Used mill for the first time....

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JerryB
Posts: 45
Joined: Mon Jan 06, 2003 10:13 am
Location: Western, Kentucky

Used mill for the first time....

Post by JerryB »

I finally got my Wells-Index up and running Saturday. I tried it out on a scrap piece of 2 inch square tubing using a 3/4inch, 4 flute cutter.
The first pass was using 250 rpm and a rather slow feed rate. Got all kinds of vibrations and a rough cut and very rough finish. On the return cut, the machined groove opened up about .025 wider than the previous cut.
I tightened down the gib a little more and tried it again. I could actually see the table "bouncing" up and down in the ways.
Some more adjustments to the gib and an increase in rpm to 600 made a world of difference. I turned the tube to a new surface and milled another slot. The chips were blue but the finish was acceptable. The groove measured .758 rather than .750. I am not expecting perfection form this old mill but closer should not be too much to ask for I wouldn't think.
I spent some time with a dial indicator and determined that the spindle had about .0005 run out but I don't believe that would account for a difference of .008 on the work piece. The piece was mounted in a large, heavy vice, but it was rather high in the jaws. I am wondering if this could account for the inaccuracy somewhat.
As always, any and all ideas greatly apperciated.
Anonymous

Re: Used mill for the first time....

Post by Anonymous »

It can be one or more things causing this. you wount be able to cut a 3/4 slot with a 3/4 end mill and hold size.The tool will deflect,tool holder will have runout,spindle runout,flexing of the machine,sharpness of tool ect...Is the knee locked?That will keep it from moving as much.Help the newbees at work and this is a common step that is overlooked.
GeorgeGaskill

How used are the collets? Collets do ...

Post by GeorgeGaskill »

wear out and allow the cutter to wobble. Might be a good idea to measure their inside diameters at each end and in the middle.

Also, try cutting a solid piece. The tubing will compress from the clamping force after a slot has been cut through it.

Also, I am surprised at blue chips. Is the cutter sharp?
Anonymous

Re: Used mill for the first time....

Post by Anonymous »

Cutting tubing is not a good test of your machine. In my shop we machine slots in a good quantity of square and round steel tubing. This is done on very good quality CNC machines. It ain't easy.

Thin walled tubing sets up high frequency vibrations if not very securely clamped. This trashes cutters and creates oversized slots. And blue chips.

Do your tests on solid material.
Jon_Spear
Posts: 87
Joined: Sat Jan 04, 2003 11:56 am
Location: San Francisco, CA

many variables to consider

Post by Jon_Spear »

JerryB,

All of the above replies sound sensible to me.

Some of the things that I wonder about are the work material, the condition of your end mill, the depth of your cut, and the method of clamping.

There probably are some other things that might be important, but I can't think of them...

Good wishes,
Jon Spear
San Francisco
Anonymous

Re: Used mill for the first time....

Post by Anonymous »

a 4 flute endmill is designed for profiling - not cutting a slot. It will always cut a slot oversize. A 2 flute endmill, more commonly called a slot drill, will cut an accurate slot provided it is sharp. If possible, slot full depth in one pass, as there is a possibilty the top of the slot will widen with a second pass.

If you had no option but to cut a slot with a 4 flute endmill,the cutter should be of a diameter less han the width of the slot, and a cut taken down each side of the slot separately.

Vincent
Anonymous

Re: Used mill for the first time....

Post by Anonymous »

Huh? Where did you get the idea a 4 flute cutter is not suitable for slotting? They work just fine.

The number of flutes is more dependent on the material and feedrate, etc than the operation. For example, use two flutes in aluminum, 4 flutes in steel and harder materials.
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