3D design to CNC mill design flow

This is one of those times when I don't know enough about a subject to even ask coherent questions. This is all pie-in-the-sky stuff, it'll be a fair way down the track before anything happens - if ever. But here goes with just a couple of simple (ha-ha) questions, hoping any answers will either point me to somewhere/somebook/something where I can start to learn in a cohesive way, or will nudge me in the right direction for asking further questions.

1. I've never used 3D CAD software. I've never had any association with CNC
machining. I'm an EE (retired), I've designed, built, and written the code for lots of scientific equipment that required servo/stepper controls and so forth, so the general mechanics of CNC machines hold no fundamental mysteries for me. But the control was by native code in embedded micros, so while I'm aware of G-code, I've never given it more than a very cursory glance.

2. The disconnect in my knowledge is the path from a 3D CAD image to (presumably) an input file for the CNC controller (MACH3 ?). This doesn't seem conceptually difficult for a 3D object containing only orthogonal flat surfaces i.e. pretty simple X/Y/Z stuff. But when the object contains surfaces consisting of compound curves then the machine will (obviously?) require additional axes (rotation about X, Y, and Z). Are there standard assignments that associate drawing rotational axes with machine rotational axes? Hmmm, thinking about that further, it probably shouldn't matter what axes the image is drawn around. Provided the CNC machine itself has sufficient axes, it should be possible to transform the image coordinate system to suit the machine (true or not?). Although it would probably be best if the design coordinates and the envisaged workholding method were designed to map directly to the target machine (true or not?).

3. The end result of this thought exercise is to determine what hardware (CNC mill) and software would be required to design and fabricate a single blade of an axial compressor. The blade would have a cambered airfoil section, with twist from root to tip, tapered thickness, and various planforms - hence all the compound curve questions. I think 4 axes would be sufficient (although possibly not with the 4th axis as the 'usual' (?) rotation about the machine spindle axis), but in any case I need to understand how the CAD design becomes suitable G-code for a given machine. Is the operation intended to be automatic, or does it need further directing by the designer?

As I said at the beginning, I barely know what it is that I don't know.

Edited By Roger Head on 13/12/2016 14:49:48

Edited By Roger Head on 13/12/2016 14:51:58

A few comments - for complex geometry, you really need CAM software to help generate the G-code. No this isn't automatic, you have to do some of the work by splitting the job into operations, and then telling the software which parts of the design each machining operation applies to.

For a single blade I agree that 4 axis capability should be enough - but it must be 4-axis continuous machining not just 4 axis indexed. Some CAM packages skirt around this distinction in the descriptions.

You should be able to find demo videos for this kind of thing on the web sites of various CAM packages. If they don't have a video showing something like this, then assume the software can't do it unless you see hard evidence that it can.

And yes, you have to tell the CAM package about the CNC machine that will be used, that isn't generally too difficult.

Thanks David, a little enlightenment plus a useful nitpick ("it must be 4-axis continuous machining not just 4 axis indexed. Some CAM packages skirt around this distinction in the descriptions). I had assumed that if something (hardware, software, ...) was described as having 'N' axes, then all could be active simultaneously. A valuable point.

Thinking about milling compound surfaces, it seems that (apart from the roughing out from an initial lump of material) it eventually becomes a case of milling 'lines', either with say, a plain endmill, or if it is a concave surface, a ball-endmill. Especially in that latter case, and accepting the variability between materials, what sort of final surface finish is achievable? Something similar to that obtained with a normal endmill on a flat plane, or is some form of finishing process typically required?

A good starting point would be Fusion 360. This contains the drawing package and Cam module in one. It has post processors for most of the hobby control systems (mach 3 and EMC being the two main ones). There are plenty of youtube videos on how it all works. NYCCNC is a good channel to see what it can do.

The good thing about it is it is free if you turn over less than $100,000 per year.

David

Roger, I'm not an expert on this (have simply had to learn enough to be able to demo one of the available packages) - CAM software typically allows you to define a maximum allowable deviation from the surface of the CAD model. The toolpaths will be worked out to achieve this. Choice of tool size and step-over is typically down to the operator, for some geometries these will influence best achievable accuracy and finish. Like many things, there will be a compromise between machining time and achievable finish. There are other subtleties to handle (like deviation of tool from nominal size (tool wear)

Others may be able to offer better insights on achievable surface finish, and likely necessity to follow up with a polishing operation. It occurs to me that you should pay particular attention to the rigidity of the 4th axis if wanting to achieve good finish.

Fusion 360 is a good starting point for 3 axis work but doesn't at the moment go to 4th axis. I believe 4th axis will be available soon. I use Sprut Cam to generate the G-code, leaving only the simple stuff that my feeble brain can cope with to manual generation of G-code.

There are other CAM packages that are free but I have not tried any.. A book worth looking up is the CNC Handbook by Peter Smid, it is comprehensive however it is a fairly expensive tome.

I thought the 4th and 5th axis was implemented in the last update. I haven't tried it though. It maybe that you need fusion ultimate to access the full features but I'm pretty sure that there is some functionality for the non paying users.

David

A little more general info, apologies if I cover something you already know

For most CNC jobs you may find 2.5D is the best fit, this is just the tool moving on one layer at a time and a lot of CNC machining is just that with 2D CAD drawings of the profiles being used.

Items like the fan blade would need to be drawn in 3D CAD but I'm not sure continuous 4th axis machining would be essential and stepped 4th axis may work fine, however you may get smoother machining from continuous 4th axis.

You can hand code for some 2.5D jobs but importing a 2D CAD drawing of the profiles into a CAM program is usually faster, programs like Fusion 360 has both CAD and CAM in the same program (you also mainly work in 3D) so no import is needed and they also have the advantage of updating the CAM if you alter the part

3D CNC gets more complicated and you generally always need a CAM program to create the toolpath. Most CAM in the hobby range will output these toolpaths as very small linear moves so a large file could have millions of lines of code. Some of the commercial CAM are now taking an allowable error and using that to create a lot of small curves.

Some CAM programs to look into:

Sheetcam - 2.5D CAM, aimed at Hobby use mainly
CAMBAM - 2.5D CAM but some drawing capability, again mainly hobby use but it's a while since I looked at it.
Vectric do a range of programs that are very good and usually are CAD/CAM in the same program.
Meshcam - 3D CAM, indexed 4th axis and mainly linear moves but I think the developer is moving towards including curves.
Fusion 360 - 2.5D & 3D CAD/CAM, very modern comprehensive program but a bit of a learning curve.

These are programs I've used and there are a lot of other programs to try but out of these I've mainly use sheetcam with some use of Meshcam for a few indexed 3D items, I now use Vectric Vcarve for most of my 2.5D cutting and I'm getting used to Fusion 360 and have used its output on my son's 3D printer.

I'm only a hobby user so my experience is limited to machining my own hobby parts so I'm open to correction but I hope I've provided a bit more information on the process.

Steve

It does 4th axis as "wrapped path" currently and I think the true ("simultaneous" 4 and 5-axis capability is due very shortly. The good news is that for the hobby and small business user, the "ultimate" version with all the CAM extras is free, so by the time you bottom out how it all works, the true "simultaneous" 4 and 5 axis CAM should be ready for you.

There's loads of good tutorials by the Fusion 360 team (and others), an active forum and a product roadmap.

As David Colwill suggests, John Saunders (NYC CNC) has also done a load of videos showing how it all works in a real workshop. Like a lot of things, it's worth spending time to learn about it before diving in an expecting quick results.

Murray

Thanks Murray

I hadn't realised that the free version was "ultimate"

Although I have had fusion I haven't really used it much. I've spent the last week tweaking my little mill (Triac ATC) and am getting the hang of the cam side of Fusion. I have run several programs now without any problems.The last job on the list is setting up the 4th axis and getting Fusion to work it..

There are a huge number of drawing / CAM options out there but I haven't seen anything else with this kind of functionality that is basically free.

One thing I have started doing which has been a great help is to create a text document that explains step by step how to do various operations eg setting tool offsets in the ATC, setting the tool table in fusion and basic workflow on running a program. I find that sometimes I don't get much time in the workshop and when coming back to these things after some time I can spend a lot of time trying to remember what I did. I have written off more than 1 expensive cutter by making a stupid mistake usually caused by forgetting to do something.

David

Thanks everyone, you've been very helpful. I've spent quite a few hours with google today, basically discovering how rare continuous 4th axis capability is. It came as quite a surprise. I imagine it is available in high-end products like Solidworks etc, but I haven't even bothered to look at their sites because I've heard what their prices are like - my pension wouldn't cover it. In that same context, Sprut CAM appear very coy with their prices, and only offer a 30-day trial, so I get the feeling that they are out of reach as well.

As several of you have pointed out, Fusion 360 sounds almost too good to be true (good product + FREE! ). I had a look at their RoadMap, which reads well, and will be even better if it becomes true. I watched one of the John Saunders videos right through. Naturally it didn't mean much to me, but I definitely liked the presentation format, and his speaking style. It looks like it would be a great resource if they are all similar.

I read through the Fusion 360 thread (http://www.model-engineer.co.uk/forums/postings.asp?th=108196&p=4) and on page 4 I see several posts by Neil Lickfold illustrating some early adventures cutting model aircraft propeller blades on his (presumably 3D) router. That was early this year, so definitely before any 4th-axis release from Autodesk. Conceptually, it's the kind of thing I am thinking about, and that has pretty much decided me on Fusion 360. It will mean using my W7-64 boot, instead of XP. Does anyone know if MS have given up trying to automatically upgrade you when they see W7 updates being loaded? And how I can stop it if it's still happening?

In my google travels I came across a technique called “Sturz Milling”, see half-way down the page at

http://blog.cnccookbook.com/2013/04/08/cnc-4th-axis-introduction/

I can see the intended benefit, but it looks like another complication for the code generator. Is this a commonly available method?

Thanks again,

Roger

Not in my experience. My medium price CAM software (VisualMill) doesn't explicitly offer it; and is, in my opinion, rather weak on 4th axis toolpaths anyway.

If you're using stepover with a ballnose mill and the surface is not far off the axis of the tool, then by default the side of the cutter is working rather than the end. But that is more by accident than design. To make full use of Sturz style milling I suspect you will need a fairly high end CAM program and/or a 5-axis mill. Or write the G-code by hand.

Andrew

This CAM stuff is beyond me, and I take me hat off to those who can use it. Having seen Siemens NX 5 axis in use i'm just left shaking me head. So all kudos to those who can use it. [ any Cam software ]

Roger

The price of Sprutcam varies according to the features you want. When I asked for pricing in June 2015, I was told that hobby users get it at half price but they only get one (non-editable) post processor. And for true 3D milling (as opposed to 2.5D milling), you need the "3XMill" version which retails at £1700+vat. So for hobby use you can look at coughing up just over £1k. Once I was able to stand up again, I rapidly forgot about Sprutcam and the more I found out about Fusion 360, the better things got.

The add-ons for the likes of Solidworks come in at full price too. If you are lucky enough to have a copy of SW, you can install the free 2.5D version of HSMworks (bizarrely it's owned by Autodesk) but this lacks all the clever adaptive algorithms that account for so much of the progress in tool paths in the last decade. And for reference, Onshape's 3rd party CAM add-ins are charged at professional rates.

The CAM that is included (for free) in Fusion 360 is basically the full, 3D professional HSMworks CAM. That was relatively simple for Autodesk to do given that they own both products - but also a radical step to allow free use for small users. Onshape, Solidworks and the other mid-range CAD developers must be seriously pigged off by that.

Fusion 360 is aimed at the professional market. Most users will end up paying - and probably quite willingly, given the eye-watering cost of purchasing and "supporting" rival products like Solidworks. Interesting times!

Murray

Posted by Roger Head on 14/12/2016 12:19:40: Does anyone know if MS have given up trying to automatically upgrade you when they see W7 updates being loaded? And how I can stop it if it's still happening?

MS now charge for the Win10 upgrade so I think the answer is "no". And if you have Win 7 (I do and like it), you can download a free utility called GWX that stops them trying anyway.

I know someone who makes small gas turbines and makes his compressor fans using CNC, I'll ask him what he uses.

And don't even think of asking about Mastercam..........

Andrew

Roger, I have sent you a PM.

Having decided on Fusion 360, I will proceed to learn how to create component designs, and then (using the inbuilt CAM capability), create output files. At that point, is there any benefit in having, say, MACH3 without any mill attached? Will it usefully perform any sanity checks on the input file?

Related to that, is there any software that accepts the CAM file and re-creates a virtual component (on the screen)?

Roger

I don't know specifically about F360, but many CAM packages include cut material simulation which starts with the stock material on screen and shows it being machined to finished item.

There are also simple software tools which will plot the toolpath (e.g. NCPlot, or indeed the screens within Mach3). Not quite the same as showing the material, but may be useful nonetheless.

Free standing simulation of cut material - see CutViewer (only 3 axis milling), CNCSimulator, or MachineWorks. There may well be others out there.

Edited By David Jupp on 15/12/2016 08:14:09