In article ,
Doug Goncz wrote:
Can Harbor Freight's Multipurpose Machine cut 18 tpi? It's not listed in the
manual on page 8....
http://www.harborfreight.com/manuals...9999/39743.PDF
There are two primary answers, and some secondary
considerations:
1) No -- not as supplied.
2) Yes -- *if* you can find the right change gears to add to the
existing set. (With a bunch of calculation, I could probably
determine what the leadscrew pitch is (it may be metric or inch,
I don't know for sure). Once I knew that, I could calculate
what additional change gears could theoretically produce 18 TPI.
(I say theoretically, because a given combination of the needed
gears might not fit on the "banjo" on the lathe. It doesn't
look as though it has enough slots and enough travel in the
existing slots to build up all the possible custom threading
combinations.
In addition to these primary things, here are some secondary
considerations:
a) Threading will be a real pain, as this machine does not have
half-nuts and a threading dial to allow you to disengage the
leadscrew, return the carriage, and re-start another pass on the
threading. Instead, you have to stop the spindle, crank the
tool out of engagement with the workpiece, reverse the spindle
to get back to the starting place, stop the spindle, crank the
tool back in enough to make the next (deeper) pass), and
re-start the spindle in forward. This means that you must cut
dead slow if you are threading to a shoulder -- or even crank
the spindle by hand to avoid overshooting.
b) Even if it *had* the half-nuts and threading dial, they would
be useful for one of the two sets of threads (either inch, or
metric, depending on the pitch of the leadscrew.) With the
other set of threads, you would still have to do as above, so
they supplied you with a cheaper machine on which one system
does not have any disadvantage over the other -- they *both* are
a PITA.
c) Since I don't see the traditional pair of gears 127 & 100 tooth
to get a precise conversion between metric and inch threading,
Also, I'm sure that there is not room on the "banjo" for that
large a pair of gears.
I suspect that one system (metric or imperial) is only an
approximation, at best. Which will be a factor of which system
the leadscrew is.
d) Certain other parts of the machine look suspect. As an example,
the compound which they call "Small Cross Slide", which has far
too little length engaged in the dovetails for the feed, and the
tool holder is part of the upper dovetail, so you can't turn the
tool holder to a different angle for better cutting while having
the compound set at an angle for whatever purpose. Where I see
this to be a real pin would be in threading, where it is
traditional to have the compound set at 29-1/2 degrees to feed
in almost along one flank of the thread you are cutting. Here,
if you did not grind a customized angle on the tip of the
threading tool, you would have to set the compound parallel to
the axis of the lathe bed. (Which *might* help work around some
of the weakness of its dovetail)
In addition, the mounting of the "bearing" plate for the
compound leadscrew looks rather far from rigid, too.
e) Even the headstock spindle only has a MT-1 taper, same as
the mill spindle and the tailstock. Normally, the headstock
spindle is at least one Morse Taper size larger than the
tailstock.
It is too late at night for me to wade through that "manual" and
determine what other failings I expect, but I would consider this to be
something to be used *only* if a better machine were totally
unavailable.
If you have not yet bought this, I would suggest that you *not*
buy it -- certainly not if custom threads are your intended application.
Good Luck,
DoN.
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