Force exerted by an end mil?

[cwm9]

Can anyone give me an idea of the force exerted on a workpiece by an endmill (say, 1/4" diameter) in aluminum?

Better yet, how would I go about determining this for an arbitrary material, feed rate, diameter, etc?

I'm trying to calculate the torque that will be exerted on my rotary table so I can calculate appropriate limits on tool size/distance from center... The table has a maximum capacity of 250 inch pounds. I'm thinking I may only be able to cut on the axis center...

[shay z]

there are too many parameters to be able to calculate the force.

it depends not only on machining conditions but also on the tool tip, how sharp the tool and even how rigidt the nachine is.

[Jason3]

This is assuming a lot, but...

Slot milling Aluminium, 6 mm 2 flute carbide stub end mill, 1xD DOC, 5,300 rpm, 300 mm/min feed rate ~ 210 N force. (I happened to be browsing an NSK catalog and stumbled apon the example!)

Best regards,

Jason

[dertsap]

http://metalworking.com/shareware.html
download machine zip

[cwm9]

Originally Posted by Jason3 This is assuming a lot, but... Slot milling Aluminium, 6 mm 2 flute carbide stub end mill, 1xD DOC, 5,300 rpm, 300 mm/min feed rate ~ 210 N force. (I happened to be browsing an NSK catalog and stumbled apon the example!) Best regards, Jason

Hey, that's great info. That's about 50 lbs, so for your example I could mill out about 4 inches along the x-axis safely, or 8 inches in diameter. I saw another example that was 20-40 lbs in a research paper, so these seem like reasonable numbers too.

I was only going to get a 6" chuck, so it looks like I'm going to be in good shape!

[Mcgyver]

Originally Posted by cwm9 Can anyone give me an idea of the force exerted on a workpiece by an endmill (say, 1/4" diameter) in aluminum? Better yet, how would I go about determining this for an arbitrary material, feed rate, diameter, etc? I'm trying to calculate the torque that will be exerted on my rotary table so I can calculate appropriate limits on tool size/distance from center... The table has a maximum capacity of 250 inch pounds. I'm thinking I may only be able to cut on the axis center...

you need to understand how metal is cut to understand how the force is determined. The first chapter of any good machining text will detail this, but basically a shear plane is set up ahead of the tool. The size (area) of the shear plane depends on tool geometry, depth & width of cut. When you know that, you take the tensile strength of what you are cutting and multiply it by the shear area and that should be the force.

as you note, you can vary the torque by what radius you cut on the RT, however this isn't practical as the plan usually determines the radius, not the table's torque constraints you would cut the distance from the axis you need and vary the torque but varying the force by varying the depth of cut. in practical terms, I can't see an RT made light enough that you wouldn't bust the 1/4 end mill long before you damaged the table

[cwm9]

Thanks, great info! I can definitely agree that most rotary tables could take the force no problem, but as this is really a home made job it's not quite true. The max torque on the gears is only 300 inch pounds, where as most other rotary tables seem to be rated in large numbers of foot pounds. At 6 inch I can only apply 50 pounds, which isn't all that much, sadly. If I stick to small end mills, I think I'd be pretty safe.

I don't have in mind a particular part I am trying to make, it's more that I am trying to determine the limits of this thing so I don't destroy it playing around.

[Astonlee]

You should be alright using such a small diameter tool, assuming the table brake is functioning. but it would have been helpfully if you told us what make/model of table you were using?

[cwm9]

It's a homebrew with no brake, which is why I'm worried about it. =)