Making Unimat DB/SL Steadies

[Andy CarlsonParticipant @andycarlson18141]

A couple of jobs I have been contemplating for a while involve making new bases to allow tooling to be mounted to the bed bars on my Unimat SL. One is a fixed steady, the other a tool rest for using watchmaker’s hand gravers.

Most will likely be familiar with the bed arrangement – two 12mm round bars 40mm apart with the M8 feed screw equidistant between them. The tooling base needs to be split horizontally so that it can clamp around the bars.

I came up with a couple of options…

One is to start with two pieces of bar stock (say 1 inch by 1/2 inch Aluminium), machine them for the clamping bolts and then clamp together (with some packing between to ensure that they will actually clamp the bed bars when finished) and then drill for the bed bars and feed screw. I’m not sure that drilling along a join line between two pieces of stock is a good idea though.

Mounting on a faceplate and boring is a variation on the above theme… particularly given that I don’t currently own a 12mm drill, but can lay my hands on something slightly smaller and more imperial. Keeping the hole spacing accurate seems like a challenge if I do this though.

The other option is to start with a single piece of stock (say 1 inch square Aluminium), drill it and then cut it to separate the top and bottom halves. The challenge here is making that cut… This is way deeper then I have ever tried to cut with a slitting saw so the risk of clogging/jamming etc. is a worry. I’m 100% convinced that I would muck it up if using a hacksaw manually. One possible option is a bandsaw – there is a Sears Craftsman style one that I could perhaps use but so far we have only used this for woodworking. I’m not sure what band saw blades would be suitable and buying a new blade just for this job will add to the cost and general bother.

I am planning to do the jobs on a bigger machine – my Faircut 3.5 inch lathe.

Your thoughts on pros and cons (or better options!) are welcome.

Thanks in advance.

Regards, Andy

[Nigel Graham 2Participant @nigelgraham2]

I would go for the drilling then reaming or boring, on the joint line between two pieces, with the work so mounted that the parts stay togther for both operations on both bores and keeping the bores parallel.

The packing is best if quite thin. If the gap ends up too fine simply take a very light skim off one or both faces.

The resulting halves need be rigid of course so they don’t distort when clamped together. One approach is to make the section of Tee-form by cutting a rebate along both sides of both parts. Using two clamp-screws each close to one way bar without actually breaking though the bore wall, is another way.

Sawing the block apart after making the holes will work but even using a band-saw might not give very satisfactory, tidy results. Sawing aluminium-alloy needs quite a coarse blade to avoid it becoming choked by the chips.

 

Does your larger lathe have a Tee-slotted saddle? If so, the best method is boring between centres.

Whichever mehtod you use, mark the halves first so they go back together with the same faces coinciding.

 

 

[JasonBModerator @jasonb]

I’ve drilled and reamer or bored across a split line countless times, usually a bearing pedestal and cap all without problems so that would be the way I would do it.

[Andy CarlsonParticipant @andycarlson18141]

OK thanks both. Starting with two pieces seems like the way to go then. I shall amend my shopping list accordingly.

… and yes the cross slide has T slots. It’s a pre-war model engineering lathe so most people did not have mills at the time. I have a couple of vertical slides… two because the second one is Faircut branded so I could not pass up the opportunity when it cropped up 🙂 . My biggest ‘mill’ is the Unimat.

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