctly, the slot dimensions are 3/4" in length by 3/4" in depth by 1/4" in width, right? If this is a blind slot, I'd use a 2 flute 1/4" diameter end mill with sufficient length to allow me to work vertically down thru the material with several passes taking a few thousands DOC per pass.

You sort of lost me with the side milling comment so I am sure I do not understand your set up, so perhaps the slot is open at one end of the CR bar?

Please let me know if I am way off here!

Good Luck!

 

[7HC]

..................................................... Accurate 1/4" slots can't be made with a 1/4" endmill.

Frank

I believe you, but why can't they. If the same cut is made progressively deeper, why would the width change?

M

 

[Kennyd]

I believe you, but why can't they. If the same cut is made progressively deeper, why would the width change?

M

Play in the table, play in the spindle bearings, backlash in the leadscrews, wobble or vibration of the cutter will all add up to a slightly (or notso slightly) larger slot than the endmill.

 

[wawoodman]

If I understand you correctly, the slot dimensions are 3/4" in length by 3/4" in depth by 1/4" in width, right? If this is a blind slot, I'd use a 2 flute 1/4" diameter end mill with sufficient length to allow me to work vertically down thru the material with several passes taking a few thousands DOC per pass.

You sort of lost me with the side milling comment so I am sure I do not understand your set up, so perhaps the slot is open at one end of the CR bar?

Please let me know if I am way off here!

Good Luck!

that is correct. The slot is in the end of the bar.

 

[brucer]

use a 3/16 endmill or a reground 1/4" endmill..

if you use a 1/4" endmill, machine or cutter deflection will cause it to walk off and cut the slot large and or out of center.

 

[7HC]

use a 3/16 endmill or a reground 1/4" endmill..

if you use a 1/4" endmill, machine or cutter deflection will cause it to walk off and cut the slot large and or out of center.

So I guess it would be a general rule that if you need to mill a slot you should always use an end mill smaller than the slot size, then mill out to the final dimension?

Thanks,

M

 

[Kennyd]

So I guess it would be a general rule that if you need to mill a slot you should always use an end mill smaller than the slot size, then mill out to the final dimension?

Thanks,

M

Depends on the accuracy required. If just milling a slot for a bolt then it probably does not matter if its a couple thou to wide.

 

[Kennyd]

(As a side question: when I make a cut, must I raise the cutter clear of the work before returning to my start point, and then recalculate my depth of cut and move in, again? Or can I just back out, go deeper, and cut? Does backing up damage or dull the cutter?)

No one addressed this yet, but yes you should clear the cutter of the material before backing up.

 

[12bolts]

Kenny,
Why is that? Unless I am getting close to my finished size and dont want to leave tool marks behind then it is just like climb cutting isnt it?

Cheers Phil