Well - Now Welcome to the  "KNAELL-THREADER-2"   Website.

(bearing block pic here eventually)

As you can see we are still hardware oriented

Pardon my mumbling here, this work is in progress. Any dates entered will be format:<yymmdd>

As a quick start here, this kit consists of the items shown. Click on Kit Contents to see a list of these items. (As of <090219> this pic is missing the 1/4" clamp collar and a second 7/64" hex key).
             

--- Discussion/Comparison of the new Threader-2 versus the old one. ---

Well, to start with a new term will be coined here.   As a result of the way this threader is built, the nut that the leadscrew engages is not a "split-nut" like its counterpart in most lathes with leadscrews.   Most lathes have a two piece nut that opens up into two halves and allows disengagement of the carriage from the leadscrew.  This articulated nut is very descriptively called a "splitnut" in these lathes.  This threading attachment, the Threader-2, instead leaves the nut on the leadscrew but disengages the nut from the carriage with a clamping mechanism designed for this application.  The design makes it possible for the nut to slip back-and-forth through the unclamped mechanism so that the motion of the carriage is unhindered to a large degree.  (Some care should be used when doing this however).  For this reason the name of "slipnut" seemed naturally to fall to this nut in analogy to its name "splitnut" in the other lathes.  So the term "slipnut" will be used very often in describing operations with this threading attachment.  It is not a slip of the tongue or a missprint.

Also two terms very basic to screw threads will be used.   These terms are "thread pitch" or more simply just "pitch" and "threads per inch" abbreviated "TPI".  The "pitch" which is the repeat distance between adjacent threads can be given in either metric or inch-based dimensions and the choice of either should either be specified or clear from the context in which it is being used.  Of course TPI implies that inches are the dimensions being considered.  Metric threads are always described by their pitch and inch based ones by their TPI.  It should be obvious that if the pitch of a thread is "N(inches)" then the TPI for this thread is 1/N.  A similar relationship appl;ies t metric threads but is hardly ever used.  Thus:

        "TPI"="Threads-Per-Inch"=1/Pitch(inches)

        "TPmm"="Threads-Per-Millimeter" = 1/Pitch(millimeters)

The second equation is hardly ever used.

---  Threading Setups  ---

Inch-Based threads using the standard 1X(16T pulley and 48T belt) and 2X(32T pulley and 56T belt) pulley set.  The * examples require the accessory dedicated and tapped nutplate.  The ** examples require the accessory 1.5X(24T pulley and 52T belt) pulley set.

The Major-Diameter of inch-based screws can be calculated according to the formula:

        Dia.(inches) = 0.060 + Screw# * 0.013

Also for the "0" series a formula can be written:

        Dia.(inches) = 0.060 - (# of zeros -1) * 0.013

Thus all the inch-based screw sizes increment by 0.013 inches from "0000" up through #10 (and apparently beyond for wood screws). A "0" sized screw has a major diameter of 0.060(inch) by either formula.

The "Thread Height" of the Unified Thread Form" is 5/8 of the Thread Height" of a "Sharp V" thread form.  Thus the "Sharp V" "Thread Height" is 1.6 times the listed number.  These two useful numbers can be used to calculate the  "Minor Diameter" once the "Major Diameter" of a particular example of one of these two thread forms has been determined.  They can also be used to estimate the amount of feed that will be used on the compound feed of the lathe to cut the thread to the correct depth.  This is from the "point of touch" of the tool on the original surface to the "final depth of cut".  Be advised that both the "point of touch" and the shape of the threading tool can be especially elusive determinations for fine threads.

Since the compound is set to 29 or 30 degrees from broadside when cutting a 60 degree thread then its feed is 1/Cos(30)=1.155 the above "Thread heights" to achieve the specified depth.  Also note that if one wants the tops of their thread to be a "Unified Thread Form" shape and is willing to sacrifice the strength of the fastener by cutting a sharp bottom with a sharp pointed tool than the feed from the "point of touch" to the required depth is somewhere (7/8)between the two.  Also the remote possibility of wanting sharp topped threads when using a tool with the UN flattened tip would require a different(3/4) feed. The sharp V thread with the sharp V" tool requires the greatest feed and the UN thread with a UN flatted tool the least.  If one has a tool that has something other than a 60 degree included angle then these depths can vary considerably. Sometimes one might want to consider shallower threads than the usual deep 60 degree shape if one is threading thin tubing for instance.  One should think about these things and it is ultimately the responsibility of the designer or machinist to understand what he/she is doing. Remember that no matter what the shape of the thread profile the "Thread Size" is usually given as the major or outside diameter(Not pipe threads of course).   This makes the recommended tap drills for the old "American National Standard"(Sharp V) threads and for the modern "Unified Thread Form" threads different.

Metric Screw Threads using the standard 1X and 2X Pulley Set.

Theoretical Aspects before getting started: -
In order to get the best results from the threadsr there are certain things that one should understand that are happening and are significant.  Some of these are obvious and some are not.  It depends upon your experience.

Wire Sizes, Maximum, Best, Minimum: -
These dimensions are determined by the geometry of the profiles or cross sections of the Unified Thread Form and the wire (a circle).  Wires of these sizes can be used for the "Three Wire" or "Measurement Over Wires" technique to measure the pitch diameter of a screw thread or to wrap the threads of a screw as described below to accurately chuck a threaded section of a thread in the lathe three jaw chuck.

The "Minimum" wire size is the smallest wire that will rise above the the top of the Unified Thread Form profile so that contact will be made on the wire rather than the top of the thread itself if a micrometer face or jaw face closes down on that pair of objects.  Note that if a burr has been raised on the thread so that it is not of the exact Unified Thread Form shape then the micrometers will contact the burr before the wire and so this smallest wire size is not a good choice to use.

The "Best" wire size is the wire that makes contact with the "V" shaped faces of the thread at the actual pitch diameter point of the thread profile. A good choice for a wire to actually use is close to this wire size or slightly larger but less than the maximum.

The Maximum" wire size is the maximum wire that can be used without interfering with another wire of the same size laying in the adjacent thread groove.  This wire size is very slightly smaller than the largest individual wire that will lay in the UNF thread form while still contacting the "V" shaped faces of the thread form.

Positioning the Leadscrew - Up/Down, In/Out, Longitudinally: -
In/Out - This positioning has been pre-determined pretty much by the machined in dimensions of the lathe kit parts and so is not a probem but can be a problem if the mounts for the leadscrew are not kept level.   In other words ...

Up/Down - Slots have been cut in the leadscrew mounts to allow their vertical movement without rotating them.  Thus the headstock-end leadscrew bearing block assembly has a vertical slot for the draw bolt and the nut-plate also has one of the same length. This vertical adjustment is necessary since the belt lengths for the different pulleys causes differing axis-to-axis distances between the leadscrew and main lathe spindle.  Therefore the whole leadscrew has to be moved up and down without tilting it in-and-out from the lathe body.  Thus the need for the slots.

Getting the up/down and in/out position of the leadscrew adjusted without having it tilted in either of these directions is necessary to eliminate binding and have it free running.

Longitudinally -  This is surprisingly the simplest or hardest location to control depending upon whether one decides to just ignore it or to deal with it.  It is easy to ignore until one starts having problems with uniformity of depths of thread cuts along the length of their finished product. In particular if there are alternately bolder and shallower cuts in succeeding threads along the length of the product then the leadscrew is likely to be cycliclly sliding along its axis as it is turning. This is more obvious with finer threads than with coarser ones.  It also is different from the previous two location considerations since the problem occurs as the screw is turning and is not a fixed situation. 

This problem is caused by the thrust bearings holding the leadscrew in position longitudinally.  The thrust bearings are the inside faces of the 1/4" clamp style shaft collar and the timing pulley used on the leadscrew where they face the bearng block.  The faces of these surfaces must be perpendicular to the leadscrew axis and run smoothly against the bearing block. While cutting the leadscrew is pulling the carriage along so the timing pulley surface is the important one.

A second alternative for longitudinally locating the leadscrew for more precision results is now considered.  It has the disadvantage of not being as convenient to set up or use but is almost without doubt the most precision method to mount a leadscrew.  That method is to use a pivot at the tailstock end of the leadscrew and thus confine it between the pivot and the clamp collar.  In this case the force of moving the carriage is against the pivot instead of against the timing pulley and it is more likely that the pivot will run without any longitudinal runout at all.  Doing this will be left to the particular application neede by the user.   However some possible mechanical/geometrical aspects to consider are given in the following layout sketch.

Some materials are noted as having good "machinability" and others are poor.  This is not just a descriptive statement but has actual measurement standards. The poorly machinable materials are generally the stronger ones and the good machinable materials are generally the weaker ones.  Thus there is not only a trade-off between creatability and end result but actual conflict.  Cutting theads requires a material that has good machinability because the cuts are generally deep and wide.  Trying to cut a thread by either a tap, a die, or single pointing on a lathe will result in metal being pushed around instead of being cut and the tops of threads will be torn away from their base or bent and will have an unacceptably rough appearance. Rolled threads are of course a different story since pushing metal around is required..

Very fine threads and very coarse ones are the hardest to cut.  There are absolute aspects of this statement and relative aspects of this statement.  Long thin threads have a problem with support of the workpiece either in the middle or at an unsupported end. Coarse threads have a problem with the width of the cut becoming large so that forces placed on all components possibly cause either deflection, slippage or breakage. Deflection is always present on any component carrying a load so this is always a matter of degree.  Fine threads have the problem that measurements are hard with normal shop tools and settings and positions are more critical than with coarser threads.   Surprisingly the very small #0000-160 has all of these problems, both being very coarse for its small diameter and being a very fine 160 threads per inch in absolute terms. The 1/2-20 thread is, surprisingly, a fine thread for its diameter but is rather coarse as far as metal removal is concerned for this sized lathe.  The 1/4-20 thread takes the same pitch as the 1/2-20 and puts it on a smaller diameter thus making it difficult to cut from a deflection point of view. If one can do some degree of machining to make these three successfully in reasonable materials then one can probably do all of the "single pointing" that can be done.

The stability of the longitudinal position of the leadscrew as it turns is vulnerable and significant.  In other words if the leadscrew shifts longitudinal position (along its axis) either repeatedly or only once per revolution, this dislocation will be transmitted to the cutting tool and will appear on the cut thread.  What use is an accurate leadscrew if it shifts randomly or repeatedly along its axial length?   This effect can also be simulated by having a leadscrew that does not have a thread that progresses continually and smoothly as the leadscrew is rotated.  The effects of this rotational problem are not always obvious but can become obvoious under some critical situations.   One of these is when using the two-to-one (16 to 32 Tooth) reduction pulleys.  In this case the leadscrew rotates only one half a turn for each turn of the spindle.   Thus each adjacent thread profile is a result of positioning from opposite rotational orientations of the leadcrew.  Errors here can result from errors in the leadscrew itself or from the thrust bearings (on either end) that position it.  It is therefore important that the faces of the hubs of the pulleys run true in the longitudinal direction (along the length of the leadscrew).  This problem if it exists becomes very obvious by using a magnifier and holding a thread cut using the 32 Tooth leadscrew pulley up to the light.      if there are problems in this regard then alternate  teeth on the cut thread will appear alternately larger and smaller next to each other.  This is not a result of the threading tool moving radially in and out but a result of it not progressing uniformly and continually as the lathe spindle turns.  Again, it may not be a problem with the leadscrew itself but with the bearings that position the leadscrew. The same result will occur if the 16 Tooth pulley's face does not run true however it is not so obvious in this case since adjacent profiles of the cut thread are determined by the same-identical rotational orientation of the leadscrew and its bearings and therefore wobble of the bearings does not appear.  One should always examine the profile of the cut thread by holding it facing a bright light and examining the profile of alternate teeth using a magnifying glass.  Alternate teeth appearing bolder than their next door neighbors are a strong indication of bearing problems when made using the 2 to 1 reduction setup.

Note that there are other ways to obtain the pitchs or leads to cut some of these threads.  In the case of the fine threads, using a leadscrew made from a very small diameter standard screw size may result in early failure of the screw or nut.  This is because the force of drag for moving the carriage will remain at some high value.  Thus the force on the screw and nut will be such that they will wear quickly or the threads may strip whereas the same thread pitch on a larger diameter will have more durability.  Unfortunately in this case a standard thread tap will not be available and a custom tap will have to be made.  Fortunately leadscrews do not have to be interhangeable and only have to work with the particular nut that it will be used with. More will be added about making leadscrews and matching nuts later.    This will add to ones thread making expertise and respect for the fasteners that we use so freely.  The only thing needed to know here is that, for clearance,  a tapped hole and therefore the tap has to be slightly larger than the screw that will go through it. A few thousandths of an inch will due in "small" threads say less than 1/4 inch in diameter but the only way to successful results is with logic and experience.   That is what the lathe is for. 

The most difficult threads to cut are at the coarse and fine ends of the spectrum. 

At the coarse end of spectrum remember that the volume(and mass)of any scaled up object increases as the cube(the 3rd power) of any of its linear dimensions.  As a result of this the amount of metal removed in cutting a thread also goes up as the cube of its scaled up size.  So looking at these threading charts where the coarsest thread is ten(10) times the size as the finest - this means that there must be removed one thousand(10**3=1000) times as much metal to form the coarsest thread compared to the finest thread if the diameter is scaled up along with the size of the thread profile.  One will find very quickly by experience that the practical result of this seemingly mathematical detail is that a "brick wall" is very definately hit.  This results from the consequence that making a coarse thread involves some very much larger cutting forces and energy than the making of its smaller version.  This puts much more force on all components involved including all the bearings.  Clamping and deflection of the workpiece, slipping and deflection of the cutting tool become important.  Cutting of long thin sections of coarse thread becomes difficult and are to be avoided unless the inconvenience of support rests will be acceptable.

At the fine end of the spectrum it will be hard to see and measure what one is doing.  In these cases having some standard screws handy to serve as "standard" gauges will probably be useful.  Burrs may be as large as the threads and one is working with magnification glasses for sure.  This gets into the clock and watchmakers trade and my experience is limited here.  However I believe the lathe and its accessories are up to the task.  Operator skill and technique are as always important here however the techniques that work will be different in these different universes.

An advantage of using a short leadscrew as is used in the Threader2 is that the nut can be unthreaded from the leadscrew, while the nut is still locked in the carriage.  Then the carriage can be backed away from the workpiece.   Later the nut (and carriage) can then be rethreaded onto the leadscrew and the relative orientation between the thread cut and the threading tool will not be lost.  This is useful to "test fit" a "test nut" onto the end of the leadscrew being cut and is shown in Fig.???

Installing The Threader

A McDonalds drinking straw save alot of time.
A large diameter drinking straw from McDonalds or Arbies (probably others) can be slipped over the 1/4" diameter leadscrew shaft and any smaller leadscrew section attached to it..  This will allow the leadscrew to slide through the nut plate without scuffing of its threads against the 5/16" diameter hole where the nut has been withdrawn.   This allows the carriage to be traversed without interference when doing a normal turnng operation.  Not having to remove the leadscrew completely when changing from a turning operation to a threading operation may save alot of time and manipulation.

A Bit of Theory: -

Some More Theory: - A bit of consideration reveals some interesting properties of the "Double Button" used to hold the leadscrew nut in place.  The drawing emphasizes the fact that the dimensions of the machined surfaces are mostly not critical and the net force on the nut does not tend to rock it from its position lying against the outer wall of its hole in the nutplate.  Once one gets beyond the thought that the buttons simply "jam" the nut to the side this definately becomes more of a problem than one in kinematics 101.  Especially if one trys to consider the bending moment in the Allen screw.

Some things on Accuracy: -

Closing a chuck on the outside of a commercial screw thread does not ensure good accuracy.  A better way is to wrap a fine wire onto the threads and clamp the jaws over these turns.  That way the thread is clamped more on the faces of the threads rather than the tips.  In this way the pitch diameter of the thread runs more true. If soft copper wire is used then it will be deformed somewhat so that probably harder brass or iron wire works a little better. 

In order to better center the end of the leadscrew in the 1/4" diameter rod when soldering a pivot tip should be turned on the end of this threaded rod. Since the drilled hole in the 1/4" rod will have a flat or somewhat undetermned bottom shape the tip of the pivot should not rest on this surface because its position will not be well determined.  Instead the pivot tip should be rounded or flat so that the flanks of the pivot rest on the tapered sides of the hole made by the pointed end of the drill.  Concentricity in all these surfaces is required.

Making the Nut for the Leadscrew (the "Slipnut"): -
I started calling this nut the "Slipnut" instead of the lengthy and awkward "the nut for the leadscrew.  Also I thought it rhymed with and replaced the terminalogy for the usual item it replaces on the threading lathe the "Splitnut".  So here we have the "Slipnut" not the "Splitnut".

About the only requirement for the Slipnut is that the central untapered region be at least 5/16" long so that the button washers can bear against this cylindrical surface.  Both ends of the nut are tapered to make it easier for the nut to slide through the hole in the "Nutplate".  When this is working well the nut can slide through the hole with little hesitation or attention needed to "thread" it through the hole.  NOte that for small leadscrew one does not need to not indeed may not want to thread the whole internal length of the Slipnut.   This not only alleviated the tapping problem but also allows for some small amount of missalignment or pointing of the leadscrew back to its bearing location in the headstock bearing support.

Making A Tap: -
Planning/Thinking Ahead - Since we will be wanting to make a leadscrew from 1/8" brass or 12L14 stock then we will have to do what is called a very light "cleanup" cut or two to true this stock and make it run concentric.   When this is done the diameter will be a few thousandths under the nominal 1/8" diameter.  However if we are going to make our tap from 1/8" stock then it too will have to be a few thousandths under 1/8"; and since the tap must be a few thousandths larger than the leadscrew the "1/8 inch diameter" leadscrew will have to be even smaller than this already undersize tap.  OK, so it makes sense to build the tap first and tap a few holes and then use them for gauges when making the leadscrew.   In other applications one might "do things by the numbers" and make measurements on the "gauges" for the internal threads and the external threads themselves using the "Three Wire Method" to have these threads interchangeable with the standard sizes.  However here we are working with small sizes and fine threads in relatively soft material. Measurements are hard to make and not extremely useful by usual shop techniques with this combination of parameters. We will "make things to fit" as the old shop saying goes.  When things are made to specifications in small sizes usually special gauges are used and general measuring techniques are abandoned. In making things to fit" the mating part is the "gauge". So making the tap first and making several "gauge nuts" from it is the way to start.  The leadscrew will later be made to fit these gauge nuts.   The gauge nuts will be used to take the abuse of trying fits on a rough and oversize leadscrew as it comes down to size.  The final "slipnut" made with the same tap will then not then have these roughened up threads.

However some sizes that were used here will be given since they worked out so well.  The Major Diameter of the tap was 0.002" under the "Nominal" 1/8" size making it 0.123" in diameter.  The "Thread height" for the "Unified Thread Form" at 80 Threads per Inch(TPI) is 0.0068" making the minor diameter 0.1095" for this Major Diameter of 0.123".  One subtracts twice the "Thread Height" from the "Major Diameter" to get the "minor diameter".  One usually must allow a few thousandths between the diameters in the tapped hole and the thread that is to go into it.  However the tap turned out to have what looked like shallower threads than the Unified Thread Form has.  This was undoubtedly due to the fact that the threading tool had become worn after more use than was realized. This means that minor diameter of the taps thread would be larger than the UN (Unified National) form and so a larger tap drill size might be used to eliminate unnecessary metal removal by the tap.   Note that we are working/thinking downward in sizes here, not upwards. So rather than making the tap drill a few thousandths smaller than 0.1095 it was decided to try an initial tap drill hole of exactly 0.1095 using a 7/64" drill to se if binding occured and if the internal threads looked to have acceptable depth.  In order to get an accurate hole size with the 7/64" diameter drill, the tap holes were all preliminarily drilled with a #37 drill of 0.1040" diameter and then the hole enlarged/reamed out using a sharp 7//64" diameter drill.  The 7/64" diameter size worked out to be ideal for this particular tap into brass.

In particular how to make a 1/8-80 tap to tap a brass leadscrew nut (slipnut).  Both making a very long leadscrew and making a tap as we shall show here pushes the state of the art as we will be doing it.  Therefore things are almost "out-of-control" as you will see.  The thing is to not be discouraged by what look to be unacceptable results along the way.  If one knows what they are doing and stay with the program then useful and useable results ensue.        This discussion like all the rest is based upon what I have personally found and my rules of thumb rather than what may be unequivocal ultimate truths.  My somewhat limited experience in making taps is that itis a whole art unto itself and requires some "getting lucky" in the smaller sizes.  There are some so called "theoretical" factors to realize at the outset that will minimize mistakes and are guiding principals.  These are

1 A tap must be larger than the screw it is made to fit.
2 A slight "back taper" to provide some "tool clearance" in our home/hand made taps.
3 There are one, maybe two ways to form the cutting edge.
4 The tap may or may not be hardened.
5 One will be aiming at and making a "Sharp V" rather than "Unified Thread Form".
6 The "Pitch Diameter" of fine threads is perhaps too delicate to measure using the "Three Wire" method.
7 Our special leadscrews and taps will be strong because of the large diameters and fine threads used.
8 The nut being tapped will be easily machined brass.

Point 1. This may seem obvious but how many time have I heard people say "make a tap from a bolt".  Well one has to find an oversized bolt to do this so that the other bolts will go in the hole left by the first one.  Since it is so hard to get good measurements on the PD of some of these extra fine threads then the starting diameter and the feed of the threading tool needs to be remembered so that a larger tap PD and OD can be made than for the screw.

Point 2. These will be special purpose personal taps that will be very carefully used for a l;imited number of times.  Maybe only once. Clearances are just too hard to obtain here.

Point3. An advantage of the "Watchmakers Point" is that it can be resharpened, rehoned, and even some "tool clearance" applied as long as sufficient thread remains.

Point4.  One can try to harden a tap for repeated use however the threads may be burnt off in the heating process.  Protecting compounds are available to protect and limit "decarburization" in such operations.

Point 5. We are making threads "to fit" rather than to be universally interchangeable unless one wants to do otherwise.

Point 6. As one works smaller and smaller the accuracy and softness of materials makes accurate measurements with standard measurement techniques relativel less precise (on a percentage basis).  For this reason I have not used the "three wire measurement" technique to determine when the thread has been made deep enough but have relied upon viewing the thread profile with a high powered hand magnifier to see its shape develop.  Whe the tops of the threads get to a reasonable degree of sharpness the thread cutting is finished. If I want to make a tap which must be larger than the thread that goes into the tapped hole then I start threading on a larger diameter.  Also the burrs raised on the end of the tap by grinding the pyrimidal faces will tend to abrade metal away that is larger in diameter than the basic thread diameter.

Point 7.  It is pointless to try to make our personally cut leadscrews to the same dimensions as commercial bolt sizes.  One can cut a longer length of thread on a more substandial piece of material with larger minor diameter than on a minimal diameter fastener size.  This advantage should be take advantage of.

Point 8.  Ultimate strength is not our final goal here although wear resistance sould be.  For this reason we will make the nut to match the individual leadscrew and the engagement length will be of reasonable value so that an oil film cam be established that will give an acceptable running fit and life span.  Also coarser threads have more face area than finer threads though this can be compensated for by making the engagement length longer as just described.

Fig. xx and xxx are two views of a 1/8-80 tap.  The enclosed angle between faces of its threads turned out to be somewhat less than the usual 60 degrees and there was not a precise thread with sharp transitions between the faces and the major and minor cylindrical diameters.  The threading tool had some wear in the process of cutting several threads and these fine points do show wear quickly.  The tap was made from water hardening drill rod but was quenched io oil in the hardening process. The teick here is to get the piece to temperature quickly and quenched very immediately to minimize scaling caused by oxidation.  The tap is held just inches above the quench medium and very quickly immersed as it reaches a good temperature color.   This color requires judgement from previous experience.  The surface of the tap is cooled much quicker than the interior of course and this is fasrt enough to harden the threadi cutting area.  The interior can remain soft with no problems.  Notice the angle of the flats on the end tends to push the chips forward just like the very effective "spiral point" or "gun taps" that work so well.   With this taps very abrupt taper (corresponding to a bottoming tap) it is best to do the tapping with both the workpiece and the tap held in the lathe so that with minimum angular shifting.

Making A Leadscrew: -
First of all it might be of interest to know that a brass leadscrew works pretty well. Ones first thought is that bearings work best when the materials that rub together are dissimilar and also purposely chosen for their properties as bearings. For this reason the use of brass for both the Slipnut and the leadscrew was thought not to be a good idea.   However a leadscrew was made from 1/8" brass stock and it works very well in a brass Slipnut.  It probably machines somewhat more nicely than 12L14 screw machine stock and might be a good choice for the first atempt at a leadscrew.  However 12L14 mmachines very well and may be a little bit more durable andperhaps more stiff(Young's modulus).  If the increase in stiffnes does not compensate for the extra machining force required cmpared to brass than the length of unsupported stock that can be machined may not be enhanced.  I do not know the answer to this at this point.  Also the use of a follower rest may increase the length of a leadscrew that can be cut and also supporting one end in a collet or chuck while the other end is supported by a tailstock center is a convenient arrangement.  This is particularly true it the screw is ended in a point and the taistock center is the female part of the support.  This is the reverse of the usual arrangement but is very nice for threading since the thread can start as it coms up on the point and this point makes a very nice start for threading on of the nuts of succeeding work.

Also before proceeding it might be of interest to point out that lapping of leadscrew is a known procedure for enhancing the performance of cut leadscrews and perhaps even ground ones.  The leadscrews for precision optical devices were known to be lapped in early days and may still be used.  One might look into this if one wants the ultimate performance from their home made leadscrews.

Most of the leadscrews for the Threader2 I envision will probably be made from two seperate pieces of material tin/lead, tin antimony, or tin silver soldered together as a final step in assembly of otherwise finished parts.  This is not the only way but it is the easiest way I can see a leadscrew being made from prethreaded stock and also for that matter from a section of stock that has been threaded on the lathe.  It appears to me that there is a best way to do this although even here there may be alternatives.   However I will give you my recommendation.  This will be in three parts which will be the fabrication of the unthreaded part of the leadscrew, the fabrication of the threaded part of the leadscrew(excluding the actual threading of this section for now, and the joining of these parts together.

The unthreaded part of the leadscrew is the easiest.   The bearing iat the headstock end has been reamed to a diameter of 0.254" to make it ready for a nominal quarter inch diameter shaft.  Note that the belt will be pulling this shaft always in the same direction so that looseness here is not of a great concern.  However as is mentioned elswhere the longitudinal movement along the screw axis is something to keep in mind.  The length of this unthreaded section can be as long as one wishes since the crank handle has been made short enough to clear the shaft no matter its length.  However a very long stub sticking out the end of the lathe is certainly inconvenient and may be easily bumped or catch on one's arm or clothes when working close to it.  The reason to maintain some length for it is however that it has to be able to move the threaded art of the leadscrew down toward the tailstock end of the lathe for any threading that might ever be needed on a long piece of work at this point.  Since most threading is done on short extensions mounted in a chuck at the headstock however it seems unreasonable to make all ones leadscrews to this unnecessary lenght.  My personal opinions is that ones general purpose leadscrew only need to be long enough to do threading for an inch of so extending out from the jaws of the three jaw chuck.  Any shorter work and work mounted in a collet will then be easily within range of this leadscrew.  So my personal preference is to make the unthreaded shaft of the leadscrew in the range of 10 to 11 inches long.

I prefer to join the threaded section to this unthreaded section by soft soldering and so a precision joint is prepared for this process.  A hole is drilled in the end of this unthreaded section so that it will center itself against the threaded section.  This hole is drilled only deep enough to make a small cup for a drop of solder that will be use to adhere to the leadscrew.  This cup will be wetted with solder or "tinned" after it is drilled and before the solder joint is atempted.  This hole should ave a rather pointed or tapered bottom so that the other section when pushed into it will go to its center line.  Since the other section will also have a well centered point on it then the two pieces will be accurately centered on each other when they are pressed together during soldering.  The most convenient way of making this pointed/tapered hole is to use a "Center Drill" with a 60 degree tapered section to it.  The small drill end of the Center Drill will not be part of this centering process and only will serve to allow clearance for the point of the opposing part just as it does when uswd in its original purpose as providing a pivot for a "center support" when "turning between centers". 

The threaded section of the leadscrew can be either threaded on the lathe or obtained in a prethreaded condition as on a bolt or section of "Allthread".  If one obtains a section of threaded stock it is not likely to have a precisely centered point on either end which we will need.  It is now necessary to put a centerd point on at least one end of the threaded section of the leadscrew and both ends if it is suspected that the tailstock end of the leadscrew will be supported in one of the methods descrbed elsewhere.

In order to turn a point on the end of a threaded rod it must be centered in the lathe headstock spindle.  Chucking the threaded rod on the outer points of its thread is not a good way.  The most important part of a thread is its flanked surface and not its inner or outer diameter surfaces.  In order to have the threaded flanks running concentrically a chucking method should clamp to these surfaces.  THis can be done by making a very accurately centered and tapped hole in some round stock or by wrapping the threaded rod with wire that lays on the flanks of the thread.  Making an accurately tapped hole is another story and will be described elsewhere tim permitting and so the quicker and easier wire wrapping method will be described here. 

A wire size must be used that has its top surface above the crest of the thread but also rests on the flanksof the thread.  In this respect this constraint is the same as required of wires used to measure the "Pitch Diameter" of threads using the "Three Wire Method".  These sizes are shown the the threading table.  The "Best" wire size is the one that sets on the flank of the thread at the exact same height as where the pitch diameter passes through the flank of the thread.  HOwever awire slightly larger than this is preferred since it will give more height above the crests of the thread and thus allow for some compression of mashing down of the soft wire into the threads and chuck jaws.   This is more necessary if a soft wire is used instead of say iron wire.   HOwever a wire that is so large that its turns will not lie in the threads without interference with each other will not work properly either.  Some give in the wire is necessary for the chuck jaws to deform it so that it will bear strongly against the thread walls.  Care is needed in doing this to get the best precision.

Ampoint should be made on the threaded end of the leadscrew stock so that it will joing concentric manner with the tapered hole in the unthreaded section.  Both these areas should be well tinned and the solder slung out before they are mounted in the lathe and soldered permanently.

The lathe can be used to hold these parts in line while fuzing the final solder joint.  With the proper pre tinning the amount of heat and time at temperature will be minimized and a very cleanb and efficient joining process can be btained.  One needs to obtain a good brand of liquid soldering flux and a high tin content solder to do this well.  Most plumber's soldering flux should work for this although there are better fluxes sold by numerous solder manufacturer's and tool companies.  A good one is --------.The best contain some small amount of fluorides.

One of the advantages of using solder here is that if the joint does not line up the sections in a suitable linear manner then the assembly can be remounted in the lathe and the joint "reflowed".  The bed of the lathe can easily be covered with cloth of even cardboard to prevent the corrosive spatter and fumes that always eminate from anything except the most innocuous electronic soldering operations.  If the leadscrew sections appear to be colinear upon carefully turning and observing the assembly in ones hands then it is probably good to use as a leadscrew.   These long thin elements do not have to be a within thousandths from end to end.

Using The Threader: -

The McDonalds Straw
The McDonalds Straw is a big time saver.  It allows one to move the carriage without damaging the threads on the leadscrew.

Steps (Machining Order) to Make a Leadscrew: -

1. Mount and turn accurate pivot points on both ends of the threaded rod section.  Flux and lightly tin one end of this section.

2. Mount and drill an accurate pivot hole in one end of the 1/4" unthreaded rod section.  Flux and lightly tin the hole.

3. Mount the unthreaded section in the headstock and check for true running.  Mount the threaded section against this with the tinned sections touching.  Flux and reflow solder. Check for true running. Repeat as necessary.

Font Ends Here.