RPM vs material ready reckoner

**jack620** · 22nd August 2011, 09:50 AM

Gents,
thanks for the many responses, especially those who posted tables. I'll take the most conservative of all the cutting speeds you've provided and apply the formula to create a table of RPMs for varying diameters of all the materials I have data for.

I understand that these will only be theoretical speeds, and that many other variables will come into play. As I gain experience I'll fine tune the numbers to more accurately reflect my setup and ability.

Enlarging and laminating the metric nomogram that Dave provided is a good idea too. I'll give that a go as well.

Pipeclay (and others),
If you have any suggestions about how specific metals, cutters or coolants behave, I'd love to hear them. I can add notes to the table for future reference. For example, I believe 4140 can be a bugger to turn. If there are ways to make turning it easier, it would be good to have a note. There's no way I'll remember what to do when the time comes to turn it. The notes don't have to relate to cutting speed. They might recommend a specific type of cutter, or cutter height for a given metal. Or a rule of thumb like "heavy cut, slow feed".

Regards to all.

Dave J · 22nd August 2011, 10:03 AM

Hi Jack,
As I said earlier if you want to scan it, send me your email address so I can send you the full size one as scanned, I think it was around 2mb.
When I enlarged the one on the forum it was hard if not impossible to read the material list on the right, but enlarging the scan I can read it easily.

Dave

**bonox** · 22nd August 2011, 10:08 AM

Originally Posted by jack620

I'll take the most conservative of all the cutting speeds you've provided

.

The tables/formulae are typically based on production environments - ie maximum through put, not necessarily best surface finish or tool life, but a good compromise of most things to keep the widgets moving out the door. If you find something that works better for you then run with it.

....

Originally Posted by jack620

Or a rule of thumb like "heavy cut, slow feed".
Regards to all.

carbide tools are effectively 'blunt' and require pressure to cut. In other words, they don't sneak up on the final size as well as HSS does.

Remove scale (ie hot finished bar stock, castings etc) as fast as possible - it's hard and dulls your cutters quickly if you make light skimming cuts over it.

The rest is pretty much a function of how rigid your setup is (includes the workpiece, the tool and the machine), how much power you've got available and the surface finish you're trying to achieve.

Other people's advice is one thing, but there's really no substitute for trying it yourself.

Dave J · 22nd August 2011, 10:28 AM

This is a quote out of the book for the tables that I posted.

These figures are based on the use of HSS, to give a total life of approximately 60 minutes, dry cutting with medium feed rate.

Dave

**Vernonv** · 22nd August 2011, 02:20 PM

Here is Dave's metric chart (might be a slightly newer version), but a bit easier to read. I think I downloaded it (or got the link) from this forum. I find it very useful.

**jack620** · 22nd August 2011, 02:44 PM

thanks vernon

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