Archive for the ‘springpole lathe’ category

Spring pole lathe details

December 14, 2012

The most popular topic on this blog, over the past few years, has been my spring pole lathe.  It is a heavy duty version of Roy Underhill’s German style lathe.  It is very rigid and stable, quite capable of doing large work.  Hope these detail shots will help anyone who decides to build a reciprocating, foot-powered lathe.  You’ll become a better turner for your efforts.

A Lathe by any other name still goes round and round

May 13, 2012

Several weeks ago, Mary and I went to visit  my cousin, Tim, and his wife, Diane.  Tim and Diane are potters.  Tim “throws” big pots, while Diane does built up and molded work.  You can see more of their work at www.millerspondpottery.com .

Cousin Tim with one of the jardineres he “throws”

While watching Tim at his potter’s wheel, I was struck by the realization that it was very much like a lathe with a vertical axis.  Of course when someone mentions potter’s wheel to me and I immediately think of Demi Moore in “Ghost”.  But as Tim explained it to me the actual process of throwing big pots is very similar to bowl turning, especially segmented turning. First a block of clay is “mounted” on the wheel and the shape is “pulled” up.  Now you might think that the big pot above would be “pulled” all in one session.  As with so many things in life, what you think isn’t always the way it really works.  Remember, clay is a plastic material and subject to the rules of gravity.  Perhaps a fourth of the overall height is established in the first session, then the vessel is set aside until it reaches a state that potters call soft leather hard.  Why do call it that?  Because the material is still pliable but can support a greater load without deformation and feels like leather.  At this point the potter adds coils of clay stock to the top of the vessel and blends them into shape.  The process is very much like adding segmented ring sections. Another big misconception many folks have is that the potter does all of the work with his hands.  I noticed that Tim had a shelf full of tools, many of which looked vaguely familiar.  He explained to me that the final shape is really a result of  “trimming” , the part of the process in which tools are used to remove stock.   Trimming, I found, was very similar to turning.  The big difference being that Tim uses no tool rest.  He simply anchors his elbows into his body for support.  Finally, Tim said “sit down and give it a try”.   So I did.

Many of the tools Tim uses are like hook tools used by some woodturners. Note the four jaw “chuck” on top of the wheel

Of course Tim tried to convince me to go home and build a wooden framed “foot” wheel and take up yet another non-revenue producing avocation.  I must admit it’s pretty interesting stuff.  But I think I’ll stick to woodworking and let Tim and Diane take care of the pottery.  By the way, professional pottery making takes up every bit as much space as woodworking.  It’s probably not something you can do in a one bedroom apartment.

Diane in the glazing area

I’m sure Mary and I will be heading back down to Miller’s Pond before too long.  It’s an idyllic spot and there’s a lot to learn from fellow crafts people.  I’m always struck by the similarities between crafts and how good ideas universally impact almost every area of endeavor.      

Getting away from pottery for a moment, Matt (a fellow pole lathe devotee) is selling a Underhill style lathe at a very good price.  If you’re interested go to his Craigslist listing cedarrapids.craigslist.org/tls/2984451622.html

Making the case for fancy firewood

November 22, 2010

I have a neighbor down the block who heats his workshop with wood.  So every couple of weeks, I’ll set out my cut-offs and scraps for him to pick up.  He stopped by not to long ago and told me that he simply felt too guilty to burn some of the stuff that I had put out for him.  I asked him what he was talking about.  He said that some of the turnings I was getting rid of could certainly be put to some good, artistic use.  I said that they had proven their usefullness by providing me with practice.  I told him to simply consider them “fancy firewood”.

I turn a lot.  Most of what I do is spindle work for furniture or architectural projects.  I turn on both a powered lathe and a springpole lathe.  And, I do a fair amount of “face grain” turning as well.  But if I go much more than a week between turning projects, I will start doing practice pieces, just simple bead and cove exercises.  Why?  Because turning is unlike most other woodworking skills. It requires the development and maintenance of a high level of manual dexterity to achieve a reasonable level of proficiency.   Most woodworkers who use power tools as their primary method, can go for months between projects and still accomplish the desire result when cutting parts, routing edges or sanding finishes.  Not so the woodturner.  You MUST practice!!!!

Woodturning is more akin playing the guitar, or hitting consistent wedge shots than it is to running boards across a jointer.  You must understand the tools that you are using at a very tactile level.  You must understand their various cutting geometries.  You must learn to control your tools with finesse, not by the strength of you “Popeye” like forearms (you can’t turn for very long with cramps in your forearms, by the way).  You’ve gotta get to the Zen of it and the only way you can do it is by standing in front of the lathe making shavings.

So if your wood burning neighbor tells you that your throwing away good stuff, just tell him that it’s okay – that you’re making fancy firewood for him and you’re becoming a better turner because of it.

Using medieval bow making technology to improve performance on the springpole lathe

November 13, 2010

When I built my springpole lathe I decided to make it larger and heavier than Underhill’s model.  The capacity increase has really paid off as I can turn up to fifty-five inches between centers and and swing twenty.  However, there was one thing that I overlooked.  I never gave a thought to the diameter of the springpoles.  With the added weight of the crossarm, treadle and larger workpieces the one inch diameter is a bit on the “skinny” side, especially as the original main spring was made from yellow pine. 

The yellow pine is more than adequate in the area of stiffness.  But after about a month, embrittlement set in and, SNAP went the original mainspring pole.  The I tried white oak.  It had plenty of flexibility.  Too much in fact.  So, ultimately I used some bowmaking techniques to improve the performance of the mainspring while staying within the 1″ diameter.  I’ve used both ash and hickory.  I’ve split them in two, then glued them back together.  The increase in stiffness is remarkable.  I’ve joined three pieces to form a sandwich of hickory and ash.  The result was a strong, durable main and secondary spring that has performed extraordinarily well for more than a year.

The Bowyer's Shavehorse

Rounding an eight foot long 1″ square block is best accomplished with a stale engine.  Most people don’t have stale engines or rounders, so they opt for the next best thing, the drawknife.  Well anyone whose attempted to shave an eight foot workpiece on a conventional shavehorse, knows that it can be quite a challenge.  So, I remembered a video I had seen on YouTube of French Medievalist Longbow maker Denis Mairine using a shave horse that allowed him to work in a standing position on overly long, thin workpieces.  It is simply a ramped bed, legs that support the ramp and allow for some height adjustment, a lever board and some rope.  In fact it would probably be best described as a rope vise that has been specifically designed to hold this particular type of work.

Simple, effective and highly portable

Note that the drawknife position is just about ergonomically perfect.  That said, it does get a little bit tricky standing on one and a half feet.  But hey, this certainly is no problem for a springpole turner.

Spring pole lathe details

March 12, 2010

I’m always surprised by the number of people who are genuinely interested in my spring pole lathe.  Many of them have asked me for more detailed information about its construction and use.  So I thought that I’d take the opportunity to post some detail photographs of the lathe.  Discussion about reciprocating lathe turning techniques will continue to be the subject of frequent posts for some time to come. 

First, let me say that I learned of this design from Roy Underhill’s writing  (human powered lathes play prominently in several of Roy’s books and I encourage anyone who may be reading this to become familiar with all of his books).  I believe that he referred to it as being German in origin.  It is quite sophisticated, as spring pole lathes go, as it uses two spring poles that are completely contained within the lathe’s framework.  This makes the lathe both highly portable and amazingly stable.  My lathe differs from Roy’s in several ways.  First, it is larger; center height is 46″, swing – 20″ and capable of nearly 60″ between centers (tailstock removed and dead center positioned in the right side frame member).  Second, the lathe is fitted with a fixed treadle that can be operated at any spot along the entire length of the lathe.  Lastly, the ways are wider and deeper,  and a set of lower “stretchers” were incorporated into my design.  The stretchers may be overkill, but I wanted to insure the lathe’s rigidity and stability and that was accomplished. 

The ability to adjust the amount of tension is very, very important.  This design provides a number of ways to “tailor” spring tension and stroke length.  The spring bridle, upper and lower connecting rod position, line position and treadle adjustment all come together to optimize the lathe’s performance. 

Enough talking, let’s get to the pictures! 

The "finished product"

Getting started

Tool rest - note steel wear bar

Tool rest slide

1/2" handle nut locks dead center into "weld nut" (available from McMaster.com)

Dead center (1/2" carriage bolt) held in place by "weld-nut"

Hickory wedges hold frame together - spring poles are "jam fitted" into "head post" (note grain orientation to avoid splitting)

"Main spring" with connecting rod (1/4" HR bar) and retainer

Crossarm rides on 1/4" carriage bolt in bronze bearing - notched keep connecting rod in position selected

Toolrest locking bolt - 1" wooden screw

Treadle - 3/8" rods ride on bronze bearings that drop into slots in the feet - allows for easy removal of treadle for transport

treadle detail - from rear

treadle detail - from rear

treadle detail - from rear

Spring bridle - note relief so spring is not damaged during movement

Tailstock or poppet, if you prefer

Just a couple of other points…

MATERIAL

Frame, toolrest and tailstock – Yellow pine dimensional lumber (2×12)

Treadle – Ash and yellow pine

Springs – laminated hickory

Threaded and tapped parts – cherry, maple, apple

FINISH – 50/50 Boiled linseed oil and Pure Gum Turpentine (elemental “long oil” spar varnish)

Sidewinder Lathe Project Update

February 21, 2010

Well, I’ve completed a number of “required” projects and now I can get back to the “fun stuff”.  The Sidewinder lathe is taking on “a life of its own”.  I’ve done some re-examining of my goals for this project.  Here’s the current list of things that I’d like to accomplish by building this lathe:

  • design and construct a lathe that is human powered, but still capable of a range of speeds that will allow for high quality execution of the work on a reasonbly broad range of diameters, up to eighteen inches;
  • be able to turn pieces up to sixty inches in length on a fixed bed (perhaps longer with a bed extension);
  • minimize the footprint, by positioning the driving wheel parallel to the lathe bed;
  • utilize contemporary work holding devices

In short, the goal is to build a big lathe that will be capable of turning large parts using modern chucking while occupying a small amount of floor space and – DO IT WITHOUT A MOTOR!

Okay, so I’ve got to start somewhere.  And, it seems to me that the logical place to begin is with the drive mechanism.  This, it would seem, would consist of the power supply (Me!), the power transmission apparatus, and the speed control system.  Alright, you’re right to ask the question – if I’m using a treadle, which is driven by human power, why do I need a speed control system?  Can’t I just increase or decrease the treadle speed as required?  Well yeah, I could.  But if anyone has every ridden an old single speed bike up a hill, you’d immediately know why some method of speed control (or more appropriately power control) would be so desirable. 

I plan to use a large drive wheel, forty-two inches in diameter.  From working on my springpole lathe, I know that about one hundred treadle strokes per minute is a pretty comfortable pace.  The math is realatively straightforward, I’ll be able to generate a pretty good amount of speed.  Ahh, here’s the problem.  The springpole lathe, you see, is all about torque.  It is a “torque monster” (as Underhill says, great for cutting multiple threads).  The “big wheel, high gear, high speed” lathe won’t be very torquey.  It’ll be kind like when Honda brought out their 250 cc four cylinder motorcycles to the race track.  Everyone thought their little rubber bands would break (but they beat everything in sight).  However, when I’m roughing in a large piece of stock, I’m going want to run at a slower speed with adequate power (torque).  Therefore, the need for some type of gear change mechanism.

So for the past few days, I’ve been thinking about methods of gear changing that I might use.  The whole issue is pretty well complicated by the fact that I have a right angle change of direction in the “power supply” line.  I thought about a step pulley arrangement but that would require the use of some kind of tensioning device (idler, etc.).  That device would not only take up valuable space, but it would also alter the direction of the power transmission (spliced rope or round leather belting).  Then there’s the problem of the type of belting I would use between the two step pulleys, as I invision them as being supported at both ends, not cantilevered.  Then, EUREKA! – a flash of insight.  Why not use two cone pulleys with a transfer idler?  Truly variably speed.  After a little simple mathematics; Speed of drive pulley X Diameter of drive pulley / Diameter of driven pulley = Output speed,  I figure that if I pump the treadle 100 times per minute, I can realize spindle speeds of between 175 rpm and 2950 rpm by simply moving the transfer idler.  Here’s a diagram of the “theory”,

So…If there’s anyone out there in “Lalaland” who’s as goofy as I am, let me know if you think that my theory holds up.  I’d be most appreciative of any input.

Obviously, this little project isn’t going to be completed within the next couple of days, so I’ll keep you posted.

SPRING POLE LATHE TOOL CHOICES

January 16, 2010

When I first became interested in spring pole lathes I assumed that I would simply use the same tools that I used everyday on my powered lathe.  I remember reading that a spring pole lathe was “safer” than a powered lathe due to its lower operating speed.  Well, it turns out that due to amount of torque generated and the fact that a spring pole lathe is a reciprocating tool, I’ve re-thought my tool selection.  Perhaps I can save some novice pole turners some frustration by sharing a few thoughts about some tools that I find useful when using my lathe. 

IMG_1530

My little "Pride and Joy"

 Understanding the “Catch” 

Most  turners  use the word “catch” to describe the moment in which a shearing tool, more often than not the skew chisel, decides to take off, seemingly of its own accord, and leave a deep diagonal line across the face of the work.  This, invariably, happens when the surface is nearly complete, necessitating an unexpected “design change”.  This phenomena might better be referred to as a “chase” or “skate” as it is created when the cutting edge has an insufficient clearance angle.  The workpiece literally drives the tool which acts like a threadchaser.  Due to the high torque of the spring pole lathe, a “skate” can happen very easily. 

The classic skew "skate"

 Rolling Beads 

Rolling beads with a skew is the mark of a skilled turner.  That said, the fact that you are presenting a cutting edge that is diagonally positioned to the rotation of the work is “flirting with disaster”.  The skew chisel will remain the best finishing tool, bar none.  However, when rolling beads on a high torque, reciprocating lathe, there may be other options that will make life a little easier.  The first is the beading and parting tool.  It is simply a narrow, double-edged chisel.  It is simply presented perpendicular to the workpiece axis, then rolled in either direction to form the bead.  The finish left by the tool is quite good as the double bevel burnishes the surface as the cut is made. 

The Beading and Parting tool - note the perpindicular presentation

 A second option for rolling beads is the bedan.  It is similar in size to the beading tool.  However, it is a single bevel tool.  This means that the cutting edge is ground at a steeper angle than the beading tool.  “Bedan afficinados” will typically work the bedan in an “upside down” manner, meaning bevel up.  I becomes a very agressive shaping tool when used in this manner.  The surface finish created when using the bedan in this manner is rather “open” and may required a little additional burnishing or sanding.  Using the bedan with the bevel down yields a nicely burnished finish.  The steeper cutting angle will require some adjustment.  The turner may find that a “bevel down” bedan offers a somewhat better finish when turning figured workpieces. 

Running the Bedan with the bevel up

Gouges – Shallow is good 

For me, a shallow gouge and a perpendicular presentation seem to work best on the spring pole lathe for creating longer or varying radius curves.  The classic “English” grind or a shallow “Ladyfinger” work especially well.  That said, I’ll frequently use a very exaggerated detail gouge for rolling convex, as well as concave surfaces.  With gouges, like straight or skewed chisels, the turner must be aware of the cutting and presentation angles.  

"English" grind shallow gouge

"Ladyfinger" shallow gouge

Sharp tools, understanding cutting geometries and practice = Great results
 
Practice, practice, practice.  And, when you get a little discouraged, just remember that some of most complicated turning ever accomplished was done on a spring pole lathe, well before the discovery of electricity.
 
“It’s a poor workman who blames his tools”

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