"Adaptive milling" by hand ???

[Dan_the_Chemist]

Recently I was milling a .516 wide by .500 deep slot across a 3" wide piece of steel. I did it the way I learned of old ... set the work up so the long axis of the slot was along the X axis of the mill, indicated it in, and then took repeated passes of about .030 DOC at a nice slow X travel... leaving about 0.005 on each side of the slot to be cleaned up in the final pass. This is shown in the first diagram.

As I was doing this, I mused about wear on the cutter. The bottom 30 thou would be doing most of the work, and the middle part would only get one bit of exercise. I have a number of mill cutters that are worn on the bottom and nearly pristine on the middle and top.


My question: What about doing a hand version of adaptive milling? Position the cutter with a .495 DOC. Then move it into the stock sideways until it's about 10 or 20 thou deep. Then move it across the slot front to back to take an "end wall" cut, move back to the beginning, and repeat. This idea is shown in the second diagram.

What are your thoughts?

(Please ignore that Fusion 360 specified climb cutting tool paths. It thinks CNC. I'd do the same sort of path but with conventional milling.)

[MattiJ]

Almost 20 passes for 0.5” x0.5”slot?

Damn you need bigger machine. Slot at full depth and finish to size on second cut.

[Dan_the_Chemist]

Almost 20 passes for 0.5” x0.5”slot?

Damn you need bigger machine. Slot at full depth and finish to size on second cut.

I'm running a normal Bridgeport, and I was taught on a B'port.

What do people think - am I being too cautious with a 30 thou DOC ?

[pinstripe]

Joe Pieczynski has a recent video on slotting. It doesn't address your question directly, but according to him, you shouldn't be "leaving about 0.005 on each side of the slot to be cleaned up in the final pass" if the width of the slot is critical.

He recommends offsetting the slot slightly to allow for tool flex, and to finish with a new end mill so that you aren't using the worn out (narrower) bit of the end mill for the bottom.

Edit: I think in metric. 0.005" on either side is quite a bit, especially with your small DOC. So it wouldn't matter in this example.

https://www.youtube.com/watch?v=QGHujqWlxtg

[KiddZimaHater]

Adaptive clearing on a manual mill, by hand, would be VERY tedious, and there are MANY opportunities for a screw-up.
Better bet would be to rough-out the slot with a .437" roughing endmill at full depth, then finish pass with a 3-flute 1/2" endmill.
Then offset each way .008", and do a skim pass to get .516"
That's what I'd do.

[wierdscience]

I'm running a normal Bridgeport, and I was taught on a B'port.

What do people think - am I being too cautious with a 30 thou DOC ?

Yes,typically slots that are "square" meaning dimensions where depth and width are close to 1:1 can be hogged out in one pass and then cleaned up to dimension.On a B-port sized mill you can however start to have rigidity issues much larger than 1/2 x 1/2,so what I do is use a roughing end mill first to waste out the bulk of the material and then switch to a regular two-flute end mill for finish.

[wierdscience]

Joe Pieczynski has a recent video on slotting.

+1 Joe has a lot of very useful information on his channel,highly recommend it.
https://www.youtube.com/channel/UCpp...ppaFa5w/videos

[Dan Dubeau]

I don't run manuals very much anymore, especially for any heavy machining or slotting such as this (mostly putting in holes, an squaring up stock). But I loved using "corncob" roughing cutters for stuff like this. Either that or plunging/stepping out the slot, then finishing the sides. Sometimes unavoidable, but shallow passes like that prematurely wear out cutters. Especially corners.

[Bob La Londe]

My only issue is rubbing and in this case rubbing is NOT racing... On a CNC machine it reverses quickly and isn't rubbing for long, but I don't think you can achieve that manually. Whether the savings on tip wear out weighs the increased overall cutter wear I don't know, but I don't think so.

[LKeithR]

...Better bet would be to rough-out the slot with a .437" roughing
endmill at full depth, then finish pass with a 3-flute 1/2" endmill. Then offset each way .008", and do a
skim pass to get .516"...

Exactly! Far faster than messing around with a bunch of small cuts. Using a 1/2" endmill to finish a slot
that is .516" is fine; if you were shooting for a 1/2" slot just drop down to a 7/16" endmill and finish...

[MattiJ]

I'm running a normal Bridgeport, and I was taught on a B'port.

What do people think - am I being too cautious with a 30 thou DOC ?

You are too cautious by factor of 10. By twenty if using vari-flute or corncob rougher.

30 thou DOC on 1/2" endmill would be suitable for chinese round post drill-mill.
Heck I would push even those harder than that!

[BCRider]

The first path option of small steps down is tailor made to wear out the cutter sooner along that first .030 or so of edge since it's doing the lion's share of the work.

I find that on mills and cutters that there is a sweet spot where you'll find good chip makeup indicating clean cutting even with a good bit of depth. Try to go more than that and you have to really torque on the handwheels to generate a proper chip from the tool. At the point where only moderate pressure is needed is the sweet spot. And for a 1/2" cutter that's roughly 3/16 to 1/4 inch per pass.

By making more of the cutter work for you it takes a lot less passes to get the job done and less passes is overall better for the cutter. Really though what you're doing is spreading the wear out over more of the edge. Which isn't a bad thing when cutter life is concerned.

You show blind slots in the sketches. And in that case you're sort of stuck with using the lower end more than the upper. But when I do a through slot I like to drop the end mill deep in the slot for the finishing cuts. Like deep to where the edges are seldom used. That makes the cut nicer but also again aids with spreading the wear out over the entire length of the flutes.

[RB211]

A rounded corner endmill also should last longer. I'm pretty good at destroying endmills with slotting myself.

[epicfail48]

You are too cautious by factor of 10. By twenty if using vari-flute or corncob rougher.

30 thou DOC on 1/2" endmill would be suitable for chinese round post drill-mill.
Heck I would push even those harder than that!

Ive pushed more than that with a mini-mill

Seriously, ive made a .1872 deep cut in cast iron with full engagement on a 1/2" roughing end mill. Cant say the mill liked it, but i get the feeling a B-port could make that easy