Thread: Nasty hole redrill problem - 42mm Merbau

Here is a simple solution: buy a 19mm spade bit. Grind each side halfway down back 0.5mm to 18mm width. File the new short edge to make a cutter. Then insert the 18mm half into the hole and start the drill and complete the hole.

Just as an extra to my post #13 - I appear to have missed the thickness of the top at 42mm so the depth of the bit may not reach - I'm not keen at all to extend bits out of the collet - however it is not a problem as there is already an 18mm hole so a template / follower bit could easily be inserted from underneath the hole [turn the top over of course] to clean out any extra as the bush would ride on the edges of the "new" hole made from the top.

Interesting problem especially as there are 20 holes to fix.

Groggy, I have not had a great deal of joy with spade bits as the length of them [when drill is handheld - drill press is ok] seems to exaggerate any lack of perpendicular and then they tend to "chatter" which will create problems.

Let us know how you get on.

Regards,
Bob

Originally Posted by silentC

It's a bit tricky with a forstner bit though because the outside teeth are flush, so you really need to start off exactly right or it will tear up the face.

A saw-toothed bit may be marginally better than a true forstner for this.

Personally I wouldn't use a spade bit at all, even if plugging the hole with a dowel, as it can wander offline whereas a fortsner will drill as straight as you can hold the drill.

If the plug/dowel is end-grain, then a spade bit will be even more prone to wander with the grain, unless the dowel was exceptionally straight-grained in the first place.

here is a really ugly (but small) pic of the ground down spade bit. The idea being the 18mm section follows the existing hole, keeping the 19mm section on track. I'd give it a go on some scrap first but I would definitely try it as there are 20 holes to do.

Hello folks - wow, I'm just back from Tas where I've been hiking and going to as many timber yards/woodworking sites as my wife would allow - she's actually getting into all this!

My 3/4" Forstner bit arrived today and I'll give it a go in a test piece of Merbau. I will certainly post the results - you guys have been extremely kind in giving my silly problem this much attention!

Should have a crack this weekend!

Cheers,
David E (Sydney)

Originally Posted by deldridg

Hello folks - wow, I'm just back from Tas where I've been hiking and going to as many timber yards/woodworking sites as my wife would allow - she's actually getting into all this!

My 3/4" Forstner bit arrived today and I'll give it a go in a test piece of Merbau. I will certainly post the results - you guys have been extremely kind in giving my silly problem this much attention!

Should have a crack this weekend!

Cheers,
David E (Sydney)

There is also a little bit of envy behind the advice offered. Merbau (aka kwila) is one of the absolute best woods available for a bench top - its dimensionally stable, heavy, tough and also a very attractive timber - many of us are privately thinking "wish my bench was kwila!

As Neil says in the blurb to the workbench forum, the workbench is arguably the most important tool in the woodworkers arsenal, and you will use it for a very long time. Its very important that the bench dogs work faultlessly - not too tight, and not sloppy. The dog holes must be bored very precisely - the forstner bit (and the saw-toothed version mentioned by Skew) is the most precise bit available, so I think you have made the right choice there.

Personally, I would fell more comfortable drilling dog holes with a drill press - more accurate and stable. Second choice would be a template with a starter or guide hole clamped securely in position. I still think plugs are a good idea.

Good luck this weekend. And how about some pics of the finished bench.

Cheers

Graeme

The only thing that concerns me about the plug idea is that if you are 1/2 mm off when you locate the new centre, you will leave a sliver of the plug behind when you drill the new hole. If your plug is end grain, as suggested, then getting the bit to centre precisely where you want it with a hand held drill will be challenging.

If you use the idea of centering a bit of ply with the 19mm hole drilled using the same bit then you will have full control over the location of the new hole and you can make sure it has 1/2 mm clearance all the way around.

Hello folks!

Finally I have done this nasty bit of work and my benchtop now has 3/4" Forstner quality holes with a wonderful result! Here's how I lucked in:

1. drilled a pilot hole in some scrap Merbau with the 3/4 bit (a fancy HSS 3/4" bit from Carbatec) as per suggestions
2. very carefully lined up the pilot scrap with a hole on the benchtop and clamped
3. with the hand drill and using the pilot, I drilled about 1/2 way through the benchtop, carefully monitoring the shank relative to the hole (this is all the depth I could get - the bit has a short shank)
4. pulled out, removed the pilot scrap and hand drilled the rest with a great result.

I did this for a few holes and thought, hmmm - perhaps this isn't as difficult as I first thought. Given that each hole had a 3mm 45deg chamfer (with the router), I thought this could be sufficient to center the bit and allow a smooth start.

So I gritted my teeth and (rather gently on a high speed) drilled by hand inside the chamfer and it was absolutely perfect. Did the remaining dozen holes in about 2 mins and now all holes are perfectly centered inside a 2.5mm chamfer... )

So, without the chamfer it would have been very tough. I think I may have been lucky but they all worked, the bit didn't grab and simply tracked straight down each hole perfectly. No damage whatsoever.

I have a pretty basic drill press which probably wouldn't have the torque for this so the Makita was called for - did it with ease!

So many thanks to you all for you wonderful supportive inputs. Now I also feel better about choosing Merbau - perhaps wasn't really sure if it was suitable being something of a beginner (well, returing after many years)! However, when it's done and if I can get over the embarrassment of some of the less than perfect joints (performed before buying a router or table saw), then I'll certainly put up some pics!

Again, thanks - what a good bunch you all are!

Cheers,
Dave E (Sydney)

Good ONYA Dave
Thanks for letting us know you went so well with the holly bench
Looks like you will go along way on the forum.Keep it up Dave.
Cheers AUSSIE

Great to hear you had a win.