BORING BAR HOLDER: I have designed a holder that will take the 3/8" diameter shank boring bars I already own. If you prefer or own 1/2" shank boring bars, the holder is simply drilled and reamed to accept that size tool. To make the holder you need a nice cube of aluminum about 2" x 2" with all surfaces milled to true right angles. A central 3/8"diameter tool post hole needs to be drilled from the top all the way through the bottom. Take the block and mount it on the tool post, squaring it to the head stock and lathe axis. Move the cross slide to place the center line of the lathe at 5/16" from the left edge of the block as you look at it from the top. Center drill, drill and ream to a 3/8" diameter (or whatever size you need) through, horizontal hole. The height of the hole is set automatically to the lathe's central axis as the block is drilled, mounted on the tool post. Drill and tap two or three vertical 10-32 set screw holes in line with the horizontal tool hole and after de-burring and a little clean up you are ready to use your new boring bar holder. Because the tool holder will be able to rotate on its mount, you will be able to orient the cutter so it geives the best performance in any given situation such as boring a blind flat bottomed bore, a through bore or even on with a step or shoulder. For really smooth boring finishes, use the auto feed feature on your lathe making sure it is disconnected as soon as the tip of the boring bar emerges through the other side of the bore. You can also bore in reverse by begining your cut deep in the bore and drawing the tool back out. You 7 x 10 easily accomplishes this with its multi directional carriage auto feed feature. The resulting finish will tend to be much smoother when the tool is draw back, which results in a planning action rather than pushing its way through the metal. Many operator will face a workpiece byt begining the cut at the workpiece center, drawing the tool out toward the edge. Give that a try!
CUT OFF or PARTING TOOL HOLDER: Basically of the same construction as the boring bar holder except that instead of a hole for a shank, a 1/2" wide horizontal slot is milled along one of the sides to hold a standard 1/2" x 3/32" x 4" cut off tool bit. The slot needs to be about .010" shallower than the overall thickness of the cut off tool so that it can be tightly held in position by a 3/16" thick plate aluminum cover. The slot's upper edge must be at the lathe center line. With a 1/2" diameter end mill chucked and running true to the spindle, jack up the tool holder with 1/4" square lengths of key way stock or 1/4" tool bits. Place the tool holder over the shims and lock it in position so the front face pointed toward the spindle is square to it. Proceed to mill the slot, checking after every pass with the cut off tool blank for fit and depth. Stop when the tool steel is almost flush but still proud by about .010". Cut a 2" x 1" rectangle of 3/16" aluminum and attach it centered over the slot with double stick tape. Locate and drill four #21 holes, one at each of the four corners of the rectangle. Just space them evenly. Drill them 1/2" deep into the tool holder. Separate the cover and enlarge those holes to a #11 and tap the #21 holes on the block for a 10-32 thread. Insert the cut off tool along the slot letting it protrude about 1/2" or less and install the cover by screwing it in place with four 10-32 cap screws and flat washers. To use the tool, you must make sure the blade of the tool is at perfect right angles to the bed or parallel to the cross slide. Make sure that the part being parted protrudes the minimum amount beyond the chuck to permit it to be cut with the tool clearing the rotating chuck. The work itself needs to be tightly secured or it might creep forward of backwards causing a tapered parted surface. The slowest possible rotation speed, steady tool feed rate and plenty of lubricant are what's needed to prevent any possible chatter during the operation.
FACE PLATE for TURNING BETWEEN CENTERS: The faceplate is made by taking a 3" diameter slice of aluminum about one inch thick and facing one end until it is true, followed by a turning cut across the sides as close to the chuck jaws as possible. Reverse mount the piece griping it by the freshly turned perimeter and turn off the remainder. Center drill and drill out to a 1/2", then begin to bore out the hole to about 1" diameter. Face this side off until true, finished turning the out side and chamfer all the cut edges. Face cut to create a recess from the hole, outward to match the flange of the lathe spindle back plate. It must be as close a fit as possible. Locate the three mounting stud holes and drill them to about 1/2 the depth of the faceplate's thickness. Tap them to 1/4 -20 and insert three 1" long corresponding studs (threaded rod is good enough). Mount to the back plate with three 1/4-20 hex nuts. Insert a #3 morse taper dead center into the spindle and check that it does not interfere with the face plate bore. If it does, enlarge it by boring out a bit more. There will be several mounting holes and slots cut on the front surface of the faceplate to accept a driving dog and clamping bolts for driving the workpieces. A 1/4" wide slot about 1/2" deep is milled across the full center line of the faceplate and three equally spaced pairs of threaded 1/4- 20 holes are drilled at right angles to the slot, also along the center line, three on one side of the hole and three on the other side. In this way, work can be either clamped to any of the pairs of threaded holes or driven between centers. Clamps can either be purchased or shop made.
DRILLING CHUCK and ARBORS: The 7x10 features morse tapers in both the
head spindle and tail stock. The head spindle's #3 morse tapered bore is accessible
only after removal of the chuck from the spindle back plate. The overall bore of
the spindle is 3/4" diameter but when using the stock chuck, only about 11/16 "
diameter work can be passed through the spindle. When the face plate is installed,
the #3 morse taper dead center is inserted and seated in the spindle bore. The
center drilled workpiece is held snugly between the spindle dead center and
allowed to spin freely against the tail stock live center. The dead center only
serves to hold the work in line and by itself cannot provide enough driving force
to turn it so the work must be clamped to and driven by the face plate. Work that
is held between centers can be removed and replaced numerous times between
each separate machining steps, being able to maintain its concentricity to the
spindle axis. The morse taper system is self centering so it is the best system to
use when the highest repeatable concentricity is desired.
To use the tail stock in drilling centered holes on the end of chuck held
workpieces, a drill chuck with a morse taper arbor is needed. I have two chucks of
different capacities in constant use. The smaller will handle drill bits from 3/8" to
#80. These chucks also have a Jacobs tapered end for mounting to the arbor.
Different size chucks will also have different size arbor mounts or Jacobs tapers.
Arbors are available in any morse taper to Jacobs taper combination. The correct
Jacobs taper designations or code is stamped on the side of the drill chuck so
there should nor be any confusion as to the correct tapered arbor to use. Using one
of my chucks as an example: 1/2" chuck has a 33JT mount and my tail stock has
a #2 morse taper. The correct arbor for this chuck is a 2MT / 33JT. There are also
morse to morse taper sleeves. These are used to adapt a smaller tapered tool to a
spindle or tail stock with a larger morse taper. An example would be a #1 morse
taper arbor tool used to fit a #2 or higher tapered hole. The smaller one fits inside
the larger one. There are some drill bits that come with a morse tapered shanks.
The smaller sizes are always in #1 morse taper and when they reach the 1/2" size
they are offered in #1, #2 and so on. If you do a lot of drilling in a few specific
sizes, it might be a good idea to obtain a few of these bits. Even if you have to buy
one in a #1 and another in the #2 size, you can always use an adapter sleeve. My
tailstock is #2 taper so to be able to use the #1 shank drill you would simply insert
it into a #1 / #2 adapter sleeve. The #2 tapered bit would obviously not need it and
it is simply inserted directly into the tail stock taper.
The only glitch with my lathe and use of morse tapered arbors is that
they need to have the locking tangs cut off the rear of the arbor or they will
simply be too long for the short morse bore on my tail stock. Just cut them off
with a hack saw ( if they are soft ) and finish them smooth with a fine file or on a
bench grinder. Some companies offer short shank morse tapered arbors but these
are pretty rare.
MORSE TAPER TAP DRIVERS: There are even morse tapered tap drivers. These are somewhat like a collet in that they are split lengthwise and have a square hole to accept the drive end of the tap. As they are inserted into the tail or spindle hole and pushed in, the collet closes and tightly clamps the tap in place. Again, these are rare and I've only seen them in one company's catalog and they tend to run about $12.00 a piece. Only one size tap can be driven by a given adapter and they are available in different morse taper sizes as well.
SHORT SHANK or SCREW MACHINE DRILL BITS: Another drilling option when not enough clearance is available between the drill and the workpiece such as when drilling out to a fairly large diameter with what can be a fairly long bit. I suppose you could cut off a portion of the drill bit shank ( not fun and certainly wasteful ), or you can simply chuck up a short shank screw machine equivalent size drill bit. These are approximately 1/2 the length of the common every day " jobbers " style bit. They are usually sold individually or in sets only through the larger tool houses. Prices will average about 10 - 20 % higher than jobbers length, I suppose because manufacturing practices tend to make anything that differs in any way from normal more expensive. If I try to drill an item clamped to my compound vise on my very small bench top drill press, I soon realize the need for one of these short shank bits.
CIRCUIT BOARD CUTTING - MINIATURE CARBIDE DRILL BITS and MILLING BITS: These mostly 1/8" shank bits are normally used in high production computerized drilling machines to locate and drill the hundreds of tiny holes on a common circuit board. They are available as twist and milling type bits. They are not cheap by any stretch of the imagination and a full set may run you into the hundreds of dollars with the average single bit costing from $5. to $10. I, being very cheap in nature, could not conceive parting with that kind of loot so I began to look for alternative sources for these. Several sources for reconditioned bits are out there ( re-sharpened bits are often as good or better than when new ). Prices will range from as cheap as $5 for twenty to $30 for a 50 bit box.
REAMING on the LATHE: The creation of near perfect holes to accept round
objects as a press, running or free running fit is probably best done by reaming to
final size. After the hole has been drilled with progressively larger drill bits to a
diameter .005 to .010" undersize, the last remaining bit of metal is removed by
slowly and evenly running a reamer through the hole. Since holes reamed for a
press fit are usually intended to hold some sort of dowel or split pin, acting either
a post for something else or to securely hold two components together, the hole
needs to be reamed to what is called a minus or under size. Reamers are available
as plus one or minus one as well as the exact fractional size, meaning that they
are available as one thousands under and one thousands over the diameter or the
pin or shaft to be inserted in the hole and the exact diameter as well. Say for
instance that you are in need of a pair of finished bronze bearings that will accept
a .250" diameter shaft as a free running fit. Shafts for your projects should always
be made out of ground drill rod because of its inherent accurate dimensions
usually within .0002" from the stated size. I would clamp the top bearing blocks
together and after centering the punch mark, drill them to the required under size
condition through both of them to maintain the hole alignment. For a running fit,
such as that required in a crankshaft, I ream the hole to a final size of .251". The
resulting hole will accept any round object of .250" diameter as a free running fit.
The same would apply if a press fit condition is desired. The hole would be
reamed with the .249" reamer, the resulting fit would then be a press fit. A pin
can either be pressed in with a vise or the pin can be frozen in dry ice which will
cause it to shrink slightly and the work heated in very hot water to expand it,
allowing it to be slipped into the hole. Once the pin warms up and the work cools
down, it will effectively lock itself in the hole never to be removed again.
Reaming operations are best performed at the same time the holes are
being drilled to ensure that everything remains perfectly aligned. After locating a
hole position and center drilling it, the hole should be drilled out and finished to
size by reaming without shifting the workpiece from the vise. Reamers are simply
attached to the tail stock drill chuck and used in the same manner as drill
bits.
Reamers are available in several designs and grades of steel. At the least,
they should be in high speed steel although they are of course also offered in
carbide. The flutes of a reamer are precision ground to insure their ability to
produce near perfect holes. Flutes can be straight or spiral. For the vast majority
of work, I do not need anything more exotic that the simplest chucking reamer
with straight flutes and high speed steel body. All of my work involves the
machining of brass, aluminum, mild leaded steels and the free cutting stainless
steels. So I do not have the need for the more expensive spiral fluted or carbide
reamers. The actual reaming operation is done just like drilling except that the
rotation speed should be only 1/2 of the drilling speed, plenty of the correct
lubricant or cutting oil (not needed with brass) should be used and the tool must
be fed in and out of the work as smooth and steady as possible to create the
cleanest and most accurate hole.
THREADING or TAPING ON THE LATHE: A simple hole threading procedure
proceeds as follows: After facing the surface of the work to be threaded, the tail
stock center is replaced with a drill chuck mounted on a morse tapered arbor. The
proper size center drill is chucked and the hole is started by advancing the drill
tip into the rotating work, turning the handle on the tail stock to drive the tip of
the center drill into the work. You only need to drill deep enough to mark the spot
being drilled so you machine a 60 degree starting hole. When you first begin to
center drill something, you must start the drill tip into the work very slowly to
insure that it will start up exactly on center. If you force it into the work, it may
have a tendency to deflect slightly out of center, although not to the degree a
regular twist drill bit might. After the center drilling is done, you can safely
proceed to drill the hole to the correct taping diameter called for by the size
thread you wish to cut. Drill to a depth about 3/32" to 1/8" deeper than the length
of the threaded portion you require as the tip of a normal tap is ground to a taper
to ease the threading process. Because the first 3/32" or so do not produce a full
thread, you have to provide a corresponding longer hole so you end up with
needed amount of thread to fully accept the screw you are using in the hole. There
are taps that will cut a thread almost to the bottom of the hole and these are called
bottoming taps. They can do this by omitting the tapered tip and can reach and
subsequently thread to almost the very bottom of the hole. A hole requiring the
use of one of these taps should first be started with a tapered tap until you hit
bottom and the final two or three threads cut with a bottoming tap as it is very
difficult to start a thread with the bottoming tap alone.
The tap itself is held in the same drill chuck used to drill the pilot hole to
ensure that the thread is started straight and into the hole. Turn the head stock
chuck by hand while you advance the tap into the work at the same rate it is
entering the hole with the tail stock advance. Don't forget the back off the tap
after every 1/2 to full revolution to break and clear out the chips produced. Plenty
of the proper type of cutting fluid is a must for clean and accurate threading.
Brass, off course, does not require any kind cutting or tapping fluid. Once the first
three to four threads have been cut with the aid of the tail stock drill chuck, the
tap can be removed from the chuck and driven with a tapping wrench supported
in line with the hole by the tail live or dead center. After the hole is completely
threaded and the tap has been removed, the opening should slightly counter sunk
to remove the burrs created by the tap to allow an easy start for the screw or bolt
meant for the hole. You could have also countersinked the hole to begin with
before tapping. To thread a deep hole that will for instance secure a flywheel to a
small crankshaft with a set screw, you first drill the hole from the top edge of the
flywheel hub until it emerges through the crank shaft hole with the tapping size
drill. Enlarge the hole from the top to a depth about 1/4" from the center hole
with a clearance size bit so you won't have to tap the whole hole (can be difficult
with small taps) since just the last 1/4" portion of the hole actually needs to have
a thread.
OFF CENTER TURNING: The time will come for either a hole or a
stepped shoulder to be machined off set from center. Such would be the case in
the nachining of an excentric cam for an engine. The cheapest but not the most
accurate or easiest way is to use a face plate and bolt or clamp the workpiece to it,
manually offsetting the work so that the punch mark is brought to the lathe center
line. A more convenient and accurate method is the use of a four jaw chuck with
independently adjustable jaws. You will also need a dial indicator and some way
to hold it to the tool post or the lathe bed. Many magnetic dial indicator holders
and stands are available and they will normally set you back from as little as
$12.00 for an imported one ( Asian ) to as much as $80.00 for a big name brand. I
myself like to use a simple cylindrical threaded magnet that has a 5" length of
steel rod screwed to its central hole, onto which I can attach my very old but great
STARRET dial test indicator. Unlike the normal dial indicator which reads .100"
per revolution of the needle, a dial test indicator usually reads about .015" in two
directions thereby giving a much more sensitive and accurate reading on any
workpiece's position. After the punch mark has been centered by adjusting the
jaws of your four jaw chuck to bring it as close to center as you can by eye, chuck
a center finder with a pointed wiggler tip snapped into it to the tail stock and
bring the point to bear into the punch mark. As you spin the workpiece by hand
you will be able to see how far off center the punch really is because the wiggler
will scribe a circular arc of twice the error. Place the test dial indicator and its
magnetic base on the cross slide or lathe bed and adjust the needle so it is
touching the side of the tip of the wiggler as close to the work as possible. Rotate
the work and watch the dial to see just how much you are still out of center. As
you continue to turn the spindle, you will note the high and low points on the dial
and it is at that point the work needs to be shifted over toward the low point.
Continue to do this until the readings are within .001" or less. Now you can turn,
face off, drill a hole in that position or perform any machining operation your
workpiece requires. One thing to keep in mind is that the work has now been
placed away from center and will more than likely vibrate if anything other than
the lowest speeds are used while machining it. In a large industrial machine we
wouldn't need to worry about this kind of vibration but in our light weight lathes
it may be somewhat of a nuisance.
Cams of many configurations and shapes can be easily milled on the
lathe by both mounting them off center and indexing their position within the
jaws of the chuck. This is used in the building of timing cams for model gasoline
powered engines of the " Hit & Miss " breed to regulate the opening and closing
of the ignition points and the opening and closing of the intake and exhaust
valves. The same technique of aligning a workpiece to a point other than center
can be used instead to truly center a shaft or other round shaped workpiece. Most
three jaw self centering chucks, excepting those in the hundreds of dollars range,
do not perfectly center the work, but instead bring it to within a few thousands
from center at any one time. The problem becomes evident when the work needs
to be removed after turning to do another machining operation elsewhere and
then returned to the chuck, it will more likely not run true. Unless you marked the
work and keyed it to one of the jaws so it can be replaced to the same exact
position, you will pull your hair out as well as mumbling a few well chosen
expletives, as it will more than likely not run true upon returning to the chuck.
Use the four jaw chuck plus your dial indicator to place that round stock to no
more than .0005" from center. This time you just place the indicator's feeler so it
touches the top of the stock you are centering. Center drill the end after facing it
and reverse it in the chuck. After re-centering it as before, face and center drill
that end. Now you can machine that shaft all you want by driving it between
centers. Even if you remove it for other milling operations, it will be
automatically re-centered on returning to the lathe as accurately as when first set
up with the indicator. That is one of the atributes of between centers turning, it is
always used in the production of the centers themselves, drill bits for metal and
woodworking, threading taps an a myriad of other cutting tools that must be made
as true as possible.
MILLING on THE LATHE: Not only can the basic lathe be used to perform turning, facing, boring, drilling, reaming, and threading, but it can also serve as a pretty good horizontal milling machine. Unlike the use of a drill press, whose spindle and quill is not really designed to be used in milling, the lathe spindle is entirely suitable for this kind of work and the normal run of the mill three jaw chuck makes more than an adequate milling bit holder. A dedicated end mill holder with a morse tapered body would of course be the pref\ferable method for holding an end mill. The only remaining problem is how to securely hold the work and present it to the milling bit. So called vertical milling attachments are available from most lathes either as a manufactured additional piece of equipment from the makers of the lathe or from other independent manufacturers. These units consist of a small vice attached to a dovetailed and "T" slotted vertical slide just like the cross slide on your lathe. This is then attached to a base unit that slips over or into the tool post bolt and locked in place in the same way as the tool holder would be. As you can imagine, the unit can be swiveled on its vertical axis from side to side to provide a wide range of horizontal angles to the lathe face. The unit made by "Palmgreen" also provides the option of vertical or lateral tilt of about 15o to either side. These two movements will allow you to attain a wide variety of angles that would normally require you to use angle blocks under the work held within the vice jaws. The vice itself will hold the work only as square as its jaws and bed ways are machined. The Palmgreen unit is by far the most accurate for the money that I have come across. The addition of the milling attachment to your setup immediately provides you with the third axis of motion required if any serious milling operations are to be considered on the lathe. A much lower cost aleternative is to use the small two inch travel milling attachment sold for the Taig for $55-$60. This unit will attach flush against the top of the cross (not the compound ) by simply making two 10-32 threaded holes to match the mounting holes of the Taig unit. I just placed the unit on top of the cross slide and aligned it so the vertical slide is flush against the left side of the lathe cross slide. With a #10 transfer punch, I marked to the two locations for the holes. There is a bit of play in the mounting system so the vise can be aligned perfectly during use. If you do not yet have one of these extras for your lathe, you can still perform certain limited milling jobs by doing the following. On lathes that have a flat, slotted cross slide carriage like some European imports, you can clamp the work to it in the position it needs to be in relation to the cutter. The height adjustment is obtained by placing the work on parallels or pieces of key way stock in the right combination of thicknesses in order to raise the work the required height to the bit. Of course since no vertical slide is available to move the work up and down as it is being cut, the work itself will need to be oriented so that all the milling cuts are achieved only by lateral movements of the cross slide. The work also needs to be passed against the rotation of the cutter and never with, so always plan each of your milling cuts with that goal in mind. Some of the many types of cuts that can be easily done with the use of the vertical milling slide / vice attachment are: Locating & drilling holes by X & Y coordinates, tapping, boring with an adjustable boring head on the head stock, vertical and horizontal slotting, milling of steps either straight and at simple or compound angles, dovetail slotting, key way slotting, surface milling with end mills or fly cutters, side milling. These are just a few of the many types of cuts that you can instantly add to you lathe's repertoire to make it the most important and versatile tool in your shop.
DRAW BAR for THE HEAD SPINDLE: Since the headstock spindle has a common #3 MT in it, you can use quite a large variety of available tooling on it. Tapered mill holders for all the common end mill shank diameters are readily available through most major mail order tool houses as are special Morse tapered collets. Unlike a dead center that is held in the tapered bore by the pressure of the workpiece held between centers, a mill holder or drill chuck on a MT mount must be securely held tight in the spindle taper with a draw bar. Simple friction will not do here. A draw bar is nothing more than a rod that threads into the back of the Morse taper of a tool so as the tool is pressed into the spindle, the end of the draw bar can be drawn tight against the outboard end of the spindle with a large nut and washer or any other similar device. This keeps the tool from possibly spinning in place or worse yet, becoming loose and flying out of the spindle. The second scenario could more likely happen during milling as the tool tends to be pulled into the work as the cutting proceeds thus lossening itself out of the spindle mount. A regular drill bit has to be forced into the work in order to cut so the tool's tapered mount is constantly being pressed into the spindle bore. In order to make a draw bar, you first need to measure the distance between the rear threaded end of the Morse tapered mount of the tool as it sits in the spindle bore and the outboard end of the spindle plus about two extra inches to allow the draw bar locking nut or handle to screw into. I made mine out of standard threaded rod. The mundane hardware store variety will do just fine. After cutting to rough length, I machined the ends to a smooth, chamfered finish. Once that was done, I began to concentrate on designing a locking device for the draw bar. Since the spindle of my 7 x 10 Minilathe has a 3/4" bore, I then machine a 2" length of 1- 1/4" diameter aluminum or steel stock to create a 3/4" diameter, 1/2" long shoulder that's a snug fit into the spindle bore. Then I drill a hole through the center of the stock to allow the draw bar to pass through. I flip the work end for end and finish face the rough end nicely. A large nut epoxied to a 1-1/4" diameter washer is all that is needed to finish the project. In use, you just insert the tool and draw bar through the spindle, slip the centering sleeve over the draw bar rod so it sits into the inner bore of the spindle. This has the advantage of perfectly centering the draw bar so there is no vibration during the turning process. A draw bar is a pretty standard component on any milling machine set up and now it can be an important part of your lathe when used as a milling machine.
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