threaded rod for table clamps

I have machined up a backplate for a new chuck and need some long 6mm threaded rod to hold a chuck down to the mill table.

The thought occured to me that I might need something a bit harder that what I can easily get from b&q.....

Any ideas on hardness spec, or could I heat treat some zinc plated rod?

Harder or stronger? With respect I think you mean the latter.

You might find stainless-steel studding suitable, but you would not be able to harden zinc-plated rod as it is just mild-steel.

One option is to see what high-tensile M6 bolts or socket-screws of appropriate lengths are available.

Otherwise you are looking at buying a higher-tensile steel (e.g. EN8) and making studs. If you do that, think on, so you give yourself a useful set of 6mm studs for other work-holding in future.

To be honest, if you need no larger than plain steel M6 studding then you won't be subjecting the assembly to milling forces excessive for such material anyway.

It might deflect though, so an approach I use sometimes is to add extra lateral support by suitable blocks, nuts and bolt in angle-plates, or similar, bolted to the table to the side of the work-piece and snugged against it.

Jon,

I made a set of studs for my milling machine from hardware shop 6mm plated threaded rod and they have been perfectly satisfactory. They are plenty strong enough.

HTH,

Rod

If I need threaded rod to tighten up a bit more than usual I simply double up on the nuts

I use regular cheap threaded rod. Yes you can strip the thread if heavy handed but no need for that kind of force if using enough clamps with the stud close to the job and the packing block as far away as possible for max leverage.

You can buy high tensile thresded rod from most engineering suppliers if you want a bit better quality. But I have never bothered.