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Fred_Farkle
02-04-2003, 08:55 PM
I purchased a large milling cutter (3" dia) that uses 4 3/4 lathe bits. The cutter has worked well for me in the past. Now the time has come to sharpen/replace the lathe bits. My question is: How should the bits be set? All at the same level? staggered in some way? The bits have been cut to about 2" in length and point down from the holder, with the carbide facing the direction of cut. I did not (as I should have) check this before I removed the bits.

Mike "the Bozo"

[This message has been edited by Fred_Farkle (edited 02-04-2003).]

Big Dipper
02-04-2003, 10:55 PM
Depends what you want to use the cutter for. For deep cuts you can step the bits up at different hieghts. This will allow a much deeper cut...each "tooth" is only taking 1/4 of the depth, but the feed rate must also be cut to 25% because there is only one "effective" tooth. For finishing you would want all the teeth set to EXACTLY the same hieght to run a "normal" feed rate and get a good finish.

Fred_Farkle
02-04-2003, 11:57 PM
Big Dipper - Appreciate the help...

I'll be wanting to use the cutter both ways. I like that. I can't afford the carbide insert cutters I drool over in the catalogs. I finally calibrated my BP clone power feed by setting the speed control to each graved line and stop watching the travel of the table Vs. some temporary marks. So now I can try to use the cutting charts given in the machine shop references.

[This message has been edited by Fred_Farkle (edited 02-04-2003).]

Thrud
02-05-2003, 12:10 AM
They should be set to the same height. This can be done by making a ring gage to hold the tool and allow the bits nose to rest upon the ring and then tightened. You will get better performance from the tool this way. In modern face mills it is common to have a "wiper" insert that is set slightly diferent from the other cuting edges - the wiper produces a smoother finish.

DR
02-05-2003, 12:15 AM
FF,

You might consider having the cutters sharpened in the head. Then they should be all the same height. This is assuming you're going to send them out somewhere to have them sharpened.

Mike L
02-05-2003, 10:42 AM
They should all be the same height.

If set at varying heights, one cutter will take most of the cut, and the one or two behind it will cut air. Set them all the same and let each one share the cutting. Uniform cutting will also reduce some of the worst harmonic vibrations.

Ever seen a 4 flute end mill with the flutes set to different heights? No, roughers are not at different heights.

Fred_Farkle
02-05-2003, 05:40 PM
Thrud - Would my cutter, as I have described it, be suitable for set up to obtain the wiper function. If so, would it be that one of the bits cutting angles be changed, or would one of the bits be slightly hi/lo? I use the cutter mostly for cast iron.

Thrud
02-06-2003, 12:39 AM
Mike
Not unless they are all inserts and Wiper inserts are available in that geometry. Wiper inserts are precision geometry and lapped. They are usually only used with short chipping and soft materials and would be set lower than the other inserts by about .o5mm or .oo19685" - they are also slightly displaced radially towards the center. The wiper only cuts on the bottom of the insert (axial cut only) Chatter can occur on long chipping materials with a wiper insert. Wipers are normally only used on larger face mills over 6" in diameter.

Your face mill should have all the bits or inserts set to the same depth - this will be hard enough to get right without a wiper. I only mentioned it in passing for your elucidation.

Fred_Farkle
02-07-2003, 10:22 PM
Thanks to all!!

Big Dipper
02-08-2003, 12:32 AM
Fred, sounds like you want your cutter set up as a standard face mill. It'll be tough to get the tool bits EXACTLY the same hieght by just clamping them in place...probably take some experimentation with clamping them and an indicator on the bottom/cutting surface.

The idea of setting the toolbits to different hieghts isn't new. Kennametal, for one, had what they called a "stepdex" cutter. The inserts were all at different hieghts. Supposed to be better for lower HP machines, and extended spindle lengths, etc., where rigidity was a problem. They made some tremendous claims for depth of cut, etc. when used on HBM's with the spindle sticking out three feet or more! They do work, but the ones we used only had one "effective" tooth (there was only one tooth at the finished depth), so the feedrate had to be figured like it was a one tooth cutter.