Rip Frame saw of the style mentioned by Roubo

 I have some left over beech from projects and have been thinking of making another style of frame saw that dates back to medieval times and before. This is now commonly called a Roubo frame saw and there are some kits available in the USA and also in Europe. However, I decided to try and make one from wood without the ironware commonly used to attach the blade to the arm of the saw.  A larger version of the saw is also called  a "Framed Pitsaw" in the book by Henry C. Mercer (1929) "Ancient Carpenters' Tools" used to saw planks in saw pits and the like.

My design was determined by the blades that I have available for my existing frame saw which includes a rip and turning saw blades (distance between mounting holes is 580 mm) and the beech timber.  Also my aim was not to make something similar to those used by the sawyers in saw pits in the past but something more modest that one person could use with comfort to rip-saw a piece of timber. I basically made my own design as I will describe below.

Cutting an arm with a large frame turning saw.

The first step was to cut an arms (historically termed the "head sills") to shape from a block of kiln dried beech. I used my large frame saw fitted with a turning blade and for the tight bends went to a 10 inch frame turning saw. I finished off the shape using a block plane and small spokeshave. The maximum width of the arm was 7 cm, length 48 cm  and  9 cm deep. 

The next stage was to make the torsioner block (I'm not sure what this is called) which contains the screw spindle that tightens the blade. In earlier designs mentioned by Mercer, the blade was tightened by using a wooden wedge rather than a screw. The torsioner block had a large mortice cut to fit the arm, i.e. the arm fits through this mortice. One problem with using wood for this (these are now mostly iron) is that the grain of the wood needs to be parallel to the blade for strength. However this means that the screw spindle would go into the end grain and so produce weak threads. The threads need to be cut across the grain so a 4 cm thick piece of beech was glued to the end of the block and a 5/8 inch hole drilled through this and a further 2 cm of end grain into the centre of the mortice. Overall the block was 6.5 cm wide, 18 cm long and 7 cm thick in which a 3 cm by 7 cm through mortice was cut by drilling and chiselling. A 3 cm long tongue was cut to clasp the rip blade.  

One arm (or head sill)  complete ready for stretcher mortices.

Drilling the 5/8 inch hole for threading the screw spindle. Guide strips were used to get the auger central and a spirit level to make sure it was horizontal.

After the hole was drilled for the spindle, the thread was cut with a 3/4 inch die. A spindle was cut on the pole lathe using a piece of ash and threaded.

Arm and torsioner block with the screw tensioner in place. 

The strecher bars (3 cm x 3 cm) were joined to the arms using 3 cm by 1 cm tenons. Historically these bars are called "side strakes" and could be several feet long. Their lengths were matched with the blade in place so that the screw tensioner was just engaged with the arm that gave about 2 cm of adjustment. Care was taken to ensure arms (or side strakes) were parallel and that the arms and strechers were at right angles. The frame must be flat. A coin was placed where the screw tensioner contacted the arm and for the opposite block a small 1 mm channel was cut to locate it in the centre of the arm.

The frame after glueing ensuring that the frame is squared and is in a horizontal plane, i.e flat.

The final steps were to tidy the frame and treat with linseed oil ready for use.

Finished frame saw with blade installed and taut.

Frame saw in use

I have now used the saw several times to cut veneers and also some slats from hardwood as shown in the photo above. I used the kerfing plane (described in this blog, the second version with a coarser blade) to mark the saw cuts and then clamped as shown to saw down the lines with a rip blade installed. This worked well but needed good support and clamping when cutting long thin slats of wood. Generally I have found using the saw made ripping easier as you use both arms and a balanced position to saw long cuts.

A wider frame saw seen in a Naval Museum in Spain. This is slightly longer than my saw and also wider. The blade is attached by iron fittings. The blade is also curved at each end similar to that shown for the Spanish bow saws.