I entered a competition recently where as the 'element of skill' you had to answer three questions, the answers to which were in the product blurb.
One question was 'what depth will the XYZ drill in wood'. In the blurb it was something like 25mm.
However, AIUI that's the maximum diameter capacity, not the depth. In theory a drill will drill any depth hole only subject to the length of the drill bit, as long as the maximum diameter isn't exceeded. So with a 6mm bit for example, a hole a metre long is entirely possible?
No, you need more oopmph to drill a deeper hole. As an example, you could easily use a 25mm spade bit on a cheapo, underpowered rechargeable drill to cut a hole through a sheet of 0.25" plywood, but try using the same drill to bore into a solid lump of wood and it will run out of steam almost instantly, whereas if your theory above was correct, it would keep on drilling until the drill chuck hit the wood surface.
I suppose it's down to friction losses between the side of the drill bit and the wall of the hole?
Generally when drill makers state capacity they do mean diameter as per the first David's post and not depth. (think about the 1m long SDS bits you can buy - I have never seen a maker claim a 1m capacity for masonry drilling before!)
There is however an element of friction that comes into play with very long bits - so the torque required will climb with the depth of hole as you are also having to turn ever more shank in contact with the material. You will probably not see this unless the bit is 250mm long or more and even then is easy to over come in most materials by pumping the drill. This clears debris/swarf from the hole and also widens the clearance for the shank a little. IME the drills that have most problem in this respect, are long narrow auger bits. I have a 6mm 400mm wood auger bit that can bind very tightly in deep holes.
The example of a spade bit was however I feel a poor one, in that these are "waisted" bits - i.e. their diameter falls after the spade part of the bit. Hence with one of these if you can drill to the depth of the spade (inch or two depending on size) then you will be able to carry on to any depth after that, since the shank makes no contact with the material. (hence why you can get extension bits for spade drills without difficulty).
It's subject to being able to clear the swarf out of the hole, and to friction. I guess that a one metre long 6mm bit would be struggling on both counts!
David's spade bit example only applies to thin material. Once you've drilled a hole deep enough for the whole cutting end to be inside the wood, the friction doesn't get any worse as you go deeper.
| Hi | | I entered a competition recently where as the 'element of skill' you had to | answer three questions, the answers to which were in the product blurb. | | One question was 'what depth will the XYZ drill in wood'. In the blurb it | was something like 25mm. | | However, AIUI that's the maximum diameter capacity, not the depth. In | theory a drill will drill any depth hole only subject to the length of the | drill bit, as long as the maximum diameter isn't exceeded. So with a 6mm | bit for example, a hole a metre long is entirely possible?
For the purposes of a competition Yes. The answer should be as long as your drill. I have a specially made. picked up cheap, 6mm masonry drill which goes through an 11 inch cavity wall just fine.
But a spade bit isn't the same as an auger. An auger is the same diameter over its whole length whereas a spade bit only has a short cutting part on the end of a long thin shank. You clear the debris by pulling the bit out while it is still spinning every now and again.
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