Proper Use of Drill Bushings

When using a drill bushing is the bushing supposed to be pressed tight to the workpiece so that the chips come out the top of the bushing? Or is the bushing supposed to be fixtured a quarter inch or so above the work so the chips come out between? I'm cross drilling 3/8 round with a No. 28 drill with the bushing pressed to the work (with a fixture). Since the work is round the bushing only contacts at two points and the chips are breaking and binding at the interface between the work and the bushing. Bushing is 3/4 long so that's a ways for a No 28 drill to bring the broken chips up.

Alan

IMHO its what suits. Like you say too much depths a issue. That said too far away and you lose some of the stability the bushing gives you. To small or tapered gap is going to be a nightmare though as your finding out. Try it a 1/8-1/4" higher and that problem will disappear.

I try to have a gap between the bushing and the work. The gap should be .5d to 1.5d.

I asked the same kind of question some time back, having trouble with the chips & a hard bushing. Another member mentioned to to just use a piece of square CRS - drill, ream or bore a slip fit for your pin & cross drill. In my case a 3/4 clevis pin with a 3/16 cotter hole. It was good for 70 pcs.

screensnot said:

I try to have a gap between the bushing and the work. The gap should be .5d to 1.5d.

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A friend bought a commercially-made jig for drilling 3/16" holes in wooden cabinet sides (for shelf pins). The hardened drill bushing was spaced about 1.25d, but even with brad point bits he had terrible problems with tearing the veneer and/or breaking the lips of the drill.

In the end he asked me to make new drill bushings that fit flush to the surface to be drilled (I made them from drill rod and hardened them). Worked perfectly, chips came out the top nicely, no more veneer tear-out, nor drill damage.

I had been doubtful about success prior to trying it, because I figured the jig's manufacturer couldnt have been so ... well, stupid ... but locating the bushings flush with the work was the way to go for us.

Perhaps the 'right answer' depends on material characteristics and hole size?

.. Gregg

gregg-k said:

Perhaps the 'right answer' depends on material characteristics and hole size?

.. Gregg

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I think you're right, Gregg. There is no right answer for every situation.

That's wood. Years ago I used a couple of lock boring jigs... the ones that allow you to drill a 1 3/4" hole through a door, and they had bushings ground to what amounted to circular razor blades that clamped tight to the veneer, to minimize tear out.

But a drill bushing in a jig designed for steel parts has a different function; it simply keeps the drill from deflecting until it has spotted itself. Tear-out shouldn't be an issue, so back the fixture away from the work until the chips no longer get caught.

Dennis

Screensnot is pretty right ON, about the bushing having clearance. Of course if you need the extra accuracy, make it flush.

Drills when drilling will some times tend to "unwind," like any spring, it makes the diameter larger and can squeal and fight with the drill bushing.

When using a drill bushing it's a bit hard on the drills cutting edge when hitting the hardened bushing. In one application I had to make a small flat drill bushing and couldn't see the holes very well. I bolted a piece of aluminum on top of the bushing and then drill backwards though it to drill though the aluminum. I then turned it right side up and could hit the aluminum without damaging the drill. The aluminum acted as a guide into the steel bushing. Worked well.

Regards,

Stan-

My thought process was that it'd be very tough to get a good enough interface, between the bushing and work, that no swarf can get in there.

Swarf is going to go there... give it room.

I would want the bushing right against the work,in the OPs place a may even grind(maybe by hand ) a rad. to suit the job, I would want chips outa the hole,not in a trapped space.

I have connected and cross WAY to many water lines in inj.molds/tools to think any other way.
Gw