Newsgroups: rec.crafts.metalworking
Subject: Re: milling on the lathe
From: jmorton@euler.Berkeley.EDU (John Morton)
Date: 13 Jun 1995 15:37:35 GMT

In article <ncliffe-1306951421130001@132.146.65.223>,
Nigel Cliffe <ncliffe@hfnet.bt.co.uk> wrote:
>In article <90877.jhall@nbnet.nb.ca>, <jhall@nbnet.nb.ca> wrote:
>
>>      I just did my first milling on the lathe, with a Palmgren 250 
>> ..... 
>> non back gear speed (about 200rpm), it seems that the heaviest cut I 
>> can take is about twenty thou and that only if I enter the work from 

This is typical of this kind of milling setup - it's just not rigid
enough to take more than that.  If you're going to do things this way
you will have to have great patience; it will take longer to do a small
job as it would to do a big job on a big machine.

>> 2)    The end mill doesn't seem to like being fed on end into the 
>> work (like a drill). Is this right, in spite of its name? 
>
>Yes, if its a four-fluted one. End-mills aren;t usually designed for

The term here is "center-cutting".  You can get center-cutting 4-flute
end mills.  As Nigel said, you can tell them by the edge which runs
right across the end of cutter.  3-flute cutters are usually center-
cutting, but I don't like them because you can't measure their
diameters!  2-flute end mills are always center-cutting, I believe.

>> 3)    I have some bits I inherited. Some four flute, some two 
>> flute, what are the different applications? 

One tends to use 4-flute cutters in tougher materials, which require lower
surface speeds to avoid burning the edges.  You can get a lower chip load
(and more cuts per inch of feed) without speeding the cutter too much.
Another good application is in thin material which recoils between each
tooth contact, e.g. stainless tubing, which work-hardens as it gets pushed
around.

A 2-flute cutter has the advantage of more chip clearance for clearing
the waste with air or coolant.  You stand a better chance of doing a
decent freehand grind on a simpler cutter.

>> Would there be a 
>> difference between a true end mill and a bit intended for boring 
>> counterbores? 

A counterbore (the tool has the same name as the feature) has end edges
at 90 deg. to the axis.  An end mill has a relief of about 3 deg., I think,
which doesn't give you a flat-bottomed hole (though close enough for many
folks :-)) but also does not scuff up the surface  finish has you cut
laterally.

>> Why would one use a left hand bit rather than a right 
>> hand bit and vice versa? 

A cutter intended to rotate counterclockwise is unusual, and probably has
some special purpose.  A cutter with the opposite helix direction (i.e.
counterclockwise as it twists away from the viewer) is, on the other hand,
very useful.  This type of cutter tends to push the workpiece away and
into the table or fixture (good for when the material is thin) and also
will not tend to such the cutter out of it's holder.



John Morton			     Mechanical Engineering Machine Shop
jmorton@euler.me.berkeley.edu	     University of California at Berkeley

Newsgroups: rec.crafts.metalworking
Subject: Re: milling on the lathe
From: jmorton@euler.Berkeley.EDU (John Morton)
Date: 13 Jun 1995 16:24:50 GMT

In article <3rkc2j$qhv@wolfe.wimsey.com>,
Mark Fraser <mfraser@vanbc.wimsey.com> wrote:
>Don't 4-flute endmills tend to want to wander into the side of the
>workpiece?  While 2-flute [and likely 3] tend to be able to handle
>things a little better, because the "back" cutting surface has
>a different force vector?  [Actually, it's the leading part of the
>mill that's producing a force vector that pushes the
>"main" cutting side edge into the workpiece].  I know I had quite a
>time trying to cut a spline on 5/8 drillrod in my little Sherline
>using a 4-flute - I recalled somewhere a year or so ago reading 
>about the 2-flute "solution", and it seemed to work.  Now, I

I don't understand this description of the force vectors, and I
can't tell just how you're using the cutter in your example.
However I can say that multi-flute cutters tend to be better in
resisting deflection, for 2 reasons:  1) each bite from the tooth
of a 2-flute cutter has more opportunity to lever the cutter to the
side before the next tooth can come around to contribute its own
force; and 2) the multi-flute cutter has a greater cross section, and
is therefore stiffer.

One solution to this type of problem is to climb your finish pass
before doing it again in the conventional direction.  This way you
are not pulling your cutter in past where you want it to go when
it's under load and prone to deflection.  This is also a good 
technique when using a wood router.

Deflection is most problematic with features like keyways, where you
have only one chance to get the slot in the right place (if your
cutter is the finish size).  For these I always use a solid carbide
cutter, which in small sizes cost about the same as HSS.  Carbide
is very stiff.

John Morton			     Mechanical Engineering Machine Shop
jmorton@euler.me.berkeley.edu	     University of California at Berkeley