Making a Drill-Press Vise

The problem

Too many C-clamps

I bought a cheap used Chinese benchtop drill press at a flea market. It was rusty, but after cleaning it up, it works well enough. It didn't come with a vise or other workholding provisions, so in all of my original uses of the press, I used various C-clamps as work holders. For large workpieces, clamping the work to the drill-press table worked well, but when drilling small workpieces, I quickly realized that the best ad-hoc solution was to clamp the workpiece to a fence that was clamped to the table.

I made a fence out of a chunk of hot-rolled 1" angle iron that I had sitting around. It worked, but clamping it in place was annoyingly difficult. The bottom of the table casting is not smooth. The cast iron is quite thin, with fairly narrow stiffening ridges. Larger clamps easily reach the flat (but thin) cast iron between the ridges, while smaller clamps have to be carefully centered on a ridge to get a firm grip.

The drill press table has two parallel slots in it for clamping. These slots are 1.5cm wide (5/8 inch), with stiffening ribs 3-mm thick along each edge of the slot. A drill-press vise designed to bolt down with 1/2-inch bolts would work, but such a vise would be a monster. Large drill presses frequently have cranks for raising and lowering the table, making the weight of a heavy vise easy to tolerate, but small bench drill press tables merely clamp to the column, meaning that you don't really want a heavy vise mounted on the table.

Making T-bolts — part 1

The older pair of C-clamps I have been using have 1/4-20 clamp screws, and my angle-iron fence is about the right weight for the job. What I needed, therefore, is a way to bolt the fence to the table. A stack of fender washers would probably be stiff enough to bridge the 1.5cm slot to support a 1/4-20 screw, but fiddling with a stack of washers and a nut would be even more annoying than fiddling with C-clamps.

The T-bolts

What I needed was something like a T-nut or T-bolt that fit cleanly in the slot in the drill press table. I opted to make a set of T-bolts because I would rather work something like a wingnut from the top of the table where I can see it than from below.

I cut the blanks for my T-bolt faces from a chunk of 8mm thick structural steel. I can't be sure what grade of steel it is, since it was salvaged from a house built in 1948, but it is probably A9 low-carbon steel (the A36 standard for structural steel only dates back to 1960).

The blanks should be cut so their narrow dimension fits through the slots on the table, that is, about 1/2 inch. The long dimension of each blank should comfortably bridge the slot, extending a few millimeters beyond the ribs on each side. These dimensions are not critical.

As I said above, the 1.5cm slots have 3mm wide stiffening ribs on their edges, so the T-bolts should have channels in their edges that are 1.8cm apart, center to center. A T-nut or T-bolt to fit this would therefore have grooves spaced 1.8cm apart to hold the nut centered in the slot. The lower edges of the stiffening ribs are basically round, so the ideal groove to mate with the ribs would be a round-bottomed groove.

Drilling the grooves

How do you cut a round bottomed groove? If I had a milling machine, a round-ended endmill would do the job. Not having a milling machine, I opted to clamp two blanks together, after chamfering the edges, and then drill along the joint between the blanks. The adjacent champfers made a V-shaped groove that helped center my center punch on the joint between the blanks when I marked two points 1.8cm apart for drilling. I used a drill just slightly over 3mm in diameter.

Drilling into the joint between two steel blocks held together by a clamp is very different from drilling into homogenous steel. Different enough that I broke a drill bit. Obviously, you do not get a continuous helical curl of swarf out of the hole, because the break between the two blocks breaks the chip after each half turn. As a result, the drill clears the chips out of the hole poorly unless you peck at the hole, pulling the drill out frequently to clear the chips. Furthermore, if there is any spring at all in the clamping, the forces exerted by the drill can spring the blocks apart with every half turn, giving chips a chance to lodge between the drill and the walls of the hole or to lodge in the gap between the blocks.

When I split the two blocks apart, I was a bit surprised at the burrs raised along the edges of my grooves. I gather that as the drill cuts through the steel, the outside corner of the cutting edge drags a little bit of material along with it just outside the eventual inside diameter of the hole. Of course, I expected to be deburring the end of the groove that was the bottom end of the hole where the drill broke through, and it took only a few swipes of the block along the face of a file to take off these unexpected burrs.

Making T-bolts — part 2

Ready to hammer

The next problem I faced was to permanently attach a threaded bolt to each of my blocks. I opted to do this with a press-fit, or more exactly, with a sledge-hammer fit. I began by drilling a through hole centered between the grooves in each block I'd made, one drill size smaller than the 1/4 inch that would clear a 1/4-20 screw. That is 7/32, significantly larger than the tap-drill for that size screw. I then drilled half-way through with a 1/4 inch bit from the side opposite the grooves, and then tapped the hole.

The tapped hole serves two purposes: First, of course, you need to get the threaded portion of the bolt through the block before seating it with a hammer. Otherwise, hammering the bolt through would strip off the threads. Second, threading removes material, giving the material displaced by hammering on the bolt head somewhere to go. Drilling out the full clearance for half the thickness of the block also reduces the amount of material that you need to displace.

I found grade-5 bolts that were long enough to reach up through the bottom of the T-nut, through the slot in the table, through the base of the angle-iron fence, and up high enough that a wingnut has clearance to spin. Grade 5 matters here, because the bolt needs to be as hard or harder than the steel block that will be the bottom of the T-bolt.

Note that you can clearly see the bolt grade markings in the two photos here. The 3 tick marks 120 degrees apart on the bolt head indicate that is made from grade 5 steel.

After one hammer blow

I filed 6 flats on the side of the bolt adjacent to the head, making the unthreaded portion of the bolt hexagonal. This also somewhat damaged some of the threads near the bolt head, but the nut will never be screwed down that far. The flats do not significantly weaken the bolt because they do not reach to the root of the threads. The purpose of the flats is two-fold: To prevent the bolt from spinning in what will be the head of the T-bolt, and to reduce the amount of metal the bolt has to displace when it is pounded in.

Each facet of the hexagonal section of the bolt shaft can safely taper slightly outward toward the bolt head. This means it will tighten as you hammer it home. In the photos here, you can see that some of the flats are slightly narrower at the head end of the bolt. That puts the taper in the right direction. If the taper is outward toward the threaded end of the bolt, that facet will end up loose when the bolt is hammered all the way into place.

To assemble one T-bolt, screw the bolt into the head from the side opposite the grooves until it is in as far as it will go. The bolt head and the hexagonal unthreaded part of the bolt shaft should remain. Then verly lightly grip the protruding threaded end of the bolt in a vise. The jaws should touch the threads but only just.

Then bang down hard on the bolt head with a heavy hammer. You are destroying the partial threads you cut and distorting the metal to fit your hexagonal bolt shaft. It took me 3 or 4 hard hammer blows to seat the bolts properly in each of the 4 T-bolts I made.

I used a 2-pound drilling hammer. Had I used a lighter hammer, it could have taken significantly more hammer blows to assemble each T-bolt.

It's a fence, it's a vise

Using the fence

I attached each T-bolt to the fence I started with using a stack of: 3 washers, a half-inch spacer, and a wingnut. The washers spread the load, and the washers plus the spacer lift the wingnut just high enough for the nut to clear the top of the fence when it is tightened down. The holes in the fence ends for the T-bolts should be somewhat elongated. I used a rat-tail file to elongate the round holes I drilled.

The first thing I did using my new fence is make its twin. Starting with a piece of angle iron cut from the same stock as my first fence, I used a transfer punch to copy the hole locations. Then I clamped the new fence to the first one and drilled each of the holes, first with a small drill before enlarging each to 1/4 inch.

Using a fence to drill a line of holes parallel to the base of the new clamp was very pleasant. Once the fence was aligned, all I had to do was slide the workpiece along the fence to position each hole. This reduced the usual 2-dimensional probem of locating a hole in a workpiece to a one-dimensional problem.

Two fences make a vise

With two fences clamped to the drill press table, I have a vise. For drilling wood, I suspect I can simply slide the workpiece between the fences, using them to hold the wood loosely so it won't spin. For drilling metal, though, the drill can really yank the workpiece up when it breaks through. To deal with that, you need to either have a hold-down clamp pressing down on the workpiece or you need to tighten the jaws of the vise.

One way to tighten the vise is to use a C-clamp to force the jaws together around the workpiece. This is similar to the way I used a single fence plus C-clamps, both when I was clamping the fence to the table with more C-clamps and when I was making the second fence.

Another way to tighten the vise is to use a pair of the holes I drilled in the faces of the fences. These fit 1/4 inch bolts, so a pair of bolts will pull the fences together, one on each side of the workpiece. If I use bolts as long as the slots in the table, screwing the nuts down could take a long time, so what I really need are some quick-release nuts.

With either clamping method, positioning the workpiece begins with the work loose between the fences and the fences loose on the table. Position the workpiece freehand with a small drill or a spud (a straight pointed rod) in the jaws of the drill press. Position the work so that the point hits the center punch mark exactly. Then bring the rear fence up to the work and tighten it down, then bring the front fence (or just C-clamps) up to the workpiece and clamp the workpiece between the fences. Finally, tighten the front fence down. The final step is to re-check the centering of the workpiece by lowering the point again to see that it hits the center-punch mark exactly.

For small adjustments, loosening just the clamping force while leaving both fences tight to the table allows gentle taps to be used to move the workpiece left and right. Leaving the work solidly clamped while loosening just the left (or right) ends allows gentle taps to move the workpiece forward and backward.