13 August 2010

Shooting board

Wandering through the internet I found the part time woodworker discussing shooting board and promising plans for the ultimate shooting board soon.  Meanwhile I thought that I could give shooting boards a try.
I fixed a stop to a piece of plywood scrap and added two screws to make an adjustable  fence.  After the back of the fence started to splinter, I rounded it like Derek Cohen did.  Seeing the price of acrylic plastic, the plastic runway is delayed and for now it is a piece of hardboard scrap,  that I need to wax before it is too late.

Fine,  now a plane.  My Anant #3 and #5 are not square,  no luck there, although I could square the sides by gluing  up and squaring thin pieces of wood.  My even cheaper block plane is better.  I even brought in my pre-war wooden planes,  they are both square and heavy.
Shooting is another story,  even if I can sharpen my plane blades sharp enough to do some shaving on my arm,  something is lacking when going cross grain,  as it is more hacking than slicing.  Looking for ways to improve my shooting board I see two tracks: - I can shorten the bench hook avoiding to work with more stretched arms and gain more control.  - I also inspected the block plane blade with a 100x magnification and there is clearly room for some improvement.  But for now shooting boards are not usable for me.  A possible alternative to planes is to put sandpaper on a square wooden block

My wooden plane blades are still nearly untouched.  The original owner bought them as a student in the thirties and kept them without using them much once he was a professional.  The top of the blades is laminated like a Japanese blade,  although thinner. The blades top is also chrome plated with a better chrome layer quality on the harder laminate.  This gives them a mirror finish even after 70 years of inattention.  Chrome plating also makes the surface probably very hard.  Looking at the environmental cost of chrome plating this is probably overkill as softer low chromium blades like A2 (with its mere 5% of chrome :-) or HSS are good enough for me.

12 August 2010

Classical Joinery

armoire de béguine
This is a post about joinery I had in mind that was triggered by  Christopher Schwarz,  when he mentioned his Classical Joinery course in Germany next September.  But it all started when I saw Norm Abram making a shaker washstand,  I saw the analogy in design with an  'armoire de béguine' I know,  as both use small heavily framed doors.

As a side note: Beguines are religious women, who among other thing translated the scriptures in French around 1250 and disappeared as a religious movement last century. I can't relate any furniture to the beguines apart from this example whose name I know by hearsay.  It is a one man (womens) eating cupboard as a plank can be drawn from under the middle door to serve as a table,  where the door gives access to the food stock and utensils. The small door opening leaves room for a U shaped internal shelve with copper hooks.

shaker washstand (Norm Abram)
Both have points in common but are also different in build up.  In the shaker style massive wooden panels are used joined together with rabbets and dados with the door as an exception.  Where the beguines cupboard solely uses frame and panels for the whole construction.  The panels are plain and thin and well made.  I see it as the product of specialized shops with one specialized in cutting timber for thin panels but also the frames as both are made out of similar oak.

shaker cabinet (Chris Schwarz)
Back to Christopher Schwarz.  His Classical Joinery course works on a small Shaker cabinet and covers "Joinery planes, including rabbeting planes, fillisters, router planes and shoulders.  Cutting joints using handsaws and handplanes, including rabbets, dados, tenons and half-laps."
But what is classical joinery?  For shakers, etc. it can be panel assembly with dados and rabbets where for others it is more a frame and panel situation.

06 August 2010

Wooden air engine - 3

This is a third post in a series exploring wooden air engines possibilities, all this inspired by Matthias Wandel models.  This time I go for higher complexity.

When searching details about  the oscillating cylinder steam engine I came along a Chebyshev steam engine concept to transform a linear movement in a circular movement in a compact way.  It is tempting to include it to make a more attractive systems in a model, but I am not sure about the quality of the movement and have no view of the geometry of his implementation.

Looking into Mechanical Movements Powers and Devices by Gardner Hiscox I found many systems converting linear to circular and stopped at 'a curiosity of old-time engineering'.  Searching further I found more information like a date and a name 1666, De La Hire and even a working model of: "Murray's 1802 Hypocycloidal Steam Engine"

Thanks to Matthias Wandel it is even possible to easily implement a plywood air engine using this mechanism as he has two template generators for wooden gears. Although cutting convex forms from the inside is probably not that easy  It is probably a good idea to follow Cotswold Heritage design by making the tooth containing the shaft hole oversized by grouping for example two teeth,  certainly because this tooth is at the end of the stroke and does not take up much force. The template here has 20 (for the generator it is -20) and 10 teeth.  It could be less as Matthias experimented with sparse toothed gears and says that even then the movement stays very smooth.
gears for a hypocycloidal movement

05 August 2010

Wooden air engine - 2

This post is part of a series inspired by Matthias Wandel air engine.

Matthias Wandel air engine is square, as it is made out of plywood. Looking in older books, in this case Mechanical Movements Powers and Devices by Gardner Hiscox, I found two examples of a square piston steam engine.

For Root's square piston engine,  no details are shown for the valves,  but it is possible to imagine rotating valves linked to the crank shaft.  When implementing this in wood as a low pressure model, a possibility to minimise friction torque is to give the valve a small diameter. At the same time leaks between in and out stream must be minimal. I see two possible solutions here, one is to put one valve at each side of the engine,  the other is to use a hollow shaft and use it as the exit port.
An alternative is to try to implement a solution close to the oscillating cylinder steam engine as both engines have points in common, in this case a translating (sideways moving) 'cylinder'  for the vertical one and ... something even more clever for the horizontal 'cylinder' as it contains a piston with sideways moving parts. It is probably a though problem as the valves for the horizontal and vertical cylinders must stay separated.
The drawing is strange as the crank shaft (b) seems to hit the top of piston C when rotating.  To avoid this  the shaft could be made of a rotating disc embedded in the sides.

The Dake square piston engine,  in this case I found  more information as thousands of them where made between 1887 and 1950.  The engine is impressive as it offers a 4 piston continuous torque engine with only four major moving parts.  As a model it would be less impressive as even a flywheel is superfluous. It is more a pizza box with a shaft in its middle.
Looking at the drawing from the patent, there is apparently a rotating valve embedded in the cover feeding the 'cylinders' through the piston.

To finish a quick sketch of the rotating valve I had in mind for Root's square engine as I am certain I will have forgotten all about it within a week. The air comes from a feeding ring directly through the valve and leaves via a covered opening towards the shaft.  The opening angles of the valve must probably be more than on the sketch,  is it 90°?

[edit] There is an animation of Charles J. Dockstader  for the Dake engine showing the steam distribution through the inner piston.

04 August 2010

Wooden air engine

 Looking for a self made horizontal mortising machine I found one (multi slot mortising machine) on Matthias Wandel website and also many other technical projects.  The wooden air engine based on a standard steam engine (here an animated presentation) looked very interesting and I am not the first to find it, as he got already over 500.000 views on YouTube.

As a ten year old it was on my wish list,  so it could be time to realise that wish.  To make it more probable to implement it I can best keep the engine as simple as possible.  Searching my memories and the internet I found the oscillating cylinder steam engine (animated version here),  reducing the engine to 3 moving parts.  I should get some wood and try to implement it as an alternative to the wooden air engine.

03 August 2010

The workmare - 3

pencil test
The workmare still needs to be finished, but it is usable?

- The twin vise seems good, I like it. It is made of two oak left over glued together. I should have glued an extra board (softwood) in between to leave room for drilling dog holes. As it is now 3/4 inch holes are to big, I need to find a thinner solution. Anyway I need a solution to compensate the lack of tail vice and be able to clamp sideways.

- I roughed up the hardboard to make it less slippery, but I think that using 1/2" MDF would have been better, as I already damaged the top with my circular saw and hardboard does not leave much depth for error.

- The stability, seems good. I tried out my pencil test, putting a carpenters pencil upright and keeping it so when hammering in all three directions. With a mass proportion close to 50 to 1, over 60 pounds for the top and 1,2 pound for my mallet there is not much moving.

- The stability is less when planing, as I can put a larger mass behind it. I even have the impression that weighting the top down did not change much as adding the gravel did change the oscillation frequency of the top from maybe 30 hz to something like 10 hz without changing much to the amplitude. It can be improved by making the legs and joints stiffer. Increasing the L shaped legs from 4" (by 4") to 5" (by 5") more than doubles the stiffness of the legs (the formula is bh³/12) but not necessarily the stiffness of the joints. Adding diagonals to the legs is probably more effective
adding toes to the legs

- When planing towards the vice the workbench tended to tilt over as most weight is at the front not in the tool tray. A solution is to add toes to the front legs. No one wants to be crushed under the weighted top. All in all if I have to redo it I would add cheap concrete slabs, from the garden center, to the lower tray, to weight the workbench down and avoid the potential danger of a weighted top solution.
leg clamp

- Holes for attaching stuff is a work in progress, I will add them in the top and the legs depending off my needs.