Solent Mk4

With its roots firmly entwined in a WWII aircraft (the Short Sunderland) that combated German U Boats and was in combat in the Korean war, the Short Solent was operated as a civilian carrier in Australasia, the UK and the USA in the late 40’s and 50’s.

This model, from MakeCNC.com has been, without question, the most complicated build that I have assembled so far.  224 individual parts may not be the most of any model (not that I have been counting), but the assembly took a couple of nights.  And plenty of glue.  The hot glue gun is proving particularly useful for these models.

Made from 3mm MDF, using the #45190, 1/16th straight router bit from Toolstoday.com on the TorqueCNC.

SolentPhoto by Kara Rasmanis

Maximising Yield – the Vacuum Table Story

For months I have been bantering around the idea of a vacuum table for the CNC router, but each time decided that screws or pins were easy enough, and the whole issue stayed in the too-hard basket.

As I have been doing quite a bit of nesting work recently, it gave me pause to thought – for a one-off, a few screws are all very well, but the combination of that, and the significant time wasting of using tabs to restrain the cut components (both drawing them, and then physically having to cut and remove them) was proving an incredible time waster.

So I finally was pushed into addressing the whole material hold-down issue.

I started doing a bit of research online, but the results were less than helpful, and I felt as a whole, a lot more complicated than necessary.  So instead, I decided to build an idea I had, and just see if it worked.

I did use the CNC for the following steps, but that is certainly not necessary, and secondly, while I am using this on the CNC router, there is absolutely no reason this cannot now be applied to other areas of woodworking.  Nor do I expect I have come up with anything novel, but in going back to first principles, hopefully I have significantly simplified the solution.

So to start, I took a thick piece of MDF (22mm or so, which I had to hand.  I would have used thicker, but the 32mm MDF I bought last time from Bunnies was only some of their promotional stock.  Not sure what they were promoting, because they don’t stock it otherwise).  With a 1/2″ ball nose router bit, I cut a matrix of tracks, 5mm deep, and about 20mm apart, both horizontally and vertically, stopping about 10mm from the edge.

Next, the edges of this board were sealed.  I know people use some edge tape, or shellac for this, but I thought PVA glue would suffice!

This board was then screwed down to the bed of the CNC machine, and a hole just big enough for the end of a vacuum hose was drilled, all the way down and right through the table.  The hose of the vacuum (connected up to a cyclone separator) was jammed into this hole from underneath.

A second thick board of MDF was laid on top of this bed, and the vacuum switched on.

Test one – does it suck? Yes it can! The first proof of concept is a winner.

Into this second board I cut the same matrix of slots.  By then flipping this board over, each of the passageways is doubled in size (adding together the bottom and top halves), and also exposes a significant area of the soft, porous core of the MDF.  Each passage is now 10mm diameter, so that gives significant passageways for the air to pass through.

The vacuum was switched on again, and the top surface of this second board (the sacrificial board) was machined away with a surfacing bit (otherwise called a spoilboard bit).  And that is what this upper board actually is – a spoilboard.  When it gets too badly cut up, it can be flattened again, and this repeated until it is too thin, when it is then thrown away and a new board takes over.  By planing away 0.5mm of the upper surface of the spoilboard, the hard, compressed (and more non-porous) upper surface is removed.

Now I have seen a number of vacuum tables, and spoilboards with a large matrix of holes drilled though it.  Don’t need it.  The core of the MDF is so porous, that the vacuum can draw air directly through the MDF.  And that in a nutshell, is my vacuum table!

Upper board (spoilboard) from underneath, and the upper surface of the lower portion of the vacuum table

Upper board (spoilboard) from underneath, and the upper surface of the lower portion of the vacuum table


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Detail of vacuum table


Vacuum connection

Vacuum connection

I’m using a basic Shopvac for this, so I do have a bit of a concern that this will shorten the life of the vac.  I possibly need a vacuum pump, but this will do in the meantime.  The cyclone separator is to try to keep as much MDF away from the vacuum, to try to stop it being killed even more prematurely.

The proof is in the trial.

With a sheet of 3mm MDF laid on top, the vacuum switched on, and voila – it sucked big time, right through the MDF.  The board to be cut was held firmly, enough to run a trail nesting job.

Without tabs.

It was a complete success.  Other than the noise of the vacuum cleaner, I could not fault the process.  The vacuum will soon find itself in the shed next to the workshop, and switched on and off with the remote power switch I happen to have in there (the actual switch is right near the CNC as it happens).

Test job, no tabs

Test job, no tabs

I cut out about 5 patterns in total, and each time it worked perfectly.

Next, I tried another idea.  If the only reason for the material between each piece is to support the piece as it is being cut, it is really necessary if the piece is supported by the vac?

So I ran a large job with a full sheet, no tabs, and only 2mm between each piece (or more precisely, between each path the CNC was trying to follow).  And 5mm from the edge.

The result?

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Yield

Pretty much nothing left, what is gone is the project, leaving this sad skeleton.

So there you have it – my poor mans successful attempt at making a vacuum table.

Sopwith Camel Article

The latest edition of The Shed magazine has just come out (in newsagents in Australia soon).

Has my 10 page article on the Sopwith Camel build.

Also includes the first two ever letters to the editor about any of my articles.  Unfortunately neither positive.  Seems coin collectors were concerned about my choice of materials (rightly so). Ah well – can’t always be right!

Photo 4-08-2015 01 46 17

T Shirt Wisdom

Photo 6-08-2015 18 43 26s4e1-jaime-hand-2

Spinning and other metal work

There are some awesome 19th century metal working workshops at Sovereign Hill.  Next week, I will be visiting one that is 150 years into the future from these workshops, but more on that at the time.

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One of the things I did want to see while I was there, was the metal spinning.  While it is a really old process, it is still very much in use today, forming things like metal bowls.  Of course technology has made things easier, but you would have to be impressed with the quality of the result from the old techniques.

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The process here involves holding a flat disc of metal against a mold.

SH-8The metal worker has a long rod that is supported against the upper arm, and against a pivot point close to the disc.

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By then gently pushing selectively over the surface while the mold and disc are spun rapidly, the metal is slowly bent in until it is flush against the mold, copying its shape.

I found it really interesting that as the metal was being spun, it actually curved outwards as the metal spinning stretched the metal.  It was then rolled over towards the mold with the rod.  This process was repeated as the metal continued to be stretched and molded to shape.

SH-6I wanted to get more background about the process, especially the traditional aspects of it, but the gentleman demonstrating made very clear he wasn’t interested in sharing.  A shame, seeing as he has been doing it for about 50 years apparently, and would have a wealth of knowledge.  He’d also have shoulders of rock doing this for so long.

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Think some areas of the workshop haven’t been cleaned in those 50 years either!

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The workshop produces many of the items for sale at Sovereign Hill – bells, plates, gold panning pans etc.  Bought one of those as well – cost all of $12 too.

Spun items (produced by hand, or by modern methods) have a distinctive fine ribbed surface.  Next time you come across a metal bowl, have a look and see if you can work out if it was produced by spinning, or some other process.

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Episode 117 Traditional Carriage Wheel Production

Wheel Steel

By far and away, my favourite area of Sovereign Hill is the wheelwright’s shop.  This is a fully functional 1880s/1890s industrial revolution vintage workshop, full of line shaft driven machinery, and some really cool specialist machines at that.

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Powerhouse

Machines need power.  It can be horsepower (literally), water power (waterwheel), but what really rocked the industrial world was steam.  I mean really rocked the world – it was (and still is) an incredible way to transfer energy from fuel to a mechanical form.  Not 20 years ago, I was still working on a steam powered warship (which used the more traditional method of flame in a boiler), but even today, nuclear power is still fundamentally a steam system, just with a different source of heat.

Sovereign Hill has wood powered boilers to drive the place.  They run at a pretty minimal level compared to how much demand there would have been with the place rocking “full steam” at the end of the 19th century, but they still go through an entire tree a day (and no, I don’t see that as particularly wasteful, or even a lot in any respect).

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The steam produced here is saturated steam, so it is not particularly high temperature or pressure, but is still more than enough to drive the steam engines around the place.

SH-83In the wheelwright workshop, the engine sits in one corner, and drives a really significant pulley and belt.  This is then distributed by a series of shafts, pulleys and belts to the various areas of the workshop.

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Creating the hub

First step, after choosing a suitable round of timber, and knocking the bark off, is to drill the central hole.  Once, this would have been done by hand with an auger bit…..

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…. but a boring machine turns a difficult and tedious task into something a whole lot easier, and faster.

The timber is processed green, very green, so it machines really easily.  It does mean that there is a long drying time involved in the process, but more on that later.  When you watch the video, look at just how much moisture pours out of the hole as it is drilled through, and in a number of steps, the amount of steam coming off the timber as it heats up from being worked.

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The drill bit doesn’t exactly look as you’d expect, but it is the shape that works best in drilling with the grain, deeply through the core of a log that is very wet/green.

The wheel on the right moves the log back and forward, plunging it into the drill deeper and deeper each time, until it pierces through to the other side.  The operator has to back off very frequently to clear the shavings.

A square-ended shaft is rammed into this hole, for mounting in the next machine – the hub lathe.

SH-81This has two cutting sides.  The right hand side planes the hub down to the correct diameter, then the blades on the left are bought to bear to shape the ends, and gently radius the hub along its length.

With the wood being so green, the timber peels off in a sheet, in quite spectacular fashion.  Easy to imagine this is not dissimilar to how ply is made.

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The hub then moves over to the mortising machine.  There are a couple of steps that this machine does.  The first is where it drills holes around the circumference, which allows the morticing chisels to work with a lot less effort.

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The second step involves the morticing chisels that cut with quite a punching action – very violent, but also very controlled.

The machine automatically raises as lowers the hub into the chisels via a large cam on the front, and indexes from one hole to the next via a auto-advancing mechanism on the left.  It is really impressive!

SH-30The hub is then shelved.  For years.

Like any other timber, a basic rule of thumb is a year for every inch of thickness for it to dry.  2-3 years for the average hub, up to 10-15 years for really heavy hubs (for really serious wheels!)

I don’t have any photos of the spoke manufacture, but you can see more in the video anyway.

The lathe creates the oval spoke, with a square end.  Next, a quick pass through a tenon former creates the initial shoulders, that will then be refined once the spoke has been seasoned.

The third machine shaves a small amount off the circumference of the spoke, near the hub end.  This is a deliberate weak spot, that allows the spoke to flex and absorb vibration, not unlike the narrow portion of a hammer handle.  A spoke only takes a few minutes to make with this method, saving hours of work with planes, saws and spoke shaves.

Once the spokes and hub have seasoned, it is remachined to final dimension (after all, there is quite a bit of timber movement during drying), and then assembled.  The spokes are hammered home, in every second hole, creating the wheel spider.  It is obvious where this name came from.  The spider is assembled in this way, other the increasing buildup of forces in the hub from each spoke would cause it to explode apart by about half-way around.  The spokes are not secured in by any method, other than friction.

SH-28Round tenons are cut on the outside edge with another machine.  This is pretty manual, but looks easy and quick to operate.

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If the workshop has a quality supply of good timber, and the required equipment, the rim timber can be steam-bent in to half, or quarter rounds.

SH-73 SH-74This is a great technique, as it ends up with very strong members, that have the grain running around the rim.

However, if the timber supply is limited or steam bending is not available, much shorter sections can be used that tie two spokes together, and this is repeated around the circumference.

These are called felloes, and are typically cut out on a bandsaw.  They are held against the spokes, and the locations marked, then drilled.  Getting the felloe attached to the spokes is a bit tricky, given they are drilled for their final location, up against the shoulder of the tenon rather than the larger diameter of the end of the tenon.

To fit these on then, another tool is needed to pull the spokes apart so they can engage the holes, before being driven home.

SH-27The gap between each felloe is quite small, but even so, a tenon saw is used to cut in between the gap to ensure the joint can close up fully.

The steel tyre is the final part, and this gives the wheel its real strength.

In an older process, the steel tyre is cut shorter than is needed.  This is calculated as a combination of the size of each gap between felloes, and a fudge factor that comes from the experience of the wheel wright.  A metal bender is used to bend the steel into the required diameter hoop, and the ends are then forge-welded together.

SH-88I am not sure what the pile of hoops outside the workshop is for – tyres are normally cut to match to the individual wheel, not in bulk.

With the undersized tyre, the next step is to get it to fit on the wheel.  This is done by heating to a black heat in a fire, which increases the diameter of the metal hoop, sufficient to be able to fit over the wheel.

The wheel is placed in a pit with shallow walls, surrounded by barrels of water.  The tyre is dropped over the outside of the wheel, and before it has a chance to cause the rim to start to burn, the barrels of water are kicked over, flooding the wheel and cooling the rim.  If the rim had burned, it would have resulted in a layer of carbon, and a great opportunity for the steel tyre to slip off the rim.

SH-26You can see an example of a pit behind these carriage wheels.

Some wheels are designed to have a bit of curvature – this provides additional capability of the wheel to flex, which also takes some of the forces that the wheel will encounter in use.

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Sovereign Hill has a rim press to fit tyres a lot easier than the fire-method.  These are more for wheels that are aesthetic (cosmetic), rather than functional.  The tyre is larger than the diameter of the rim, and the rim press compresses the tyre onto the rim.

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They have had fun with this press, including trying to see what would happen if they kept going and going.  Not surprisingly, the wheel failed, which each spoke snapping at the weakest point.

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So that is the story of carriage wheel manufacture at Sovereign Hill, or at least as much as I was able to absorb from watching their demonstration.  The associated video is in the next post, and it is as good as I could get, shooting handheld in the middle of a large crowd of jostling people.

Following that, I’ll put up another post, showing a certain 4′ carriage wheel that I purchased from the place, made with all the traditional techniques.

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