End Milling Into a Corner Without 'Snipe'?

What's that Lassie? You say that Doug White fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Mon, 18 Feb 2008 03:25:57 GMT:

If you take a light cut this won't happen as much. Rough out the shape(leaving a 'snipe'), then go back and finish cut (to remove the 'snipe' from the first pass).

Dan

You can minimize the problem by "sneaking up" on the final dimensions. Cut a little under (maybe 0.010 or so) and then take a final cut to take that last ten thou... Or, as an old machine shop instructor put it, "On the last cut, make Brillo..."

Jerry

Use a slot drill (two flute centre cutting cutter) if you really must avoid the digging in. It will protect you because the front flute will be clear of the cut before the back flute is close enough to risk digging in.

Mark Rand RTFM

That's a good idea. I don't have many two flute end mills, but it's something I should invest in.

One question: If the idea is to make sure it's only making contact on one edge at a time, should I use a straight flute end mill? I don't have to worry about lifting chips out of a pocket for my immediate problem, and it seems to me that a spiral flute end mill would defeat the advantage of two flutes for this operation.

Thanks!

Doug White

Easy.

Before you begin cutting the pocket, move to each corner location of your pocket (final dimensions!). Drill just under the endmill's diameter (between like 1/64" and 1/16", depending on the size of the endmill), and then plunge down with the endmill. Now you've created your finished corners.

When you're machining your pocket, your cutter will actually come completely out the cut as you reach the corners, instead of having a

*massive* chip load increase (as you're experiencing now) which flexes the cutter.

You can't simply rely in "slowing down" at the corners. We're not CNC machines - we're flimbsy, fleshy, squishy humans, and the machines have backlash.

Climb milling is a good idea for your finishing cuts. When on a CNC, you normally climb mill because it results in a better finish and longer cutter life. Just make sure the machine is tight and you're paying attention (listening, feeling and looking).

Additionally, climb milling should help with the issues associated with taking light cuts in stainless. When you climb mill, the chip load is at its max as the flute enters the work (good). When conventional milling, the chip load is at its smallest as the flute enters the cut (bad). This alone will let you take light cuts in stainless successfully.

Lastly, make sure you know which way to turn the handwheel as you switch your axis feed! This is no time to be second guessing! Draw arrows on the machine just above the handwheels. *Always* think in terms of where the cutter is going to go - not which direction the axis will be moving (i.e. turn the handwheel clockwise to move the CUTTER towards me). Different machines move in different ways so always think in terms of cutter direction.

Regards,

Robin