Re: Re: Re: New Acme or similar--recommendations?

Gerald Abrahamson <jerryab@xxxxxxxx> wrote in
news:sko0b490m6j6vaflffgiilltgbovgfs3a8@xxxxxxx:

On 23 Aug 2008 17:02:35 GMT, D Murphy
<spamto154@xxxxxxxxxxx> wrote:

Gerald Abrahamson <jerryab@xxxxxxxx> wrote in
news:q1pua45s0jd17245s9hiirgfa12sq9hq18@xxxxxxx:

None of the screw machine shops mentioned a rotary broach
anywhere, nor did they say they could do it (make the spline
on the machine). They stated they could *not* make the
spline on the machine. Possibly, they did not want to do the
job--so they effectively "no bid" it.

It depends on the spline. If it is an involute spline with any kind of
tolerance then rotary broaching is out of the question.

On a CNC Lathe or Swiss you might be able to hob it right in the
machine.

Another option is to use this "shaving" cutter from Schwanog. You take
five passes on the first tooth, then one pass on each subsequent
tooth. This system works very well.

<http://www.schwanog.com/produkte/produkt.php?id=75
&PHPSESSID=e5479a18dd077b76156c52504b336ba7>

or <http://tinyurl.com/5dyv4o>

If your parts are high volume you would be better off to design the
spline in such a way that it can be rolled as a secondary operation.
Rolling is by far the least expensive way to manufacture a spline.

We are talking about 60 splines in a 360 degree circle, each
6-degree spline identical (center-to-center or
valley-to-valley). The front of the spline is open (no
material blocks access). The problem is the spline is .030"
in front of a feature that is a "wall" that can't be moved.

Can the 0.030" be relief? IOW, if it is the same diameter as the spline
then it becomes difficult to rotary broach as the broach will leave long
burrs, connected chips actually, on the surface of the part. One of the
big problems with multi spindles is that you can't recall a tool. So
there may be no way to come back and re-cut that diameter to remove the
attached chip.

The other issue might be that there simply aren't enough tool stations on
the multi to accoodate the broach. The other weakness of a multi is there
are a limited number of tool stations and they are best suited to simpler
parts that have fewer features.

Providing an undercut between the spline and the shoulder (wall) is that
it might make it possible to roll the spling from one of the cross slides
on the multi spindle. Again not being able to see the whole part makes it
difficult to know whether or not all the positions are being used for
other ops.


The Schwanog looks good (as long as it does not require more
than say .025" clearance behind the cut area), but is it a
time hog? Adding seconds to the total cycle time is no big
deal, but adding a minute (or more) would be a killer.
Initially, the idea was to broach in the CNC. Then it was
changed to rotary broach (while still in the CNC).

Same issue as the rotary broach as far as relief. The Schwanog will be a
lot slower than rolling, slightly slower than rotary broaching, and a
whole lot faster than hobbing.


I think getting a complete part out of an initial--but more
complex--setup on one machine will be cheaper (overall) than
doing a finishing secondary operation on a second machine. I
am thinking runs of 5k to 10k at at time, for now.


Complete is almost always better. You'll never be able to run 5,000 piece
lot sizes as efficiently on a multi as on a single spindle. Particularly
with a complex set-up. Just as a single spindle will never run a million
piece lot size as efficiently as a multi.

And a 3" capacity multi will choke on small parts.

Perhaps it would be best to vend out the lower quantities until the
volume ramps up? Or maybe consider an operating lease on single spindle
equipment until the volume gets to the point where a multi spindle makes
sense. With an operating lease you simply return the machine at the end
of the term.

In any case partiing off large diameter parts from bar is a problem. On
the multi you might want to consider a Watkins saw attachment.

<http://www.championscrew.com/watkins.htm>

Another possibility would be to use automated six or 8 spindle chuckers
and feed them pre-cut blanks.

Shimada Machinery makes great quick change over CNC multi spindle
chuckers.

<http://www.smd.co.jp/en/multi-spindle.htm>

<http://www.smd.co.jp/en/products/cn660.htm>

You could use an old clapped out multi to cut the blanks to feed the CNC
chucker. This could be advantageous since you are cutting aluminum. Your
RPM won't be hampered by bar whip.

Some more food for thought...

--

Dan

CNC Videos - <http://tinyurl.com/yzdt6d>
.