Forces in X,Y and Z

[PotatoMill]

Do someone her know what forces to expect in the X,Y and Z direction for different materials, feed rates and chip-load? Or if there is equation for it?
I'm especially looking for some general number for aluminium and mild steel ( very general question). It's mostly to understand what to expect when doing FEA for stiffness and deflection on a router design. I guess X and Y would be the same.

[Robin Hewitt]

If you cut downhill, as you should, you don't need much force at all.

Concentrate on speed and rigidity. Nearly everyone fits motors that are way too big, I know I did, cutting force is unlikely to be one of your problems.

[PotatoMill]

Thanks for the response.
Stiffness, rigidity and forces are correlated. If there is no forces there is no need for a big sturdy mill to cut steel for example. Or is there something i'm missing?

Regarding speed, so for example Nema23 3Nm (425oz) motors are strong enough, but too slow? Why do someone use nema34 at all?

[Robin Hewitt]

If there is no forces there is no need for a big sturdy mill to cut steel for example.

Don't think I am getting at you, but have you actually tried turning the handles on a vertical milling machine?

It is very tempting to cut up hill and accept that the tool will bend in to the work piece rather than away, because cutting downhill it can run away with you. You are not so much pushing the tool as trying to stop it.
If there is any backlash everything has gone wrong before you get a chance to compensate.
You can try tightening the Gibb's to get something you can push against but that makes your arms ache. Perhaps that is the force you are thinking about?

[PotatoMill]

I have used vertical milling machines a few times but i'm always using automatic feed. So I guess I have no feeling for it. I do neither know the usual gearing ratio on the handles on a vertical mill.

However in statics, deflection is dependent on torque or force. In both conventional milling and climb milling there will be some forces. There will not be any deflection without it, hesne sources of backlash, rigidity, and stiffness. I'm thinking about designing a machine that potensially can do HS tool-paths, and without knowing the right variables for calculating deflecting it could easily become a overly expensive or a shitty machine.

[PotatoMill]

I found what I was looking for here http://www.mycncuk.com/threads/1524-...ghlight=forces.
Rough estimations
Typical forces in XY
Wood > 5N
Aluminium > 20N
Steel > 75N

[fnm]

If anyone is interested in prediction of cutting forces in aluminum milling I would recommend to read the article:
"A comparison of analytical cutting force models" published by WIAS
There you can find very simple models to compute cutting forces for aluminum end milling as a function of chip thickness and axial depth of cut.
Here I try to resume Kinzle-Victor model for predicting forces for end milling Aluminum
The Kinzle-Victor model predicts Fi(Fr,Ft) tangential Ft and radial Fr milling cutting forces
Fi, according Kinzle-Victor model, can be predicted through this formula:

Fi(Fr,Ft)=Ki(Kr,Kt)*a*h^(1-mi(mr,mt)) where

“Fi” is force in N,
“a” is the load per tooth in (mm) ,
“h” is the depht of cut in (mm) and
“Ki” and “ mi” are constants that depend of “h” values

For end milling aluminum the values of constants Ki(Kr,kt) and mi(mr,mt) are:

Kr=39 for (0.001 < h <0.01) ;
Kr=99 for (0.01 <= h <0.1) ;
Kr=298 for (0.1 <= h <1)

Kt=336 for (.001 < h <.01)
Kt=493 for (0.01 <= h <0.1) ;
Kt=667 for (0.1 <= h <1)

mr= 1 for (0.001 < h <0.01);
mr=0.8 for (0.01 <= h <0.1);
mr=0.32 for (0.1 <= h <1)

mt=0.53 for (0.001 < h <0.01) ;
mt=0.45 for (0.01 <= h <0.1);
mt=0.32 for 0.1<= h <1

For example for a cutting depht of 0.5 mm and a load per tooth of 0.1 mm the forces for aluminum are:
Ft=Kt*a*h^(1-mt)=493*0.5*0.1^1-0.45=69 N
F=Kr*a*h^(1-mr)=99*0.5*0.1^1-0.8=31 N

Model computes tangential and radial forces located at xy plane but doesn’t compute axial force at z axis and I don’t know if are average or peak forces