Tag Archives: technique

Connecting Rods & Big Ends

The connection rods were a nice between-centers turning job, and then a selection of milling set ups.

Rather than write a lot, I will put some pictures below – the main thing to note was that almost all of the milling and boring was done with the partially machined big-ends attached to the partially complete rod – in order to ensure a good level of concentricity….

Nice New Main Bearings

As discussed in the last post, I decided to remake the bearings as drawn/described from  a solid Phosphor Bronze (SAE 660 aka Gunmetal) block – being as how I had needed to remachine the crank journals after assembly, and the first set of fabricated bearings were a bit “naff”..

So the first job is to cut the block in two (longitudinally) clean these two pieces into neat cuboids, and then soft-solder them back together for machining.

This time I decided to machine the bores first, and then mill the seatings for the housing by measurement from the bores – in this way you would be able to “guarantee” that the resulting bores all lined up!

Much more success!

One of the problematic things was how to measure the distance from the bore to the outer facing – this would need ball-faced micrometer, not something I had. After some thought this idea occurred: by hot gluing a ball bearing to the anvil (and remembering to subtract the diameter of the ball from what I measured) everything would be fine – and it was!

Home made ball-headed micrometer (ball bearing hot glued to anvil)
Home made ball-headed micrometer (ball bearing hot glued to anvil)

So  by first machining the back face of the bearing housing, and the bottom of the bearing housing to the correct dimension from the bore we knew that things would line up. Then the forward face could be machined to be a snug fit in the housing.

Lastly the top surface was machined to ensure the bearing keeps would provide a little “crush” when tight.

I cut everything to allow for a little hand-finishing (to make sure there was no slop), and then unsolder the two halves, clean up and try them on the journals – they were too tight!

But this was “kind of what I had planned”, so then fitting the bearings in place, and a few hours with the engineer’s blue and hand scraping we wound up with a crank fitted and turning pretty freely. (this description skips over the machining of the ends of the housings to provide for the correct end float, which was a bit “trial and error” – but all came out OK.

A slide show of the process…

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So Far So Good

Well I  have turned the first 7 sheets of chipboard into moulds and am half way there…

Paul (from SFD) clarified my confusion, I was thinking that the frames marked on the drawings were like the ribs on some of the pictures of his designs, just square and laminated onto undersized moulds – but they are full bulkheads cut away as needed to fit under sole and behind seats and lockers – at least I figured this out before I cut more than one undersize 🙂

plastic batten providing a smooth curve from the marked offsets

plastic batten providing a smooth curve from the marked offsets

Using the plastic batten to produce a smooth curve round the offsets from the mould drawings really works well, and has highlighted 2 or 3 occasions where I had miss-measured or mis typed a dimension, so hopefully we are going to wind up with a fairly fair jig!

The game plan is to a few 3/4-inch panel pins into key marks, and then pull the batten round… normally 3 or 4 are enough, and the fact that the batten will normally then automatically align itself with the other poinst marked from the offsets  from the plan show wat a good job SFD’s computers do in fairing the design.

clamps hold the batten in place, and a few panel pins set the line of the curve

clamps hold the batten in place, and a few panel pins set the line of the curve

The ally clamps just hold the batten down and stop it jumping out. Then when it’s all in place you just draw round it, pop it out, pull out the pins and break out the jig saw!

…and tonight Paul from the Castle of Comfort (my local) came round to help move the next 8 sheets of chipboard in to cut the rest of the moulds…


Sawing Straight (not)

Having clamped a pair of mould-half panels together, I figured I could just cut them out with a jig saw….

The "Offending" Saw - as always it's the bad workman who blames his tools!

The "Offending" Saw - as always it's the bad workman who blames his tools!

So off I set, slowly and carefully sawing along the line – 2 inches in I  encounter the first problem – there is so much dust I can’t see the line… At this point I engage “smug-mode” and pick up the shop airline, and with the spare hand blow the dust clear as I saw…

… I reach the end and discover (horror) that the b*&^&^y saw has cut at an angle to the vertical – and (double horror) this mis-cut has resulted in the lower panel being significantly undersize (we are talking about a ~5mm undercut!) grrrrrr….

I check the saw and the blade is square to the foot, so I am mystified…

A number of posts to the Selway Fisher Builders Yahoo group follow… (this really is a great group of people) and a deal of suggestions emerge within a few hours. These range from observations that cutting 1.5inches of chipboard in one go is too ambitious, thru to real Zen-like encouragement to chill more, take up a pipe and cut them with a Japanese hand saw – excellent!

So, I take some of my scrap chipboard (I just made a nice new bit of this) and draw curved lines and practice my sawing (by hand and other approaches) – including sawing it an inch oversize and improving my planing and surforming technique.

In the end two key factors emerge 1 – you cannot saw two at a time (you were right Graham) and 2 – I was going too slow! By setting the variable speed JigSaw to “flat out” and keeping my feed rate slow the desired results emerge….

The first three moulds - halves bolted together, showing the marking out

The first three mould-halves bolted together, showing the marking out (Nos 1,12 and 16)

I leave the workshop with three assembled and very “boat shaped” moulds – life is good again!


Marking out the moulds

We progress. Having cut the first 7 sheets of chipboard into panels sized to provide the first half-moulds we set about marking them and cutting them out.the first few mould half panels cut...

Selway Fisher provide a set of mould shape drawings, these have a set of horizontal lines at fixed distances above and below the water line (like +50mm, +100mm etc.) and for each of

a stick cunningly modified to provide a ruler with markings corresponding to the verical mould shap offsets

a stick cunningly modified to provide a ruler with markings corresponding to the verical mould shape offsets

these a distance from the centerline of the boat to the edge of the mould. So the first step was to produce a “ruler” with these “vertical offsets” from the waterline marked.

Having first located the waterline on each sheet (by treating one edge of the sheet as the bottom of the hull and then measuring up to the waterline datum position), the ruler is then used to mark the positions (and then draw in) the horizontal lines on which the offsets will be measured.

Then measure and mark the offsets onto the boards. Once this is done I then nailed small panel pins into some of these locations and used them to locate and bend a batten (I used a bit of the plastic finishing strip from a laminate flooring project) to the shape of the edge of the mould. It soon became clear that the batten needed holding against the mould in a couple of places, so bent scraps of ally were srewed into the chipboard to hold everything in place.Moulds showing marking out and

This bit was VERY satisfying, as you could see how the batten automatically took up a smooth (fair?) curve that passed thru the other marked points. I had miss located acouple of points but these became immediatly visible (because the batten “missed” them by  a mile).

My plan is to laminate the frames/ribs onto the moulds before planking, so I chose a batten which was the same thickness as the frames (ribs), so for the moulds that were located where the frames were to be located I drew the cutting curve on the inside of the mould and for the moulds where the frames were not located I drew to the outside of the batten. (I am still a bit nervous about the actual thickness of the frames, as I can’t see this marked on the drawings, so I am awaiting an answer from Mr Fisher when he returns to his offices next week). Actually I spent most of a day computing a set of offsets for the moulds with ribs, but the math was pretty complex, and so in the end I adopted Louise’s suggestion of drawing the inner mould shape from the outer one, as described above!

Removing the batten left some very boat shaped lines on the moulds – then I marked on the hog and clamp cutouts ready for cutting (again these are fitted before the planks) … filled with positive vibes I clamped the mould halves in pairs and picked up the jig-saw and things to a turn for the worse!



First Build day!

Steel meets Wood for the first time! Moved the first 7 chipboard sheets to the main workshop I spent the morning chopping (sawing) them into blanks for the jig moulds. As suggested we are making them in two halves (the tumblehome demands it really) – it seemed to go OK – one slightly crushed foot (dropped a sheet on it – break out the toe-tecters!) and no accidents with the circular saw (although cutting mould 13 was done with some care!)…

Cutting the Moulds - day #1

Cutting the Moulds - day #1

So far the planning has worked – I drew out the overall sizes for each mould and shuffeled them onto 8by4 sheets in AutoCAD…

Laying out the half moulds for the jig onto 8by4 chipboard sheets

Laying out the half moulds for the jig onto 8by4 chipboard sheets