Re: [CAD_CAM_EDM_DRO] Harbor Frieght's Micro mill ...... cnc quality????

On Tue, 22 Jul 2003, Harvey White wrote:

> On Tue, 22 Jul 2003 03:52:03 -0700 (PDT), you wrote:
>
> >Hi...a lot of talk in the past about Harbor Frieght's "Mini-MIll", but
> > none that I know of about using the Micro Mill for cnc and general
> > quaility of the machine.
> >
> > Anyone has experience with the Micro-Mill, I would like to hear what
> > they think of the machine and if it would be a good candidate for cnc.

I think so. It's definitely better than the mini-mill as far as
conversion goes.

> I got one. If you wish to get one, and if there is a local HF store
> near you, go and ask them if they will sell it for 149.00. It was on
> sidewalk sale for that amount a while ago. The local stores seem to
> be closing them out.

Only one of the several stores by me even carries them. I was lucky just
to get one for the $279 price.

> That said, it seems to be a decent quality mill, The Z axis is screw
> fed, but will need a gas column lift or counterweight to balance the
> head. There is no counterforce on it. Z axis will be the most
> complicated to do, by the way.

The Z axis is puzzling. It would have been so much better to use the same
acme screw for the Z as the X and Y. The Z axis has standard 60deg.
threads that create friction when there is much load on them. The acme
would have been much smoother and they could use the same screw stock for
all 3 axes.
I just decided to go straight to a ballscrew for the Z. It's pretty cheap
from McMaster Carr if you get the 5/8" size. The counter weight may not
be needed with the ballscrew.

> X and Y axis can have a motor mount with a simple piece of U channel,
> as it appears that a stepper can be mounted with direct coupling
> rather easily. (Nema34).

I made bearing blocks for the X and Y that use standard 6mm x 22mm ball
bearings. They are fairly simple and easy to make if you have a 4-jaw
chuck and a boring bar. Even if you keep the machine as a manual the
bearings make the screws much smoother.
The motor mounts I hacked out of some wierd surplus gizmo's I found on
ebay. The surplus gizmo's come with a NEMA23 motor, helical coupler,
very short ballscrew/nut, and a heavy aluminum cylinder.
Here's one:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2546365676&category=25290

> Spindle power seems adequate, fit and finish seems reasonable, but you
> can tell where they have cut a few corners, mostly in the means of
> adjusting the gibs.

The gib adjustment isn't the best but it is better than the mini-mill.
The mini-mill only has 2 gib screws on the Y axis and it's difficult to
get that axis adjusted for no play. The table on the mini is also too
narrow and it's flexy because of that.
The micro-mill is designed better overall than the mini-mill I think. If
they made the micro-mill the same size as the mini it would be almost
perfect.

> There is an anti-backlash adjustment for each axis.

That's a nice thing to have. It even works halfway decent. If it lasts
for awhile I may not even bother converting the X and Y to ballscrew.

> for 149, it's an excellent CNC machine. (uses MT2 tooling). The
> capacity is a bit limited, but then again, you kinda knew that.

Even for the list $299 price it's still good.

> The quill has a 2 inch stroke, but if locked in place, the whole head
> can be moved with a stepper.

That's the best way for CNC.

Hopefully I'll get this thing running sometime this weekend. I'm putting
together the electronics now and I still need to finish the Z axis. But
it's coming along.

Also. there is a Yahoo! group specifically for converting the micro-mill
to CNC. Not much traffic yet, but it's still a fairly new machine.

http://groups.yahoo.com/group/hf47158tocnc/

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