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The Portable (??!!) Workbench, equipped with twin screw chain linked vice

A dissertation on Stopping Things Moving, and the Virtue of Vices…

One thing I discovered when teaching martial arts was that when an impact technique moves a person around, it substantially loses power and accuracy. This led to a principle I apply in many areas, which I call ‘Apogenik Circuits’ (for more on Apogeniks see http://www.apogeniks.com).

An amazing amount of power is absorbed in ‘pushing’ a person with a technique, which is generally a useless drain. Thus the ingenious forms of martial art use a rather harder to master method called ‘reverse hip’, which projects the limb at high velocity like an arrow from the string, and transfers energy to the target as a percussive wave, without moving it – like dropping a pebble in a pool, or striking a drum.

When I started working with wood, this issue of not moving things around became a preoccupation. What I found was even a small amount of spring or racking in a bench had a considerable impact on speed of work and accuracy. For example, if cutting with a chisel resulted in a small deflection in the bench structure, the point at which the cut actually happened would be unexpected.  Further, there is a tendency to push harder, to overcome the spring, so when the cut actually happens the resistance to the spring goes, and the bench boings back.  The result is inaccuracy and unnecessary effort.

If the workbench structure is completely rigid, the amount of spring is negligible and the cut happens precisely and under perfect control. The energy of cutting goes into the cut, rather than deflecting a spring.

So in working accurately, possibly the most important aspect is first of all to immobilise the workpiece, and reduce any ‘slack’ in the circuit between me and the immobilising structure. Metalworkers know this, and require great rigidity in their machines. Slack in (for example) metal lathes will produce vibration, leaving a chatter pattern on the workpiece. Something similar happens when planing wood in a wobbly vice, where the plane chatters and sticks as power is repeatedly sucked away and then sprung back. Unwanted oscillations of all kinds come from a similar principle – something is ‘slack’ in the circuit, acting as a spring.

A decently equipped workshop will have a good workbench that has minimal spring, good mass and is bolted to the floor. The vice will be a serious affair, securely held to the bench. The happy woodworker using such a device will be pleased to note how easily his plane functions, how swiftly his saw cuts, and how thin and accurate are his chisel parings.

But here is the problem. What if one is *not* at the workbench? What if one is obliged to shift location, to move the work area to the project, like working on a boat?

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The Knock Down Bench

One of my past projects was the knock-down workbench.  But this takes up a bit of floor space, and is impracticable on board a boat.

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Sjobergs SmartVice – not bad, but too small (I felt)

About a year ago I saw the Sjoberg  Smartvice.  The idea was good – a clamp-able vice with small worktop.   But I felt the vice was too small, the mass of the whole thing was too low, and the table was only about a foot square. Was there a way of translating my twin screw ”knock down’ vice into a similar portable format?

Well I happened to come across a second hand but unused Veritas Twin Screw Vice kit on ebay for a song, and snapped it up.  And it has been sitting in my workshop waiting for an opportunity to build my version of the portable workbench.

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Veritas Twin Screw chainlinked Very Nice Vice kit.

The Veritas twin screw vice is a serious and very nicely made piece of kit – two long 1″ screws linked by a chain, heavy cast iron fitttings. And the finished version of my bench ‘grew’ out of the vice specifications.

I spaced the screws at 16 3/4 inches, the maximum for the chain size, and ended up with  a 23″ wide vice, 6 inches high.  The front face is 2″ thick, the back about 2 1/2.

As a base I used a piece of very good quality birch plywood, and for the table and table supports I used 40mm thick keruing – tough, dense, heavy, and plentiful, as I have a large pile of it!

When I build things I have a preference for putting minimal load on fastenings.  This can usually be accomplished by decent joinery.  For this job I decided to use shallow housings to locate the components. These housings would take any sheer forces and torque between the clamped baseboard and operations on wood held in the vice.

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Rear view, you can see the housings for the table supports

The two perpendicular table supports were housed into the birch ply and held there by screws, and also into the rear vice face and the work surface.  The worksurface was glued up from three pieces of keruing, and housed into the rear vice face. The work surface was coachbolted to the rear vice face, and also the supports.  The ply extends to the front of the rear vice face, so the front vice face is free to move.

Then I drilled the front face of the vice and the table with 3/4 inch holes to take bench dogs – I happened to have some Veritas ones from long ago, some of which have a neat screw, useful for clamping irregular shapes.

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Finished table, sporting fancy Veritas bench dogs.

The resulting table is 23 inches wide and 17 inches deep (including the rear vice face), and just over 1 1/2 inches thick.  The vice is excellent, with good depth (6 inches) and a substantial gap between the two screws.  The gap between the base and the work surface is enough for a hefty clamp to fit easily (I use the Irwin variety).  And in all it weighs about 25 kilos!

Obviously it will be necessary to adapt it to each situation – some places it can be clamped, in others maybe temporary bracing will be needed to secure it.  I will have to see…

 

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20170626_121102_New Quay Court

The  knock down portable work bench

One of my favourite principles in doing pretty much anything is what I call ‘circuits’.  It’s all about getting the energy you are putting in, precisely to the place you want it.

Anyone familiar with metal cutting equipment like lathes and milling machines knows that a great deal depends upon stiffness.  The tool and the workpiece must be held rigidly.  When the tool is presented to the workpiece, any ‘slack’ in the physical path between the tool holder and workpiece will be taken up before cutting happens, causing wasted energy, inaccuracy and vibration.  The ‘circuit’ between the two must not have any energy leaks.

The metal worker, operating at thousands of an inch or less, knows that these ‘leaks’ are visible enemies, and will destroy his work.  They will cause the workpiece to deflect, set up vibration patterns, even cause ‘dig ins’ as the vibration pattern is superimposed on the force attempting to cut.

The woodworker is operating at bigger tolerances, so this problem is not so obvious. When a piece of timber moves as it is sawn, it is often just accepted.  When it bounces as it is struck with a chisel, it is accepted.  When the workbench wobbles as a piece is planed, it is accepted.

Well, not by me.  The point is that *any* slack in the system creates an enormous loss of power and accuracy.  I don’t really think many people realise how much energy is used in moving stuff around, rather than cutting, and what this actually means.

For example try this experiment.  Secure a piece of 1″ x 1″ wood in a vice so it is sticking out about 10″  Then try to cut it with a saw about 6″ from the vice.

You will instantly notice that the wood will vibrate as you cut it.  The energy you are using starts to fight against you.  The vibrating saw cut jams the saw.  It is impossible to cut a straight line because the wood always wants to bend.  The jamming of the saw causes the saw to vibrate and the wood to bend even more.

Now try the same experiment cutting very close to the vice.  All the thrust on the saw goes into cutting.  It is easy and accurate.

The difference between these two experiments is pretty obvious.  Cutting at a distance from the vice turns the wood into a spring that absorbs the energy of the cut, and then releases it in an unhelpful way.

If you properly secure a workpiece in an immovable vice, the effect is astonishing.  Cuts are effortless and take a fraction of the time. you can be stunningly accurate, paring off transparent shavings.  Everything is way, way better.

Securing your workpiece and cutting it close to the vice or clamp is second nature to craftsmen.  But how do you know your clamp is secured? What is going on between that clamp and the ground, and the ground and your feet? All you need is a slight wobble, a slight give in your bench, and all that sharpness vanishes.

A workbench is like a system of springs between you and the workpiece.  As you apply pressure to a workpiece the springs give, absorbing your cutting energy.  The more they give, the more energy is absorbed.  Only at the point that the wood you are cutting cannot resist the force of the ‘spring’, will the wood actually cut.

If there is any slack in the system, your workpiece will travel the distance of that slackness before it is cut.  So you are cutting a moving target, that springs back as you cut it.  The result is far lower accuracy and far less cutting power.  Even a small amount of spring makes a massive difference.

One question that came up some years ago was whether it was possible to construct a mobile workbench with very high stiffness, that could be taken apart easily.  Here is my solution, that is still going strong.  It could certainly be improved upon, but it is way better than most static workbenches, let alone mobile ones.

The basic principle that is essential in a mobile bench is that the circuit between the operator and the bench must be closed.  In practice this means that the bench must include a floor on which the operator stands.  The good old Workmate actually does address this, by having a platform you can put a foot on whilst using it.  But it is extremely springy, and the modern version is very poor quality.

My solution was to have a portable floor.  I made this from OSB, but I think a good quality plywood would be better,

The easiest way to describe it is to show you how I put it together.

Components are the floor, a base, three legs, the bench top/vice and three clamps.  The whole thing takes a couple of minutes to knock down and build, and easily fits in a car.  The bench part has only a single M12 bolt holding it together. The bench and legs are made from Keruing, a hard dense and heavy tropical timber, that I happened to have on hand.  I would recommend a heavy hardwood, because the mass definitely helps.  The base is softwood.

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The components.

The base that holds the bench is made from two pieces of timber in a ‘T’ shape. The  upright of the T is dovetailed into the long part.  The ends of each part are mortised to take the bench feet.

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Softwood base, dovetailed together

The bench itself is two pieces of hardwood, that clamp over the legs.  The legs are half-dovetailed into this, to that once the two pieces are held together, the legs and bench form a rigid structure.

The third leg is bolted through the bench.  This bolt is the only fastening holding the whole thing together.

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The third leg.  This bolt is the only fastening!

Once the bench is fitted to the legs and the bolt loosely done up, the whole thing is placed on the base and the tenons on the legs slotted into the mortises.

Then the base is located on the OSB floor.  The floor has captive ‘T’ nuts underneath that take the bolts that go through the base.  The bolts pass through timber clamps that fit the angle of the legs, and effectively create a kind of dovetail effect.

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The clamps bolts the bench to the base and create a dovetail effect on the legs.

This structure is amazingly rigid.  With forces along the vice, it is exceedingly stuff, better than most static work benches.  There is a small amount of lateral movement owing to the flexibility of the OSB but I have got around this by putting weights on the floorboard, or wedges underneath it at the back. An updated version might include stiffeners for the floor board.  I tend to use the centre of the vice for sideways loads, as the forces are resisted very well by the rear leg.

20170626_121102_New Quay CourtIn using the bench, one stands on the board.  Thus the circuit between the user and the bench is always fixed.  You can stand in front or behind.

The vice is fairly primitive, using captive nuts and 16mm studding.  At the time I had only basic metalworking equipment.  Ideally I would have sliding bars to prevent racking of the vice, and maybe handwheels.

Some kind of stop could prove useful. You could even put an end vice on it!

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In action, turning a chunk of oak into a Samson post

 

Eeek!

20170618_164409_New Quay Court20170618_164405_New Quay CourtFor years my lovely gaff cutter has been hanging around next to our massive houseboat project, sadly neglected.  Time to find out what is going on.

I knew that the starboard side deck and after deck had rot, so off they have come, revealing the bones beneath.  It is a painful thing running a circular saw across your boat’s deck.

Well, it’s not too bad.  The eyebrows had to shoot up at the timber selection of some of the deck beams.  My goodness, some serious grain run out, to the point where a couple of the half dovetails have parted.  Still these will be fairly simple to replace.

A bit more thought will have to go into a section of the carline, which is certainly rotten at the top edge.  I’m not yet clear how far it goes, but it may be a case of scarfing in a repair.  I certainly want to avoid replacing sections of it.

The samson posts on the aft deck have decayed sufficiently to weaken them at deck level,  One problem was insufficient clearance between them and the transom, so water has been trapped.  I’ve made a new design that gives me  a bit more clearance.

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The timber I have to hand does not quite fit the new pattern, but I’ve found some that’s close enough and I can get away with a small shim to make up the extra width.

It’s always fun searching around for timber that fits a shape, and then revealing the inside.   This piece is a 5″ thick board of oak I have had hanging around for about twenty years, and the grain matches quite well to the angle between the sloped transom and the more vertical post.  My lovely Sedgewick planer and bandsaw will do the rough work…20170622_185235The worst rot revealed by lifting the decks was unexpectedly in the port quarter block, a sizeable chunk of timber that connects the beam shelf to the transom, provides corner strength and holds one of the large iroko davits.  This is sufficiently decayed to merit complete replacement, so I’m fishing around in the wood pile for something that works.

Deck plywood has arrived from Robbins, and bronze nails, so I’m really looking forward to quick progress!

We’ll see…

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