Drilling matching holes

[jdeacon]

Does anyone have a good trick for lining up newly drilled holes with existing blind holes?

I have to put a brace under a sagging table. The brace will go under the existing leg plates (Ikea tubular metal legs). Ideally I'd like to line up the new holes in the brace with the existing screw holes; but they're blind holes and I can't just mark through. It's MDF and I don't want another set of 20 holes (5 per plate).

Previously I've used a piece of paper feeling for the holes and poking through with a pencil. But these holes are rather far apart for that.

 

[Myfordman]

Pop in some old scrap woodscrews, part way and straight then file a point on, mark the new timber and take the screws out with pliers

 

[marcros]

use a transfer punch, which is effectively what Myfordman is describing.

 

[jdeacon]

Excellent. Thanks. Come to think of it, I've heard of a transfer punch but I don't think I've seen one.

I'll get filing on those screw tops. All 20? Or perhaps I can do each leg, loosely fitting it and moving on to the next. I suppose the trick is to sink the screws far enough that the geometry isn't distorted but no so far that you can't remove them again.

 

[bugbear]

use a transfer punch, which is effectively what Myfordman is describing.

It's also strongly analogous to "dowel centres"

http://www.axminster.co.uk/faithfull-do ... s-ax911311

BugBear

 

[dickm]

If my understanding of a transfer punch is right, that's not actually what MM is advocating - transfer punch has to go through the reference hole to mark the new spot. But the analogy with a dowel pop is close - something sticking out of the blind hole with an outward facing point. My only worry with MM's proposal is having enough sticking out of the existing hole to be able to grab it and take it out after use, without risking getting the marked holes out of line. Maybe make a flattish cone point with a screwdriver slot across it?

 

[jdeacon]

Job done. Wood screws with the heads removed and replaced with a sharp point - worked a treat. In fact I used the original screws as they would now be too short. This also meant the best chance that the original holes ended up with only one thread inside.

I left about 3mm protruding, which was enough for some good vice grips to get hold of. I held the new piece as near parallel to the table top as possible before tapping it, to keep the geometry correct.

The new batten was hard and dark wood so I also added an old staple of my lock fitting days - a tiny dab of lipstick (bright pink) on the points. I did one leg at a time which I then loosely fastened before moving on to the next leg.

 

[Knot Competent]

Haha! I bet you're going to try telling us it was your wife/partner's lipstick!

Actually that's a very good tip. I've got a white liquid marker that would work. Thanks for the idea!