Limits to DRS

I have been spinning about 7 years, and I converted my wheel to differential rotation speed (DRS) about 6 years ago.

As a DRS wheel, my traddy is likely nearing its maximum potential.

# 0 flyer (The Competition)

With its accelerator, it will insert twist at speeds approaching 5,000 rpm.  I do not think there is much room for improvement.  Ball bearings on the drive wheel and accelerator would reduce effort, but are not likely to allow much faster spinning.  While others are modifying e-spinners to DRS, I doubt if they will actually produce yarn any faster.


The other flyer/bobbin assembly is:

#1 flyer

(The Airplane)

With a range of flyer whorls for this flyer/bobbin assembly, I can spin yarns at desired twists between  about 9 tpi and 30 tpi.   For example 9 tpi yields a firm worsted single of  ~ 5,600 ypp and a medium woolen yarn of ~ 4,800 ypp - about the lowest grist yarn that I produce.  And, 26 tpi yields a worsted single at about the spin count ( ~75 meters/ gram) of the Rambouillet  that I get from Anne Harvey.   (The higher twist flyer/bobbin assemblies were set aside when I installed the accelerator.)  Compared to most modern spinners, I like thinner singles, and the yarns constructed from thinner singles, so this system produces the range of singles that I like.  The Competition runs noticeably faster, and is prefered for high twist singles.

On the other runway, The Airplane will produce a hank (560 yd) of 5,600 ypp singles in an hour. While it is actually slower than the #0 flyer, the Airplane is large enough to produce a full continuous hank of 5,600 ypp single, or 1,200 continuous yards of 11,200 ypp singles.  This allows plying 500 yards of 5-ply gansey yarn from continuous singles; and  allows plying  1,000 yard long skeins of  6-ply, 1680 ypp sock or "gansey" yarn from continuous singles.  

The Competition could produce continuous 1,200 yarn lengths of fine singles ( 30,000 ypp and finer, if I  just made another whorl for it. It is not a priory at this time.  

I do not need singles longer than 1120 yards, so I am not going to make the effort to get a larger DRS flyer. 

 Plying is done on a ST Ashford Jumbo flyer running at ~ 1,600 rpm.  It allows me to easily produce  500 yards of 5-ply sport weight or 250 yard skeins of 10-ply Aran yarn from continuous singles.  That is as close to "ART" yarn as I want to be.

There is a universe of different yarns out there. It is just a matter of  dreaming them, and sitting down in the morning's light to conjure them out of the chaos of a bin of fiber.  Commercial producers are constrained by the cost of twist, and perceived price points in the market.  As dreamers, we can consider durability, warmth,  luster, care, flammability, softness, color, grist, drape, hand, and other issues as we plan the yarns for our fabrics for our objects.  With an accelerator/DRS wheel,  the effort to spin fine singles becomes much less of a consideration.

 For a class of objects such as seaman's sweaters, there are still a galaxy of suitable yarns.  There is nothing sacred about worsted 5-ply.   If it is a voyage to the poles, 6-ply (840 ypp) or even 10-ply (500 ypp) may be better. If you are crossing the equator, then 3-ply (1,680 ypp)  may be better.  If the boat is leaving this week, then MacAusland's Heavy 3-ply is the faster knit. If I had to have such a fast knitting yarn tonight, I would spin it up on the Ashland Jumbo flyer without resorting to DRS.)

Why?  Because with a thick yarn and small bobbins, the change in the effective bobbin circumference and hence the rate of takeup increases so that the inserted twist is reduced below what is required for a yarn competence.  Likewise, plying changes the effective diameter changes rapidly.  Commercial  DRS systems use large bobbins, and  mechanical systems to continuously detect the effective diameter of the bobbin and change the rate of wind-on, so that twist insertion remains constant.  DRS for the hand spinner is much easier with fine singles and big bobbins.

If you really like thick singles, then DRS is not for you.  If you spin fat singles because thin singles seem like too much work, then you should know that DRS may be a path to fine and/ or very fine  singles.

And truly, there are good olives and bad olives.

This olive wood bobbin is perfect for fine singles 

on The Competition. 

GW 2

These days, I do not keep a great wheel.  I do have 2 motor driven spindles and 2 spindles that fit onto my treadle wheel.  None of these are as impressive to look at as a GW, but they are faster. And, they all allow me more use of both hands for drafting true worsted.

The motor driven spindles are easy to pause or stop, but hard to reverse.  Therefore, I had to learn how to wind-on with the spindle going in the same direction as when spinning.  It can be done, the answer is "out there", and I have no interest in teaching driven spindle technique.

If one does not have to reverse the spindle, then one does not have to stop, or pause the spindle, and the spindle can rotate continuously in the same direction.  One CAN spin a entire hank of single on a great wheel without ever reversing the wheel to wind on.  This can be much faster/easier than reversing rotation to wind-on depending on the inertia of the rotating system.

Nevertheless, the spindle must be slowed at various points in the spinning/drafting/wind-on process. Even though the spindle/wheel always rotates in the same direction, the slowdown/speedup cycle wastes energy. And, the wind-on cycle slows production of yarn. 

A spindle on my treadle wheel can insert twist many times faster than the flyer/bobbin assembly,  but the DD flyer bobbin assembly will spin and wind-on much more yarn in a minute or an hour or a day.  One of the motor driven spindles can insert twist many times faster than either spindle on my treadle wheel, but net production of single is not much different. Net production of spun yarn by a spindle is limited by the nature of its cycle, rather than by its peak speed.

A DRS flyer/bobbin assembly is the fastest hand spinning device for most natural fibers. Ring spinning can be faster for silk, but that is a specialized application.  Yes, those old double drive spinning wheels were the fastest way to spin.  They used the two loops of the drive band to synchronize the rotation of the bobbin and flyer to insert just the right amount of twist as the yarn was wound in at just the correct rate for the inserted twist. They did not have the drive band slip that is built into modern double drive wheels.  The result is that a double drive wheel without drive band slip that can produce singles much faster than a great wheel.  This is a truth that you have heard before.  It is just that all  modern DD wheels do have drive band slip and thus, spin more slowly than a GW.   In fact, a DRS flyer/bobbin assembly can produce true worsted spun yarn 5 times faster than a great wheel.  Every sock knitter should think about that.

And, since DRS is faster, sock yarns of more and finer (true worsted spun)  plies are possible.  These are very nice yarns that are simply out of reach of even the best spinners using a GW.  The use of DRS opens up spinning true worsted 5-ply gansey or even 10-ply Aran yarns.  And, it makes spinning true worsted warp for the loom much more feasible.

 On the other hand, a DRS flyer/bobbin assembly requires real skill to setup and maintain. I have seen two old DRS double drive wheels where the original DRS ratios had been "repaired", and the wheel converted to  modern standards.   As a result of the repairs, they could spin lower grist yarns, but could only do so --- slowly. These had been true collector's items and the owners were very proud of how fast they could spin -- if they only know how fast those wheels had been originally designed to spin, they would have been agast!   The difference between these wheels as designed and these wheels as "repaired" was only millimeters, and yet it made a huge difference in their performance. If one can teach the basics of using a GW in a 4-day workshop, then I would say that one could teach the basics of using DRS in a 4-week workshop.

Yes, Holin, my old Ashford can spin/ply a 500 yd hank of sport weight, worsted spun, 5-ply (gansey yarn) in an easy day.  How long does it take your GW?  In less than 14 hours, I can spin/ply a 500 yd hank of  worsted spun, 3x2-ply cabled, 1,600 ypp "sock yarn".  How long does that take your GW?  Shall we set up a demonstration in front of a judge and jury?  I want spinners like Judith MacKenzie and Stephenie Gaustad who know, and appreciate,  worsted spun yarns involved.

I have only been spinning for 6 years. (And, I was sick with Lyme Disease for much of that time!)  How long have you been spinning?  What will I be spinning when I have spun as long as you have been spinning?

Spinning at more than 210 wpi

I recently mentioned that 56 count wool spun at its spin count is a bundle of 20 fibers. Such a bundle  is just over 125 microns in diameter. The best parts of the Rambouillet fleece that I get from Anna Harvey are 80 count or ~18 microns in diameter, so a bundle of 20 of those fibers will be just over ~90 microns in diameter -- easily much less than 1/210 of an inch, so we can expect wraps per inch of 210 or more from a bundle of 20 fibers.

Drafting 20 fibers from 80 count wool is not that different from drafting 20 fibers from 56 count wool. Making yarn from those drafted fibers just takes some 22-24 tpi, fingers sensitive enough to control the flow of twist up into the drafting triangle, experience to know what the single you want looks like, and the courage to spin that fine.  Oh!, and very well prepared fiber that drafts easily.

The path to spinning 80s (210 wpi) is:

1. Knowing it can be done.
2. Wanting to do it.
3. Having the tools.
4. Building the skills.

Today the main problems are that most spinners do not know it can be done and the tools are not widely available.  However, any wood turner with the skill to make a functional wine barrel spigot has the turning skills to make the appropriate bobbin and whorls.  You can find somebody like that at any wood working club, and there are wood working clubs everywhere.   Alden Amos's Big Blue Book will give YOU a path to the calculations for the necessary whorl diameters.

ANYONE who says singles of 210 wpi cannot be spun is ignorant of both science and history.

I will say that double drive, with  differential rotation speed is far, far, and away the easiest way to spin 80s. Then, a spindle of ~15 grams - I use a drop spindle with a removable whorl so as the copp builds, I can take the whorl off and use the copp as the whorl.  Then, comes Scotch tension.  And this afternoon, I just cannot seem to be able to tweak my IT enough to spin 80s on a practical basis.

The steps from 10s at 75 wpi to 56s at 175 wpi are easier than the step from mediums at 175 wpi to fines at 210 wpi.  Thus, I suggest that anyone planning to spin 80s make up the whorls required for 10s, 20s, 40s, and 60s, and the build the skills required for spinning each of these threads in a step wise fashion.

=> I use flyers where the flyer whorls are threaded to fit onto the threaded end of flyer shaft.  Then I use threaded inserts in the center of the flyer whorl.  The threaded insert is placed in the whorl blank, and then the whorl is turned on a bolt screwed into the insert, and held in the jaws of the lathe. Required precision for turning flyer whorls for spinning 80s is about 1%, so a 50 mm whorl needs to be turned within 0.5 mm or 1/50" of the design dimension.  Lower count singles require much less precision in their whorls.

Baby Talk

I have been accused of talking to my readers like children.The following sites talk to spinners as if the the spinners are babies and not a spinner complains! 

• http://www.spindizzy.net/Howto/dd_flyer.html
• http://joyofhandspinning.com/how-the-spinning-wheel-works/
• http://kromskina.com/single-drive-vs-double-drive-wheels/

In contrast, I give examples with actual measurements.  And, I tell you how to get better results.  Try asking Kromski how to spin fines! 

Spindizzy invokes the the same differential rotation speed (DRS) that Alden and I talk about.  We  do the math, and CAJ does it qualitatively.  The thing is: DRS is a clockwork mechanism, and  to make good clock work mechanisms, one needs to do the math, and get it correct. Then, one needs to fabricate the correct clockwork mechanism.  When spinning fines, a difference of 1 mm (1/25 ") in whorl diameters is important. DRS is simply not something that can be done qualitatively.

Joy of Hand spinning extols a high degree of twisting efficiency in DD,  just like I do.   Except, I use a tachometer and do the math. I tell you how much twist efficiency you can actually expect, and how you can improve your twist efficiency. These details are learned by doing.

Kromskina notes that DD generally spins the finest yarn.  I say, "DD will allow spinning fine yarns, much faster, but to use DD to spin the fine yarn quickly, the spinner needs the correct DRS."  The DRS that comes standard on Kromski is ~1.6, which is very good for spinning 1,600 ypp singles. Note that Kromski does not  supply the DRS for its whorls. By having the correct diameter of whorls to provided the needed DRS, I avoid slippage.  
 It is terrible for trying to spin 5,600 ypp lace singles. It will do it, but it is no faster or easier than Scotch Tension. The 5,600 ypp lace singles want a DRS of ~1.04, which is very different from a DRS of 1.6.  And, the flyer whorl that provides a DRS of 1.04, will NOT allow you to spin the singles for worsted weight 2-ply. As expressed, the Kromski statement is nonsense baby talk, but nobody complains.

If my wheel is set up at a DRS of 1.04, AND I need to spin worsted weight, I either change flier whorls or I run it single drive.  

I assure you that one can spin 45,000 ypp singles running single drive, but that you can spin such singles, twice as fast using DD with the correct DRS. And, 3 times as fast using DRS and an accelerator wheel.  That is the magic of DRS.

The continuous and limited take up of yarn as controlled by DRS allows the self assembly of the yarn. It is not discussed in the Big Blue Book, but it is this the self assembly of  yarn that makes DRS so productive. It is similar to the formation  of  yarn in the old flyer frames circa 1820. This self assembly of worsted yarn is rather similar to the formation of woolen yarn from a long draw draft. It means that the difference between true worsted and true woolen is simply the fiber preparation.  It means that one can spin worsted yarn much, much faster than one can inch worm draft such yarn.  I am sure it is why Alden gave the topic so much space in his Big Book of Handspinning.

The single drive setups are like pliers or adjustable wrenches.  DD is more like a mechanic's socket drive set. The socket drive set is fast, powerful, protects the nuts and bolt heads, but you need the full set.  The pliers and adjustable wrenches are handy, but they will not get into places that a socket drive set will get into, and adjustable wrenches are not as powerful or as fast as a good socket set.

Good mechanics have pliers and adjustable wrenches, but their socket wrench set(s)  let them work quickly and do high quality work.  I have a socket set for working on machines, and I have a set of DD whorls to provide the proper DRS for working on fiber. They allow me to work quickly and do high quality work.

These days every good mechanic uses a power screw driver/ nut and bolt driver.  It improves productivity.   Likewise, I use an accelerator wheel to improve my productivity.  Just as power bolt drivers work better with sockets than with adjustable devices, the accelerator wheel works much better with DRS than with single drive flyer bobbin assemblies.  Spinning worsted with single drive systems requires drafting techniques that cannot be sustained at those speeds, while with DRS and properly prepared fiber, worsted yarn of the correct grist/twist will self assemble a the end of the drafting triangle. A typical commercial spinning wheel can insert twist at about 1,000 rpm. With DRS and an accelerator wheel, spinning at ~3,000 rpm is easy, and spinning at 4,000 rpm is sustainable, and 4.500 rpm is possible when highly motivated.  The drafting process for woolen is very similar, but carded rolags are used instead of combed pencil roving.

Some readers have noted that some of my 10s are "twitted", (the term of art for thick and thin yarns resulting from small variations in roving density as a result of storage or transport). It is easily avoided by re-combing (or by spinning ever so slowly and inch worming the draft) .  On the other hand, when my hanks are within 5% of the correct grist and the twitting does not affect the final objects, I do worry about it.  Sometimes it is nice to be able to use roving out of the bag.  

I judge my final objects, not my yarn. I simply make sure that my yarn is within specification to make a good final object. And always I ask, " Did I get value?".  Or, Did I go over budget? Or, was my level of effort too high?  An object that goes over budget is just as bad as an object that is not functional.  In fact, I would say that a small amount of twitting is desirable, as it adds 'home spun" character without detracting from warmth, durability, drape, or hand. 

Spinning

I do not care if you are buying Italian designer suits or underwear at Target, the bulk of nice textiles are produced from thin yarns.  If you want to claim to be a spinner, you need to be able to produce thin yarns. And, if you want to be able to claim to be a spinner, you need to be able to produce a useful quantity of those yarns.

When I came to spinning 6 years ago the offered tools were various spindles, single drive wheels, and double drive wheels.  However, the whorl profile on the (commercially produced) DD  whorls had been corrupted, so that the DD wheels were actually single drive wheels in disguise.

There was a residual mythology about DD wheels being "better".  This was supported by the DD wheels with the corrupted whorl profiles being a few percent faster than single drive spinning wheels.  I was spinning 5-ply sport weight gansey yarn and the DD system was better.  Soon I was spinning those "lace weight" / 75 wpi singles at 150 yards per hour.

However, spinning finer was still difficult, and I went back to a Scotch Tension "Lace Flyer" to learn to spin 80s / 45,000 ypp / 200 wpi. Spinning those fine singles was slow and difficult.  Everything about it was hard.  Fiber preparation had to be perfect. Great care was required to prevent the single from burying itself. Mostly, it was slow - less than 100 yards per hour.

For the last couple of years, I have used double drive with differential rotation speed (DRS) exclusively.  DRS is the source of the myth that DD wheels are better. They are faster and allow spinning finer.

Now using DRS, I routinely spin the singles for gansey yarn at more than 500 yards per hour. A 500 yard hank of 5-ply is an easy day's task.  Last night while watching Pride and Prejudice, I spun an ounce/ 1,600 yards of shirting warp (22,000 ypp) from 60 count long wool.  And, I can spin 80s / 45,000 ypp / 200 wpi using fiber with only ordinary preparation. And, I do not have to worry about the single getting buried because, it is spun under much less tension. And it is faster.  My production rate with the Scotch Tension "Lace Flyer" is still less than 100 yards per hour, and my production rate with the DRS DD is about twice that.

DRS DD wheels are better for producing useful quantities of fine singles for high quality textiles.  Why DRS DD wheels are not sold is a mystery.  Why people do not learn to use such tools is a mystery.

Only in California

Wind, gusting to 40 knots, on the starboard beam.  Triple reefed, and the lee rail awash. And, in shirt sleeves.  Only in California.

On the other hand it was a reminder that I must get the new gansey finished before it turns cold.  I have a couple of pounds of hand-spun 5-ply yarn in the project bin and another couple pounds of worsted long wool of singles ready to ply.  I guess the question was whether I wanted to add a ply or two of woolen Rambouillet to the yarn for extra softness.  I have pounds of the Rambouillet singles, it is just a matter of plying. Time to quit pondering and knit like a demon.

I was spinning, and spinning, as I worked out details of better spinning gear.

I have an new accelerator:

 Oh, Yeah!

There were several issues to solve, so it took many tries to make it work. (And, a few extra singles were spun along the way as gear was tested, fixed, and retested.  And, there were some skills to learn, resulting in more singles.)   They are not all great singles, but there is no such thing as a bad lace weight single.  They will do just fine as sport weight 5-ply singles.

However, now the AA #0 flier runs at well over 4,000 rpm on a continuous and sustained basis. The bobbin core is .95" the bobbin whorl is 48 mm, and the flier whorls are set for 9, 12, and 18 tpi. This pretty close to the twist required for 10s (75 wpi) , 20s (100 wpi), and 40s (150 wpi). The only ball bearing is the one at the orifice.  Most of the bearings are graphite impregnated Delrin, from Henry Clemes.  It is very nice stuff.  Production of 10s from 60 count combed top seems to be about 650 yd/hr.

This morning I did the calcs, and early next week will make up new flier whorl(s) for 60s and 80s (200 wpi).  In theory, I should be able to spin 60s and 80s at better than 200 yards per hour - enough to be useful.  However, it would be more of a demo thing than a matter that I want to make fabric that fine - and all of my guild as already seen me spin fines.  Still, I do believe that a competent spinner should always be ready to spin fine wool at spin count,  so maybe I need whorls for 50s  (hosiery singles from Suffolk)  and 70s (from that cheap, flock-run, Merino).  However, my big projects are loom tissue from 10s and  40s.  40s were the traditional weight of shirting, and bolt of shirting requires a quarter million yards of single.  That is real spinning!

I love the big "50 mm" whorls because they give me much more precision with the differential rotation speed.  In addition to the 10s, there are hanks and bobbins of 20s and 40s around.

In the past, I did not finish whorls. Now, I finish them with Danish oil because I get a more uniform layer of  belt dressing adhering to the whorl.  Belt dressing tends to form clumps and lumps on whorls without the oil finish. 

The sweaters are being knit  from sport weight 5-ply with a soft ply twist on 14" hollow SS 1.65 mm needles with a Shetland knitting belt. These needles tend to collapse when used with a wooden knitting sheath. It is a good, fast, inexpensive system.  It works.

I got left at home to make dinner so:

 New flyer whorl for 50s, 60s, and 70s.  It really is amazing, I hook it up to some moderate grade Merino and let it rip, and there are 20 to 24 fibers in resulting thread.  That is the yarn that combination of takeup and twist insertion favors.  The spin count of the Merino likely in the 75-77 range so 22 fibers would give me a grist of just under 40,000 ypp, and the whorl works.  There are still some geometry issues (drive bands coming off), but right now I do not know a faster and easier way to spin 38,000 ypp singles. I have to dig around and find 60 and 50 count fiber to test the other grooves.  (Actually, I know where they are, but I have to get the sawdust out of my hair and bake a cake.)

50 mm whorls

The new whorls are about dialed in. I am pleased that they allow sustained bobbin speeds in the range of 3,400 rpm.  That is not peak bobbin speed, but is sustained bobbin speed. When spinning 5,600 ypp worsted (10s), that is 10 yards per minute.  Suddenly, turning out a knot free hank of 560 yards in less than 90 minutes is not a problem.  The intended weight of such hanks is 45 grams, and mine are running between 40 and 50 grams.  I think pretty good for hand spinning.  Spinning 20s (22 grams) goes at about the same rate or even a little faster.

My critics look at my pix, and say that I spin "thick and thin".  Perhaps!, but the average comes out to the grist that I want.  Can they sit down and spin their "uniform" singles, to produce 560 yards of the grist that they intend in 90 minutes?

With DRS, and these speeds, the spinning process is different.  There are videos of the way that I spin on this blog.  The top is wound onto the distaff, and is pulled off with my right hand.  DRS controlled takeup pulls the yarn out of the tip of the drafting triangle, while  my left hand controls how much twist runs into the drafting triangle.  The fibers in the top are parallel, and remain parallel in the drafting triangle, so that the final thread is full worsted. In other modern worsted drafting techniques, the fibers have a tendency to become skewed in the drafting triangle, and thus they must be pulled out straight and parallel again. This skewing of the fibers is inherent in the tension required to oppose the continuous take-up from a flyer/bobbin assembly not controlled by DRS.  I do not have  to resist that continuous take-up so I do not bunch up the fibers and push them out of their parallel alignment. My right hand controls attenuation, and my left hand controls twist, I do not draft per se.  This is not a process that works with Scotch Tension, Irish/German Tension, or double drive where DRS is not strictly controlled. It works better with finer singles. This is the fast and easy way to hand spin fine worsted singles.  And, If I have the drive band in the correct groove in my whorl, I know that the resulting hank will be close to the intended grist.

A video of the process shows me sitting there, making tiny hand motions.  It looks like I am treadling and nothing is happening.  The flier is moving much too fast to be captured on video. And, the video does not capture the thread being formed and wound.  At higher grists, the thread just disappears, so it looks like I am just sitting there treadling with no evidence that thread is being formed.

Yesterday, I did make a whorl for shirting/hosiery singles (soft and firm twist 40s, 22,400 ypp).  In a world where much of the wool was 40 count, it may very well be, that for spinners, it was faster to let the fiber flow through their fingers as above, to produce 40s, than to put extra effort into drafting thicker singles.  That is, the spinners traded more treadling effort for less drafting effort. And, the weavers gladly accepted the finer plies because it gave the fabrics a much nicer drape and hand.

Wood blanks to make whorls for "fines" are stacked  on the work bench beside the lathe. These will be for the #0 flier, but I have not designed that bobbin yet.  And, there is a real chance that fines will need a higher ratio accelerator.

A good production rate for shirting using these tools/techniques is 5 or 6 yards per minute, and the drafting technique works better at rates above 3 yards per minute.  This makes it seem like 240 yards per hour (bobbin =3,000 rpm) was a good commercial rate for a hand spinner.  Thus, a spinner could likely produce 4 worsted hanks per day.  Woolen spun requires more twist for the same grist, and thus with a wheel, my woolen yarn production at this grist is close to 200 yph.  For spinning fines, I have pushed bobbin speed as high as 5,000 rpm, allowing fines (more than 30,000  ypp) to be produced at 5 or 6 yards per minute.  This is fairly high effort and noisy, and I am not sure whether this could be a commercial rate.  

This rate of production can be easily sustained without ball bearings.  A wheel running at 3,000 rpm using leathers, bronze against steel and wood against metal bearings can sustain such speed when lubricated with lard oil. It is noisy, but all those bearing surfaces seem to last for at least 4,000 hours of use.

All in all, I think that professional spinners with flyer/bobbin wheels could have spun between 200 and 400  yards per hour of singles in the range of  5,600 ypp -10,200 ypp and between 200 and 250 yph  for grists in the range of  22,400 ypp (e.g., shirting and hosiery) .

Twist and Grist

I have been accused of getting my twist numbers wrong.

That is unlikely.  I may have made a typo here or there, but over all, I am the one hand spinner that always knows his twist.   I use differential rotation speed (DRS) without slip to control twist insertion.  Once I install the whorls on the wheel, I know how much twist will be inserted.  If I want a thicker yarn, I do a more woolen preparation.  If I want a thinner yarn, I do a more worsted preparation, and thus I can get a range of yarns from particular whorl combination that inserts a specific twist.  However, I can always look at the whorls on my wheel and know how much twist is being inserted.

Thus, I have to know the twist for every yarn that I plan to make.  Once the whorls are (made and) installed -- the twist is set.  How fast I treadle does not affect inserted twist.  How fast I draft does not affect inserted twist.  Yarn build up on the bobbin does affect the effective diameter of the bobbins and hence rate of take up and hence twist.  However, this is a known factor that is predictable.

I know that when the whorls that produce 9 tpi are on the wheel, and I am spinning worsted I get 10s (5,600 ypp).  I have measured, and validated this hundreds of times.  I know that when the whorls that produce 17 tpi are on the wheel, I get 40s.  I have measured and validated this many times. I also have whorl combinations for 5s, 20s, 30s, 50s, 60s, 70s, and 80s that have been have measured and validated. Each allows me to produce a specific grist of worsted and a different, specific grist of woolen and intermediate grists of semi-woolen and semi-worsted.

If I want to sit down and just play with a fiber, then I am likely to set the wheel up as single-drive, bobbin lead (Irish Tension).  Most of my plying of hanks of  5-ply  gansey yarn or 10-ply Aran weight are done using the Ashford ST Jumbo flyer. Thus, every week, I do work with ST and IT fliers. With IT or ST my twist is as fallible as anyone's. However, most of my spinning is done with DRS because it is more productive and my twist more precise.    Spending a lot of time working with precise twist makes me a better spinner when I am using ST or IT.  Sock weight yarns with large numbers of plys are plied using DRS control of  the AA #1 flier. This holds twist to within a few percent. That limits my sock yarns to skeins of about 10 grams or about 80 yards.  Small skeins are my penalty for demanding precise twist in my 6-ply sock yarns.

On the other hand, my WPI measurments tend not to be consistent with several other authors.  I worked with yarns of known grist and practiced doing WPI until my measured WPI for 5,600 ypp (10s) was a consistent 75,  my measured WPI for 11,200 ypp  was just over a hundred, my WPI for shirting or hosiery yarns was 150, and etc. This seems different from other authors, but most do not write about spinning this fine. In every case, my WPI tests were done with worsted spun rather than woolen yarns., and this may explain some of the difference. However,  I always pack to refusal, because it provides more consistent results. At this time, I do not trust my WPI for woolen spun yarns.  It is likely off by 10 % when it should be accurate to 6%.  Thus, to get the grist of woolen yarns I weigh a measured length.

I think some authors do not pack to refusal, so their WPI and hence estimated grist and required twist are different from my numbers.  My numbers work - consistently.