Re: [CAD_CAM_EDM_DRO] Newbie Question - speeds and feeds

exeric1 wrote:

> There are those of us that are new to machining that would like a
> little help in calculating speeds and feeds for different materials
> and thicknesses. I have Machinings Handbook and I know it includes
> ways to calculate these things but you have to wade through a lot to
> get to the parts specific to your needs.
>
> My particular calculations regard milling. My understanding is that
> you need about 8 inputs: tool cutting diameter,number of flutes or
> inserts, tool cutting depth, tool cutting material(HSS, carbide,
> etc),material to be cut (al 6051,al 7075 etc.),finishing or rough
> cut,horsepower of milling machine. Finally if rpm is given -
> calculate feed rate and depth of cut. Or calculate all three.
>
> When looked at in total these are not trivial calculations. I wish
> there was a program out there that could do these calculations for
> me. It might even be able to be done in spreadsheet form and it sure
> seems like the kind of problem computers were made for. Anyone out
> there know of a cheap program that does these calculations? It would
> be nice to have it integrated with a cam program but I fear that
> adding it would be just the excuse a company would need to jack up
> the price. It might be more convienient to just have a stand alone
> product. Any help would be appreciated.

It really isn't all that complicated. For the most part, there are only
2 tool materials, HSS and carbide. HSS can't handle heat, it loses its
hardness, so you have to either cool it or keep the cutting speeds low
enough to not overheat the tool. Carbide loves the heat, and works
well when the cips are coming off blued from the heat. So, characteristic
speeds for the two tool materials on some representative workpiece
materials will do. Something like 400 SFPM for most aluminum alloys,
and 100 SFPM for mild steels with HSS tools, and about 3 times that
for carbide are good numbers to start with. If you have a table of
cutting speeds, you may want to stay with the lower end of the listed
speeds, as you are most likely more concerned with tool life than production
rate. Harder and tool steels may go as slow as 50 SFPM, some other
non-ferrous materials may be between steel and aluminum.
So, this sets your spindle speed.

The diameter of the tool and width and depth of cut determine the
chip load per tooth, therefore the feedrate. 'Plowing' a slot at full cutter
width requires slowing the feed way down. Otherwise, mill less than
1/2 the cutter diameter for width of cut, and no more than the full
cutter diameter for length of cut. When plowing, use even less length
of cut.

At least for production work, the spindle horsepower determines the
width and depth, as using the optimum feedrate will draw so many
HP, and it can't exceed your spindle HP. There are calculations of
Cu. In. per minute per HP for various materials. Aluminum alloy
usually gives you 3 Cu. In. per minute per HP, mild steel is roughly
.6

There are some programs that will so some of this. Mr. Machinist and
machinist's toolbox are two that I've tried. They are not all that great,
but they do put most of the info in one place.

Jon