Making a house number sign with the MPCNC

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We moved house a year ago. To feel more attached to our new home I thought it would be nice to make a replacement for the existing, and somewhat shabby, house number sign attached to the wall next to the front door.

The basic design I had in my head was a wooden oval with brass numbers screwed to the face. To make it more interesting, both aesthetically and to machine, the edge of the oval was to be raised up, with the face which have the numbers attached recessed. Further it would like nicer to look at, and it would be more durable, if the edges of the raised edge were chamfered or beveled. After hunting around on eBay I purchased some European oak: about 800mm long by 250mm by 24mm thick. The brass numbers were also sourced from eBay.

Before starting out with this project I decided my MPCNC needed one important upgrade: a new spindle. The Dremel was fine to start out with, but wasn’t really cutting it (bad pun, sorry) with bigger cuts. It’s also extremely noisy. I went for this spindle, which you can find on eBay and other places.

Fitting the spindle required a mount. After looking at several, I settled on this one from thingiverse. It seems to hold the spindle well. For extra piece of mind, I’ve attached some Kapton tape above the mounting point. If the spindle ever slipped down the tape would crease, showing me that the spindle had moved:

Getting the spindle working also required a mounting “box” for the PSU. After looking at several on thingiverse I decided that none of them were quire right so I designed my own:

I have not yet uploaded this design because I had to make some manual changes (drilling out some holes) before it would fit the power switch correctly.

Finally, the spindle uses collets instead of a chuck. I’d previously not had any experience of these, but I’ve learned that they are required because drilling metals requires a much better “grip” on the cutter then can be achieved with a hand-tightened chuck. The spindle came with around a dozen collets, in sizes from 1mm to 7mm, in steps of 0.5mm. I found a nice holder for the collets on thingiverse which I’ve printed, which will hopefully mean I’m less likely to loose them. The holder is sat on top of the PSU in the above picture.

Back to the house sign.

Here’s a picture of the design in Fusion 360:

The maximum thickness is 22mm. The step down to the main base is 4mm. Fusion 360 deals with chamfers in two ways:

  • As a component of the model.
  • As a cutting step against a regular path.

After struggling with the first, I opted for the second. Hence the design above does not show the chamfers around the inner and outer edges of the border.  Reading the Autodesk forums, not supporting machined chamfers from information contained in the model appears to be a known shortcoming.

After creating the model, I did a quick paper print out of the design in order to verify that the brass numbers would fit nicely; they did. I then jigsawed off a section of the oak stock. Either I’m getting better at using the jigsaw, or the new blades helped, but in any case this was done easily and without any fuss.

The next stage was to switch to the Manufacturing mode in Fusion and create the needed machining steps.  In the process I created configurations for the cutting bits I would need.

A good many steps were needed.

The first was a facing operation to cut the ridge down slightly. In retrospect this was probably not needed as only 2mm of material had to be cut down. A 5mm flat end mill was used:

Next an adaptive clearing operation to get the ridge down to its final height. Again a 5mm flat end mil was used:

Next another adaptive clearing operation to cut the centre section down to its final depth of 2mm+4mm=6mm. This was the longest operation. Again a 5mm flat end mill was used.

The chamfer was next. The inner and outer edge of the ridge had a 2mm chamfer applied with a 5mm wide 90 degree spotting bit. Initially I believed this bit had straight edges on the cutting face, but looking at the bit more closely it is slightly curved. To be honest, I’m not sure if this is the correct bit to use.

While I have the workpiece in the CNC bed, it made sense to drill out the mounting holes. I could have done this by hand but why not use the CNC? The boring operation was used to cut 4mm wide holes all the way through. A 3mm flat end mil was used to do the cutting.

Finally the sign was cut out of the workpiece using a contouring operation. Tabs were created to stop the sign coming away from the stock before it had been fully machined. Again a 3mm flat end mil was used:

The simulation tool within the Manufacturing mode of Fusion is amazing. I would have not been able to get this part made without it. It allows you to simulate each operation separately or to see the whole sequence as one.

All of the above operations were performed at 500mm per minute cutting speed, with a step down of 1mm. Possibly it could have been done faster, but since this was my first big project it made sense to be a little cautious.

The above describes the theory of the operations that had to be performed in order to produce the wooden base for the sign.

I was pleased that in actual practise the machining went well, though some interesting aspects are noted here.

Firstly, since my MPCNC lacks auto-homing endstops I had to create my own origin position. Previously, for simple engraving operations, I’ve used any random position towards the corner of the stock, so long as the tip of the bit has been resting on the top of the stock at the start. For the house number sign something different was required. In the end I settled on using the physical extreme position (bottom left, when standing in from of the machine) as the origin, with the Z axis origin being the top of the stock. This worked well.

I started of with clamps holding the stock to the bed. This worked fine for the first few operations, but later on I became worried that the clamps (and the threaded rods holding them down) would get in the way of the moving gantry so I screwed the stock down with two long wood screws instead. Naturally this was done without moving the stock.

Finally, I’d planned to use a 5mm end mill for the final contouring cut to free the sign. It would have performed the job much quicker then the 3mm cutter, with the only downside being more chips generated. But the 5mm cutter was not long enough to reach the bottom of the stock so I had to switch to the longer 3mm bit.

I made a few videos as the MPCNC was working and edited them together with some static shots:

One detail not shown in the YouTube video is the tabs. I was amazed at how well they worked:

Freeing the workpiece was easily done with just a craft knife, followed by some light sanding.

The other thing to bear in mind is that the spoil-board had barely a scratch on it; the dept of cut was spot on to just reach the bottom of the stock without cutting into the board beneath. The same can’t quite be said for the mounting holes, which required a quick drill through the last 0.5mm of wood by hand.

Before attaching the numbers, I gave the wood a coat of varnish to protect it. I don’t really know much about the multitude of varnishes, but here is a picture of the tin I used:

Just for completeness, here’s a nice picture of the finished sign screwed to the wall outside the house:

Overall I as very pleased with how this little project came out.

The next post will return to the normal theme of electronics and retro-computing.

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