Re: [CAD_CAM_EDM_DRO] Re: wrong guy, but have servo question.

-----Original Message-----
From: Jon Elson <jmelson@...>
To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
Date: Monday, November 27, 2000 10:59 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: wrong guy, but have servo question.

>Well, SURE! You are making cuts that the Bridgeport Series-I is not really
>designed for, and should expect trouble. I would not ever take such a
>cut on my machine, no matter what the quill position!

Hi All:
I run a Bridgeport clone .
With a Sandvik 2 flute positive rake cutter, a 1/8" pass and a 95% stepover
in P20 is the kind of cut I take all day long, when I'm roughing out a
cavity.
Admittedly, my machine is near new, and has 3 horses to drive it.
Any less, and I can't justify owning the machine, because it is not
competitive.
The position of the quill matters a lot when I take these kinds of cuts.
My point was not that you will not get a useable CNC by driving the quill as
your Z axis; what I was pointing out is that this choice leads to some
significant compromises in the performance of the machine.
I was making my comparisons from the point-of-view of a commercial user
whose choice has to compete with other brands of CNC on the market.
Just to put everything into perspective here:
I was quoted $5000.00 CDN per axis for servos, ballscrews etc, etc once upon
a time, so $15000.00 to get a knee mill conversion kit. (I know prices have
come way down since then)
My time, even working for someone else as a toolbreaker, is worth about
$30.00 per hour.
Doing the conversion is at least 100 hours work before everything runs as it
should.
If I buy a converted machine off the showroom floor I pay about $23,000.00
CDN.
I can buy a brand new Haas VMC with toolchanger for $30,000.00 CDN.
A Haas against a kneemill conversion is like Secretariat against Elsie the
Cow, in terms of performance.
My question to you all:
Why are you spending this inordinate effort on the CNC guts and then bolting
it on to such a limited machine?
If you really LOVE tinkering, then my comments obviously are of no
importance, but if you're thinking in terms of using a machine like this in
a commercial application, and are hoping to save bucks...have you really
made the best choice?
Has anyone of you out there considered building a decent machine base to
take all this incredible effort on the CNC guts?
Even if you farm out all of the milling and surface grinding, I bet you
could come up with a pretty decent machine base for less than the cost of a
kneemill.

Just some sobering thoughts, guys

Marcus