Re: Form tapping blind holes, what coolant?

On Wed, 09 Jan 2008 04:44:49 -0800, BottleBob <bottlbob@xxxxxxxxxxxxx>
wrote:

Matt Stawicki wrote:

Yeah, I remember. I also remember how back asswards it seems:-)
They keep talking about chip load, and how it needs to be constant,
but yet they program in IPM and intentionally mess with chip load
every time there's a variation in RPM! Plus, to calculate chip load
they HAVE to calculate the feed per revolution anyway! Why on earth do
you have to convert it to IPM?? You want .0005" per tooth chip load on
a 4-flute cutter - .0005" x 4 = .002" per revolution. Done deal. No
matter what rpm you run, you got a .0005 chip load. Even if the
spindle bogs down on a heavy cut, ya got a .0005 chip load, and no
chance of over loading your cutter.

Has to be a hassle. I've never done it, but from what I've read in
this group, to do a pocket in a part, it seems that with the same
cutter you constantly have to change feeds. Ramp in at one feed, move
over at another, slow down for the corner, speed up for side 2, slow
down for the next corner, Etc, etc, and then clean out the center at
yet another feed.

Now, lets change the rpm cause I'm smoking the cutter. How many feeds
are you going to have to change??? Let's hear it for IPR! Who cares
what you do with the RPM, you still have your constant chip load. Make
perfect sense to me:-)

Matt:

Heh, you know, that almost sounds like it makes sense. BUT even if you
were programming in IPR you'd have to slow down in the corners (by
lowering the chip load), where there is more load on the cutter due to
cutting with a larger percentage of the circumference, as well as in
full width slotting. And you would be able to speed up when taking
smaller radial cuts (increasing the chip load), and slow down in ramping
in if your angle is steep (lowering the chip load again).


I understand that feedrates are constantly changing because of corners
or varying depths of cut with the same cutter. We have the same
parameters to deal with. *Especially* on Swiss machines where we
don't, in most cases, have the option of roughing and finishing. Once
you remove material from the OD of the barstock, you *cannot* suck the
material back into the bushing to take another cut. Most every move is
a finish cut, no matter how much material your trying to remove.

There is also a serious limit to the number of tools that can be used.
Especially on the older machines. My CNC Swiss, for example, only has
5 turning tool positions. Two of those positions can hold cross
drilling or milling units. One position *has* to be used for a cut-off
tool. I have had parts that have had to be milled, cross drilled, and
s.p. threaded. That leaves only ONE position for turning the entire
profile of the part, including grooves and chamfers. You usually have
a different feedrate for every move that tool makes.

I recently had a job that had 7 turn diameters, and 3 grooves. One of
those grooves was .050" wide, and it had to have a .005" fillet in
each corner of the groove. Little .002" edge breaks on all OD's, and
the inside corners for diameter steps had to be sharp. I cut the
entire part with one tool. Meanwhile, I had to use a dead sharp tool,
and since the .050 groove had to have a .005 fillet on each side, my
tool could only be .040" wide.

Just went out and looked at the program. There were 33 feedrate
changes for that one tool.

My point was, and is, if I was cutting in IPM and wanted to change the
RPM, but wanted to keep the chip load the same as it was, I would have
to make 33 changes to my program, and waste who know's how much time
re-calculating all those feeds.

Using IPR, if I make an RPM change, I don't have to do anything else.
My feeds stay exactly the same as they were. The time to get from
point A to point B will change, but the feedrate, i.e. chip load, i.e.
finish on my part, will remain exactly the same. Unless, of course, I
do something stupid and fry my tool. LOL. Been there, done that:-)

So it seems your gains may be illusory since you'd have to be
constantly changing the IPR rate due to the variables in endmill loading.

Nope. The feed remains the same. A .0005" per tooth chip load on a
4-flute cutter, is .002" Per Revolution of said cutter, i.e. the
spindle. Doesn't matter it the cutter is spinning at 1 rpm, or 10,000
rpm's, it still going to feed .002" Per Revolution of the spindle.

The cutting *time* will change, but the feed, i.e. chip load, will
not.

Trochoidal machining, or Surfcam's truemill toolpaths may get away with
this, but add their own complexity to toolpathing.

Lol. Had to look that up. Still don't really understand it, which is
why.......

We doen't use no steeenking CaadCaam :-)

(Although, I did recently purchase BobCad/Cam because I'd like to
learn something about it. The price was right and I may be getting my
hands on an old Hurco)

Matt
.

Relevant Pages

  • Re: Form tapping blind holes, what coolant?
    ... the RPM near machine maximum for your rigid tapping cycle. ... I had programmed 1000 PRM and 25 IPM, but I chickened out and ran it ... They keep talking about chip load, and how it needs to be constant, ... cutter you constantly have to change feeds. ...
    (alt.machines.cnc)
  • Re: What is the best speeds and feeds reference?
    ... I want to write a calculator to figure out the best speeds and feeds ... Cutter diameter does not factor into "feed per tooth" a.k.a. chip load, ... into surface feet per minute for determining RPM. ... determines how fast your axis feed can be to maintain a given chip load. ...
    (rec.crafts.metalworking)
  • Re: Form tapping blind holes, what coolant?
    ... RPM, but wanted to keep the chip load the same as it was, I would have ... Using IPR, if I make an RPM change, I don't have to do anything else. ... My feeds stay exactly the same as they were. ... 4-flute cutter, is .002" Per Revolution of said cutter, i.e. the ...
    (alt.machines.cnc)
  • Re: What is the best speeds and feeds reference?
    ... I want to write a calculator to figure out the best speeds and feeds ... Cutter diameter does not factor into "feed per tooth" a.k.a. chip load, ... into surface feet per minute for determining RPM. ... determines how fast your axis feed can be to maintain a given chip load. ...
    (rec.crafts.metalworking)
  • Re: What is the best speeds and feeds reference?
    ... I want to write a calculator to figure out the best speeds and feeds ... Cutter diameter does not factor into "feed per tooth" a.k.a. chip load, ... into surface feet per minute for determining RPM. ... determines how fast your axis feed can be to maintain a given chip load. ...
    (rec.crafts.metalworking)