piggybladder
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Bod":1basz7xh said:
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Best way to parallel drill holes in box aluminium?
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Eric The Viking
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Piggy*,
A few things spring to mind:
(1) Fundamentally, 10mm sounds like a huge hole for cramp head pins. I have several sets, and IIRC, they all have around 1/4" pins (the newer, metric ones are 6mm). If yours are similar, the cramp heads will swiftly wear the holes in use, and regarding accurate alignment, "go where the fancy takes them". The pins need a snug fit in the holes, so they bear on a large area. Which brings me to...
(2) You'd probably be much better off using something like straight beech for the bars. It needs to be quite a bit deeper than the metal ones. I have one 6ft bar, which is about 3" deep (those clamp heads are (again) pretty standardised at 1" wide for the bars). You can use the pin holes as drill guides, but the best set I've got has diagonal slots for actual use, and guide holes for drilling next to the slots on one end. If it's going to have to take a lot of pressure (and they can, surprisingly so), plane the opposing side to be a gentle convex - this seems to help. The pins have the whole thickness of the bar to bear on and that seems to leave the holes almost unworn in use. Box section aluminium is (a) made of cheese, so it extrudes, and (b) designed to have thin walls to save on material. That's not a good combination in this context. Aluminium, if not anodised, will also leave dark marks on the workpiece as it rubs - the sort of clamps with slots for the pins will tend to move as they snug down, so I'd expect that to be a nuisance.
(3) Are you using any sort of drilling lubricant? I havent tried a lot of different ones - the metalworkers here will advise, but I use Trefolex for almost anything metal: I get much cleaner cutting, the drill bits last longer, and there is a LOT less burr on the breakout side. I have no idea why the latter works, but it does. I used to make a lot of things in aluminium boxes (for electronics), and it was a must. One other of its advantages is that it's not quite as messy as the really runny things (although it does get flung around and it's a bit smelly). Cleanup with meths usually. A little goes a long way - for me as an amateur, one tin will do a lifetime (had my tin for +20 years and it's still half full!). As i said, I'll defer to experts on what's actually best though.
(4) Finally, if you go with aluminium, you might consider packing one end with a tightly-fitting hardwood plug, and drill the hole for the screw-clamp end through that. I know theoretically you can set the pair of heads anywhere along the bar that is convenient, but to be honest it almost always ends up at one end, simply because it's easier to turn the clamp screw. That means that end gets a disproportionate amount of wear on the holes and bending force on the actual box section. Reinforcement will improve the life a bit, although, when it wears or fractures, I daresay you might just saw the end off and use it slightly shorter!
The other thing abut plugging it is that these cramps usually benefit from feet, to stop them tipping over (it's a PITA when doing stuff single-handed). But you don't always want feet on them! Aluminium will take a self-tapper readily, but it will also pull out. If you have hardwood inside, any threaded holes you make will last just a bit longer...
Probably TLDR above, but hey.
It's really annoying having a cramp fail or fall apart in the middle of a glue-up.
Have fun,
E.
(* I keep thinking of William Golding - surely this needs a better shortening!)
A few things spring to mind:
(1) Fundamentally, 10mm sounds like a huge hole for cramp head pins. I have several sets, and IIRC, they all have around 1/4" pins (the newer, metric ones are 6mm). If yours are similar, the cramp heads will swiftly wear the holes in use, and regarding accurate alignment, "go where the fancy takes them". The pins need a snug fit in the holes, so they bear on a large area. Which brings me to...
(2) You'd probably be much better off using something like straight beech for the bars. It needs to be quite a bit deeper than the metal ones. I have one 6ft bar, which is about 3" deep (those clamp heads are (again) pretty standardised at 1" wide for the bars). You can use the pin holes as drill guides, but the best set I've got has diagonal slots for actual use, and guide holes for drilling next to the slots on one end. If it's going to have to take a lot of pressure (and they can, surprisingly so), plane the opposing side to be a gentle convex - this seems to help. The pins have the whole thickness of the bar to bear on and that seems to leave the holes almost unworn in use. Box section aluminium is (a) made of cheese, so it extrudes, and (b) designed to have thin walls to save on material. That's not a good combination in this context. Aluminium, if not anodised, will also leave dark marks on the workpiece as it rubs - the sort of clamps with slots for the pins will tend to move as they snug down, so I'd expect that to be a nuisance.
(3) Are you using any sort of drilling lubricant? I havent tried a lot of different ones - the metalworkers here will advise, but I use Trefolex for almost anything metal: I get much cleaner cutting, the drill bits last longer, and there is a LOT less burr on the breakout side. I have no idea why the latter works, but it does. I used to make a lot of things in aluminium boxes (for electronics), and it was a must. One other of its advantages is that it's not quite as messy as the really runny things (although it does get flung around and it's a bit smelly). Cleanup with meths usually. A little goes a long way - for me as an amateur, one tin will do a lifetime (had my tin for +20 years and it's still half full!). As i said, I'll defer to experts on what's actually best though.
(4) Finally, if you go with aluminium, you might consider packing one end with a tightly-fitting hardwood plug, and drill the hole for the screw-clamp end through that. I know theoretically you can set the pair of heads anywhere along the bar that is convenient, but to be honest it almost always ends up at one end, simply because it's easier to turn the clamp screw. That means that end gets a disproportionate amount of wear on the holes and bending force on the actual box section. Reinforcement will improve the life a bit, although, when it wears or fractures, I daresay you might just saw the end off and use it slightly shorter!
The other thing abut plugging it is that these cramps usually benefit from feet, to stop them tipping over (it's a PITA when doing stuff single-handed). But you don't always want feet on them! Aluminium will take a self-tapper readily, but it will also pull out. If you have hardwood inside, any threaded holes you make will last just a bit longer...
Probably TLDR above, but hey.
It's really annoying having a cramp fail or fall apart in the middle of a glue-up.
Have fun,
E.
(* I keep thinking of William Golding - surely this needs a better shortening!)
Lons
Established Member
I would have suggested hardwood as well Eric but thought he had already bought the aluminium.
I have a set of cramp heads I've had for many years and they work very well indeed on the 1.5 metre hardwood bars I made out of some mahogany ex school bench tops I had. They aren't used every day but never let me down yet.
Bob
I have a set of cramp heads I've had for many years and they work very well indeed on the 1.5 metre hardwood bars I made out of some mahogany ex school bench tops I had. They aren't used every day but never let me down yet.
Bob
Phil Pascoe
Established Member
I suppose you did "Lord of the Flies" for "O" level as well, Eric. :lol:
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