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How would you cut this?

FanMan

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#1
This is a semi hypothetical question, the milling operating I had in mind turned out to be unnecessary, but the question remains: say you need to mill some amount off the side of a workpiece, considerably deeper than wide. For example, maybe 1/8" cut by 3/4" deep. Setup restrictions prevent laying it over and cutting it 1/8" deep by 3/4" wide. Anyway, one could make a shallow cut the full 1/8" wide, advance the spindle, and repeat until the 3/4" depth is reached, or position the end mill at the full 3/4" depth and make repeated shallow cuts with the side of the cutter until the 1/8" is reached.

Which would you do, and why?
 

Tony Wells

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#2
One question first. Why are you restricted to a 1/8" end mill? Am I not visualizing the cut correctly? A larger end mill would take it in a single pass.
 

timmeh

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#3
All dependent on size/power of machine and Dia. of cutter to determine how much material to remove per cut.

But regardless of size/power of machine and Dia. of cutter, set cutter short of final size radially-say .010". Work your way down axially in steps-say .200", .200", .200", .140". Leaves .010" in both directions to clean up to size.

Don't take a full 1/8" x 3/4" cut with a 1/8" diameter cutter, it will break.
 

Tony Wells

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#4
Usually the problem with stepping down in -Z- is that you wear the end mill on the diameter and length based on your step down. Then on the final pass, unless you have the length (and it is not a blind slot, for example) the dullest portion of the flutes will not cut as easily and it can leave a noticeable step at the bottom. However, if you have sufficient flute length, increase your -Z- increment to put the "used" section of flutes below the work so you can expose flutes with little to no wear. Your shoulder or edge of part will more likely be square due to lack of pushoff from the dull end mill section.
 

tq60

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#5
No mention of end mill size.

Would suggest simular as above in that cutting just less than the 1/8 depth of side cut and plunge in part of the depth and cut the lender and repeat until just short of full depth.

Use a roughing or not so new cutter.

Switch to "good" cutter as finish cutter and first cut to depth then sneak up on the side.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

RandyM

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#6
Why not a slitting saw?
 

FanMan

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#7
Right, I never specified the end mill size, I was picturing something 1/4" at least, maybe 3/8 or 1/2". Anyway, this is what I was trying to describe. As I said, I could cut the full 1/8 with the end of the mill and step down, or start at the 3/4" depth and go back and forth across the part until the 1/8 dimension is reached. Assume the workpiece is sufficiently rigid and the end mill flutes are long enough. I know either would work but I'm wondering which would be the better approach, and why.
IMG_20170709_094140~01.jpg
 

ddickey

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#8
Plunge mill, leave a few thou for final cleanup then side mill.
 
Last edited:

tq60

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#9
Some restrictions to consider is part may flex and aluminum may load up.

So one could plunge in but not at full depth so small bites so to speak and bottom of mill is doing the work.

After most of the material is removed leave at full depth of cut then sneak up taking small cuts at high speed to help avoid loading the mill.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

mikey

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#11
I would use the largest diameter end mill you have and take it in one pass. This is a simple profiling cut for an end mill and the biggest problem will be to stabilize the material so it can sustain the forces of the cut without moving around. Obviously, clamping it horizontally would be ideal but if you must cut it vertically then it is going to vibrate unless you support it; clamping additional support pieces on either side would work.

As for why I would take this in one pass, it is mainly to utilize the cutting edges efficiently. Plunging in tiny bites is fine if all you have is a tiny end mill but if you have a larger one then you will wear the end and sides of your end mill much more than if you took a single pass. As long as you get the cutting speed and feeds right, an end mill will handle this cut easily.

Keep in mind that the material and the end mill will deflect; you can't get away from it. If you just need to get the material off then take it in one pass. If the cut has to be accurate, rough it in one pass and finish it with a second pass. If you want to get even more practical, rough it with a roughing end mill and finish it with a sharp new end mill.
 
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