• We want to encourage those of you who ENJOY our site and find it USEFUL to DONATE and UPGRADE your membership from active member to donating or premium membership. If you want to know the differences in membership benefits, please visit THIS PAGE:


    Donating memberships start at just $10 per year. These memberships are in fact donations that help pay our costs, and keep our site running!
    Thank you for your donation, God Bless You

  • As some of you know, I have wanted to stop managing H-M for some time. It's a tremendous strain on my personal life. I want to set up my own shop. In September, September 15, to be exact, it will be 8 years that Hobby-Machinist has been in existence.

    We've seen a lot of changes. In March, 4 moderators left to start their own site. They took some of you with them. So now you have split loyalties. You know who you are. They didn't like my way of managing this place, and thought they could do better without me. They didn't. The only thing holding them together is that they hate me. Their site was down until mid July. That is why I wanted to stay involved on here until they could learn to run this place. But they wanted me to leave right away, without the training part.

    Anyway, I have been training VTCNC to run things here. Dabbler is going to learn too. I feel that they are ready to start taking over the operation. I will be here to help in case they need, but I don't think they will. Tony Wells is and will be here also to consult with. I will be doing backups, upgrades, and installing addons. Other than that, I don't want to know about this place.

    What about the 4 moderators who were disloyal? I don't care. It isn't my call anymore. I would think that, rather than fumble, they ought to come back and do good work. That's up to them. If they want to return to try to lead more members to their site, I am done caring. I suffered too much aggravation worrying about it. I don't plan to spend any more. What they do impacts on them. I have my own opinions including those of you who followed them there. No longer my problem.

    I am leaving this place in good operating condition, and financial condition.

Facemill options

[10] Like what you see?
Click here to donate to this forum and upgrade your account!

PT Doc

Active User
Dec 27, 2012
What is the general recommendation for a 3hp knee mill when considering a face mill with intergral r8 shank ? Option available is 2.5” diameter with 5 flutes or 3” diameter with 6 flutes?

This will be a new purchase so I can’t try both out. They both use SEHT inserts so 4 cutting edges are a plus.

Thanks in advance for the help.


Carbide Guy
Dec 15, 2014
PT Doc:
Insert milling cutters are great! And your choice is particularly good for most materials. I was a technical resource for Kennametal salesmen for 35 years and milling was always fun. The 20 deg. positive insert with the "H" tolerance is tough to beat. Now, the R8 platform is very good for small diameter milling cutters, but, they do have some limitations. I would recommend the 2.5" cutter with 5 inserts, but if you need the 3"diameter and plan to take a full width cut, you may want to remove 3 of the inserts so you don't run out of horsepower and stall the spindle. Bad news on a knee mill since the feed motor may continue to drive the table.
There is a simple metal removal calculation that will work for just about any application you will ever encounter. Only materials that are very high strength will need reduced parameters. Most metals, including pre-heat treated 4140, 17-4PH, 15-5PH, stainless steel, and many others will machine at 1 cubic inch per minute, per horsepower. To calculate a cube we only need three dimensions, length in per minute IPM), depth of cut (DOC), and width of cut (WOC). To calculate hp. requirements multiply IPM x WOC x DOC.
A 2.5" cutter has a periphery of .6545 ft. A 2" Width of cut on 4140 bar stock would run easily at 350SFM, 535RPM. With a feed per tooth of .005, the IPM would be 13.375" (5 x .005 x 535). A 2" WOC would allow 3 hp. to be consumed at a depth of cut of .112DOC.
13.375 IPM x 2" WOC x .112 DOC = 3 cubic inches per minute and at 80% efficiency, that equals roughly 3 hp. and gives you a little wiggle room for positive vs. negative, dull vs. sharp, etc.
For a couple of other materials:
Aluminum will net 2 to 4 cubic inches per minute
Cast Iron will net 2 cubic inches per minute (G3000, G3500, G4000 CI)
TiAlN/ALTiN coatings are universal and work well on many materials. Since your knee mill has fairly limited rpm compared to CNC machines, choose tough grades for best durability. Grades described as 30, 35, 40 will give excellent service and they will take a beating. Higher the number, the tougher the grade, but you will sacrifice a little wear resistance and a little heat resistance. For Aluminum go uncoated, TiCN, or TiB2 for best results.

Good luck with the new cutters.
Best Regards, Gary
[5] [7]