Re: Calculating mechanical forces

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Stephen Wille Padnos
<spadnos@s...> wrote:

> cnc002@a... wrote:
>
> >In a message dated 8/1/2005 11:05:01 PM Eastern Daylight Time,
> >elson@p... writes:
> >
> >Think your round ways and linear bearings can keep the
> >machine within it's tolerances with 332 Lbs of force? Well,

maybe you

> >have a
> >smaller motor.
> >
> >Jon
> >
> >Jon:
> >
> >For years we ran round Thompson type bearings and ways on our CNC

routers

> >with 12 to 15 Horsepower motors, turning 20,000 rpm and cutting

thru wood,

> >particle board, fiberboard etc. at speeds up to 400 inches per

minute. We held

> >+/- 0.001" tolerance with no problems on materials where you could

measure

> >that close. I think round bearings and ways would work just fine

with a very

> >small motor like most mills run. Plus, the cutting speeds are

also slow.

> >
> >
> I'm no expert here, but I suspect the difference lies with the

spindle

> speed and cutter diameter.
>
> Your spindle at 20k RPM is 100x faster than the spindle in Jon's
> example. The torque (and cutting force) is therefore 1/100 as

much.

> Your motor is 10x the power, so in the end you have roughly 1/10

the

> force on the screw. Also, the cutters you used were probably much
> smaller than a 2" diameter - that would also linearly reduce the

force

> on the drive screws.
>
> Am I way off here, or is that close to the answer? :)
>
> - Steve

I took a advance machining class in college and they tought us how to
calculate the forces in each direction. Here is a link to one of the
homework problems that explains how to figure it out.

http://www.me.mtu.edu/~wjendres/MachiningProcessesCourse/HW04_Solution
.pdf

Here is a links to the problems themselves

http://www.me.mtu.edu/~wjendres/MachiningProcessesCourse/Problem_Manua
l.pdf

But by far the easiest way to figure it out is using the simple
approximation equation Fc=UcA = Uc(h w) where fc is cutting force
uc is the specific cutting energy h is uncut chip thickness and w is
width of cut.

Hope this helps you out a bit