Lockdown CNC: Custom Dado Rail!?

Last updated on 1st December, 2020

Picture this: you are mid lock down and figure now is an excellent time for some house decorating. You start to clear the room, pack up all your stuff, dismantle the wardrobe… And discover 40cm’s of missing dado rail!

The real issue here is that we live in a fairly old house and most of the features, including the dado rails, are old designs. Not to say you can’t buy them anymore, but they are not easily picked up at the local B&Q. And especially when you are mid COVID-19 lockdown and only need 40cm of the stuff. Last thing I wanted was to buy a 3.5m length online to discover it was the wrong profile! So, there is only one thing for it, some Sunday morning CNC work. Not interested in reading this one? Skip straight on to the cheesy summary video!

Need some dado rail making? I’ve had a lot of request to make some dado rail – which I’m more than happy to do. If you need something making, get in touch via the contact page or leave a comment below.

Getting the dado rail profile in CAD

Luckily, I had a lovely square cross section view of the same dado rail profile elsewhere in the house and was able to take a clean photo. The image was then imported into CAD/CAM Fusion 360 as a canvas. I added a reference line of 68mm (the height of the dado rail) so that I could scale the canvas to the correct size. Then it is a relatively straightforward task of drawing over the canvas with a series of straight lines and spine curves – playing dot to dot if you like!

So now I had the outline of the profile I needed and knew it was the right size, a simple 45cm (40cm plus 5cm of spare!) extrude gave me my dado rail ready to be imported into Fusions’ CAM module.

Time for CAM

The CAM set up was simple enough. I had a old blank of 200x500x25mm pine which I used for the stock and positioned the dado rail along one edge of this. I decided to do this job in a few operations using 2 tools: a 6mm flat end mill to do all the roughing work and a 6mm ball end mill to do the finishing work. Firstly, I used the 3D adaptive clearing to rough out most of the material. Next I followed this up with some 2D contouring and a trace operation to clean up the tight edges and finish the flat surfaces. The final step was to profile the surface.

Like I said, I used a 6mm ball end but needed to determine the best step over. The step over is the distance between the profiling paths. The CNC Cookbook has a great article on step over selection which is well worth a read. I selected a step over of 0.5mm (1/12 of the 6mm diameter) gives a good enough surface finish for me. Although, I probably could have increased this to 0.6mm or 0.7mm to increase the speed.

By default, Fusion 360 tried to run the profiling passes perpendicular to the length of the dado rail. This would have resulted in a really rough finish. So I manually changed the direction to run along the length of the dado rail – hopefully giving me a better finish. And much more like how dado rails are actually made!

Its dado rail cutting time

Now it was over to the CNC side of things. I have a Stepcraft 840 machine which I was lucky enough to inherit a few months back. I am using UCCNC software coupled with a UC100 motion controller. I’ve only being using this for a month or so now but it seems pretty intuitive and very reliable. Loading up the GCode from Fusion 360 is simple enough and, with the material clamped down, we are almost ready to go!

The Stepcraft uses a standard 43mm clamping collar (euro neck) which accepts most routers sold here in Europe. I have a few routers and spindles knocking around and decided to use a cheap and nasty 0.6kW router for the roughing work. I have no idea what the run out is on the router but for roughing work in wood – who cares? The power of this router is more than enough for 10mm passes though pine. Although, I still have a lot to learn when it comes to speeds. I found that I had quite a bit of heat build up in the tool for certain passes. I was able to compensate for this by manually adjusting the feed rate in UCCNC.

For the finishing passes I used a 320W Bosch POF 50 router. This is a really old router that I have but it is incredibly quiet and smooth running. It always leaves a clean cut so it is a great choice for finishing. The Bosch also fits the Stepcraft frame very nicely as it has a large clamping area and a relatively small body. Since the majority of the material had already been removed in the roughing steps, the finishing pass only needed to remove 1mm or so. So after about 130 passes – we have an almost finished dado rail!

Trimming the finished piece

Learning points?

So is custom CNC’ing a dado rail a thing for the future? Probably not! But for a Sunday mornings work, a bit of scrap material and playing around learning some new skills – why not! There is definitely some things that worked well here and some things that need improving.

• Importing an image into Fusion 360 via a canvas is a very useful way to CAD. Especially when you are working with an already existing design or profile with unusual curves.
• The Fusion 360 manufacturing module with Stepcraft post processor works flawlessly. Assuming the programmer knows how to set up speeds and feeds….
• Speeds and feeds – a huge topic in itself. The mistake I made here is that I assumed that deep slow cuts would be preferred to shallow fast ones. This is not the case (in my case!). This just resulted in poor chip removal, increased tool heat and nice burn marks on your dado rail!

Cheesy summary video

And here is a quick little summary video including a few time-lapse shots – enjoy!