The slot mortiser is useless until it is mounted to the underside of a sturdy worktable. Since you will be pushing and pulling on the router and the fixture it is attached to, the worktable should be rigid and heavy.
You can use a workbench or a substantial router table as the worktable for the slot mortiser. But remember that you have to drill and countcrborc mounting holes,as well as holes for threaded inserts. You will surely want to etch a grid into the tabletop to facilitate setups. These add up to alterations you may not want to make to a good workbench or router tabic. If you have space for it. and if you will use it often enough, you can always build a separate worktable for the slot mortiser. I lowcver you choose to deal with this matter, here's how to outfit the worktable, thus completing the fixture.
1. Mount the mortiser to the worktable. A
couple of points before the actual work begins.
First, die worktop to which you mount the mortiser should be at least I'/: inches thick, and it should be flat widi top and bottom surfaces parallel. If it Isn't thick enough, the mounting bolts will protrude above the surface. If the surfaca aren't flat and parallel. Ix>lling the mortiser tightly to it will wrack the chassis, throwing your new fixture out of kilter.
The second point has to do with the gap between the chassis's leading edges and the mounting board. The gap will be about yAo inch, and you probably don't want that much space between the mounting board and the worktop. I Therefore, try to set the chassis back from the worktop ! edge about V32 inch.
I found the easiest way to lay out the holes for the I mounting bolts was to make a template from the mortiser J Cut a 5 X 12-inch piece of '4-inch plywood. Set it on top of 1 the mounting bolts, and align it flush with the front edges I of the chassis sides. (Hold a straightedge against the chassis, I and slide the plywood template up against it.) Tap on the I template at each bolt, denting the template. Flip it ovcr.and drill a %>inch hole centered in each dent.
lay the template on the worktop, and align it.The edge of the template represents the front edge of the chassis,and I you want to set that back a bit. By drilling Va-inch holes for I the Vurinch mounting bolls, you give yourself just a little I room for adjustment. So line up the template and clamp it I With a nail or awl. mark through the template on the I worktop.
Remove the template to drill a 1-inch-diameter.1 i-incb- I deep countcrborc, centered on each mark. Switch bits, and drill Va-inch-diamcter through holes for the mounting bolts, I Drop a V«-inch-I.D. flat washer into each counterboitB Position the chassis under the worktop, and push the mounting bolts up through the holcs.Turn a nut onto cadi I bolt, and lightly scat cach. Install the mounting board, and adjust the chassis position under the worktop. You want the I face of the mounting board to be parallel to the worktop1» I edge. When the mortise is so aligned, tighten the nuts on the I mounting bolts.
2. Fine-tune the mounting. Once you mount the I fixture, you need to check it for alignment.There aretwl ways it can be misaligned:
1.The axis of the router bit can be out of parallel with I the bench top.
2.The bearing shafts can be out of parallel with the II bench lop.
Any misalignment must be corrected by fitting shins I between the chassis and the underside of the bench top. I The alignments can be checked by chucking a sud I dowel pin, a centering pin, or even a router bit into the ruua I (with the router unplugged) and measuring the height of the I dowel pin above the bench top with a dcpth-mcasuria|H vernier or dial calipers.The height, when the router is all the I way to the left, must be exactly the same as when it is all tk way to the right: the height must be the same whether ft* plunged or fully retracted. If it isn't, mark the corners of tk I chassis where the measurement is high, loosen the ntft II holding the chassis, and insert paper shims to shim thr I
TOGGLE CLAMP PAD LAYOUT
Pilots for toggle clamp mounting screws
The mortiser mounting is properly aligned if measurements taken at the limits of the mortiser's lateral travel and with the router both fully plunged and fully retracted are all exactly the same. Take the measurements from the bit to the tabletop using a pair of depth-measuring dial calipers, as shown.
chassis down at the marked corners. Then tighten it up and check the measurements again. Repeat as necessary until the ■easurcmcnt at all four points is the same.
3. Grid the worktop. Using the fixture requires accurately positioning the workpiccc on the bench and damping it there. A grid of reference lines permanently jeribed in the bcnch top is useful.You can adjust the lateral travel according to these lines, as well as position the work-piece to them. I suggest that at first you simply use pencil lines. Once you know what kind of a grid works best for
Mounting a toggle clamp to the worktable requires only a single bolt turned into a T-nut in the worktop. You can swing the pad-mounted clamp around the bolt, orienting it for the best contact with the work. Big clamps have a longer reach and apply more pressure than small ones. But both can be used productively.
Hole for mounting toggle clamp; T-nut on underside of table.
Counterbore for mounting bolt
Grid lines VS increments
Grid lines 1" increments o
Counterbore for mounting bolt
Grid lines VS increments
your purposes, scratch the lines in with a sharp awl. and fill the scratches with a dark wood filler
It's important to he able to position clamps on the workpiccc as close as possible to the mortise. The most convenient way to clamp is with toggle clamps. But of course, you don't want to clutter the worktop with toggle-clamps.
Instead, install T-nuts at key spots on the worktop. (Bore a hole through the tabletop and tap the T-nut into the underside.) Mount a couple of large toggle clamps—I use IX'-Sta-Co'STG235-U—on slotted pads made of Vinch plywood.'I\irn a bolt into the T-nut, and catch it in the slot of the toggle clamp's pad. Tighten the bolt, and you've got a toggle clamp just where you need it for the job at hand.You can use the T-nuts directly or via a toggle clamp to secure positioning stops for production runs.
As with the grid, it's probably better to develop a sense for where T-nuts are useful, rather than pock the worktop with them haphazardly. The layout I use is shown in the Tabletop Layout drawing.
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