45 or 90 Degree Face Mill?

Of course if you can afford it, it’s great to have both 45 and 90 degree facemills, but what are the pros and cons for each?

Both Sandvik and Kennametal will suggest the 45 degree face mill is a better bet for general purpose face-milling. Incidentally, this is the sort of thing that’s a perfect topic for CNCCookbook’s Machinist’s Search. Try searching “45 degree face mill” using Machinist’s Search in one window and Google in the other window.

The arguments given by these two for choosing the 45 are:

- Cutting forces are better balanced so that axial and radial forces are about even. Lowering the radial forces so they’re more balanced with axial can not only enhance the surface finish, it’s also kinder to your spindle bearings.

- Cut entry and exit are better behaved–less shock, less tendency to break out.

- The 45 degree cutting edge is better for demanding cuts.

- Better surface finish–the 45′s leave a noticeably nicer finish.

- The chip thinning effect is at work and leads to higher feed rates.

- The 45′s tend to have less tendency to chatter as well.

At one time, octagonal face mills were at war with the 45 degree face mills for supremacy. The octagonal inserts have more edges, so you can rotate the insert if one gets chipped. But, tooling costs are usually only about 3 percent of the manufacturing cost, so the greater efficiency of the 45′s eventually won out. Lately, you can get some face mills that use a 45 degree insert that’s double sided, so we have the best of both worlds since these inserts now have 8 edges like the octagonal inserts.

Here’s a 45 degree lead facemill slogging right through a weld–they are a little tougher than 90 degree face mills!

Is there never a case where the 90 degree face mill is a better choice?

It’s biggest advantage is it can cut a square shoulder. In addition, 90 degree face mills are generally a little more compact, with a smaller body diameter, and they can reach a greater maximum depth of cut.

I keep a 2″ diameter 90 degree facemill in my shop as well as a 3″ Glacern FM45 45 degree face mill. The FM45 sees a lot more use for sure.

Calculating feeds and speeds for these facemills is easy with the G-Wizard calculator because not only will it figure the feedrate adjustments needed for the 45 degree (or other cutters with a lead other than 90 degrees), but it can also load manufacturer’s data for these cutters and their inserts. Given the wide variety of inserts available and their different characteristics, its helpful to tune the last bit of performance by selecting the exact insert and material combination being used.

One last thought about face mills–they’re horsepower hogs. Don’t try to use too large a face mill on your machine. I’ve stalled the spindle of my mill running my 3″ pretty easily.

Related posts:

1. Custom Tool Data for a Sandvik R390 90 Degree Face Mill
2. More Shaper Tricks on a CNC Mill: Cutting Splines
3. G-Wizard Custom Tool Cribs
4. Cutting Edge CNC Knee Mill From the 70′s
5. G-Wizard Picked Up in Tormach Face Milling Video

4 Comments

• 
  Louis 2011/02/12 at 2:05 am

  Be careful where you use 45 and 90 degree cutters. A workpiece that is not well supported, will deflect under a 45 degree cutter due to the high axial forces. A 90 degree cutter will produce a more consistent cut and the corresponding decrease in chatter will extend the life of the cutter.

  Reply
  • 
    Bob Warfield 2011/02/12 at 2:19 am

    Louis, thanks for raising that issue. You’re quite correct about the 45′s higher axial forces and the issues they may cause for a workpiece that is not well supported or perhaps that is simply a bit thin.

    Reply
• 
  Louis 2011/02/12 at 2:05 am

  Be careful where you use 45 and 90 degree cutters. A workpiece that is not well supported, will deflect under a 45 degree cutter due to the high axial forces. A 90 degree cutter will produce a more consistent cut and the corresponding decrease in chatter will extend the life of the cutter.

  Reply
  • 
    Bob Warfield 2011/02/12 at 2:19 am

    Louis, thanks for raising that issue. You’re quite correct about the 45′s higher axial forces and the issues they may cause for a workpiece that is not well supported or perhaps that is simply a bit thin.

    Reply