Tuesday, February 25, 2014

Maths, physics, and logics

I hate it when somebody talks down to me, so I try not to do it.

However, it seems that I must talk "baby talk" for Gorden to understand me.

Here goes:

I have a Ashford Traditonal with double treadle and  ~550 mm drive wheel.  On this wheel, I use custom "fliers" (as opposed to generic flyers).  The whorls on the fliers are approximately  19 mm (plus or minus 3 mm).  Thus, my ratio is ~29.  As an old bicycle racer, my normal cadence is 90 strokes / min,, but I can sustain a cadence of 180.  Thus, if there is no slip in the drive band, the bobbin speed is in the range of  2,600 to 5,200 revolutions per minute (rpm).

My first real lesson in spinning was that drive band slip with spinning wheels is huge, and much, much larger than indicated by the literature. This lesson was rudely delivered by my digital tachometer.   In particular, I discovered that the Ashford  lace flier had huge belt slip and did not go nearly as fast as predicted by ratio (near 30) times cadence.  In fact, it did not matter how fast I treadled or how tight I cranked up the tension, it did not go faster than ~1,600 rpm.  Despite this low rpm, I spun a great many miles of lace weight singles on that flyer.

The first flyer on which  I was able to sustain a flyer/bobbin speed of over 2,000 rpm, was the Ashford double drive flyer with the flyer whorls turned down so that the flyer/bobbin assembly had a differential rotation speed (DRS) of 1.06 and thus, no drive band slip was required.   This setup was some 25% faster than the Ashford lace flyer at the same treadle cadence.  It has been 4 years since I first  broke the 300 yards per hour barrier for 9 tpi  lace singles using the DD/DRS.  Calculation of DRS is described in Alden Amos' Big Book of Handspinning in detail, and in all of the early 20th century manuals for professional spinners. The latter are available on the internet.   DRS is part of the traditional knowledge that every competent spinner knows well.  I accept that one can be a good spinner without math skills, but math skills are absolutely required to become an excellent spinner. When you can do this math, then you know that twist is inserted by the rotation of the bobbin, not the flyer. The flyer inserts some twist, but not enough to make a competent yarn.  It is the bobbin that inserts enough twist to make yarn instead of a dust bunny.

Three years ago, I had Alden Amos make me a couple of small, high speed fliers. For these fliers, I turned additional bobbins and flier whorls, as noted above. About this time, and critical to my success, I switched to a drive belt tension using 2 weights connected by a spring.  This device keeps drive belt tension very uniform and helps dampen vibration. These fliers and drive belt tension device allowed me to spin more than 400 yards per hour on a sustained basis.

Sometimes, I spin single drive, bobbin lead (Irish or German Tension)  The AA#1 flier, starts to have significant windage and hence take up at around 2,800 rpm. This about the speed that I spin 11,200 ypp (20s) singles.  Lower grist (e.g., 5,600 ypp, 10s) singles need more take up, and thus must be spun faster.  At about 3,000 rpm, take up is enough for 2,800 ypp singles.   I used this setup to spin 17,000 yards of woolen loom weft last fall.  Irish Tension on this flier works for grists in the range of 2,800  to 11,200 yppp.  Another 17,000 yards of loom warp was spun last fall using a  double drive with differential rotation speed control ( DD/DRS) set up. Thus, I have a direct comparison between the  Irish Tension and DD/DRS.  

(When was the last time that Gorden spun 20 miles of single for a project? Perhaps the truth of the matter is that Gorden does not really spin very much. )

Sometimes I spin single drive, flier lead (Scotch Tension, ST). The brake band is a piece of  heavy nylon fishing line, tensioned with  small weights.  This set up allows changing grist very quickly. On the other hand, using  Scotch Tension, it is hard to maintain consistency.  Mostly I use ST for grists in the range of  22,400 to 45,000 ypp.  Note that with my double treadle, drive belt tensioning, and cadence, I am spinning the flier/bobbin assembly in the range of 3,000 to 4,000 rpm.  This works because I have put a lot of time and effort, to make it so.  It is a fast way to spin at the spin count.

That leaves double drive.  This is where it gets interesting. When Alden Amos or Henry Clems  or Robert Ashford set up double drive systems, they design in some slippage between the drive band and the flyer/bobbin assembly. (See Alden Amos for details.)   I avoid such slippage.  DD/DRS was the first system that I made that avoided substantial slippage. As a result, it was 25% faster than either IT or ST. At the time, this was a very big deal, and I loved it.  Now, I have other ways to go fast.   In DD, rather than the slippage discussed in AA, I either spin a bit (10 grams) of thread and wind off before the effective diameter of the bobbin changes, or I make flier whorls with different drive band grooves so the DRS ratio can be changed as the bobbin fills. This seems like a lot of effort.  Why do I bother?

My  DD system inserts a consistent twist. I can use that constant twist as a feed back to produce more consistent yarn.  Some spinners want to make spinning as difficult as possible, but I want to make spinning as easy as possible.  I want tools that help me produce better yarn.  I know that if I put this whorl with that bobbin, I will get 9 tpi, which can help me draft a 5,600 ypp (plus or minus 10%) single.  DRS helps me draft the correct grist, and to keep it consistent.  And, since there is no need for slip between drive band and the flier/bobbin assembly, the bobbin inserts twist wicked fast. I have bobbin and whorl combinations for every grist (e.g., tpi) that I commonly spin.  To make the system work, you do need to know the math. You either need a little cheat sheet in your spinning journal, or you need to do the math every time you select a flier/bobbin assembly for a project.

Also, using DRS, I can draft at a low grist for the inserted twist, and produce yarns that would drift apart if I tried to spin them using either Irish Tension or Scotch tension.  The only other way to spin such soft yarns is on a supported (or driven) spindle.

For a few minutes of spinning, DRS takes longer to set up, and provides no real advantage.  However, if you need to spin miles of consistent yarn, DRS is the easy path.

So, if I am spinner and I need to spin a hank of 56s from Shetland or Suffolk, I would likely just use Scotch Tension because I can just spin a thread of 20 fibers, and I will have the correct grist. However, if I need to spin 40s hosiery singles (17 tpi/ 22,400 ypp) from Rambouillet, then I can set up a DD/DRS system that will give me the correct twist per inch, and all I have to do is draft.  If I set my DD/DRS system to 9 tpi, then I can spin 10s  from Rambouillet, Shetland, Suffolk, Romney, or Lincoln and I know that I will get about the correct grist (5,600 ypp).

That said, if I am spinning 56s (31,000 ypp)  from Shetland using Scotch Tension, there is some likely-hood of the single burying in the spool and breaking off. This is a major pain in the neck, and spinners like Northrenlights avoid this by laying straws or slips of paper across the bobbin to keep the thread from burying.  However, DD/DRS can solve the problem by winding the yarn on at a much lower tension.  The lower tension makes burying/break off much less likely.  If I have to spin a significant amount of fines (34,000 - 45,000 ypp), it is well worth making up a DD/DRS bobbin/whorl for that grist. This is a non-trivial effort as difference between the two drive band grooves is likely to be less than 0.2 mm and this is difference tends to affected by changes in humidity, build up of drive band dressing, and knots in the drive band.  On the other hand, getting the DRS correct for a fine spinning project makes the project much easier and faster. And, at this point, I have the bobbin/whorl combination for dozens of different grists on hand.  All in all, I would say that DRS increases my productivity by ~10% over Scotch Tension or Irish Tension, and maybe a bit more for fines. When you are spinning miles and miles of singles, that 10% adds up into useful and valuable blocks of time.

Fine yarns need a lot of twist to hold them together.  Wool is easy to pull out in very thin strands, but having been pulled out, it needs twist promptly or it falls apart. Fine singles are easier to spin fast than to spin slowly.  DD/DRS is ideal for for fines because it does not tension the single before the twist is inserted.  In retrospect, I would say that DD/DRs was my training wheels for spinning fine. There is no slip so it inserts a lot of twist, and take up is always proportional to twist inserted.

One final point, at high speed, the yarn tends to get blown out of the heck array.  And, take up needs to be kept as high as possible to avoid the pig tails that can form instantly at high speed, but the fines that require the high speed spinning are delicate, and do not tolerate too much take up. DD/DRS controls take up, so there is no slack to get blown out of the heck array.  If your yarn gets blown out of the heck array, there will be a tangle and a break-off, and that will slow you down.

Spinning fast and fine is the mark of a good spinner. If one can spin fast and fine, then one can spin other yarns well.   For Gorden to get any respect from me, he needs to report how many hanks of  what grist he can spin in a day.  I think a man's man can spin a pound of wool into 5,600 yards of single in a day.  Using Irish Tension, that is 11 hours work. Using  DD/DRS it is only 10 hours work, so I get a lunch break.  I like lunch.  The moral of the post is:  Spinners that cannot do the math for DD/DRS, do not get lunch.

I do not spin fast for the sake of spinning fast, I spin fast so that I can reasonably take on larger and more interesting projects, and finish them with time to do other things.  I spin fast so that I can have a lunch break
  :  )

Actually, the bobbin whorl on the wheel right now is a large DD/DRS bobbin set to insert 12 tpi, but the ratio is only 18, e.g. the wheel is only running at about 2,200 rpm because I am working on a mix of commercial Merino that is very difficult to draft. So I am only  spinning about 300 yards per hour.  I am actually reasonably proud of this, because just after buying the fiber some 3 years ago, I thought it was impossible to spin.  It is one of those things that put me off of "Fiber of the Month" clubs.  I am sure that the report back to Ravelry will be;" Like any beginning spinner, Aaron has trouble spinning Merino."  And, that report will be made by someone that never in their life has spun that fine, that fast.  Ah, Yes, How fine is it? What is the grist of worsted at 12 tpi?  Gorden?  Anybody?


Anonymous said...

Riding your bike while pedaling 90 rpm does not necessarily make you a bike racer. You must of picked up that bit of information reading one of Lance Armstrong's books. 90 rpm didn't come naturally to him and he had to work really hard to change his cadence. Did you works as hard as Lance? And remember that some great cyclists do just fine on the World Tour smashing big gears.

Rach said...

I'd really love to see photos of the yarn you've spun.
Perhaps you could post a photo of the yarn from a full day worth spinning on your blog?

Aaron said...

I never met Lance, but I did meet Eddy Merckx who made going faster look like less work.

The guys that use big gears have fast twitch muscles -- that is a matter of genes. Guys that do well in the Paris-Brest-Paris race tend to have slow twitch muscles.
: )

Aaron said...

Did you notice the pix of 2 lb of gansey yarn? That is 6 miles of singles. Or, the 12 pounds of loom warp and weft?

I spin because I want to use the yarn, so the yarn goes to bobbins or cakes or . .. . and not into photogenic skeins. Folks said pix of bobbins or cakes do not count, so why should I bother?

If you want a demo, send me an invitation.

Rach said...

Hi Aaron,

I didn't see the yarn photos, I haven't read all the posts.
Photos of bobbins and cakes are cool, why do only skeins count?
Do you have links to the posts?