OTish: a silly bit of metrication

As part of the day job, tomorrow I have to drill about 100 holes for 12mm bolts through 7" thickness of hardwood, with counterbores at
each end.
Wood bits until fairly recently came in imperial sizes, in fact some still do, but my local supplier's stocks of auger type are now metric. In the past I would have used a 1/2" bit for a 12mm bolt, holes in timber aren't usually clean enough for 0.5mm to really matter too much. Guess what size their metric * 1/2" * bits are now? Yes, they are THIRTEEN mm! A full, genuine 13mm, not 1/2" relabelled. That means a 12mm bolt will flop about and not do the job as intended - plus it will probably fall out (they have to go in from underneath) before I can get the nut on. I can probably do something about it, maybe grinding the OD down a bit but that's going to be a real pain over 8" length.
12mm bits do exist, I could probably get one to order & I've got one as part of a Chinese set, but (a) it's not long enough, and (b) I was using the 16mm bit out of the same set, in the same timber, it was cutting beautifully until the screw tip pulled itself off the end of the bit, & left me with a hardened piece of steel at the bottom of a deep, unfinished, blind hole. I have no wish to repeat that!
Cheers Tim
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Tim, it maybe easier to sleeve the bolts with heat shrink. That should account for some of the play.
Joules
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wrote:

It's a thought, though I can see it getting crumpled/torn off when fitting the bolts. These bolts have to be watertight - that's done by sealing under the head, but having clearance around the stem isn't a good plan for that reason, also they lose their 'dowel' effect. The other thing is that a loose bolt is a liability in the bottom of a boat if it looses its head throough wear/impact, or the nut becomes slack.
Cheers Tim
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Tim Leech wrote:

Switch to 13mm bolts?
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Wally
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Oh yeah, can you find me 100 off M13 x 180 cup squares, plated, for tomorrow?
Cheers Tim
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If a 12mm bolt in a 1/2" hole works... would 1/2" bolt in a 13mm hole work....
You *might* be able to find 100 1/2" cup squares x 7".. maybe :-(
Alternative might be to drill the holes 12mm, then open them up with a D bit made from a bit of 1/2" silver steel.
Pain in the *** whichever way you go.
wrote:

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Jonathan

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Screwfix do a 12 mm multibit 130mm long or 12 mm Forstners.
If you have them in drill press they ought to go in reasonabl straight.
Aah Just thought, in 7 inch timber debris removal is the problem?
Regards Robi
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wrote:

Drill press is not an option here. The item being drilled is 70' long, 7' wide.

One of the problems. The main problem is that standard bolt dia and standard wood bit dia are not the same.
Cheers Tim Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
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wrote:

Why not use a 12mm bit? You may have to drive the bolts in, but that will just help the water tightness. put some grease in the threads to help things along.
Mark Rand RTFM
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On Thu, 15 Dec 2005 21:48:18 +0000, Mark Rand

Because I can't get hold of one off the shelf. That was the whole point! <g>
Cheers Tim
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wrote:

Won't help you for today, but next time try axminster.co.uk.
regards Mark Rand RTFM
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Tim Leech wrote:

Eat your heart out! :-)
http://advantage-drillbits.com/auger.html
Tom
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Yeah, but I need it Tomorrow. Literally. <G>
Cheers Tim
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Tim, can you get a 12mm spade bit in the right sort of length? If not I'd have thought you could make an extension for one pretty easily.
I've got one here in 12mm that I'm pretty sure came from a DIY shed.
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Nigel

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On Fri, 16 Dec 2005 00:04:02 +0000, Nigel Eaton

I bought a 1/2" flatbit at the same time as I picked up the long 13mm auger bit, so that I had a fallback plan. I can file this down a little to 12mm and braze an extension piece on. Not as quick as an auger bit, & sometimes leaves a slightly ragged hole, but it'll get the job done. I'll be on the phone when the shops open to see if anyone else nearby can supply decent quality 12mm auger bits off the shelf. My original post wasn't to say " help, how can I do this?", rather a comment on what seemed to me an absurd situation. I assumed I could just nip into the local (quite good) tool suppliers and pick up an auger bit the right size for a standard bolt, preferably a long one. Now I know the situation, I can look around in good time if I have a similar job coming up and get a couple of proper bits ordered in advance.
Cheers Tim
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Tim Leech wrote:

I had a quick delve in a Buck & Hickman's cat and they offer both metric & imperial, long n short.. So a quality wood butcher supplier should do even better.
Tom
Tom
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I managed to find a local supplier who had 12mm bits this morning. The crazy thing is that he *didn't* have any 13mm, everyone else I spoke to had 13mm and nothing else near. I could only get standard length, so had to contrive an extension for the 'extra inch'
Got about 70 of the holes drilled, counterbored & bolted up today, the rest have to be drilled from below, so they can wait for tomorrow <g>
One of the side benefits of having machining facilities is that I can now make decent one-off counterbores for this sort of thing, in this case about 38mm OD with a 12mm pilot, a piece of old EN8 prop shaft turned up, milled with 3 flutes and ground up on the T&C grinder. Many moons ago, when we were doing this sort of work regularly, I made them up by welding silver steel 'wings' on to a round bar stem which doubled as a pilot, then ground the cutting edges freehand. They did work, but not as well as the new high-tech model !
Cheers Tim
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Tim Leech wrote:

=======Burn 'em in? Bore undersized holes, heat the bolts red(ish) and drive them in. If heating the bolts is a concern, heat a sized rod or sacrifice one bolt. JW =======
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Tim Leech wrote:
<snipped a bit>.

Reminds me of the 'Italian Metric' bolts and screws we had on (italian) Metalmeccanica moulding machines back in the 70's. No standard replacement metric pitches would ever fit these when they were replaced. We would swear they deliberately used odd pitches for some reason, and we always had to re-tap the holes during maintenance and repair operations. Mind you the machines did have an od combination on them - all the platen bolt holes for tool mounting were imperial 1/2" or 5/8" BSW but machine parts were metric (italian sized...)
Peter
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Tut, tut, talking about 7 INCHES, where is your conversion table?
Alan
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