For years I kept a collection of odd bolts, nuts and washers for the purpose of clamping workpieces to the lathe and miller. It wasn't a particularly well thought-out collection either, for each job some combination was cobbled together which was approximately the right size and later thrown in the box for possible subsequent use. As a result none of the items were ever quite right for any particular job and a compromise was always necessary, perhaps a stack of washers or a nut hanging on by a few threads. Further, the box of bolts was always raided for suitable bits for other jobs. When I bought my new lathe I thought it was about time I did something about this sad situation and decided to make a set of of clamps specifically designed for the purpose.
I first made some spare standard length T-bolts, and considered making a whole range of these in stepped sizes. But cutting many feet of 5/8" bar down to 5/16" was likely to bury me in swarf - an alternative was required. I remembered seeing in an old ME mag a picture of a single tubular T-bolt threaded to take a length of studding, so decided to use this method as a design for a set. All I would need was about 6 of these bases and a range of different lengths of threaded rod. To cover all possibilities I also made some flush T-nuts (i.e., height was just below the level of the boring table surface), and also some T-nuts to fit the slots of my faceplates. Some time later I made a similar set of T-nuts threaded 1/4" BSF to accept socket headed screws. Later still I added larger T-nuts to fit the milling machine table so I could use the same set of 5/16" threaded rods, and then when I aquired a rotary table (which unfortunately had yet another size of T-slot) another set of nuts had to be produced. The latter were a little more specialised as the T-nuts needed a rounded end to fit as close to the centre of the table as possible, but the nuts still accepted the same size of threaded rod and screws. By the way, 5/16" is plenty sturdy enough to cope with any likely clamping job on either machine - sufficient in fact to warp or even damage a lathe cross-slide if over tightened. Always remember when clamping a workpiece for machining that a good seating is at least as important as the tension of the clamp holding it in place. Keep the seating surface area as large as possible, if mounted on parallels use the widest that will fit. There should be no need overtighten the clamp bolts to prevent the workpiece moving under cut.
The pictures show all the components of the set laid out, and with them most any job can be tackled. The tubular nuts have sufficient length of thread that the rods can be adjusted for height, and whilst I've not come across a problem yet it would be a simple job to thread another length of 5/16" rod if it became necessary. Nuts are mostly of a standard size though I keep a couple of extra long ones for special jobs. Washers are all 5/16" bore (of course) but range from 5/8" to 1-1/2" diameter to bridge large holes or recesses. Not shown are a range of clamp bars with holes to match the distance between the boring table T-slots.
I believe the time spent making the clamp set has been more than saved by avoiding having to fish around in my previous box of oddments attempting to find something suitable, maybe having to cut bolts to size. These specialised components no longer get used for jobs other than machine clamping, I always have something to hold the most awkward workpiece, and I know the job is properly secured first time. I had already made my set of clamps before recently buying Geo. H. Thomas' book 'Home Workshop" only to find he also recommended making a set along similar lines. Nothing is new in this hobby I guess. Naturally, his version is somewhat better designed (tubular T-nuts are made from 7/8" bar offering better support in the T-slots - and look better machined too). Still, my set does the job, and I hope you are convinced it's worth the effort to make something similar.
(c) Chris Heapy 1996.
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