End Mill as Finish Toolpath

[redwood]

Well now I know why Michael used a ball nose bit to pocket the earth in his Celestial Trundle Toys.

[mtylerfl]

Well now I know why Michael used a ball nose bit to pocket the earth in his Celestial Trundle Toys.

Actually, I used the 0.0625" Tapered BN for a couple reasons:

- the tip is small enough to get into the nooks and crannies (especially the "Earth" continents)

- the taper of the bit minimizes chipout (sort of an automatic "Draft angle")

- the tapered BN is much stronger than a straight 0.0625" EM so it won't break as easily (in fact, I've never broken a tapered 0.0625" BN...I did break a 0.125" long-reach BN once, though. But it only had a 1-degree taper, so was more fragile)

[martin54]

did break a 0.125" long-reach BN once, though. But it only had a 1-degree taper, so was more fragile

More deflection on a long reach bit which probably didn't help either

[mtylerfl]

Neither did plunging it at full 5/8" depth in a corner of a rough out that still had a full thickness (3/4") of material left over! It was Maple, so the bit didn't have a chance!

[Rcnewcomb]

Executive Summary:
If it works and is safe, great!

There are cases where the end mill might be a good choice as a 3D finishing tool. Consider this: with a ballnose bit we use a small stepover to reduce the ridges we get because of the curvature. We are essentially using the "flattest" center of the bit.

Only a small portion of the bit ever comes in contact with our material so we could trim away part of the bit with no impact to the cutting results. That is basically the idea of a half box core bit. You only need a portion of the curve.

As the diameter of a bit gets larger its profile approaches a flat line.

If we took a 0.25" cross section of a 100 inch bit it would look very similar to an end mill. For 3D surfaces with very small changes in Z using an end mill even at a 40% stepover might produce similar or better results than using a 100" ballnose with a 4% stepover.

[martin54]

If we took a 0.25" cross section of a 100 inch bit it would look very similar to an end mill. For 3D surfaces with very small changes in Z using an end mill even at a 40% stepover might produce similar or better results than using a 100" ballnose with a 4% stepover.

The problem with 100" bullnose bits though is you can't get them with a half inch shank so they don't fit in my spindle

[SteveNelson46]

I have never seen a 100 inch bit. My guess is that it would take a pretty big machine to use it.

[dwilli9013]

I have never seen a 100 inch bit. My guess is that it would take a pretty big machine to use it.

I see what you did there.

[TReischl]

I used to have problems with the "halo" effect.

Finally solved it by using an electronic touch plate.

There are two varieties of touch plates. One is movable and can be placed anywhere, the other one is fixed in position on the machine.

When doing a job that has 3D and large flat surfaces I use them both. The movable one is used for the first tool. After it touches off it moves to the fixed one and stores the information. After that, subsequent tools only touch off on the fixed one.

That is very different than using a floating touch off for each tool for obvious reasons. Essentially the software knows precisely the difference in tool lengths.

I run mine from Ger21's most excellent Screenset 2010. Best $20 I ever spent for my machine!

If you are using a single touch off or the old "paper shim" method on a multiple tool job, it is problematic at best.