We all have manufacturer speed & feed charts and have used their recommendations.

But sometimes those charts just don't apply.

For example manufacturer charts assume you are using their endmills at a certain stickout length, flute length and at a certain depth of cut.

But in the real life you rarely match all these conditions.
Sometimes you need to use longer endmill. Sometimes your flute is longer than what manufacturer gave you speeds and feed for.

What i am trying to say is that whenever your real life conditions differ from "normal" you "need to adjust accordingly".
In fact this is what is printed below many charts.

Too bad not many sources tell you how and what to adjust.

While failure to adjust cutting parameters often leads to chatter, poor surface finish and even tool breakage, one of the biggest mistakes people do when machining is

HSM or High Speed Machining is becoming more and more popular each day.
Many of us have seen those youtube videos where endmlls remove large amounts of material at high speeds/feeds.

While definitions of HSM may vary between tool manufacturers and even individual shops, the physics behind it remain the same.

In this article i would like to explore flat endmills.

HSM is not about ramping up your speed/feed overrides to 200% and puling out your smartphone to record another youtube-worth video.

What is HSM?

HSM is a complex of programming, machining and tooling techniques aimed at radical increase of productivity.

Programming

The cornerstone of HSM is low radial and high axial engagement of an endmill with the workpiece.

There are many CAD/CAM systems that allow you to create HSM tool-paths. Mastercam's Dynamic milling and SurfCAM's Truemill are some of them.

When radial cutter engagement with the material is smaller than the radius of the tool an interesting thing happens.
Chip load- the distance the tool advances per cutter revolution per tooth- does not equal the actual chip thickness anymore.
Chip thinning mainly happens at radial engagements below 30% of the diameter.

In order to get compensated chipload you need to multiply recommended by manufacturer chipload by the chip thinning factor.

Usual Radial Engagement for HSM toolpaths however is between 5 and 15%.

Axial depth of cut varies depending on geometry, but

Radial Chip Thinning HSMAdvisor Screenshot

Sevaral weeks ago i saw a post on CNCZone.

A HSMadvisor user Peter Neil used it to calculate cutting conditions for cutting a block of pre-hardened stainless steel.
His machine was Tormach.

Here is an exact copy-paste from that forum post:
_____________________________________________________________________________________

Did a test cut on the Tormach today using feeds & speeds from the latest version of the excellent HSM advisor.
To make it interesting, I did the cut using some 1.2085 pre-hard Stainless Steel as I have plenty of stock of it and have a job in mind for this, and wanted to see how it cut on the Tormach.
The material is like a stainless P20, at 16% Chrome/1% Nickel & 0.5% Sulphur (which makes it slightly free-er machining) and is hardened to around 33-35 Rockwell C, so I used the HSM advisor guidelines for machining P20 rather than Stainless. Cutter was a 10mm 4-flute Carbide TiAlN coated EM.

So...... ticking the HSM/Chip thinning option I got a speed of 5120 and feed of 2214mm/minute( 87 IPM). I used a DOC of 10mm and WOC of 0.5mm/0.020" - and turned off the flood cooling to machine it completely dry. The finish pass on the 1st level was 15mm DOC and 0.5mm WOC and slightly lower speeds/feeds.

Loaded up a 40mm x 63mm block , pressed the start button, and it went from this....





...to this!

Sometimes people ask me: "I tried your calculator, and i liked it, but it seems to me a little too aggressive...do you actually do any testing?"

Well, to those I say that not only i do testing, but i run production jobs 100% calculated with my own HSMAdvisor.

Many machinists say that nothing beats an experienced operator holding his hand on feed hold button and playing with speed and feed override trying to find the "sweet spot" where cutting speed and feed rate are maximized and chatter is eliminated or reduced.

And it is correct, but not any machinist is experienced or actually knows what he is doing.
Many machinists also finish their apprenticeship program and never learn a single thing about new tooling types and materials since. They bag years of experience, but their knowledge is stuck on a level it was when they first got their license.

Also not a single person can possibly know cutting conditions for hundreds of materials and remember all of the jobs he had ever ran.

This is where tool database comes in.

Not only can you save tools to cut down and in many cases eliminate entering parameters for every calculation.
But you can (and should) save cutting data for each particular case.

A single tool entry can contain an unlimited number of cuts attached to it, so machinist never has to remember everything.

Here is a i made video of slotting D2 with variable helix hi-performace endmill.

Material: D-2 Tool Steel 200-250 HB
Tool: 0.500in 4FL Carbide TiAlN coated Solid HP End Mill
Speed: 360.0 SFM/ 2751.6 RPM
Feed: 0.0023 ipt/ 0.0094 ipr/ 25.76 ipm

Engagement:  DOC=0.330 in   WOC=0.500 in