End2End - Self Centre Tool

Age brings on wear'n'tear....my eyes are not as good as they used to be. Glasses get put down...somewhere.

I need to mark up a centre line and sometimes make a bit of a guess with a rule and a sharp pencil. Not good.

I did have a piece of wood with dowel pins and a hole for the pencil to aid with this but it always annoyed me that I couldn't mark the whole length due to the pin going off the edge of the wood.

There are lots of variations of this tool - home made ones, cheap plastic stuff and fancy anodized aluminium ones but all very similar. I had made a plywood prototype a few years ago but was a little disappointed as it wasn't accurate enough for my liking, but I picked it up a few weeks ago and thought I'd give it another bash.

Its simple, adaptive, cheap and relatively quick to make.

Scrap wood - this example is from an old window frame

Metal pins - steel, brass, 4,5,6mm doesn't matter. I made mine from an old shop fitting hook - 4mm chromed steel

Bolt - I used 6mm allen key head

You'll need tools to cut and drill - preferable a drill press.

A finishing substance - boiled linseed oil, wax or similar

The wood was cut to 24mm wide and apx. 30mm deep and requires a length apx 136mm. I marked up a centre line (with found glasses and a good rule and sharp pencil!) and used a compass to mark pivot/pin points 44mm away from the centre as well as 'shaping' circles for later.

These measurements can really be whatever but I wanted a more compact tool so this is based on:

Pivot points are 88mm apart - material width 24mm = 64mm maximum wood width to mark a centre line

Initially drill the centre point out with a 5mm drill. I'm using a sharpened M6 threaded bolt to be my marking centre tool so if you're using something else use a drill bit accordingly (see notes at the end). Use a thread cutting tap or just the bolt to cut a thread into the wood. But before you do this see the next step.

Set up the drill press so the piece of wood can be spun. The idea is that if the centre point hole is fixed then you drill out the pivot/pin hole - spin the wood- drill out the second hole. In theory the holes are then exactly the same distance apart. Of course you need to make sure its drilled on the centre line as well to make the tool as accurate as possible.

So find a base board that will fit on the drill press and thick enough to accept a threaded hole. If you place your workpiece on this and its fixed in the middle can you then spin the wood freely? (not the base). If so, using the M6 bolt secure the work piece to the board, enough so that it can rotate easily. Using a 4mm bit - as my pivot pins are 4mm - line up the drill to drill a hole in one end. Once lined up clamp the board in place and secure the work piece, then drill the hole all the way through. Unsecure the work piece - not the board - and spin the wood and align the drill bit to the centre line and drill again.

You now have a piece of wood with a central 6mm threaded hole and two end holes 4mm, exactly the same distance apart.

Now that the holes are done it can be cut perpendicular to the holes. Initially I pencil mark one edge to keep track of each piece placement. Using my table saw, I cut the wood so that each piece is 12mm thick. So now I have 2 pieces 12x24mm with identical holes.

The top piece is cut and rounded (12mm radius). The initial marking was done with a compass but I also had a steel washer the same size. Once done the top piece can be placed back on the second piece and the ends traced around.

Using the washer and rule I marked up the second piece to be cut diagonally from each end circle (picture 3). This is done to make a more compact folding section with the longest 'arms' possible. I then cut this on the band saw and shaped with a Dremel sanding tool.

You end up with two identical arms with a pivot hole. Lightly sand all surfaces and edges.

So now you have one top piece with 3 holes and rounded ends, and two bottom arms. I oiled the wood with boiled linseed oil and allowed to dry. I then hammered the pivot pins into the top piece. If the M6 bolt was also used in theory you could use the tool like this (picture 3) but the arms need to also be placed. Also fitted with the hammer but gently (picture 4).

I used initially a M6 threaded bar with a slot cut in it but replaced it with an M6 bolt that had an internal allen key fitting. A normal bolt of some kind would do. I sharpened the end up on the grinder enough to mark timber.

This bolt was then screwed into the top piece enough to project slightly out of the other side by about 2mm.

Generally this is to be used on timber 60mm wide or less. As you can see from the photos you unfold the arms so the flat sides run along each side of the wood to be marked. By applying pressure to each arm centralizes the tool and with a little downward pressure will score the workpiece as you slide the tool along.

As you reach the end of the workpiece, because the arm is an extension of the pivot pin, allows the tool to still run centrally to the end.

This was tested on wood and aluminium channel and then measured with vernier callipers to check accuracy. Spot on.

Its compact. Relatively quick to make. Cost nothing.

Its accurate enough to mark up to my liking.

In theory you could make these different lengths to deal with wider pieces of wood but in the end its what you mostly work with.

The M6 bolt - could it be smaller - yes. An M4 would do nicely, but I have a very odd thickness of pencil that I also cut an M6 thread into using a die so that if I want just a pencil mark and not a scored line it can be done.

So this is where the design can deviate.

Your central marking hole needs to accommodate a 'tool' - whether a pin or a fat marker - and if its to deal with all then a shim system is required to handle the different object sizes, but would this just be introducing a lack of accuracy?

Another method would be to initially drill your central hole to only be 2mm and have a thicker piece of wood so that you can make 2 or 3 top pieces in one go - but where you can drill out the central hole to accommodate different markers on each one. Then you just swap the pin arms to the top where required.

Thanks for reading