MR BRIDGES – THE GURU IMPARTS MORE OF HIS KNOWLEDGE OF MECHANICS

AS YOU MAY RECALL, LAST MONTH I WAS MAKING SOME HOLD-DOWNS FOR THE PILLAR DRILL SO THAT THE HOLES END UP IN THE WORK PIECE AND NOT MY, OR YOUR, FINGERS (FIG.1).

Ihave a large ‘nodding donkey’ reciprocating hacksaw that happily cuts even quite large pieces of steel, which made the job quite a lot easier than using a manuallypropelled hacksaw, or if YouTube is to be believed, everybody’s prime choice of metal cutting tool – the 110mm angle-grinder equipped with a cutting disc. I’ve also got a Rage 4 cut-off saw (Fig.2) which I use for the occasions when I’m out and about, or it’s more convenient than lugging lumps of steel to and fro between where I’m working and the nodding donkey. While it isn’t any quieter than an angle-grinder, the Rage saw does cut straighter, is easier to use with a degree of accuracy, and isn’t likely to set anything on fire… although the metal chips it chucks out’re still pretty hot, and you really do not want one in your eye, so don’t let the lack of sparks fool you into believing you won’t need safety glasses. The only problem I’ve ever had with it’s been with idiots using it – the blade works by having small pieces of tungsten carbide attached to it, and starting the saw with the blade in contact with what you’re trying to cut tends to knock them off (as does slamming the blade into the work piece). Start the saw at the top of its stroke and slowly lower it to whatever you’re cutting, and the blades’ll last a lot longer. The one in mine was getting a bit tired, but still managing to cut things without any real drama when I replaced it with a new one, despite missing a few bits of tungsten (Fig.3). If you scour eBay

you can buy a new one for around £100, and blades can be found for £10.

The trouble with the hold-downs I made in last month’s article is that while they will clamp things down, and’re quick and easy to make, they’re a bit susceptible to bending if over-tightened. To remedy that,

I made a sturdier version from the same 10mm x 25mm strap and some 16mm round I had in my scrap pile. 16mm is a bit of an odd size, the equivalent of 5/8” in imperial, but not ludicrously obscure. The point of choosing it was that it’s a little bigger than the 12mm studs I used for the hold-downs – if I’d have used 10mm studding, then 12mm round bar would’ve worked.

The dimensions involved’re more a matter of fitting it into the available space than any exact size, but I cut two pieces of the 10mm x 25mm strap that were 6” long just because I like to mix my measurements (Fig.4). I only needed one piece of the 5/8” bar and that was a shade over 2” long (Fig.5). I cut it slightly long to allow for sanding a shallow radius on one end – the idea of that was so that when the hold-down’s angled down towards the surface it’s clamping, then the clamping force isn’t being applied by the edge of the end face, which’d leave a dent.

For the other end of the hold-down I could’ve used a second piece of the 5/8” bar, but I chose to use an M12 nut instead (Fig.7). With the 5/8” bar welded between the two pieces of strap at one end, and the M12 nut welded to the bottom faces, that was the job done. The idea here is that the end with the 5/8” bar is the clamping end, the space between the two pieces of strap allows for it to sit over a stud located in a nut set in the table, and the other end uses a second piece of stud as a height adjustment (Fig.8). Taking a hole-saw, and making some suitable washers from some thick steel plate, would be a useful addition, but it was a very hot day, and I couldn’t find the holesaws. However, Fig.8 gives you the general idea.

Clamping the work down makes for improved safety, as well as better accuracy, which’s helpful for things like helicoils, or drilling snapped bolts out where drilling round holes that’re concentric with the original one improves the chances of the operation succeeding considerably. Hopefully you’ve come to the conclusion that they’re not too hard to make either, but it’s still worth finding a box to keep them in, and build up an assortment of them over time. If you have a decent vice for your pillar drill, that’s capable of

gripping round bar securely while it’s vertical to the table (unlike the one in the pictures), then there’s an occasionally useful technique that you can use for making crush tubes or blind threaded bosses. I have a 5/8” capacity chuck for my pillar drill, but it was wearing the ½” one on the day and, as I might’ve mentioned, it was hot. That limited me to using 12mm bar so this’d mean a crush tube, or threaded boss, for at most an 8mm bolt.

Cutting the bar off with the cut-off saw would’ve been an ideal start, but not everyone has a cut-off saw to get the ends at least reasonably square. To get a reasonably square end on the cut piece of bar, you can put it in the chuck of the drill (Fig.9) and, with the drill running, bring it down on to the face of a file clamped down on the bed of the drill – this’ll true the face up for you (Fig.10). Obviously it can be flipped around to ensure both ends are square, but if a reasonably accurate length is what you’re after, and you need to face both ends, then it’s going to take you a while.

Once the ends are taken care of, then keeping the work piece tight in the chuck, attach the vice to the work piece (Fig.11). This tends to require more hands than the average human being has (because on average human beings have 1.998 hands) so, either enlist the help of a friend or find some weights to attach to the feed handles of the drill. The idea is that the work piece gets clamped into the vice while it’s still clamped in the drill chuck, and the vice’s in contact with the bed of the drill. Once that’s been achieved, the vice can be located with a pair of hold-downs (Fig.12).

At this point the drill chuck should be centred on, and square to, the prepared piece of rod, and using a centre drill (more commonly used on lathes) a start for a hole can be made on the end (Fig.13), before swapping the centre drill for either a tapping size drill or a clearance drill (Fig.14). Normally I use a mill vice that came from a car boot sale or an autojumble for this, as the cheap drill vice in the pictures isn’t really up to the job of keeping everything square but, again, it was hot, and the milling vice is heavy.

Something that involves rather less effort is engine turning – the swirl pattern seen on the dashboards of Bugatis and Bentleys, and occasionally on the workings of a clock or watch. It’s perfectly possible to do this free-hand and, in fact, it obviously was on Bugati dashboards, but some sort of regularity to it might be desirable. I used a piece of

wood that went in the chuck of the drill, and rounded it off with the file because I’ve seen the price that B&Q want for a piece of dowel. Having found a piece of board to sit on top of the table, and a slightly thicker piece of wood to act as a guide, I clamped the guide to the table with a couple of hold-down clamps (Fig.15) so it was sitting against the “dowel” in the chuck. A dab of valvegrinding paste on the end of the dowel, and I fired the drill up and brought the dowel down on a piece of aluminium for a few seconds before lifting it up again, moving the aluminium along by half the width of the dowel, and repeating the process until I’d covered the entire length of the piece of aluminium. At that point I slackened off the holddowns, and moved the guide by half the width of the dowel, then repeated the process with the dowel off-set from the previous row, remembering to apply a little more valve-grinding paste at intervals. Depending on the appearance you’re after, then you can use a hardwood dowel without any abrasive, or different types of abrasive, or something like a ScotchBrite RoLoc pad on an arbour. If you’re using abrasive, its generally best to wash it off with a suitable solvent rather than wipe it off, and risk marking the finish (Fig.16).

Hopefully that’s thrown a little light on the uses of a pillar drill, and if you join me next month you can find out if I managed to sort out the front brake on the KLR… but it is hot.

MR. BRIDGES