Feeds and Speeds calculations

[WillAdams]

Things which I'd like to see / understand:

- a calculation of chip size / shape
- estimation of how much energy is required to shear a chip off per revolution at a given cutting depth
- estimation of how much power is needed (at minimum) to rotate a tool of a given diameter and length
- the relationship between feed rate and cutting time and given a given feed/speed, how much increasing the former requires one to decrease the latter

I'm agonizing over whether or no it's worth the risk of breaking off a new end mill, or if I should try the stop-gap measure of purchasing a Chicago Electric Cutout Tool from Harbor Freight (I've been putting things off for a while, and don't want to wait until I can afford a DWP-611 and Precise Bits collet).

So to turn this around, is there any Feed / Speed calculator which will estimate the difference in performance between a 192 Watt tool and one rated at 420 Watts?

[Improbable Construct]

All of the speed and feed calculators I have seen are for industrial machines that assume that there is no slop, twist, or flex in the machine.
Using one of those for a shapeoko would be like using F1 car standards to see how fast to drive a corolla around the track.

With the shapeoko it is going to be trial and error.
There is no way yo say that what works for one person will work for another.
There is too much variation machine to machine.

Start slow and ramp up your speed from there.
It is best if you have some scrap and can to some test cuts.

[cvoinescu]

I concur that the Shapeoko is a seat-of-the-pants affair, much in the spirit of Antoine de Saint-Exupéry; a by-the-book approach won't get as far.

[WillAdams]

Okay, given that _Wind, Sand and Stars_ is one of my favourite books, I'll try to approach things from that perspective.

[Screwtape]

All of the speed and feed calculators I have seen are for industrial machines that assume that there is no slop, twist, or flex in the machine.
Using one of those for a shapeoko would be like using F1 car standards to see how fast to drive a corolla around the track.

With the shapeoko it is going to be trial and error.
There is no way yo say that what works for one person will work for another.
There is too much variation machine to machine.

Start slow and ramp up your speed from there.
It is best if you have some scrap and can to some test cuts.

I'm glad I read this because it helps to confirm the sort of the conclusion I came to after playing with the GWizard calculator and HSMAdvisor etc. Although I think I learned a lot playing with those calculators and figuring out how the different parameters relate to each other and what are the really important things to pay attention to and how they all relate to each other at a high level, they seem to really be tuned for a different type of machine (or at least a machine that is much less variable from user to user than a Shapeoko). When they are recommending ~3000mm/min and I was still trying to comfortably run at 600 mm/min through plywood with a dremel (which has bit the dust since) I started to wonder whether I was talking apples to their oranges.

[calica]

I have really good luck with FSWizard: http://zero-divide.net/index.php?page=fswizard

To combat the lack of rigidity, I use a smaller DOC. I haven't broken an endmill in quite some time. I also use LinuxCNC, so I can adjust the feedrate in realtime.

[WillAdams]

Well, I guess I have learned something --- what was an impenetrable array of values now makes sense.

Seems to me that there should be some initial values for the percentages for SFM, Feed as well as for max. RPM which would be appropriate for a given machine. Wish the desired RPM were more controllable.

[Enraged]

A good one that I have found: http://www.cnccookbook.com/CCGWizard.html

You can try a trial of the full version, or you can buy the Lite version: http://www.cnccookbook.com/CCGWizLite.html

There are other calculators around, but what Bob Warfield has done is combine all the knowledge into one tool, so it might be worth it for you.

[WillAdams]

What does that do?

Load a G-code fileand optimize feed rates for a given material on a specified machine?

[Screwtape]

Oh interesting, I didn't know they sold a Lite version of GWizard, somewhere down the road I might pick that up.

WillAdams: You plug in your tool dimensions, the type of material you're using and it will help you figure out your depth of cut, feed rate, stepover etc. It will also give you a lot of information about the amount of deflection to expect and the chip load and others. Give the trial a shot it's fun to play around with, I learned a lot.