Low profile clamps

[kwackers]

Having spent many times trying to hold thin parts in the mill by any and all means possible, I thought I'd get round to making some low profile clamps.

Picture below pretty much sums them up. I've made 8, 4 can be seen holding the casting to the bed, three others are sat to the side and the one in the bottom left is in it's component parts to show what's involved.

To fit my mill the T nut is a piece of 3/4" bar cut to length and drilled 2 x 8mm, one holds a 16mm long grub screw, this is used to clamp the nut to the bed, the other is a 16mm cap head screw used to perform the 'cam' action for the clamp.

To work as a cam the cap head screw has it's head machined 1mm eccentric (chuck some bar in a 4 jaw, drill and tap, move the bar over by 1mm, screw each screw in and turn the head round - it'll now be offset by 1mm). The brass head is a length of 1" bar, drilled 8mm clearance and the bored out leaving a couple of mm using an endmill (flat bottomed hole). The cap head should be a nice fit in this - being eccentric turning it will provide the cam action necessary to clamp the workpiece.



Finally make sure the length of the clamp isn't too long. It never occurred to me until I had a set made and then I couldn't drop them into the gap on my table. Fortunately before I hacksawed them up into ordinary T nuts I realised I could machine the corners off to enable me to drop it in at an angle. The shot below should show what I mean.

IMG_5611 by zx12, on Flickr

Next step is to see if the 10 year old blacking solution I've got in the cupboard still works - if so I'll black them up. (The grub and screw are stainless so they'll be fine)

[raynerd]

They look amazing Kwacks and will certainly be a future project.

Chris

[cidrontmg]

Excellent. To be copied as soon as I get some 6 mm grub screws - my mill has far narrower slots (BF16). Monday, that is.    Many thanks.
 

P.S. Did I see a couple of tool marks on the mill table...  (?    anyway...)

[kwackers]

Excellent. To be copied as soon as I get some 6 mm grub screws - my mill has far narrower slots (BF16). Monday, that is.    Many thanks.
 

P.S. Did I see a couple of tool marks on the mill table...  (?    anyway...)

Yeah the mill came with those (it's an old Elliott 00 Omnimill), saves me doing them - plus if I ever added any myself I wouldn't want to cry every time I saw them.
(they're not bad enough to warrant any effort in repairing - the light makes them look worse).

[Chuck in E. TN]

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?

[kwackers]

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?

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]

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.

[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 

John S.

[kwackers]

Excellent idea John, I was thinking about stops too. Even better if I can 'multi use' the stuff I've already made.
I don't think I'll get away with 8mm dowels, I may not have enough space between the two screws but if not 6mm will work a treat.

The main reason I made so many is because I got carried away machining my brass bar! Plus set up time is so expensive, doesn't add a lot to make more...

[DMIOM]

......The main reason I made so many is because I got carried away machining my brass bar! Plus set up time is so expensive, doesn't add a lot to make more...

If you're ever making more, you may find it useful to slightly taper the OD of some of them - put a couple of degrees on so that when the cam presses in, it also helps hold down as well.

And their use isn't limited to the T-nuts - if you have a repeat task and you have a jig/fixture or a sacrificial plate, just pop the mounting holes into that plate - though I don't use them that often, I use Mitee Bite clamps almost as much that way as with the T-slot nuts.

Dave

[Ned Ludd]

Nice clamps, even more for the tu-it list.
Could somebody be making a Potts drill sharpening jig?
Ned

[Stilldrillin]

Nicely made, shown, and explained Steve.   

There's always summat else I need to make....... 

David D

[kwackers]

Nice clamps, even more for the tu-it list.
Could somebody be making a Potts drill sharpening jig?
Ned

Well spotted Ned!

[Ned Ludd]

Call me psychic (as opposed to psychotic) 

I bought my set of casting from Kirk about two years ago at the Midlands show, but have yet to finish them, only got the base parts done so far up to the part you had clamped to the table.
Some questions for you;
How are you getting on making the jig, what difficulties have you come across?
Did Kirk ask you to do a write up too?
Why did you choose the "Potts" version over the "Duplex" one?
Ned

[kwackers]

I haven't machined anything on it yet in fact it was whilst staring at the castings and trying to figure out how I was going to machine that I decided to make the clamps.

I think I probably bought it at the same time/show as you! I've a number of other Hemingway kits - both finished and unfinished. The Potts jig was bought to use with my cutter grinder (another from Kirks), I'm not sure what the difference between the Potts and Duplex versions are (other than there are apparently some mods mentioned in the notes).

I'll be up at the exhibition again in a couple of weeks although I'm under strict orders from my brain not to buy anything that requires any machining at all! I don't get much time in my workshop and at this rate I'll have nothing but tools to show, be nice if I get round to some non-tool projects  (once I've finished all the tool projects currently staring accusingly at me from under the workbench...)

[Ned Ludd]

Why bother even thinking about making anything other than tools, there are never too many to have. Toy steam engines are all very well, but tools actually do something useful. (Very much said with tongue firmly embedded in cheek.)

The Duplex jig is made from standard stock materials (barstock) and therefore much cheaper to make, plus there are step by step instructions (ME late 1951).
Ned

[madjackghengis]

I believe I'm going to have to make another "to do list", these are great and look to be a solution every machinist runs into on a regular basis.  Thanks so much for the clear and lucid design and demonstration on making them.  Kudos for the ingenuity mad jack