The Trouble with Heat

One moment you are working away quite happily, the CNC is humming along and everything is just so.

The next, things are NQR – items are breaking loose, engravings are either too shallow or too deep, and the vacuum table is not doing its job.

It is the afternoon of a warm day, and the MDF spoilboard had suddenly started to warp and flex, pulling away from the vacuum table. It wasn’t something I had experienced with very thick MDF, but once the thickness had come down to around 8-12mm or so, it was a real problem.

I first thought the solution was easy – buy more 32mm thick MDF, after all, the first lot came from Bunnings.  But there was a problem.  That was apparently intro stock for the new store, but not something they were going to carry in the long run.

I got to thinking, and one thing that I had tried unsuccessfully, was to place a piece of 3mm MDF on top of the spoilboard (on top of the vacuum table). As a trial it was unsuccessful – to many losses in the system.  But what if I ditched the spoilboard altogether, what then?

So I milled the base really flat, (still a sacrificial piece), then instead of placing a spoilboard on top, I placed a simple sheet of 3mm MDF on top.  It is thin enough that air is drawn straight through it without having to mill off the heavily compressed portions top and bottom, and it is a very uniform thickness.  Also, rather than having to mill, and re-mill it flat as it gets chewed up, it can be flipped over and the other side used, or simply discarded and another $2 sheet bought in.

The other main drawcard of the 3mm spoilboard, is it is thin enough that the vacuum base pulls it flat whether it wants to tend to curve or not.

The first few runs really proved how effective it is.  Not only was the sheet being cut held down well, and very flat, there was significant vacuum that kept the pieces in place as they were cut free, and drove the dust deep into the cut groove.  This was packed rather tight, so the bits did not move even though no tabs were included, even when the entire board was picked up and turned over to sand the other side.

Small refinements to technique, as a result of an adverse situation.  Happy days.

Episode 113 Spoilboard

Episode 101 David and Goliath

Featuring the smallest, and largest Amana Tool router bits from (at least those that fit a standard 1/4″ and 1/2″ router).  Surfacing is done on a Torque Workcentre.

Music by Lis Viggers

Natural Art

Sometimes a piece of timber catches my eye, and although at the time I have no idea what it will be used for, I grab it and store it until it has a chance to tell me what it wants to be.

It has been like this long before I had any decent tools (or skillset) to actually do with the piece what it wanted to be.  Many would argue that the skillset is still lacking, and I’m not going to argue with you on that score!

One such piece was at a woodshow a few years back.  I probably blogged about it at the time.  It was a slab of camphor laurel, and it has been sitting in my wood store for a few years now.  It was always intended to be a coffee table or some such.

I have just received the surfacing/spoilboard bit from, and it was a great opportunity to put the bit through its paces, and to make something from the slab itself.

To the bit for a sec (and I also shot a video of it all, so that will be up soon).  It was called a spoilboard bit, which is not a term I was familiar with.  Turns out (from a Google search), that it is basically what it sounds like, and comes from the CNC world (but machines in the serious spectrum).

These CNC machines utilise MDF as a base material, not (just) because they are flat, but instead because of their porosity.  If you have ever tried to use a VacClamp on MDF, you find it is very difficult to maintain a vacuum, until you seal the surface.  These CNC machines work the other way around – they pull a vacuum right through the MDF, to clamp the material to the MDF surface.  The rolled outer surface of MDF is therefore a barrier to this working effectively, so it needs to be machined off, and that is where the spoilboard bit comes into its own.  Spoilboard – which is as it sounds, another term for a sacrificial board, or base.  Not unlike how we use MDF on the Torque Workcentre.  Doesn’t matter if it gets cut into – it is designed to be used, and eventually replaced.

The same cutter is also perfect for slabbing, and that is how I primarily intend to use it.

Photo 19-06-2008 0 56 42It is a different design to other surfacing cutters I have come across.  They all have the vertical carbide cutters (either replaceable or not), which have a scraping action, but this cutter also has two cutters positioned on the base, creating a shearing action across the surface as well.  It is also a monster of a bit, at 63.5mm diameter! (2.5″).  This is not a bit for handheld work!

With either a CNC machine, a Torque Workcentre (or other slabbing setup), this bit will work to flatten a large area quickly.

I’ll have more detail of the setup in the video.  The slab was secured down, and with a number of passes, the surface flattened.  The bit handled some substantial cuts – at one stage it was cutting over 5mm deep across the majority of the width of the bit, and didn’t notice or complain in the slightest.  I’m sure it could handle even more, but I wouldn’t deliberately push a router bit to its limit.

Once the slab was flattened, a quick burst with the Festool belt sander, then onto the ROS with 80 grit paper.  Both these steps took next-to-no time – as you’d expect.  I didn’t have time to finish sanding (up through the grades), but wanted to at least see how it would look, so rubbed some Danish oil over part of the surface.

Talk about “POP”!

Photo 17-05-2014 17 03 24

When whomever it was cut the slab, they were particularly frugal, and it was very thin to start with.  With the amount of resulting twist/warp, the slab was very thin in some sections (down to about 10-15mm).  Too thin to make a generous table.  However, the timber was already telling me it didn’t want to be a table anyway, and instead wanted to become a piece of natural wall art.  Who am I to argue?!

So I will finish off the sanding, then oil it right up, before mounting on the shed wall.  The only decision now, is which wall of the shed to use!


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