Magnetic chucks are not really made to take great side loads so your flycutter may well just launch the bar across the workshop, though suitable placement of stops will help. I am assuming it is the 30mm face you want to work on.

A better approach may be to buy or make some low profile side clamps which will grip the edged of the bar and pull it down to the table leaving the top clear for machining.

If you have a lot to do consider getting a face/shell mill as you will be able to feed a lot faster than you can with a flycutter.

There are mag chucks for milling machines. Really expensive and need care using them. When the material gets thin, ie under 4mm thickness, their ability to hold properly really starts to diminish. Even with packers around it.

Vacuum chucks work really well on supported thin stock, and so does double sided tape also works well. Just can’t expect to be taking big cuts or cuts with high loads. Sharp tools help to keep the loads down.

Need to be careful taking thin stock off that has been held down with double sided tape as it can bend etc.

A plate held in the vice or clamped to the mill bed can be used.

Got a pic of the part? There are many ways of holding parts these days and there are also non traditional vices that work well for parts that a normal vice does not hold well. Can be made from 2 long pieces of steel, with hold down bolts and studding or bolts to bring together etc.

Then there is the softjaw method, where it is cut to support the part and has slightly tapered sides to force the part to fall to the inner of the softjaws instead of flexing up for example.

Neil

My ow magnetic chucks are both 5×10″ so just too short, but 12×6″ are certainly listed in the Eclipse range.
The ones my size are often expensive on eBay, but as you get larger, they sometimes get cheaper, and are often collection only, which might work to your advantage.
Yes I have used mine on the Centec for similar jobs, but there’s a few things to consider.
One is surface finish on the chuck side of the workpiece, as a poor finish will adversely affect the magnetic circuit, and thus the holding power.
Consider the direction of cut and loading, then make sure the end and side stops/fences are in the right places.
For a long narrow workpiece, you’ve not listed the width, I’d add a pair of thinner strips either side of your workpieces, say 5mm thick, to add more resistance to sliding.
One problem is chip clearance, less an issue with a fly cutter, or maybe a shell cutter, but certainly a potential problem with smaller mills and slot cutters. The chips don’t clear well leading to a poor surface finish, or even cutter breakage. Vacuum and paintbrush helps clearing up after a run when changing workpiece.
I was looking for an on-line copy of the Eclipse manual, and found one on here;
https://www.model-engineer.co.uk/wp-content/uploads/sites/4/documents/eclipsemagneticchuckhandbook.pdf
There is a specific section on milling using a mag chuck.

The later brochure is available on their own site, and even lists a model called Supermill, though I guess you’d need deep pockets to buy new.
https://www.eclipsemagnetics.com/site/assets/files/2866/magnetic_workholding_literature.pdf

Bill

If you have a lot to do, you could always make a jig to hold the bars, from thicker bar you could bolt to the machine bed. clamping by a series of 4 or 5mm screws holding the edge, or a 300mm long hold down.

Chris Gunn

I would consider sweating the part you can’t hold to a piece of material you can hold with soft solder. Then simply un-sweat it off and clean it with wire wool afterwards. I have done this with parts that are hard to hold in a conventional 3 or 4 jaw chuck.