Thanks, kwackers.
So both holes in the t-nut are tapped, and the brass eccentric is tapped as well or does just tightening the cap screw rotate the eccentric enough to clamp?
Chuck in E. TN
Yep, both holes are tapped. The brass isn't.
I'll outline how I made the eccentric and brass section - should help.
Probably easier to start by making the brass parts. I made these from 1" bar (that's what I had), if you've hex about the same size then even better.
I chucked the bar in the 3 jaw and drilled a 'loose' clearance (8.2mm) for my 8mm bolt that I was using.
I'd measured the head of the bolt and it was around 12.7mm diameter - so I assumed I'd lose a little over a mm from the diameter of the head when I turned it down. Having a look around I found an 11mm end mill (to cut the counter bore). The height of the head was 9mm and I wanted 10mm high brass section. So with the intention of shaving 1mm of the height of the bolt head I fed the end mill in 8mm leaving 2mm of brass at the base. I then parted off that section at 10mm thick.
So what I have is a disc with a 11mm diam x 8mm deep counter bore in the centre and a through hole of 8.2mm for the bolt shank.
I continued down the bar until I'd made enough.
Next I need to turn the bolt heads eccentric so they'll fit the pocket.
To do this I chucked a piece of steel in the 4 jaw, centred it and drilled and tapped it for my bolts (M8). Then using a dial gauge I shifted the bar off centre by 1mm.
I then screw each cap screw in to the hole, nip it up and turn it down to a nice fit into the brass counter bore. I then faced off the head of the bolt to make it about half a mil under size for the depth of the counter bore (to prevent it protruding if it's not fully tightened).
What you should have is a bolt whose head is eccentric with regards to the shaft and is a nice fit into the brass disc.
Rinse and repeat.
Finally, if you're not using hexagon you'll need some flats for the faces of the brass discs. To do this I simply ran a long 8mm bolt through, placed them all in the milling vice and tightened up the bolt and vice, faced across the top and then flipped them over.
In use the eccentric would be half to a full turn from locking down the brass disc - the eccentric is adjusted so the brass jaw is away from the workpiece and the nut slid up so that it makes contact. The set screw is tightened to hold the nut in position then the eccentric rotated (the brass jaw will be stationary) until the jaw is locked against the workpiece.
You'll find with only 1mm of work it's possible to turn the eccentric to 'fully tight' at this point the pressure applied seems very high.
Hope this helps.
Steve.