Tag Archives: bow saw

Turning Saw – Putting It All Together

Turning Saw 9After shaping the frame parts, all that was left was construction of the two handles and the winding toggle shown in the picture above.  Unfortunately, I’m not fond of trying to photograph while using power tools, even the lathe, so I’m afraid you’ll have to settle for my descriptive prose.

The toggle starts life as a ½” diameter cylinder easily made from offcuts from the saw (at least in my case).  The ends are rounded and a cove us turned near one end.  The cove retains the tensioning strings and allows the toggle to pivot when under tension.  After parting off, the opposite end is flattened into a paddle shape.  There were several ways this could be done, but I chose the stationary belt sander as the most expedient – 60 seconds start to finish.  Just hold by the grooved end and press the opposite end to the belt.  Flip and repeat.

Turning Saw 10Yes, the handles are cocobolo.  I didn’t have any thick hickory, and didn’t care for putting a glue line right in the middle of a knob.  I know the wood is still strong, but it bothers me for some reason.  Besides, I had some leftover turning squares laying around by the lathe.  I started to use mesquite, but found a cocobolo blank that was just the right size.  I grabbed one end in the chuck, bored a ¼” hole for the blade pin, and shaped a handle.  The form is simple, and makes a good turning exercise.  Again, precision is NOT required.  The second one quickly followed.

After completing the handles, the blade pins are glued into place.  The butt end of the pins has a series of concentric grooves connected by a lateral channel – perfect for gluing.  I followed the recommendations and used a slow-set epoxy.  I dribbled some into the holes and then pressed the pins into place.  You might want to have some sort of clamping device standing by if the fit is a bit tight.  That little bit of extra pressure can make all the difference.  This is when you find out what that channel is for.  As the pin presses in, some of the epoxy is squeezed back around the flange in the middle of the pin.  Just be ready with a paper towel and wipe as it appears.  This works better than trying to get all the squeeze-out at once.

My choice for a finish was my usual shop-grade one – diluted boiled linseed oil flooded on and wiped off in two coats.  Simple and effective.

Turning Saw 11All that remained was to assemble the final product.  The stretcher fits into the mortises, and the blade is hooked into the pins just like a coping saw.  I followed the recommendations for stringing and used 50lb braided fishing line.  It had been a long time since I bought braided line, and I was unprepared for the change.  This stuff looked more like monofilament, than the braided nylon I was used to, and I was more than a little skeptical about it.  After all frame was assembled and the blade was in place, I made four slightly loose loops around the two horns and tied the ends together.  The toggle was placed on the inside of the loops and twisted to tension the blade.

A word here about tension: The notes on the TFWW website are vague about the amount of tension required, and after a bit of fiddling I understand why.  Tension is a very subjective thing.  I’ve been very conservative so far, after reading the dire warnings about the perils of overtensioning.  How much is enough?  I’m not yet sure.  For now, I’m playing with the following numbers:

“Slack” is considered to be the point where, when released from the stretcher, the toggle won’t unwind on its own (about three turns).  “In tension” is five or six additional turns beyond that.  “Overtensioned” is the point where something cracks – something I don’t really want to find.

I’ll spend a little time with the saw, learning its quirks and finer points, and then report back with what I’ve learned.  Till then, I highly recommend that you try one for yourself.  It’s a fun and simple project that yields an inexpensive fix for your saw problem.

Advertisements

What I Screwed Up This Week – December 12, 2010

Welcome back for another edition of What I Screwed Up This Week!  Once again, we’ll be looking at a problem with building the turning saw.

The Problem:

Screwup 121210

After affixing my templates to the hickory, I went ahead and cut the pieces out without taking into account that I needed to bore pin holes (bottom circles) and chop mortises (upper circles).  This left me in a situation where the pieces would not be properly supported during these operations.

The Solution:

Turning Saw 4&5I used cabinetmaker’s handscrews to hold the pieces in alignment during the drilling and mortising.  Handscrews can, when properly adjusted, provide excellent holding power for irregularly-shaped objects, and can act as a flat reference surface when performing operations like drilling.

Lesson Learned:

Whenever possible, plan to do operations like mortising or drilling BEFORE cutting the curves on parts.  It’s often possible to establish flat reference surfaces parallel or at right angles to the area that needs to be worked.  Then, proceed with shaping the piece after the machining or joinery is finished.

Turning Saw – Shaping the Parts

Turning Saw 4&5My next step was to bore the holes for the blade pins.  If I had been smart, I would have done this, as well as chopping the mortises, before I cut the blanks to shape.  Since I’m not, I had to use a handscrew clamp to hold the pieces in proper alignment.  That done, I then chopped the mortises for the stretcher, again using a clamp to hold things steady.  The size of the mortises isn’t critical, since they simply align the stretcher.  In fact, they should be a bit oversize to allow it to shift as tension is applied.

Turning Saw 5The tenon stretchers are a bit more work.  They were cut to length during the rough-out in the previous episode, but now are cut to width, and the shoulders curved to match those of the mortises in the saw cheeks.  I transferred the width with the marking gauge used to define the mortises, but had to adjust the length slightly due to the fact that the cheeks are a bit thicker than the stretcher.  I then sawed down to the tangent of the shoulder with a dovetail saw, and removed the waste by paring straight down with a gouge.  In this case, a #3 sweep carving gouge was perfect.

Now, it was time to shape the parts.  For me, this meant saddling up the shavehorse and breaking out the spokeshaves.  If you don’t work that way, don’t worry – there are plenty of other ways to perform this operation.  The stretcher has a tapered octagonal shape that is easily done with the spokeshave.  Another option would be to make an oval instead of an octagon.  Don’t make a big deal of slavishly copying the pattern here.  The whole point is to lighten the structure somewhat and make it easier to work the toggle.  Go for smooth flowing lines.

Turning Saw 7 and 8The cheeks are a collection of various shapes.  I decided to begin by rounding over the bottom of the cheek where the pin passes through.  To do this, I clamped the piece in the vise and cut facets on the corners with a rasp.  These were then rounded into a semicircle with rasp and file.
The finger rests were then shaped using the round side of a rasp, which makes a perfect indentation, then cleaned up with a half-round file.

Turning Saw 6A close look at the pattern reveals that the horn end of the cheek tapers to about half its original thickness.  For this, I went back to the shavehorse and gently worked the taper with a sharp spokeshave.  I then shaved as much of the bullnosed edges of the cheeks as possible, then switched to rasps & files for the rest.  This was followed up with a general clean-up and smoothing with sandpaper.  I paid particular attention to the horns, removing any distinct corners and creating a near-oval shape.  This area would hold the string in tension, and I didn’t want any sharp corners causing fraying.

Turning Saw 9With that, the basic frame pieces were made.  Next time, I’ll touch on making the handles and toggle shown here, add blade pins, and finish.  We’re in the home stretch.  Stay tuned!

Turning Saw – Roughing Out the Frame

While I was waiting for my 1” mortise chisel to arrive to complete the dummy frame, I decided to start on another project.  The dummy slats had left me with a surplus of hickory that I decided to use for something I had been wanting to build – a turning saw.  For those unfamiliar with this tool, a turning saw is a type of small bowsaw that performs many of the functions of the bandsaw.  It has a thin, tensioned blade something like a coping saw, but is larger, generally in the 12” range.

Tools for Working Wood has a wonderful turning saw for sale, but for about $150 – a little more than I wanted to spend.  However, they also provide the parts and free plans to allow you to build your own, and this is a project that should be within the skill range of most woodworkers.  In addition to the parts and plans, there is an excellent page of construction notes to make your life much easier.  Kudos to Joel and his team at TFWW for providing this excellent reference.

I started by ordering the set of pins and three blades from TFWW.  Since I have a lathe, I would make my own handles.  I then downloaded and printed out the plans.  Remember to use legal-size paper and turn scaling off to get a properly scaled set of plans.  That said, the plans are excellent quality and very easy to work from.  One page is even a set of templates to cut out the cheeks and stretcher, hence the need for proper scale.
Turning Saw 1
I cut out the templates for the cheeks and stretcher, and attached them to the selected pieces of stock with spray adhesive.  It’s important to use straight-grained stock, as these pieces will be subject to a considerable amount of stress.  Once dry, I cut the pieces to shape using my scrollsaw.  A bandsaw with a narrow blade would work as well, but mine was set up with a wide blade, and I didn’t want to change it out.
Turning Saw 2
Once the pieces are cut out, remove the templates and you’re ready to go.  My favorite way to remove patterns attached with spray adhesive is through the use of a heat gun.  These are more useful in the workshop than many give them credit for.  Not only can they strip paint or thaw pipes, but they can even (with judicious use) accelerate the curing of epoxy in cold conditions (judicious, I said).  A quick wipe-down with mineral spirits removes the rest of the residue.

If your cutouts are a little off, as mine are in places, don’t worry about it.  There’s really very little that’s critical about this design.  Sure, you want the two pin holes to line up as well as possible, but even that’s not as big a deal as you would think.  Remember, the whole thing is just a way to tension a blade and let you hold it while you cut.  It’s certainly not rocket science or laser optics.  You can even out most mistakes later.

Next time we’ll turn these parts from rough chunks to finished components.  Also, we’ll make the knobs and winding toggle.  Stay tuned!