View Full Version : what's your tip radius preference

dan s
10-13-2008, 11:53 AM
I need to order another batch of inserts. I've been considering picking up some #2 tip radius inserts to see if they will yield a better surface finish.

Since I'm still new to inserts I wanted to hear what other had to say. Thus if you use inserts, what tip radius do you normally get, and why?

Frank Ford
10-13-2008, 11:58 AM
I use the pointy "1" radius most because I make mostly small stuff.

Yesterday I turned down 5/8" of the end on some 5/16" dia. x 4" long 12L14 rods to .249". Including setup time, I managed 540 of them in about 3-1/2 hours. Cutting full depth at 2500 RPM and traversing quickly by hand, I got a great finish with the 1 radius insert. I'm still trying to learn how to get a good finish, and this time I was able to mess with speed and feed a lot because I had so many to do.

10-13-2008, 12:44 PM
:) When I use carbide it is because I want to take off a serious amount of metal. Usually I use HSS and a nice sharp point for finishing passes. Once you get the hang of it, they are very easy to sharpen and are much cheaper than carbide. Plus they give excellent surface finish without all the fuss of trying to find the right insert to buy.

But when I use carbide, its a big radius. The sharpest inerts I have are some TCMT 32.51 inserts I got with some cheap Grizzly insert holders before I got hooked on HSS. I've got some really big hunkin' pieces of carbide that get used with the Pacemaker I have up and running. I was taking .1 DOC at .035 lead on some seriously hard metal. It was an old motor shaft and my poor old HSS wouldn't touch it. It just squealed and gave up the ghost. Boy did it leave a beautiful finish, though. You had to take big DOC to get it to bite, but once I got that figured out and the high lead figured out, it looked like a mirror. Too bad I couldn't drill through the damn stuff with a HSS drill bit.

dan s
10-13-2008, 01:41 PM
I'm not replacing my HSS (spent a few hours using it last night) with carbide. I'm finding my self using carbide more often recently because I'm running at sfpm that would smoke HSS.

I already get excellent finish with my inserts, I'm just looking to see what's the best i could get.

10-13-2008, 02:02 PM
#2 will give you a good finish at a faster feed rate. I use 2s for general work 1s for when I need to have sharper corners and 0s for threading.

10-13-2008, 02:16 PM

i'm using ccmt with a 0.2 tip, i have same 0.4 for bigger cuts but the 0.2 gives a good finish.


Forrest Addy
10-13-2008, 02:54 PM
Several because my work mix goes from roughing to fine finishing. It aall depends. Generall you want the tip radius to be about 4 time the feed rate but that's only a guide, not a commaandment.

dan s
10-13-2008, 02:54 PM
Some might find this interesting.


if you what to look at what is "theoretically" possible, you can use the following equation that i derived from a few sources (thus take it with a grain of salt).

RMS = (35631*f^2)/r
f = fed in inches
r = tip radius in inches

for example if we use a feed of .005" then we would get the following "theoretical" surface finish.

http://img520.imageshack.us/img520/4246/sfby3.jpg (http://imageshack.us)

10-13-2008, 03:58 PM
Hmmm, that's worth remembering Forrest. I have experimented with tip radius and figured there should be a simple rule to use.

10-13-2008, 05:14 PM
Hmmm, that's worth remembering Forrest. I have experimented with tip radius and figured there should be a simple rule to use.

Ditto - those little rules of thumb, while not perfect, save alot of time in the shop! If nothing else, it gives you a place to start experimenting from. Thanks Forrest!