Re: [CAD_CAM_EDM_DRO] Desktop CNC Machines?

canadabrianb11 wrote:

>Firstly, I would like to introduce myself. My name is Brian Buchan,
>and I live in Kamloops BC Canada. I own a small manufacturing
>business. I have an electronics background focusing on industrial
>robotics, so CNC is not totally new to me. I look forward to being a
>member of this group.
>
>We are starting to do more and more custom work, and my bills at the
>local CNC shop are killing me.
>
>Most of my CNC requirements are for small pieces machined of Delrin
>or 6061 aluminum, and maybe the occasional piece of 12L14 steel. Lot
>size is typically 10 to 50 pieces. The biggest piece we would do
>would be about 7 x 1 x 1 inches, mostly quite a bit smaller.
>
>I'm thinking about buying (or building?) a small desktop CNC machine
>and starting to do this work in house. I've spent a bit of time
>looking at some of the available machines, but it's gotten a little
>overwhelming. At the absolute high end of my budget, the CNC Jr.
>seems a little big (read "expensive") for my requirements, but I'm
>not really sure if the smaller machines (ie MaxNC, etc.) are up to my
>needs. I don't think I need to wring every last second of machine
>time out of whatever I buy to make this a cost effective thing to do.
>
>

You certainly can't do 12L14 on the lightest machines at any reasonable
rate of metal removal. I'd be real skeptical about anything put together
from bits and pieces. That works fine for a wood router, but not for
milling steel. It is even iffy for aluminum. If you mean to CNC retrofit
a commercial manual machine, that's a different story.

Pointer 1. Watch out for round-column machines. You lose your X-Y
reference
point every time you need to raise or lower the head. There are dovetail
or square column machines available in all sizes, if you look for them.
They
don't suffer from this problem.

Make sure the spindle is beefy enough for real milling work, and not just
a re-labeled drill press. Also, check the available range of spindle
speeds,
as it sounds like you might be doing small parts with small end mills.
make sure you can get at least 4000 RPM, and the more, the better.

I have a 150-Lb Chinese mini-mill (the same model is sold by dozens of
different sellers) which I have CNC'd for demo and testing purposes.
I have done just a few small milling tasks with it to see what it could
do, and it is pretty bad. The vertical column flexes way too much, probably
where it bolts to the base. Milling with a 1/4" end mill in some aluminum,
I was getting what appeared to be up to 1/4" movement of the spindle.
Some of that was probably the entire machine rocking, but it was so much
more vibration than my Bridgeport, that it scared me!

Jon