Re: Need advice: MaxNC or Sherline or other or nothing

Message: 2
Date: Tue, 22 Jun 2004 10:12:24 -0000
From: "CrazyDudeII" <apullin@...>
Subject: Need advice: MaxNC or Sherline or other or nothing

Hello. So I am looking for advice on which machine I should purchase.
As you can see from the title of the post, the machines I am
considering are:
MaxNC 15CL2
Sherline 8020 CNC

[Most people think that the 5400 Sherline is better as a base for CNC work
(that's #8540 as a CNC-equipped machine.) The extra tilts of the 2000 frame
are good for manual setups for machining odd angles, but are less useful in
CNC work, and detract from overall rigidity, which is important, especially
when machining metals.

As well as these machines, you might also look at the Taig 2027 CNC mill,
which seems to come closer to what you're looking for in size and heaviness
of construction. See http://www.taigtools.com/cmill.html ]

So I'm probably going to do most of my work in aluminum, but it would
be nice if I could do work in copper/brass/steel, even if I have to
go super slow. I do have access to GibbsCAM, so adapting my toolpaths
for a large number of passes should be fairly easy.

I'll go through my though process here, so if you see anything
glaringly wrong, please let me know... that's why I'm here!

- It seems from what I've read that the sherline machine is built
better, more solidly, and would probably end up being more repetable
and able to work with steel when I need to.

[Both Sherline's and Taig's mills are built better than MaxNC's, which has
taken some design shortcuts that compromise function over the long term.
Among these are the all-aluminum construction with only a thin layer of blue
anodizing protecting the gibs, using the bearings of the stepper motors
(held on by two of four mounting lugs) to handle all thrust loads,
plastic-bodied antibacklash nuts glued into incomplete holes with Loctite,
rigid couplings with no flats for set screws, and a spindle motor of low
quality mounted on two shaky standoffs. Some of these issues can be
remedied, if you're willing to do some work; here's a link to one MaxNC
owner's modifications: http://hans-w.com/cnc.htm ]

- However, the two major shortcomings of the sherline are the
reduced X travel (only 9" as opposed to 12" on the maxNC), and the
stepper motor drive.
- I can probably live with the reduced X travel, as I am not making
anything that is too huge (yet)... I also have >some< access to a
large FADAL machine... is it realistic that maybe I could fabricate a
new X table and retrofit the machine? I dont really want to have to
do that though, unless I know it'll work nicely.

[If you're up to fabricating things on a Fadal, then I think you'd be better
off designing and building a mill from scratch; you'd end up with just what
you wanted, not a kludge of your parts and another solution's inherited
problems.]

- I worry about stepper motor drive in the event that I do miss a
step and throw the whole program off. Should this be a realistic
concern? Would the closed loop servos on the MaxNC really deliver a
more reliable operation over these sherline steppers?

[They call them "servos", but they're actually just stepper motors with
encoders. While the "closed loop" function does shut down the machine with a
"servo error" when the encoder count is off too far from the commanded
position, it doesn't correct for position errors on the fly like a true
closed loop servo system. Some users have been plagued with these errors,
which tend to increase as the brushes in the spindle motor wear out. Used
within its limits of torque and speed, a well-designed and maintained
stepper system won't lose steps. If it does, that's a sign of something
wrong.]

- I'd have to set the spindle speed manually on the sherline, and
can't do it with the program... but I dont think thats >too< big a
deal, is it?

[The Sherline spindle motor is a high quality DC motor with a good speed
control; it's more powerful than the motors supplied with the MaxNC (or the
Taig), although it weighs about the same. You do have to set it manually,
but you have to change tools manually on these machines anyway (although
I've seen an after-market toolchanger kit for the Sherline) and the spindle
speed generally is constant for each tool used.]

- So, like I said before, I have access to GibbsCAM, so software
isn't an issue here. I am pretty good with Linux, so I should be able
to set up EMC with the sherline system without a problem.

With all that being said, I am seeking advice on which machine I
should go with. I am leaning towards the Sherline because I've heard
good things about them, and they are a fair bit cheaper.
I would greatly appreciate any advice or input on this decision....
if you could address any of my worries, that'd be great.

Thanks,
Andrew Pullin

[Both Sherline and Taig are good companies to deal with; they make products
that are good value for the money, and they stand behind them.]

Andrew Werby
www.computersculpture.com