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Calibration: Essential for the Best Feeds and Speeds

Feb 23, 2012   //   by Bob Warfield   //   Blog, FeedsSpeeds, Software, Techniques  //  No Comments

Professional machinists are involved in a highly competitive business.  They need to eek out every drop of productivity they can.  Recently on Practical Machinist, someone asked where to get the best feeds and speeds chart, which produced quite a bit of discussion from the readership.  There’s a lot of wisdom on that board.  One individual, who grinds and sells cutters for a living flat out said no such charts are possible because they don’t convey enough information.  I agree, charts are limited to just a few variables while our G-Wizard Feeds and Speeds Calculator considers over 50 variables.  It would take many pages of charts to convey the types of calculations it makes in chart form.

Here was the response I gave as a post:

I’m with CarbideBob.

To get good feeds and speeds, you need two things: a good calculator and calibration.

As some have said, the calculator will get you a starting point. It performs an even more important role though, which I’ll come back to in a second. First, let’s look at this idea of calibration.

Calibration means bringing the real world experience and data into the equations that the calculator uses. A feeds and speeds calculator starts with its own internal tables of what the chiploads, surface speeds, tweaks for different materials, and all the rest should be. That’s a database, and the best calculators will make it possible to “calibrate” that database with your experience, your tooling, and your shop’s best practices.

You can plug in your tooling manufacturer’s recommendations right away to the database. There’s a few other things to plug in as well if the calculator is able to take them, such as what the spindle power curve looks like.

But then the experience and shop best practices have to kick in. Every time you make a cut, you have the opportunity to learn something. Make it a little faster than you did the last time. Fiddle the variables. And keep a record of it. Whether the cut works well or breaks the cutter, both are important as they’re helping to map out the envelope for that cutter, that machine, and that tooling under your shop’s best practices. All that information needs to go into a database that’s linked to calculator for best results. Done right, it’s easy to track and easy to take advantage of. That calculator + database should do most of the record keeping work.

Once you have some of that data to go from, the real value of the calculator emerges. While a lot of variables have to be calibrated, there are also a lot that can be calculated and that are very predictable. Radial chip thinning is a real effect that works the same every time on every machine. The role of different tool engagement angles for HSM toolpaths are well understood. Tool deflection is predictable and can be calculated.

This means your precious data collected from real jobs is reusable in new jobs that may have slightly different parameters. The stepover or depth of cut may need to change for a new job, and maybe you will only make one or a small number of the parts so no experimentation is possible. Take your calibrated database which is hopefully built into the calculator and let the calculator tell you what to do there. Since it’s been calibrated by your real world experiences in your shop with your tooling, it’s going to be pretty bang on right about it.

Combining a database with a calculator that considers a lot of variables (about 50 at last count) is what G-Wizard does.

The database portion of G-Wizard is what we call the Cut Knowledge Base, although the ability to download and customize manufacturer’s data, Tool Cribs, spindle power curves, and all the rest are also database features of the software.

 

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