Correct hole size for M10 coach screw?

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gzt

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#101531 3-May-2012 13:07

Does anyone know the exact correct hole size to drill for an M10 coach screw?

The guys at the hardware shop were guessing more or less. I called EDL (they are EDL brand fasteners) but there was a bit of a silence before the guy kind of took a guess at 10mm - incorrect, that is the outer shaft size. They are going to look up some technical manuals and get back to me on that one.

Kind of surprised. I figure it will be a well known metric standard, but my googling has failed so far.

nickb800

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#618852 3-May-2012 13:15

Perhaps the question you should be asking/googling is more like: what is the correct size hole to tap an m10 thread? (even though it sounds like you are just driving it in rather than tapping the hole first) Im sure there is a standard literature on this.

Have to ask, what is the application that it needs to be so precise, and why havent you just had a go with different size holes in a scrap piece?

mattRSK

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#618862 3-May-2012 13:32

Hi, I have had a small amount of experience with them. I have always used a drill bit that is slightly smaller than the thickness of the shank at the widest point of where the thread is. I just go through my drill bit set placing them over top until I can see all of the thread sticking out the side and just slightly the shank.

It's kind of hard to explain. Maybe I should make a picture.

edit: Picture, red is the drill bit

Jaxson

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#618873 3-May-2012 13:58

as above, nice one mattRSK.

If you can move the bolt in and out by hand then you've probably drilled it too big....
If you hear a lot of wood splitting as you swing on the spanner to tighten the damn thing, then you probably drilled it too small.

Best approach is as mattRSK described. What's it for?

edge

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#618915 3-May-2012 15:35

Apart from the helpful advice above, it also depends what sort of timber you are heading into. I can assure you that when I'm putting a hole into a post for a gudgeon to swing a farm gate off (same principle as a coach screw obviously) it depends whether I'm going into a brand new pine post, an old pine post or, for example, an old totara or hardwood post thats been in for a few decades!!

Basically the softer the wood, the smaller the hole I drill. Clearly you have to take into account the sort of loading it might be subjected to and, as noted above, the liklelihood of splitting (never a problem drilling into a strainer post!!), so the aforementioned can only ever be a generalisation :-)

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Niel

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#619160 4-May-2012 05:54

EDL sources fasteners, I'm not sure they manufacture them. Good luck with any technical answers from them unless you eventually get hold of a sales engineer. As above, Google is your friend (for your specific applications).

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riahon

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#619175 4-May-2012 06:41

mattRSK: Hi, I have had a small amount of experience with them. I have always used a drill bit that is slightly smaller than the thickness of the shank at the widest point of where the thread is. I just go through my drill bit set placing them over top until I can see all of the thread sticking out the side and just slightly the shank.

It's kind of hard to explain. Maybe I should make a picture.

edit: Picture, red is the drill bit

That's the system I use with the assistance of an optical eyechrometer ensuring secondary viewer is disabled.

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jevvv

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#619196 4-May-2012 07:41

Mr Builder-Hubby in my house says he usually does about 8mm for hard wood and 7mm for soft wood.

That is hard wood not hardwood, and soft wood not softwood - technically there is a difference.

The he described the picture that MattRSK drew for you (no he hadn't seen it)

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BlueShift

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#619222 4-May-2012 08:24

jevvv:
That is hard wood not hardwood, and soft wood not softwood - technically there is a difference.

Yes, biologically speaking, balsa is a hardwood - but not a hard wood.

gzt

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#619500 4-May-2012 13:44

Thanks for all the replies. I usually use mattRSK's method with a bit of give and take depending how I feel about the timber (as described by edge).

Every individual large EDS coachscrew sold retail has a little tag on it saying "Call 0508 EDL FAST for technical information" - given that I was a bit surprised at the lack of response from them.

The application is kind of weird (and a repair of an existing structure) but it will be going through the side of a 100x50 radiata nog at approx 45 degrees. This is replacing a nail which used to perform the same function. Not a huge load involved. If that sounds a bit dodgy, that's because it is. I am considering rebuilding the whole thing with a better design, but there is a fair bit of work involved in that.

I'll grab one of those cheap verniers to confirm the inner shaft size. Given how much research is done on radiata engineering in NZ I was surprised not to find an exact specification.

Pock

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#619994 5-May-2012 09:47

What I usually do is start small, then start winding it in, to see how it feels and drill a bigger hole if needed.

mattRSK

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#620016 5-May-2012 11:11

riahon:

That's the system I use with the assistance of an optical eyechrometer ensuring secondary viewer is disabled.

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