Re: [CAD_CAM_EDM_DRO] New Mini mill/drill

> Hi folks,
>
> I've been looking at a new mini mill/drill machine that Harbor Freight
> (item 44991-0ARA) and Grizzly (G8689) are selling. It looks like a
> great candidate for a CNC conversion. Has any one had experience with
> this model?
>
> The machine looks identacl from both mail order catalogs. However
> Harbor Freight clams their machine has a R8 taper spindle, and
> confusedly says it comes with a JT33 chuck taper. The Grizzly catalog
> says only a M3 taper.

A common situation on moderately large manual mills (ie, bridgeports)
is to have a female R8 taper in the spindle. Male R8 tapers, as found
on collets and end mill holders, have threads in the back for a
drawbar which is essentially a long bolt that goes up through the
spindle, so they can't fall out. For drilling, you get an adapter
(arbor) which fits in the R8 taper and has a male taper on its other
end that fits into the body of a Jacobs chuck. These chucks have
their own unique series of tapers - things like JT6, JT33, etc. If
the machine comes with a drill chuck, it probably includes the arbor
for it. You may end up deciding to replace both with better quality,
though.

> I'm wary of using a morse taper for milling. In my drill press the
> chuck is held in by probity a M3 taper.

While some large drill presses do have morse taper spindles, many
smaller ones (delta, and the import copies) have male jacobs tapers
that fit into chucks, just like the arbor you would use with a milling
machine. The problem is that often the tapers on the spindle and/or
chuck are not made precisely enough, and so the chuck falls off. When
this happens with an R8 spindle mill, you replace the drill chuck and
its arbor. When it happens with a drillpress, you replace the whole
machine (unless you feel like extracting the spindle, mounting it in a
lathe, and trying to regrind the taper).

Some smaller mills (including certain older bridgports) do have a
female morse taper in the spindle. These are less preferable (plus
the collets and tooling to match are much more expensive). I believe
they do have a draw bar, but the tools are probalby more likely to
spin in the taper and score it.

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT