Choosing the right milling machine for making RF coils for MRI

[aot]

Hi,

I was hoping to get some advice on getting a small CNC mill for making PCB's at my lab.

In addition to standard analogue/digital pcb's we also will be making RF coils for use in Magnetic Resonance Imaging - 'coil' is really a legacy word from in the 70's when actual solenoids were used, these coils mostly consist of wide tracks of copper that make some sort of geometry (such as a ring) which is then tuned with capacitors to RF frequencies (in the region 60 - 400 MHz).

The main design requirements for them are that they are made precisely with minimal burrs etc.

The ability to be able to mill things in 3D would also be useful for making the housing.


So, my main question is can anyone suggest a nice, easy to use, compact and relatively inexpensive (under £5000) system? If it doesn't come with software then we would also need that recommending too.

I've done a bit of searching online and found a few systems, although I have no idea how well they are suited for our needs.

Roland MDX-15E/20E http://www.techsoft.co.uk/modela.htm, http://www.rolanddg.co.uk/public/por...x?id=53&type=1
Denford PCB Engraver http://www.denford.ltd.uk/index.php?...165&Itemid=102
BZT PFL330 http://www.bzt-cnc.com/product_info....T-PFL330.html/

To me the Roland system looks the best, in terms of ease of use and easy to set up.

I was also wondering, is it possible to mill pcb's on 0.2mm FR4? and would any of these machines be able to do that, or are there any others to look into?


Thanks very much for all your help.



Aaron

[mactec54]

Hi Aot

If you want to make the magnetic resonance imaging coils you will need a 4 axes machine I was making these coils about 15 years ago on a Bridgeport size 4 axes machine these coils are very hitec as we were getting $20,000.00/ to $60,000.00 each for them they are not just some wide tracks of copper as you say

They could be done on a smaller machine but you need a long Xaxes up to 600mm of travel to make the longer coils this depends on what kind of machines you have for your coils as well & to what size coils it can take

[aot]

Hi Mactec, thanks for your reply.


The types of coils that we will be making will be for experimental purposes, and mainly for a small bore 400MHz system, so we will not need to make huge coils. I presume that you were making large body coils for use in clinical systems (such as a Birdcage resonator or TEM coil), our requirements are slightly different to this.

Presently we are making the coils just by cutting out shapes in copper foil, for example a ring, outer diameter 30mm, inner diameter 20mm, split into 8 segments so small hi-Q chip capacitors can be used to tune, and then a few extra pads for the decoupling circuit and balun. We are not engaged in coil research, or manufacturing for commercial use, these coils are just for use in certain experiments.

The axis sizes of the systems in my first post will be fine for our purposes, my main concern is whether they will be accurate enough, particularly on curved geometry. Also can thin (0.2mm) fr4 be milled?

Thanks

[mactec54]

Hi Aot

No we were making small coils like 60mm was about the large size down to around 40mm
we hand wound ours with copper wire but the foil sounds like a good idea but quite hard to cut out, & placing the copper foil in the coil body will be a bigger challenge as the thin copper will stretch out of shape unless it is the perfect size/profile for each layer

Our coils started the same way as you are doing & then went on to do some commerical coils to cover costs of the machines they now have 4 mags 400MHz 700MHz & 500MHz

The machines you are looking at should do the job as long as the 4 axes has enough height for doing the coil body I had another look at your machine choice & did not see any with 4 axis so this will be a problem one thing I did see was you may be able to use the knife cutting to cut out your foil

[Zig]

Hello Aaron,

We are milling 0.2mm core material for multilayer boards.. both sides.

If you need any coils manufactured, send us your design data in either Gerber of DXF.
If in DXF include notes on final dimansions. With Gerber files we do milling isolation to gerber outline but also require a mechanical outline layer.

Just starting up with a home made 3 axis engraver, positional resolution 0.005mm and a tooling complement capable of producing 0.1 mm features.

Hope to get the plating process up and runing in a few weeks.