Insight: 3-Axis CNC Machining
Hi and welcome to this week’s insight video. Today we are going to take a closer look at 3-axis CNC machining.
Now any google search will soon reveal a number of blogs about 3-axis vs 5-axis machining and you will see that the latter is very much thought of as the cool kid on the block. Excuse the obvious pun!
Indeed, you might assume that you should just plump for 5-axis machining, but often this is an expensive mistake, and with a bit of thought and planning 3-axis machining will be a better choice.
But first let’s briefly run through the differences. As the name suggest a 3-axis machine allows a part to be worked in the 3 axes X, Y and Z. This means that you can work any one of six faces.
A 5-axis machine adds extra movement to the part. The fourth axis adds rotation around the X axis – we call it the A axis, and then the fifth adds rotation around the A axis. Don’t worry if you can’t quite get your head round this – it basically means that you can move the part in multiple directions and angles so that you can machine, drill or thread to achieve more complex shapes and angles.
Now before you say great give me a 5-axis machine for my part, don’t write off the 3-axis option just yet.
First of all, a 3-axis machined part will typically cost you far less. This is because five axis machines are far more expensive to buy and also for a given size of part are far bigger. When you think about it, they have to grip a lump of metal or plastic securely and move it through several planes.
I’ve seen 5-axis CNC machines that occupy the same floor space as your average sized lounge and the capital investment can run into hundreds of thousands of pounds. It’s a big investment because all five axes can move and cut simultaneously to give highly accurate complex parts.
For high precision parts for say the aerospace industry then yes 5-axis machining is sometimes the way to go. Indeed, we have invested in 5-axis machining at Protolabs.
But let’s not ignore 3-axis machining, it has more to offer than you think.
I’ve already mentioned that it’s less money to produce a part, but also because there are way more 3-axis machines than 5-axis machines, there is more capacity out there and this could affect your delivery times.
Another reason is that the parts produced by 3-axis machining are normally bigger than those from 5-axis machining, which is due to the relative size of the machines. From us, for example, we can produce a part in stainless steel 17-4 PH that is between 3 to 4 times bigger in the x and y axis than from a 5-axis machine. And it’s a similar story for other materials.
And when you get down to it you can do far more than you might think with a 3-axis machine. I’ve got a great design aid here to show you what I mean – it’s a design cube manufactured from aluminium.
As you can see there’s lots of great features possible. Holes, slots, threads, different finishes, bosses and raised features – I could go on – but what I want show you is this. You would be forgiven for thinking that this contoured surface was produced by a 5-axis machine, but no as I said this design cube was produced on a 3-axis machine. This surface here was produced using ball milling.
As an engineering designer there is a lot to be said for keeping a design simple. Just because you can achieve more complex shapes and more precision does not mean that your part needs it. And you will generally have to pay for that geometry, complexity and precision.
It’s also way harder to design parts for a 5-axis machine and mistakes are far easier to make. It could be for example that drilling at a certain angle might affect another nearby feature. Of course your supplier should be able to check your CAD design, but when you start to push the limits, well…
So don’t discount 3-axis machining, sometimes the discipline of designing within certain parameters is a good thing. You won’t always need those extra geometries or precision and perhaps you would rather have the advantages of a bigger more cost-effective part that is easier to manufacture.
At the end of the day, it comes down to judgement. Just because you can do more, if you pay extra, does not always mean that this is the best choice.
And with that final thought I’ll say goodbye and I hope you can join me again next Friday.
With special thanks to Natalie Constable.
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