When I removed the saddle from the bed for cleaning, I found considerable
binding just as the saddle came even with the end of the bed -- no overhang
yet, just on the very last bit of the ways. What I discovered is that
the lathe serial number, which is on the top surface of the ways, at the
back on the tail end, is stamped. The stamping process raises the metal
displaced by the stamp into a bump around the stamp impression. If
this happens on the ways of a lathe, it will interfere with the travel of
components that have their gibs or guides adjusted for the unaffected part
of the ways. I solved this by using a flat file to remove as much of
the raised metal around the serial number as possible without cutting into
the (unhardened) ways anywhere else. In the event, I put a few minor
scrapes and nicks in the area around the number, but none of them have raised
metal and none are in the area normally traversed by the saddle. The
tailstock, of course, uses only the inner edge of the ways, and the number
was stamped at the outer edge -- so, points to Sieg for putting the serial
number where it won't interfere with normal operation, but only partial points;
that number could just as readily have been stamped on the lower portion
of the bed casting (say, the top surface of the foot lug), where later application
of paint wouldn't have made it unreadable, but it wouldn't intefere with
removing the carriage when needed. Update:
I've since found, in connection with the tailstock movement, that the ways
are a small amount thicker (something like .005" to .010") at the tail end,
compared to a point a few inches left of there; this most likely contributes
to the binding of the carriage at the extreme end of the ways. Again,
this isn't a big deal in normal use, because the carriage can't travel that
far even with the tailstock off and threading dial removed; it's only of
concern when removing the carriage for cleaning, maintenance, upgrade, or
repair.
Cross Slide travel limited by splash guard
I had occasion to use the full travel of the cross slide, when facing
a part that extended slightly beyond the diameter of the stock 3-jaw chuck.
I wanted to keep the compound at 90° so I could use it for infeed
while the carriage was locked on the (disengaged) lead screw, and I needed
a particular tool angle to get a good finish with a "drag" facing cut, out
from center. I found, however, that I couldn't get the tool to center
because the back end of the cross slide hit the splash guard. Well,
I have a long term plan to make a taper attachment, and the spalsh guard
would have to go before I could mount something like that behind the lathe,
anyway, so unscrew four screws, and the splash guard is off. Part faced,
all is well. Added bonus, I can now (if needed) remove the cross slide
from the carriage without having to take the tailstock off, dismount the
right lead screw bearing, and run the carriage off the rack to the right
-- that makes me much more likely to take the slides apart and clean the
grease out of them, now that I'm sure they're better off with only oil.
Gear spacer stuck on left end of lead screw
When I first tried to change the gearing from the factory setup fine feed
(256 spindle revolutions per inch feed, A:20, B:80, C:20, D:80 in the lathe's
gear chart convention, or 16:1 reduction on a 16 tpi feed screw), I found
that the spacer sleeve that keeps the final 80T gear at the proper position
to mesh with the outer gear of the compounded pair didn't want to come off
the screw, though the gear itself came off with a carefully balanced pull.
With some effort, I was eventually able to pry the sleeve off the shaft,
cleaned up the burs created by removing it with a file, and filed away the
burrs I could feel on the edges of the keyway. The gear setup I needed
had the sleeve on the outside, instead of the inside, and it went on snugly
but not with undue force. When I went to remove it, however, I found
it stubborn again (though less so than previously). After closer examination
and some careful tests, I found that the keyway in the lead screw is of non-uniform
depth; deeper at the shaft end, where it might reasonably have been measured
in an inspection (giving Sieg the most credit for trying to build these little
lathes well -- they have been responsive to end user input over the past
ten years in terms of adding features and capacity), but shallower close
to the pillow block; the gears would slide on with a little push and come
off without too much pull, but the metal sleeve would jam in place. After
carefully cleaning up the sleeve (which had burrs inside both ends of the
bore, with the black oxide coating covering both burrs indicating it was
never properly deburred in manufacture) with a half-round needle file, I
used a tiny square needle file (needle file set and handle left over from
model airplane building) to file the keyway slot deeper in the sleeve, until
it would slide freely to the farthest point on the screw shaft that would
be needed. No further problems in changing the gears on the lead screw.
Some gears are rather tight on the B/C bobbin sleeve, but given that
the gears are plastic, I expect that to be a self-correcting problem over
time.
Through bore in three jaw chuck too small
The spindle bore in the Seig mini-lathes is about 13/16", just about the
biggest it can be without reducing the contact length of the #3 Morse Taper
socket at the chuck end of the spindle. Unfortunately, the 80 mm three
jaw chuck that comes with the lathe has a through bore of just about 5/8"
-- which is much too small to pass 3/4" drill rod. Since I've been
working with 3/4" drill rod quite a bit lately, I've been noticing this shortcoming
quite a bit, though I should emphasize that this isn't so much a defect of
the lathe as a consequence of choosing the 80 mm chuck as the standard one.
A larger chuck would naturally have increased the price of the lathe
(especially given that the chuck supplied is of surprisingly good quality
for the price of the machine), but would have had a larger bore.
Fortunately, careful examination and disassembly of the chuck revealed
that nothing structural would be compromised by boring the center hole in
the chuck to a larger size, though if I went more than a whisker over 3/4"
I would wind up cutting into the heads of the three screws that secure the
scroll retainer inside the back of the chuck.
I removed the jaws, scroll, pinions, and the retaining pins for the pinions
before starting this operation, but had to have the scroll retainer and its
screws in place so that the resulting bore would be the same diameter all
the way through. Using my newly completed boring bar holder and the
nice new set of boring bars I purchased a week or so ago, I started boring.
One of the first things I noticed was that the metal of the chuck didn't
produce long, curved chips like the aluminum and steel I've machined up until
now; instead, the swarf comes off as fine particles, not much larger than
beach sand. Once I saw how black my hands got, I decided that must
mean the chuck body, at least, was cast iron (which makes perfect sense;
it's much cheaper than steel in that size chunk, machines well but can have
required machining reduced by casting in most of the final shape, and is
plenty strong). I took it slow and easy, never trying to take a cut
of more than .020, using the power fine feed (about .004" per revolution),
then stopping the spindle, reversing the feed, and power feeding back out
without changing the cut depth before adding more in feed. Periodically,
I'd gage the hole with a piece of unmachined 3/4" drill rod. When I
got to the stage where the rod would pass the near end of the hole, but would
interfere partway through, I started making repeated passes inward and outward
without changing the feed setting; after about eight passes, the tool had
mostly quit cutting, and the 3/4" round bar passed easily through the chuck.
Now, when I want to end face and center drill a piece of hacksaw cut
3/4" rod, I can keep the end I'm working on short and stiff, and keep the
center in the center.
#2 Morse Taper arbor too long -- ejects at 5/8" tailstock ram travel
This isn't a problem with the lathe proper -- I purchased the tailstock
drill chuck and its attached MT2-JT33 arbor from Harbor Freight, separately
from the lathe (because Homier doesn't sell any of the accessories; otherwise,
I'd have gotten the drilling chuck and a couple other things with the lathe),
but it's related to the design of the lathe, in that the tailstock ram doesn't
have enough internal clearance to accept full length #2 Morse Taper shanks,
even without a tang end. Several people have recommended simply cutting
off the tang and/or a half inch or so of the taper on the full length taper
arbors in order to gain that half inch of clearance for drilling -- more
critical on the 7x10 (which is really a 7x8 using between centers measurement)
than on the 7x12 or the Micro Mark 7x14 -- but I wanted to keep the full
length of the taper; my thinking was that shortening the taper would reduce
the contact area between the arbor and the socket, and might increase the
likelihood of damage such as fretting or spinning .
My solution to this dilemma was to mount the entire chuck and arbor assembly
into the three jaw chuck on the spindle, with the lathe chuck jaws gripping
the hard, fixed section of the drill chuck that has the round holes for the
center pin of the chuck key (the chuck body itself). By advancing a
dead center into the center drill mark in the end of the MT2, I was able
to push the drill chuck against the lathe chuck's center hole and have everything
self align as I closed the lathe chuck's jaws, and the drill chuck body (even
on this very inexpensive chuck) was hard enough that the lathe chuck's jaws
left no mark. With the chuck and arbor assembly mounted in the lathe
chuck, I then removed the tailstock (to get clearance for the carriage) and
mounted a 3/8" twist drill in my newly made boring bar holder which, having
been drilled in place on the lathe, is precisely at center height. Careful
adjustment of the cross slide allowed me to feed the twist drill into the
center drill in the end of the MT2 with the carriage handwheel and drill
a hole about 3/4" deep. I thought I was done at that point, but a test
in the tailstock revealed that the ram screw, though it would enter the hole,
was engraving very shallow threads; I needed to enlarge the hole a bit.
After remounting (and recentering) the chuck and arbor in the lathe chuck,
I put my smallest, shortes boring bar in the holder and used it to bore the
hole in the MT2 another .030" larger (total I.D. theoretically now at .405"),
which handily clears the ram screw in the tailstock. The arbor now
ejects at about 3/32" from the zero mark on the tailstock ram, which I find
much more acceptable -- enough so that I haven't bothered to drill and bore
the hole the extra little bit that would be required to get to the zero mark,
and won't unless I find I need that fraction of an inch clearance to end
drill a part at some point. Best of all, the hole still fits inside
the reduced diameter nub at the end of the MT2 taper, so the exterior form
of the taper arbor is unaffected.
Carriage handwheel gears collect chips and jam
Nearly every web page with extensive information about the Sieg made mini-lathes
mentions putting a cover of some sort over the open handwheel reduction gears
in side the apron. As provided from the factory, these gears are completely
exposed on the lead screw side of the apron, and the grease that's recommended
to smooth operation and prevent wear catches chips and holds them in place
where they'll pass through the mesh of the gears again and again -- chips
that can be large enough to completely stop the carriage motion, possibly
causing the machine to stall during a cut, or leading to variations in feed
rate that in turn cause variations in cut depth as the tool cuts through
the deflection in the work where the feed slows.
I finally found the situation annoying enough to prompt me to disassemble
the carriage and fix the problem. Of course, I had to dismount the
tailstock, remove the right end pillow block supporting the long feed screw,
and then run the carriage off the rack to the right, followed by loosening
the rear gib enough to pass the thicker section of the back way and sliding
the carriage off the ways. After removing the apron, I reinstalled
the saddle and slides, knowing I'd probably need to use the lathe while the
apron was off.
Complete disassembly of the apron, thorough cleaning to remove the lithium
grease I'd put there when I originally cleaned and set up the lathe, and
disassembly of the split nut mechanism, left me with a bare casting and the
pressed in axle for the rack gear. I set the split nut sections back
in place and used them to mark the necessary clearance so the installed guard
wouldn't interfere with their movement; this mark was extended across the
full height of the apron and across the top and bottom surfaces to provide
a referense. Then, using a sheet of .032" brass (I'd have used
.025" or even .015" if available, but this was the only thickness the hobby
shop had when I stopped in), I laid the apron casting on the brass in position
so that the factory cut edges of the stock would form two edges of the finished
guard, and scribed around the edge of the apron to mark the shape onto the
brass. Ten minutes with a pair of aviation snips and fifteen with a
file, and I had a neatly cut and perfectly matched brass plate that would
completely cover the gear well milled into the apron casting -- except that
it didn't have a hole for the rack gear. Okay, I'll come back to that.
A little careful dry fitting confirmed what I'd read on at least one web
page about this fix; I'd need to reduce the thickness of the gears by a fat
smidgen to avoid having them rub, hard, on the cover plate. In fact,
the best I could measure suggested the gears were about .010" proud of the
flat surface of the apron -- so I needed to take about .015" off them to
provide a running clearance. The handwheel gear was pretty easy; it
had a flat face on the exposed side, and a raised bearing area around the
shaft that passes through the apron to accept the handwheel. After
pushing the saddle into position and tightening the back gibs (which I had
to adjust anyway after removing the carriage, because in working adjustment
it's too tight to pass the tail end of the ways) and chucking the gear by
the shaft (which, I'm gratified to report, was hard enough that the jaws
didn't mark it at all), I faced off .015" and was done. The carriage
gear was a little more challenging; here, I couldn't easily face from the
plate side of the gear because that was the side with the shaft, but the
opposite side has the raised bearing surface that rides on the cast iron
of the apron around the pressed in axle. Okay, well, it's not that
difficult. I chucked this part by the shaft as well (with the gear
protruding into the newly enlarged opening in the chuck -- it wouldn't have
fit before I enlarged the chuck bore, as the gear is 17 mm across and the
old hole was only 16 mm diameter) and started by facing .015" off the relieved
portion, leaving the bearing surface proud by a total of .045" or so, then
faced the same amount off the bearing surface to reestablish the same clearance,
but with the entire assembly shortened by that critical amount.
That done, I measured carefully, marked the location of the center of the
carriage gear's axle, and drilled through the brass with a 1/2" twist drill
-- in this case, since I was going to have to enlarge the hole and fine tune
it's location anyway, I didn't both to step drill. I then used a nibbler
to enlarge the hole, followed by a round file to bring it back to round and
fine adjust the position until the plate would mount over the gear shaft
and take the right position. Five carefully placed punch markes, and
I was ready to drill the screw holes in the plate. Those holes were
used to locate the punch marks in the apron, though the thinness of the brass
meant I couldn't use a transfer punch; as a result, the holes weren't perfectly
aligned. No matter; they weren't far enough off to cause trouble drilling,
and in a short time all five holes were center drilled and drilled to the
tap drill size (I think it's #44, but the drill that came in the tap and
drill set isn't actually marked, that I can see), 1/2" deep, and a little
later they were cleanly tapped as deeply as the 4-40 plug tap would cut.
I had to adjust the positions of three of the holes in the brass in
order to get the screws to fit in all the holes, the work of a few minutes
with a round needle file, and then it was time to start putting things back
together.
I adjusted the split nut gib much more snugly than the factory setting; now
the split nut has almost no play (or "shake") when engaged; the bottom, adjustable
piece has nothing discernible, while I wasn't able to tighten the top section
enough to remove the last .005" or so -- but if one jaw is solid, there shouldn't
be any end play when the split nut is engaged. In combination with
the tension adjustment on the handle detent (a spring loaded ball bearing
that holds the handle in the disengaged position) I was able to set things
up so that the handle moves readily, but won't vibrate into engagement (which
could cause a disaster during a chattery cut). Careful alignment of
the apron with the lead screw was easy before tightening the apron mounting
bolts in their slotted openings, and now everything moves smoothly -- and
despite making about half a pound of chips since installing the guard, there's
no evidence of binding or hesitation in the long feed either when hand feeding
or under power.
Broken 80T change gear
I'm embarassed to admit how I broke this, but it is something I've had
to fix on the lathe, and is related to a deficiency in the design.
First, in order to do accurate facing, one must lock the carriage in place;
otherwise, the cutting force may move the carriage and result in the tool
backing off from the cut, producing a sharply conical face (and losing any
zero setting that might have been made). The 7x12 lathe, however, comes
with no means of locking the carriage other than to overtighten the screws
on the carriage retainers; these plates have been known to break after prolonged
use of the lathe, because the three screws that tighten them flex the plate
against two locked screws, similar to those on the cross slide and compound
slide gibs, that set the clearance of the plates against the underside of
the ways. If one doesn't wish to lock the carriage with the guides
(which is also annoying to do, since they have to be tightened with a 5 mm
hex key from underneath, and only the back side locks are accessible), one
can put the tumble reverse in neutral and close the split nut on the feed
screw; the angles are such that even if the screw were as frictionless as
high quality ball bearings, it wouldn't turn under pressure from the carriage.
Unfortunately, with a stock machine, the carriage travel toward the headstock
is limited by the long. feed hand wheel bumping into the motor controller
housing; if that controller is relocated (as some users have done), the next
limit is when the back of the saddle hits the motor cover or the inside of
the splash guard. If one is working close to the headstock, was just
using power feed to make a cylindrical cut, and then (with the lathe power
off, of course) closes the split nut to lock the carriage, one might not
notice (while trying to cut right up to the spindle flange, say) on powering
up the lathe motor that the lead screw is slowly revolving.
The creaking, cracking sounds from the change gear housing serve as an
immediate reminder; I stopped the lathe with the panic button, but it was
already too late; the split nut was locked closed by the force of the lead
screw, and the hand wheel was so hard against the motor controller housing
that I couldn't even take the pressure off the split nut. I tried reversing
the lathe motor, but nothing happened -- that was when I knew I'd broken
something. Okay, obviously I'm going to have to take things apart to
get the carriage free anyway; off with the gear cover, and once again reverse
the motor; no good; the final 80T gear turns, but it doesn't turn the shaft.
Looking closer, I can see plastic shavings extruded by the Woodruff
key. This is Not Good.
Well, it wasn't that bad; I had no significant problems disassembling
the gear train, and though the 80T gear might have been salvageable, I don't
have a chuck large enough to chuck the gear in order to bore and sleeve the
center hole (a 4" four jaw would do it easily, but the 80 mm three jaw that
comes with the lathe is about 5 mm short with the outside jaws). At
this time, I also didn't yet have a faceplate, and in any case I'm not sure
how I'd go about indicating in a gear without any smooth circular surfaces
I can measure for runout. Fortunately, a replacement gear is only about
$5 from LittleMachineShop.com, and with online ordering and even economy
shipping, I had the gear in hand before I had time to miss it properly; the
one setup where I needed slow feed, I used an 65T in that position and lived
with a coarser feed without undue hardship.
From one way of looking at it, in fact, this was a good thing -- a plastic
gear that's cheap to replace (a full set of these gears is only about $30)
is a far better thing to break than twisting or bending a lead screw, cracking
a split nut, or springing the change gear banjo.
Adding a 21T change gear for better metric threads
Honestly, I haven't tried to cut a metric thread yet. Certainly
there are a bunch of gear combinations that will do reasonably acceptable
jobs of appoximating metric threads -- typically with less than half a percent
error, which is plenty close for a thread that will engage for six to ten
turns, as in a nut. However, a specific metric conversion gear is better
than hoping you can come up with a bizarre combination of gears that will
give the change you want and still fit on the banjo. The perfect metric
conversion gear is 127T -- with the inch legally defined as 25.4 mm, this
gives an exact conversion (though if you have an inch based lead screw, you'll
still have to keep the split nut engaged and reverse the lathe for each cutting
pass). Unfortunately, a 127T gear won't fit on the 7x12; it'd be huge,
and there isn't room inside the cover or between axles on the banjo. Next
best are 63T and 21T, both with very small errors in common metric pitches.
LittleMachineShop.com sells a gear that can be made into a 21T change
gear; as sold, it's 12 mm thick, with a similarly thick 14T gear molded on
as a compound set.
Following the instructions LittleMachineShop.com provides on the page
where they list the gear, I faced off the 14T adjunct and reduced the thickness
of the 21T gear to 8 mm, aka 5/16". I then drilled out the center to
1/2", and bored the resulting hole to 15 mm (actually, I left it about .005"
undersize). The plastic of the gear machines like very soft metal;
it forms a curly chip that sticks to stuff from static charge, and chatters
if you don't maintain enough feed; cutting speed seems to like about 50 sfm,
give or take. In the facing process, I managed to push the gear out
of the chuck twice before I had the combination of cutting speed and feed
rate figured out, scarring up the teeth; I trimmed off the burrs with a sharp
knife, and the gear seems to mesh okay (though I haven't, as of this writing,
tried a cut with it).
After machining the hole, turned a piece of 3/4" hot rolled round to 15
mm O.D., then drilled and bored to 12 mm I.D. I parted the piece off
with a hacksaw (don't have a parting tool yet), squared up the ends
and faced to a little thicker than the gear. Check the fit: a little
snug; rechucked the gear and took the finest cut I could manage off the inside,
and repeated until the bush was a light press fit (being careful to deburr
everything before each fit attempt). Two minutes with the hack saw
yielded a slot in the bushing; five minutes with a needle file widened it
until the bushing would slide nicely over the sleeve that holds the B/C gears
on the banjo, without binding on the key. Press the bushing into the
gear -- now it won't go on; the slot closed up a little. Okay, take
a little more off the inside of the gear, until the bushed gear is a snug
slip fit on the keyed sleeve. Finally, press the bushing out of the
gear (had to use the back of my MT2 drill arbor, pushed with the carriage,
as an improvised press -- wouldn't think of it if real force were required,
but this only took a couple pounds; I just couldn't get my fingers in the
hole), an chuck it with the sleeve inside to trim the bushing to the same
width as the gear before pressing it back into its final home.
I think the bushing is looser than it ought to be -- if I hold the sleeve
with the gear on it, I can slip the gear on the bushing with my fingers,
but that may be more force than the gear would experience, especially as
this one would normally be on the stud, where the torque is lowest. I'll
update here when I have a chance to try something like a 1.5 mm or 2.0 mm
threading cut.
