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Milling Pockets

Posted: Tue Jul 03, 2018 9:18 am
by tornitore45
I learned something today

When conventional milling a pocket at the end of one side as soon as the mill contact the other side and bites, it deflects into the side you just finished and it may overshoot the target.

Climb milling direct the forces in the opposite way and favors ending up with the correct dimensions.

Morale, switch early from conventional milling roughing to climb milling finish.

I am been too averse to climb mill with anything more than 0.005 but need to get over even if it means more passes.

Re: Milling Pockets

Posted: Tue Jul 03, 2018 1:58 pm
by Magicniner
Always leave enough material for a finishing pass, then it doesn't matter so much ;-)

Re: Milling Pockets

Posted: Tue Jul 03, 2018 2:08 pm
by SteveHGraham
Wait. If you climb cut, when you get to the end, the mill will be pushed against the end of the cut, won't it?

Re: Milling Pockets

Posted: Tue Jul 03, 2018 2:32 pm
by tornitore45
If you climb cut, when you get to the end, the mill will be pushed against the end of the cut, won't it?
Climb milling as you reach the end of one side the end mill will touch the next side (90*) and try climbing on it deflecting away from the side just completed, making it "metal safe".

It helps to make a sketch and visualize.

Conventional milling will try to oversize the pocket. Climb milling will not by itself, unless you dial it over size.

Re: Milling Pockets

Posted: Tue Jul 03, 2018 3:55 pm
by SteveM
Also, if you use a 2-flute cutter, it won't deflect sideways when it is cutting the sides.

Another things you can do to rough out a pocket is to plunge mill with a center cutting end mill to move most of the material out.

Steve

Re: Milling Pockets

Posted: Fri Jul 06, 2018 3:00 pm
by Rick
SteveM wrote:
Tue Jul 03, 2018 3:55 pm
Also, if you use a 2-flute cutter, it won't deflect sideways when it is cutting the sides.
This to me is a bit misleading, all cutters will deflect. There are many variables that determine how much they deflect but they all will deflect.
The procedure to leave a small amount for a finish cut helps minimize the amount of deflection. There are ways to help control deflection like shortest cutter length, largest dia. possible , sharpness, speeds and feeds, chip load, type of coolant etc. etc. Sometimes it seems the phase of the moon comes into play.
Deflection of cutters and if using a lightly built machine the machine itself all have to be taken into consideration.
Just my 2 cents

Re: Milling Pockets

Posted: Fri Jul 06, 2018 3:51 pm
by Harold_V
Rick wrote:
Fri Jul 06, 2018 3:00 pm
SteveM wrote:
Tue Jul 03, 2018 3:55 pm
Also, if you use a 2-flute cutter, it won't deflect sideways when it is cutting the sides.
This to me is a bit misleading, all cutters will deflect. There are many variables that determine how much they deflect but they all will deflect.
The procedure to leave a small amount for a finish cut helps minimize the amount of deflection. There are ways to help control deflection like shortest cutter length, largest dia. possible , sharpness, speeds and feeds, chip load, type of coolant etc. etc. Sometimes it seems the phase of the moon comes into play.
Deflection of cutters and if using a lightly built machine the machine itself all have to be taken into consideration.
Just my 2 cents
I agree. Add to the list the manipulation of the screws as you near the corner. Seemless windows can be machined by doing so. Zero undercut, with size held quite precisely.

H

Re: Milling Pockets

Posted: Sat Jul 07, 2018 5:56 am
by tornitore45
Zero undercut,
I assume the undercut is the result of tool deflection. Never thought of that aspect.

Re: Milling Pockets

Posted: Sat Jul 07, 2018 3:10 pm
by Harold_V
When taking finish cuts, the end mill achieves 90° of engagement as it enters a corner. Given the opportunity, yeah, it deflects as the tool gets loaded by the increased surface area of the cutter in contact with the part. It likes to chatter when that happens. By keeping close watch on the dials (or DRO), and unloading the screw being approached, the cutter tends to walk around the corner. Done properly, there is no chatter, and there is no undercut. With practice, the results tend to be very good. Doesn't hurt to have a reasonably snug machine. The resulting radius isn't exactly perfect (it can vary, depending on how well the screws are manipulated), but it looks perfect, and should be well within tolerance when a radius is specified on the print.

H

Re: Milling Pockets

Posted: Sun Jul 08, 2018 5:00 pm
by SteveM
Rick wrote:
Fri Jul 06, 2018 3:00 pm
SteveM wrote:
Tue Jul 03, 2018 3:55 pm
Also, if you use a 2-flute cutter, it won't deflect sideways when it is cutting the sides.
This to me is a bit misleading, all cutters will deflect.
That's why I specifically said "sideways".

When the flutes are in contact with the sides, there is no cutting edge in contact with the end of the slot to throw the cutter sideways.

A four flute will be cutting the face of the slot at exactly the same time as it is cutting the side, and the sidewards deflection of the cutter will make the slot oversize.

But, yes, ALL cutters will deflect. Just a question of how much and in what direction.

Steve

Re: Milling Pockets

Posted: Fri Jul 13, 2018 2:20 pm
by Magicniner
SteveM wrote:
Sun Jul 08, 2018 5:00 pm
Rick wrote:
Fri Jul 06, 2018 3:00 pm
SteveM wrote:
Tue Jul 03, 2018 3:55 pm
Also, if you use a 2-flute cutter, it won't deflect sideways when it is cutting the sides.
This to me is a bit misleading, all cutters will deflect.
That's why I specifically said "sideways".

When the flutes are in contact with the sides, there is no cutting edge in contact with the end of the slot to throw the cutter sideways.

A four flute will be cutting the face of the slot at exactly the same time as it is cutting the side, and the sidewards deflection of the cutter will make the slot oversize.

But, yes, ALL cutters will deflect. Just a question of how much and in what direction.

Steve
So you're using cutters with straight flutes or in applications where the spiral doesn't permit simultaneous frontal and side contact?
That's a really limited set of circumstances which you need to specify more clearly!

Re: Milling Pockets

Posted: Fri Jul 13, 2018 8:34 pm
by SteveM
Magicniner wrote:
Fri Jul 13, 2018 2:20 pm
So you're using cutters with straight flutes or in applications where the spiral doesn't permit simultaneous frontal and side contact?
Yes there are some cutters with such a steep spiral that one cutting edge, if the cut is deep enough, will wrap well around.

My 2-flute cutters don't have spirals that steep, so unless you REALLY had it buried in a pocket, it won't be substantially hitting the front and the side at the same time.

Steve