Help! > Mistakes, muckups, and dangerous behaviour

Mill Creep

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Mosey:
Needed to mill a large slot, 1" x 5/8" deep x 3" long in aluminum bar, so I put a 1/2" roughing mill in a collet in my mill, and carefully set the depth to allow a little cleanup.
I had oiled the spindle this week and noticed a seepage out of the spindle nose which indicated that the oil had reached the spindle nose.
As I was milling along the piece I noticed under the huge pile of chips that the depth of the slot had grown! It was now well into my finished workpiece.
Apparently the roughing mill has so much bite that it walked out of the collet, especially one that was freshly oiled. The collet is a well-used one, so it probably doesn't hold as well as it should. I will check its inside dimension for wear and wipe it dry.

I have never had this problem with regular end mills. Also, I prefer ER collets to W-20's becasue I think they hold better, but they are not readily available in my spindle size.
So Dave, here is another place to use those metric change gears...to make an ER x W-20 collet holder
Mosey   :'( :'(

b.lindsey:
Mosey, did you notice the problem before the end mil depth spoiled the workpiece?  I suspect the oil is what allowed it to creep in conjunction with the helical milling forces pulling down on the end mill. I hope you may have caught it in time.

Bill

Jo:
Why were you using an end mill to cut a slot  :headscratch:

End mills are designed to cut on the side not the face. If you try cutting a slot with them you get pressure on the two side and the front teeth, pushing the cutter backward and causing an over width slot. I would suspect the backward push is what also encouraged the cutter out of the collet  :-\. Did you damage the collet as well  :(

W20 collets are very good and like all collets they should be used dry  :) Schaublin do both ER and the W series collets, they decided that that W series were better for use in their mills so I will  :NotWorthy: to their greater knowledge on this matter.

Jo

Mosey:

--- Quote from: b.lindsey on January 04, 2015, 03:20:01 PM ---Mosey, did you notice the problem before the end mil depth spoiled the workpiece?  I suspect the oil is what allowed it to creep in conjunction with the helical milling forces pulling down on the end mill. I hope you may have caught it in time.

Bill

--- End quote ---
Bill, The problem became visible just as the mill spoiled the work, hidden by the large pile of swarf. I will clean and dry everything and make a test cut before proceeding. It is possible to cut most of the one-sided recess ( I should not have described as a slot) away on the table saw, so I may see about that to eliminate the large milling event.
In my experience ER collets hold better than W type, but are not as accurate in centering of short pieces. They are much better at releasing the mill or other piece. I think they each have their advantages in certain circumstances, not a universal one type better than the other situation.
Mosey

cheepo45:
This is a well known issue in production machine shops where the depth of cut and the feed are much more aggressive than in home shops.
I prefer to use end mill holders with set screws to avoid this. This is also the cause of the tapering gouges found on many used milling machine tables!
I hope your part can be saved or you have more material. The rest of us can learn a lesson from this. Thanks for posting.
            cheepo45

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