According to Bill Schwab :
Hello all,
I am considering adding a lathe to my growing collection of toys - make
that toolsg, and want some guidance on what to get. Scanning some
previous threads suggests that you will promptly ask what I plan to do
with it. The most important thing at first is to learn how to run a
lathe; it is getting to be time for me to do that. A mini-lathe would
probably be fine for starters, but I would likely want to remove the
training wheels after some practice.
Understood.
I would want to turn dowels pins and other (probably small) parts for
assembling things that I design and build, and I would no doubt find
many uses for a lathe once I have the capability. I design and build
prototypes, so there would be many opportunities to use round parts.
Hmmm ... dowel pins are usually hardened and ground to final
dimension. Now taper pins are mild steel (or at least the ones which I
have used so far), but for those you need matching taper pin reamers.
There was a time when I wondered why anyone would want to cut threads on
a lathe, but I get it now. While I will no doubt end up winging it
other ways, I have a project that would be well suited to a round part
that just happens to have some threads on one end. I could use a dye,
but I would have to have a suitable diameter part with the right shape
on it, which is still really a lathe job. Total length there would be
eight inches or so, and the diameter about half an inch.
Hmmm ... with that ratio of diameter to length, you should make
sure that your lathe comes with a steady rest and a follower rest,
because that length at that diameter will flex when working out near the
end -- unless you are supporting it between centers.
I suspect I would quickly outgrow a mini-lathe. I like the price of a
9x20, but am leaning toward the Enco 12x36. At 900 lbs, it should be
manageable with my hoist and pickup (thinking ahead to local moves, not
to mention getting it down the driveway grade and in the garage), the
price is (gulp!) ok, and it has a removable block. So far, the biggest
diameter I have in mind is three inches or so, but the gap sounds like a
nice idea.
One which we had at work had a gap bed, but the professional
machinist in our shop refused to allow it to be removed, saying that you
could never get it back in place with sufficient precision. (This was a
Jet from Taiwan back around 1985-1990 I think.)
Are the advantages of geared heads limited to convenience? Did any of
you buy the belt head and hate it?
I have a belt driven Clausing 12x24" machine and am quite happy
with it. One advantage to the belts is that you have a safety fuse in
that the belt will usually slip before the machine is damaged when
something goes wrong.
It is prewired to 220, but can apparently be wired for 110. There are
no 220 outlets where I envision this living for the near future. Any
strong thoughts on whether I should fix that or is 110 ok?
What is the horsepower of that motor? My Clausing, with a 1-1/2
HP motor, would pop the circuit breaker when starting a bit too often
when wired for 120 VAC. I re-wired it to 240 VAC and ran a longer cord
to an existing 240 VAC outlet, and have had no problems since. (You
draw half the current for the same horsepower from 240 VAC compared to
120 VAC, and the 120 VAC staring surge is just a bit too close to the
breaker size for the typical outlet. So -- I would have a 240 VAC
outlet installed -- or do it yourself if you have the skills and won't
violate local codes.
It seems unlikely that I will shell out for a DRO. There have been a
few times when I will admit it would have been helpful to have my mill
equipped with one (mainly when clamps interfere with measuring), but
rules, calipers and the dials have served me well. I would much rather
put the money toward a larger mill, once I figure out what to buy. I
have looked, but I can't find an 8x36 with a 12 inch cross travel that
weighs around 1000 lb 
Wading through the trade offs can wait.
Why would you need a 12" cross travel on a 10" lathe?
Typically, the tool only needs to move half of the swing (5" on a 10"
lathe, or 6" on a 12" lathe), but a bit more will help free you from
having to be too picky in your tool position so you can reach from the
maximum diameter to the center. (You might want to go 1/8" past the
center to be sure that you have turned off the tit left, and perhaps a
bit more if you are running the lathe in reverse and turning the ID of a
workpiece.
What else should I be asking about a lathe?
What kind of attachment method for chucks to the spindle. If it
is a threaded spindle and the chucks simply screw on, you have to be
very careful when turning in reverse, or the chuck will unscrew under
power.
My Clausing came with a 2-1/4x8 threaded spindle, and now has a
L-00 spindle instead, so things are a lot more comfortable. There are
also the D-? series (also called Camlock) which are similarly good for
reverse turning.
You want the lathe to have separate power feed -- both across
and longitudinal, so you have fine feeds available.
You want a quick-change gearbox, or you are likely to not bother
to set the speed to what is most appropriate for your job.
You want the spindle to be capable of handling collets (5C is a
good size -- up to 1" through the spindle, and up to 1-1/8" for short
workpieces). This will be a lot better for doing your small parts like
the dowel pins. If you expect to be making a lot of small parts from
rod stock, you want room past the end of the spindle to support the
excess rod so it does not start whipping -- which can be quite
dangerous.
The collet closer will be far quicker to use if you get a lever
style closer instead of the handwheel style.
And for making lots of small parts from rod stock, a bed turret
and appropriate turret tools (Geometric die heads, box tools, and
various other things) can speed up production significantly.
A taper attachment is useful if you expect to *make* taper pins,
but you can buy them in gross lots for very little, so I would not
bother, unless you need a custom size. However, there are other times
when a taper attachment is useful as well.
Check the dials for the cross feed and the compound. They
should be something even for a full turn, like 0.100" or 0.050". I have
seen ones which instead are 0.127" for a full turn, which means that the
leadscrew is metric, and it has simply been calibrated in inch
measurements. This is particularly a problem when you need to make
multiple turns of the handwheel. You'll need a calculator to figure out
how many turns and partial turns to move the distance which you wish.
(Here is where a DRO can make up for the awkward choice of leadscrew
pitch -- just ignore the dial and read motion from the DRO.)
Of course, if you are expecting to do mostly metric work, get a
lathe whose dials and thread cutting are set up in metric units. In
particular, metric threads on an imperial lathe, or vice versa are a
serious pain, even with the set of transposing gears. In particular,
your threading dial won't be of any use when crossing systems. (Of
course, there are machines with two leadscrews which can cut imperial or
metric threads without problems -- but this is talking about a lot more
money than you seem to be thinking of.
Check how slow the slowest spindle speed is. If you are cutting
a coarse pitch thread, you want as slow a spindle motion as you can get.
IIRC, my Clausing goes down to 55 RPM at the bottom. Even that can be
exciting if you are threading a coarse pitch to a shoulder.
I'm sure that I will think of lots of other things to say as
soon as I send this off.
Best of luck,
DoN.
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