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| kwackers:
--- Quote from: Chuck in E. TN on October 03, 2010, 07:10:38 AM ---I might be missing something, but it looks to me like the casting shown above could slide out of the clamps toward the operator. How does this style of clam work? Any drawings, C-O-C? --- End quote --- The idea came from these http://www.wixroyd.com/products/pdf/1215-clamps-low-profile-eccentric.pdf the incentive was the cost... They work because the head of the bolt that holds the brass head in place is eccentric, the bolt isn't tightened so can be rotated causing the brass to move. The eccentric is 1mm so the clamp is pushed up against the object, the set screw tightened to hold it in place and then the screw rotated to tighten up the clamp. The casting in the pic was just a test, I probably wouldn't machine it like that. (Having said that I couldn't move it and don't think there'd be any issue machining it as is). |
| Chuck in E. TN:
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 |
| kwackers:
--- Quote from: Chuck in E. TN on October 03, 2010, 07:28:37 AM ---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 --- End quote --- 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. |
| Chuck in E. TN:
Thanks for the details, Steve. Sorry, I didn’t read thoroughly the first time, missed the eccentric on the cap screws. Makes sense now. Got to go make some. Chuck in E. TN |
| John Stevenson:
I have two of the tee slot thingies like Steve has made but I drilled and reamed an extra hole between the two tapped holes, 8mm in my case to tale a dowel pin. These can be used as a dead stop for repeat work or with different sized sized dowels, to locate into existing holes, again mainly for repeat positioning. Got a pic somewhere and if I can remember what it was saved as I'll post it :wave: John S. |
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