Category Archives: Charkha

Round n’ round

Yikes, talk about a long “on hold” period. After a nice projects-filled weekend I finally managed to make some headway on my Box Charkha project; specifically the drive wheels.
Charkha drive wheels
To catch up- I’ve been using this excellent article (now available in PDF) from Interweave’s 1996 Spin-Off on building a cigar-box charkha with some modifications. After amassing all the supplies and working on a plan I realized I didn’t have access to a drill press need to drill perfectly centered and balanced holes for the wheels. I was rather amused at the suggestions that everyone “knows someone with woodworking tools”. We’re 20 something techies, everyone I know is more likely to fix your computer or network than build you a cabinet.
Thinking it was too bad I didn’t live near my parents anymore I finally realized I could just ship the marked up pieces to my Dad to drill for me (thanks Dad!). I got the pieces back and it was promptly put on the back burner again by other projects. So, (somewhat) fast-forwarding to now here’s what I did.
The large drive wheel is made of the suggested two “basswood plaques” that are glued together right sides facing. The other larger wheel is a sandwich of three wooden circles with the smallest in the middle to create a grove that holds the drive band. A wooden spool is the smaller underneath wheel.
For the support rods and bearings I deviated from the article. I sawed plastic sewing machine bobbins in half to use as bearings instead metal tubing- easier to cut. Also easier to cut than the suggested metal support rods were bamboo knitting needles. This worked well since knitting needles come in such a variety of sizes, obviously. The bamboo needles were chosen to fit the inner diameter of the bobbins and the wheels drilled to the bobbin’s outer diameter. The mounting blocks should be drilled to the exact needle size and the rods tapped in tight. My measuring was off however and my holes were a bit large so I improvised with wrapping an o-ring around one and using another bobbin half as a spacer for the other (and wood glue, lots of glue).

Under the large wheel, not shown, is a “washer” made from cutting out a circle from an empty plastic food container. For the drive band I used jewelry beading hollow tubing (not sure what this is called) since it was easy to cut to size. In the photo above you can see the double wheel is flipped over to show the spool/smallest wheel. I think I’m going to replace that one however with a smaller one, especially after referring to my own calculations (duh) as it’d put me closer to my desired ratio. The other reason I discovered while taking these photos- the box no longer shuts, oops.
I originally sawed one of the spools in half, as it was a bit taller than it needed to be but my hand sawing leaves much to be desired. Even after lots of sanding it was far from level. Well the double wheel assembly comes off the post for storing and I laid it in the box to make sure it’d still fit with the full-size bobbin. It did; so I thought, great I’ll just use that. Forgot to take into account the support rod which also includes the height of the mounting block, heh. That’s kind of how this project has been going, trial and error. But I’m enjoying the creative challenge-next up, the spindle assembly!

Drive around

Now that I’ve assembled my parts for building a charkha I’ve started assessing everything. I decided to start with determining what drive ratios I want to create, as this will dictate the main components. Drive ratios on traditional spinning wheels are pretty straight forward. For each complete turn of the drive wheel, how many times it turns the driven object (such as bobbin or flyer) is the drive ratio. This is determined by dividing the diameter or circumference of the drive wheel by the diameter or circumference of the driven object. Abby’s Yarns has a good in depth post of basic drive ratios that goes into that further. For a charkha, or ‘accelerated’ wheel, there are two drive wheels, and the ratio of each is multiplied together to determine the final spinning ratio.

So using my set up as an example (I’ve used metric here because hey- it’s easier math) the formula is:
A1 / A2 = C
B1 / B2 = D
C * D = Drive Ratio
So we get, 108 / 22 = 4.9 and 50 / 12 = 4.2 which gives us 4.9 * 4.1 and a ratio of 20:1
Craptastic lighting!
Here you can see my actual pieces that will give this ratio. Basically, the greater difference in size between wheels of one drive band, the higher the ratio. I’ve found a variety of those little wooden spools work great, already predrilled to the desired size and interchangeable. I also have a 1/2″ or 12mm spool I can use for A2 that I’ve calculated will give me an even higher ratio of 37:1. If I want to push that even higher, I’m looking for a smaller spindle pulley (around 1/4″) that would allow me to interchange spindles to change ratios- up to 75:1. This would be closer to the true Indian charkhas that typically have ratios around 80:1 – 125:1, great for cotton.
In the other direction, I’ve calculated a simple flip of B1 and A2 from the above illustration would produce a 4:1 ratio with spindle 1 or an 8:1 with spindle 2. Thus lowering it enough to be suitable for longer staple fibers such as wool.
Can you tell I’ve had fun playing with numbers? Here are a few other notes on the wheels that I’ve learned. At one point I had thought about having the second drive band simply connect to the spindle/knitting needle rod directly, with washers on each side to hold it in place. This would obviously push the ratio way up, but I have since realized with such little surface area for the drive band to grab onto, traction, and therefore slippage, becomes an issue. Additionally, the farther apart the wheels are placed helps create more surface area contact between band and wheel and again, improves traction.

Reinventing the wheel

So what’s all this crap? Well I’m hoping to turn it into my very own Charkha spinning wheel based on these instructions. In fact, I’ve been rather obsessed with it since the idea rooted itself in my head. I’m modifying several of the components from the article however. Some things are stuff I’ve come up with and others are from tips I got off the Charkha yahoo group list. It’s been a good practice in overcoming functional fixedness for sure. I think half the fun has been strolling through craft/fabric/home improvement stores looking at everything as possible pieces.
The new craft room’s paint is dry and furniture put in place, now I just need to organize everything. I hope to have some photos soon along with some, you know, actual blogworthy knitting.
11/9/2009 – Just a note that the link to the Spin-off PDF on Cigar Box Charkha’s has changed. You know need to sign up to download it but it is still free!