It is not exactly *possible*, so you do the best you can. If
the register and face are turned with only one setup, and the hole for
the peg to fit the hole in the center of the rotary able is bored in the
same setup, they will be concentric. This is the best that you can do
there.
Enjoy,
DoN.
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OK, just thinking aloud here: I get the unfinished adaptor. I attach it to
the RT by means yet to be determined. I center it (and the RT) using an
indicator. I start milling the periphery of the register disk carefully till
it fits my chuck. Feasible?
Actually -- you first center the table on the mill using the
indicator, then once the axes are locked down, you center the workpiece
and clamp it.
But -- if you are centering the plate on the table, and are
clamping it by the OD (using the T-slots), you have your clamps blocking
the milling cutter.
And the ID hole is probably too small to reach through and use
the T-slots at the inner end.
So -- you center it as best you can, clamping by the OD, then
start drilling three or four holes at the smee radius (depending on the
number of T-slots present), remove it from the table, and finish
drilling through. Then you put it back on the table, with T-nuts in the
slots below the holes, or with T-studs passing up through the holes,
then lightly tighten the nuts and re-center the workpiece, and once
centered, tighten them a bit more and then more until they are snug
without shifting the workpiece on the table.
But -- when you talk of an "unfinished adaptor", you mean a
purchased one made to adapt the chuck to a lathe? That will have a
boss which is intended to go around the spindle and then a step back to
a thinner section, so you won't have a flat bottom to bolt to the table.
I would suggest buying some cast iron of the proper diameter and
starting from scratch.
Once you deal with the lack of rigidity from the central boss,
yes. And starting with a cast iron disc, you will need to mill both
sides flat, since the disc will have been sawn from a length of rod
stock, and not really be that precise a surface.
Good Luck,
DoN.
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Hey, i remembered to center *something*. That's progress :-) !
What is the hole in the center of RT like? I was thinking a short 1"-8 bolt
for the adaptor tapered the other end to fit into that hole. Oh, wait, I
would need a LATHE for that!
That depends on the rotary table. Most of them have a stub
version of some Morse Taper in the center. The Emco-Maier 6" one which
I have has a plain cylindrical hole. I've turned (on a lathe) a plug
which fit into it, and which fit into the larger center hole in the
workpiece which I was machining (machining a circular T-slot, FWIW).
Yes -- either to generate the Morse taper which likely fits your
Rotary Table, or to take a standard blank Morse Taper and turn your
threads on the blank end for a hold-down.
Actually -- for what you are doing, something like a 3/4" thick
aluminum would work fairly well.
Good Luck,
DoN.
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The discussion went from turning the diameter of a 4" workpiece in a lathe
to the suggestion of utilizing a rotary table with a small mill.
IMO, a 6" RT is too big for use with the mini mill you have. I have a 6"
Phase II horizontal model that isn't particularly easy to mount to a 6" x
16" table on a 12x20 3in1 combo machine.
Cranking a RT isn't fun either, so I added a small worm drive motor to it,
for making disks without center holes and/or large holes.
FWIW, the base of a typical RT is larger than 6", mine overhangs the 6"
table I mentioned.
If one wanted to side-mill the circumference of a disk using a RT, securing
the disk to the RT becomes an obvious step. If there are no holes in the
disk (that can be used to mount the workpiece to the RT), it's likely that
some shop-made accessory will be required.
I've seen an example of a rigid truss-like bar over the workpiece with a
vertical screw/thrust bearing clamping device which acts like a lathe
tailstock pressing a disk up against a chuck or faceplate.
The truss-like bar needs to be secured to the machine table, elevated over
the workpiece on the RT.
A truss like this could allow some features to be machined on the face of
the disk too, just not near the center.
The indexer type head you mention (no handwheel) is primarily used for
repeatability of indexing to even/odd locations of a revolution.. for
example, 2 opposed flats on a round shaft, 4 flats, hex, or sprocket teeth,
well you get the picture.
The rapid indexers I've seen generally use power to advance the rotation to
the next indexed position, as an automated setup, and some are quickly
advanced by the stroke of a pneumatic cylinder.
For milling in general, bigger (larger diameter) cutting tools require more
motor HP.
At some point, a small motor just can't make a large cutting tool cut
material.
For reading dials, I've found it most important to know how much metal is
removed per tick on the dial (regardless of what the tick supposedly
represents). I can see 1/8" much more easily than I can see thousandths of
an inch. For an precision dimension, pausing to take more actual
measurements reduces errors. If it's an important dimension, I'll sneak up
on the last .001" more slowly/cautiously.
I just enjoy converting good metal into chips, just for the pleasure of it.
I'm not required to achieve any high levels of precision, some times it
matters, most times it doesn't.
Actually I was puzzling about the speed ranges of the various lathes
available and things went on from there.
I suspect a 4" RT will overhang mine.
I was thinking a 3-jaw chuck - most of my plates have a hole in the middle.
The problem I have with the plates is two-fold:
1) The edges. I can handle those quite well now by other means.
2) The faces - that is more tricky and a proper facing procedure with a
lathe would be useful and improve the product beyond what I am getting now.
That is the part I cannot see done on a RT. I was thinking a flycutter 360
degrees but I am told the rate of rotation would have to be very regular
else it will show in the surface finish.
I was trying to determine a centre of a cylinder to drill a radial hole. I
was walking up to it form one edge. It seems that I screwed that up too -
off by 20/1000"!
I agree, but there is a certain need to do things as well as possible given
the circumstances. If a machine will not cut to tolerances, well, so be it.
Live with it or buy a better one. If I the result is poor because I screw up
the math, that is less acceptable as it is totally avoidable.
I forgot to mench, in using small home machines, I've found it useful to
check several areas of the machine's rigidity to get a visual/mental image
of what are reasonable expectations of performance. Performance, as in terms
of expected accuracy relative to dial readings, anticipated cutting depth,
feed rates and the other variables involved.
For starting out with a recently acquired machines, I like to start by
placing a length of stock in the various workpiece and cutting tool holding
devices, and applying finger pressure on the extended (bar of stock usually)
to get a general idea of overall soundness and rigidity of the various
holding devices/mounting points.
These checks are just a bit of diagnostic evaluation to get acquainted with
any issues that might result in poor performance, and to investigate any
correction procedures.
I mention these checks since the topics are proceeding towards adding
various accessories to your machine which may require the mill head to be
raised away from the machine base and table.
The larger the space in the work envelope gets, the less rigid the setup
becomes. Keeping the spindle nose close to the table will likely result in
the most rigid setup.
I think I recall some similar checks that you've performed with our new
machine.
I encountered these issues with the 3in1 machine I've mentioned earlier.
These combo machines have an unusually large work envelope when considering
the fairly poor/minimally adequate rigidity of the machine (particularly the
mill head when it needs to be raised on the column).
Many users probably need to develop particular habits (adjustments etc) of
minimizing the adverse effects of movement/flexing associated with certain
machine characteristics, to obtain the best results that can be attained for
any particular machining operation.
Changes in the rate of feed (pertaining to maintaining a consistent speed
while using a rotary table) in nearly all applications will effect the
surface finish, and even more so on less than perfectly rigid machines.
Operator error/aahhhshit moments happen, but a chunk of metal really isn't
ever totally wasted until it's all reduced to chips.
Other methods can be used to add metal to a dimension or rework/resize it..
welding, brazing and knurling are a few, or one can sometimes adapt a mating
part to fit.
I did this in a sort of random, unfocussed fashion. I leaned on things and
watched the indicator move. It moved less than with the drill press but
still moved.
A principle I should write somewhere on my wall in large letters.
There is one of these machines sitting in the local House fo Tools.
Supposedly someone bought it and then they changed their mind. I have been
looking at it a little more each time I pass. Just out of curiosity. The
impression I had was that it had a more umphy motor than either of their
mini-machines separately. The milling set up looked certainly unstable, but
I wondered if the lathe part of it actually benefitted from the concept: A
bigger swing, bigger motor etc. Although the spindle speeds are limited to
117-1300 rpm if you can believe the web-site info.
The question always is: Is it better or worse than the current method? Angle
grinder with sand paper and then random sander. The first step is the
difficult one as the marks from that often show up at the end when one is
doing 400 grit finish. If they were regular it would not perhaps matter so
much. I tried to spin the plate using an angle grinder on my "red-neck
lathe". The speeds with which I can turn it are quite impressive not to
mention scary but the results were poor.
I borrow heavily from wood-turners: The part, just like their bowls, ends up
different shape and size. I won't even go into rescuing the plates if the
etch goes sideways...
You'll know what you want the machine to do after you finish a job to
taste by hand polishing.
And the "cylinder" was slightly tapered, right?
I'd make two identical aluminum square plates and drill out their
centers to a press fit near the large and small ends of the taper. I'd
scribe a line across one plate first and drill on it, then use that
line to align the spindle with the centerline of the cylinder. The
work could be clamped in the vise by the plates but it would be more
secure if held by the (parallel?) ends of the cylinder.
A step drill will make a smooth hole in thin aluminum and will hold it
in place better than a twist drill when you loosen the vise to remove
the smaller-hole piece, to drill the larger one by itself. If the
cylinder is between step sizes don't drill all the way through, leave
a thin tapered lip that can be pressed onto the cylinder. Or use a
tapered reamer.
You could use extruded flat bar stock. If you can clamp the cylinder
by the ends the plates don't have to be machined to exactly the same
length and the holes needn't be centered, only the same distance from
the lower reference edge.
That's a good idea of yours as long as the diameter matches a punch
size. It would also match a lathe collet.
You can use regular pointed dividers. Set them very slightly large and
observe how far the point can slide down the side of the cylinder. The
point's taper magnifies the motion. The feel is better if you rock the
dividers toward the edge to see if the point catches or slips over it.
Frugal Yankee here. I stretch two meals out of one can of soup with
rice. Home-made boring head:
http://picasaweb.google.com/KB1DAL/Tools#5277053481061578594
You can see the pattern my Toolmaker surface grinder leaves.
I'm not sure how much of this technology you are aware of, or exactly
what you are or will be doing, so I briefly describe how various
accessories solve problems. Plus I hope other beginners might find it
useful, or real machinists disagree and suggest better methods. I
watch others carefully and read a lot, but a fair amount of what I
write here is home-grown, see above.
Yes, in time and materials lost. I consider it an educational
expense.
Jim Wilkins
"Proper" being in the eye of beholder :-) I see much experimentation in
future.
I think the taper was minuscule. Less than 1 mm over 25 mm.
I am a bit confused here. The purpose of this is a) better workholding of a
slightly irregular shape, b) easier centre finding, or c) both?
OK. Will try.
Coincidentally yesterday I found a DVD on making a boring head for "next to
nothing". OTOH if I put the $40+ for the DVD towards a new boring head, I
shall have a half of it already! Not to mention that the "next to nothing"
concept probably does not apply to the skill level.
Did you design your own boring head or did you use somebody's existing
design. What is the capacity (how big a hole can you bore)? Of course for
the MT? taper - you need a lathe, right :-)?
Makes sense. I have seen a boring head in use both on a lathe and a mill. I
have in fact thought of a project I would need one for. However, if you gave
me one right now I would have to refresh heavily on the nitty-gritty of its
use.
Maybe I should buy a few more DVDs anyway.
That's a great looking boring head, Jim. If you have drawings, dimensions
etc, the details would be an excellent addition to the dropbox.
When I had an interest in getting a boring head, I stumbled upon an eBay
seller that had lots of the 3 primary parts (bodies, slides and screws) for
sale, so I bought some of them.
These were 2" models made in the USA by a company named Mesa from San Diego
CA, that seemed to be liquidated finished parts of a discontinued product
line.
The heads only needed a set of setscrews, a gib and a shank to be working
tools. The only finished dimension that wasn't completed by Mesa was the
1/2" bar holes needed to be reamed/finished to 0.500" for an interference
fit.
The 40 tpi feedscrew heads didn't have the graduations marked, like a
store-bought one does.
It was carved out of likely-looking scrap, the "plans" were a catalog
photo. I guessed at the internal details, and as usual made each new
part to fit the previous ones. The screw is 1/4-20 so the brass dial
has 50 lines, the longer ones indicating 0.010" of hole diameter. The
hex adjusting hole in the end was broached with an Allen wrench ground
flat. The collar that forms one side of the bearing was brazed on. The
rest of the bearing is on the back of the dial. The dial locknut is
thick enough to use a standard screwdriver but a flush one might look
better.
The integral gib probably should have been a separate piece held down
by two cap screws. It required closer tolerance on the finished
dovetails than I could manage, so I opened it up to accept a strip of
shim stock, which works OK but slides out frequently.
Eventually I found a boring head on sale at Travers Tool with a B&S #7
arbor that fits my mill; the home-made one's arbor was MT2 padded with
aluminum tape, removed now to use it as an offset tailstock in the
lathe. They only list B&S #9 now, maybe I got the last #7.
The screw on the real one is 7/16-20 and threads into the body. A
groove in the head of the screw engages a rib in the bottom of the
slide. Since the screw is one piece there is room for numbers, but it
sinks back into the darkness as the boring bar advances.
Jim Wilkins
Unless you have located the spindle over the axis it probably
won't. And with the tapered workpiece, it is likely to encourage
skidding. With a totally horizontal surface (flat) you don't have as
much chance of skidding off center, and the center dill will work quite
well.
The other advice -- very shallow milling on the top surface
gives you both a narrow flat, so things won't want to walk, and makes it
easier to judge the true center. But your tapered workpiece with the
ability to tilt under pressure is a problem anyway.
Ouch! (But then, you aren't measuring from the Z here.)
The same trick can be used on a lathe to check whether the
tailstock is offset or not. Trap it between two hardened centers, one
in the headstock and one in the tailstock, and an angle will tell you
which way to correct. (You may be wondering *why* the lathe has the
ability to offset the tailstock. This is one way of turning tapers,
between centers. Lathes with taper turning attachments are
significantly more expensive. But -- if you are doing multiple parts,
you need to make sure that the distance between centers is the same for
each one, or the taper will vary.
:-)
I've not yet tried it, because the ruler technique works well
enough most of the time, but it is really a good way. If you are doing
a lot of the same kind of part, you can either drill undersized, ream to
just barely clear the drill bit and harden, or drill oversized to accept
hardened drill bushings -- so the sides of the drill don't enlarge the
hole as you work, introducing the possibility of more and more error.
Yes -- tilted surface and perhaps the spindle not at true right
angles to the table, so a longer drill will touch down at a different
spot than a stubby center drill.
Hmm ... what *store*? One which would stock Starrett tools, or
one which would stock only the cheaper tools?
It is. I use them for a lot of things -- including scribing a
line parallel to an edge of the workpiece.
Well -- I once saw an excellent answer to that sort of comment.
This was in alt.folklore.computers, IIRC, and a young poster (who had his
girlfriend in his dorm room at college, and was posting between
sessions) commented that it was nice to have two more erogenous zones. :-)
But still get that first spilt-point drill -- just so you can
see how much nicer it drills. :-)
Enjoy,
DoN.
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Basically, the speed range is determined by the maximum swing
(the maximum diameter which can be rotated over the bed). It has to be
slow enough to produce a SFM (Surface Feet per Minute) rate within
reason for turning the workpiece material with HSS (High Speed Steel).
So this determines what is a reasonable minimum speed.
Maximum speed is determined by the smallest diameter workpiece
likely to be used, and perhaps boosted by using carbide instead of HSS
as a tool material.
As a result, large lathes tend to start with very slow speeds,
and go up to speeds which are scary with the size of chuck which they
will handle. (My Clausing will go up to 1600 RPM, which is quite scary
with a 10" 4-jaw chuck.) It goes down to 35 RPM.
A secondary factor making slow speeds very useful is when
single-point threading to a shoulder. While your reaction time can be
improved with training and experience, it is safer to start with a very
low speed with anything but the finest threads. (Perhaps 20 TPI on down
to 224 TPI or so you can use higher speeds, but when you plan to cut a 4
TPI thread, and are turning towards a shoulder, you really need to be
able to disengage the half nuts before the cutter crashes into the
shoulder.
A lot of the small import lathes do not offer speeds low enough
to handle coarse threading unless you already have good reaction times.
If it is mounted directly to the bed's T-slots, yes. If you
make a mounting plate, you can handle a larger one.
BTW How much space is there between the vertical dovetail on the column
and the back of the table with the table cranked as far back as it can
go? This can determine what overhang you can tolerate.
A 3-jaw chuck can have the jaws expanded inside such a hole to
grip while turning the OD -- but the trick is how to make that hole in
the first place. If you use your older methods to turn the OD close to
size, you can then use reversed jaws on the 3-jaw chuck to grip it by
the OD while you machine the ID on the mill. A lathe would be better
for this.
And -- with the plastic gears, at some point a larger cutting
tool will result in striping the gears.
Get spare plastic gears *before* you need them or you may be out
of service for some time while they are ordered.
O.K.
1) You can't use a fly cutter on one which is held by a 3-jaw
(or 4-jaw) chuck without risking cutting the jaws. (Unless you
set up a chuck with soft jaws, and mill a step shallower than
the thickness of the workpiece so you can access the entire
surface at once.
2) Using a fly cutter typically will show an artifact in the
finish a short distance from the edge as the cutter "rings" from
the impact as the cutter moves from air to cutting metal.
3) I would consider using a smaller cutter and making multiple
passes at decreasing radii until the entire surface is cut to
the desired thickness -- and then try the finish called "engine
turning" -- an abrasive embedded in the end of a dowel, or an
abrasive rubber spin in the chuck, brought down onto the
workpiece surface (making a series of concentric rings) then
lifted, and the table is rotated about half the diameter of the
rod and it is brought down again. Repeat until you have a
complete circle, then move in by perhaps 3/4 the diameter of the
rod and repeat. It can make a high-tech *looking* finish,
although you can do it with only a drill press and a rotary
table.
I don't think that you will be able to get a better finish than
that with a mill and a rotary table.
Every time I see you display thousandths of an inch in fractional
form I get slowed down in my reading. The common way in machining to
show such dimensions is as a decimal fraction with a leading "0" if
there is no integer part -- so that would come up as '0.020"'. Among
other things which slow me down is having to make sure that there are
only three zeros after that one.
The leading '0' before a decimal point (if there is no integer
part) is to make it more difficult to miss that there is a decimal point
there at all.
You mentioned "howlers" in another article. This is not exactly
a "howler", but it is awkward at best.
Fractional notation is normally used for powers-of-two
fractions: 1/2", 1/4", 1/8", 1/16", 1/32", 1/64", 1/128" and multiples
of those. 1/128" is the finest that I have ever seen used in machining,
and that only with very old tools. And of course, since fractions are
more difficult to work with (just listen to the Metric advocates),
decimal fractions are preferred -- especially since the micrometers and
modern calipers read in decimal fractions. (Some recent digital
calipers have taken a step back -- approximating a reading as the
nearest fractional size as an option.)
If the machine will not cut to tolerances may *require* buying a
better one -- depending on how necessary the tolerances are. For your
project making sundials -- no real problem I think. For someone making
parts to repair or built a machine -- if it won't cut to tolerance, the
part you make is just so much scrap metal.
Good Luck,
DoN.
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My initial point was that there is a discrepancy between the lowest speeds
of the mini- and bench lathes and the swing. The speeds were too high to
accommodate steel workpieces for the given swing. This has been addressed in
at least some of the mini-lathes but by no means all. I know at least one
person found a way to slow the minimum speed down in a mini-lathe by
tweaking the electronics.
1.342"
Now you tell me :-)!
Good thought! Like the proverbial ostrich I have stuck my head in the sand
and have not even enquired about spare parts availability.
I was thinking for the surface finish I could stick the whole plate to
another plate (clamped to the table) by a double sided sticky tape like they
do at MIT.
OK, I have not considered that. Or maybe just buy a lathe ...:-)
But seriously, I have enough now to get going on *something*. One can
theorize only so far.
Not a howler. Perhaps a faux-pas. I will endeavour not to slow you down.
As far as I am concerned, the whole imperial system of measurment can be
sunk into a deep hole and covered by a thick layer of excreta. But I have to
admit that on some days I do not feel as moderate...
Still, you have not lived until you grew up on a decimal money, then had to
learn to give change in pounds, shillings, pence, half-crowns and farthings
and *then* had to relearn the decimal system *using the same coins*.
Nietszche was right!
Absolutely. Style over substance any day (pun almost intended...)
O.K. The mini lathes are not good examples of much of anything. :-)
And just running the speed down by slowing the motor loses
torque which is most needed at large diameters and slow speeds. Serious
lathes (assuming belt drive) have both multiple steps on the pulleys to
get multiple speeds (or a continuously variable speed pulley, which
tends to consume horsepower compared to a fixed speed belt) and a back
gear, which reduces the speed from a given belt setting by something
approximating 6:1, and boosts torque at the same time.
But *really* serious lathes (which I don't have) have gearboxes
in the headstock to give all the speeds, and typically only one belt
speed. These will produce more torque than most belt drives, which is
both good (when needed for cutting large tough workpieces), and bad
(when you have a crash, you don't have the belt slipping to minimize
damage to the machine). For a starting user, belts which will slip are
a better choice. :-)
Good -- you can add to the maximum size of the rotary table then.
This helps counter the overhang beyond the diameter of the table. And
measure the overhang needed based on an orientation for the rotary table
which will point the crank towards you -- and so the crank won't hit the
table when you try to turn it.
:-)
Right *now* -- open the top and count the number of teeth on the
plastic gear. (If it is all metal, that is different, but if plastic,
get replacements *now*.) Then measure the OD of the gear, and the width
of the teeth (thickness of the gear) so you will have some information
when it is time to order more if the maker no longer supports it. You
may need to try your hand at cutting gears yourself -- which will need
the rotary table or better an index/dividing head, the proper form
cutter (you'll have to know whether it is a metric "module" gear or a US
gear, and the pitch, and the pressure angle (determined by the shape of
the teeth). Better if you can buy replacements without having to take
out a second mortgage.
Hmm ... perhaps the grinding sounds when you were drilling was
the gears reacting to too much torque requirement from the drill bit.
O.K. That could work -- if you stick to a fairly small diameter
cutter. The larger the diameter, the greater the forces which will be
trying to make the tape slip.
Good -- get experience. But don't include destroying the
plastic gear (assuming that yours does have one) until you have spares.
[ ... ]
I suspect that it slows others down too. I just was one who was
replying to your articles, and happened to think of mentioning it when I
encountered it for the Nth time.
:-)
I grew up with it -- and most of my machine tools are only
calibrated in that system, so a complete change would be difficult. I
*do* make things to metric dimensions when it makes more sense, but it
is more difficult (especially threading) except on the Compact-5/CNC
which has a switch to go between modes.
Ouch! I know the basic units and their relationships, but a lot
of the names for the various coins tend to slip away -- especially when
the coin may be marked "N pence" or "N shillings", but be commonly known
by a name such as a "Bob". :-)
I which of the things which he said?
Enjoy,
DoN.
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