# Counterbore, countersink and clearance hole for metric screw



## inventor (27 Apr 2007)

Combined counterbore-countersink-drill bits are pretty common, such as 
http://www.axminster.co.uk/product-Tren ... -22341.htm but
(a) they concentrate on drilling an adjustable depth pilot hole for the screw thread rather than a clearance hole for the screw body
(b) they are all for ye olde gauge style screws
Nowadays, screws rarely need pilot holes, and are fully threaded, so if I want the screw to pull two pieces of wood together, I need a clearance hole in one piece.

Does anyone make a combined counterbore-countersink-drill bit for modern metric woodscrews? I especially need one for 5mm screws, drilling an adjustable depth 5mm clearance hole and producing a 10mm diameter counterbore.


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## jasonB (27 Apr 2007)

I use the trend TCT tipped ones. They take a standard 4,5,6 etc mm drill bit which can be adjusted for length so you can get a clearance hole throgh the top piece of wood, they will then countersink and if pushed further will do a counterbore to suit trend plug cutters. And they fit the snappy system.

The 5mm with countersink is SNAP/CS/5MMTC though I think the counterbore on the 5 & 6mm is 12.7mm

Jason


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## Paul Chapman (27 Apr 2007)

inventor":14n3kkln said:


> Nowadays, screws rarely need pilot holes



:shock: :shock: I always drill pilot holes.

Cheers :wink: 

Paul


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## Scrit (28 Apr 2007)

Paul Chapman":4uphu9mw said:


> I always drill pilot holes.


I think I'd agree with that, too, for hardwood or thin softwoods. Even Spaxs or Reissers can cause splitting at times.

Scrit


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## woodbloke (28 Apr 2007)

Paul Chapman":8y3h4hxe said:


> inventor":8y3h4hxe said:
> 
> 
> > Nowadays, screws rarely need pilot holes
> ...


Agree with Paul and Scrit here - Rob


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## Anonymous (28 Apr 2007)

woodbloke":35iit0y5 said:


> Paul Chapman":35iit0y5 said:
> 
> 
> > inventor":35iit0y5 said:
> ...



Ditto - wood often splits if not and MDF nearly always splits if screwing into the end without a pilot hole


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## andycktm (28 Apr 2007)

Something like these?

http://www.screwfix.com/app/sfd/cat/pro ... &id=18731#


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## jasonB (29 Apr 2007)

Unfortunatly the screwfix ones and most flip bits come to that only drill a pilot hole not a clearance hole so you are likely to experience jacking. Also they are not too good in hardwood and clog very easily.

I find the TCT counterbores and drill countersinks here work a lot better.

Jason


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## Scrit (29 Apr 2007)

For brass screws in hardwood I'm still old fashioned enough to use Fuller taper drills like this:







which I've found to be excellent. I have a bits and pieces set of the most used sizes with stop collars, countersinks/counterbores and matching taper plug cutters. main problem is that almost everyone offers those cheap and nasty Chinese copies which I've found aren't a patch on the real thing. The distributor who I got these from has ceased trading, so does anyone know who imports them now?

Scrit


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## Chris Knight (29 Apr 2007)

Scrit,
Might be worth trying these http://www.mcfeelys.com/subcat.asp?sid=75 McFeelys seems to have a good name. I would guess that these http://www.woodcraft.com/family.aspx?FamilyID=772 are the Chinese knock-offs you mention?

I've no idea if they can be had in the UK but importing a few drill bits shouldn't attract too much attention from the taxman I would think.


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## jasonB (29 Apr 2007)

Scrit, try Trend and Dick

Jason


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## Scrit (29 Apr 2007)

Thanks for the suggestions. I was rather hoping there might be a UK based supplier. The Dick ones appear to have those awful press-on hex ends which loosen off very quickly in use. I'll take a look at the Trend ones if my local dealer has any

Scrit


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## Pekka Huhta (29 Apr 2007)

Just make one yourself. It's very simple, just get a drill bit, put it on your drill and grind away with a bench grinder or a belt sander. 






I've done a bunch of them for several screw sizes and store them in the appropriate screw box.

Pekka


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## Shultzy (29 Apr 2007)

jasonB, unless the screwfix drills are not as pictured, they have a counterbore.


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## jasonB (30 Apr 2007)

Shultzy":2ddfxm3p said:


> jasonB, unless the screwfix drills are not as pictured, they have a counterbore.



Which gives a very poor hole, ragged edges that show when you plug the hole and being made fron unhardened steel loose what edge they have in no time when used in MFC/MDF. Also the drill bits are for pilot holes OP wanted clearance for 5mm

Jason


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## inventor (30 Apr 2007)

Thanks for all the suggestions, everyone. Fortunately, I use straight-core screws, not tapered core, so I don't have that particular challenge. However, nobody has come up with quite the product I want. I'll try to manufacture a tool myself (but don't hold your breath).

Is there a published standard for the geometry of metric woodscrews (like these: http://www.screwfix.com/app/sfd/cat/cat ... &ts=15402#
or these: http://www.screwfix.com/app/sfd/cat/pro ... 0&id=22474)
or does each manufacturer just make something vaguely the right size? If there's a standard, I can make the tool to meet it. If there's not, I'll have to go round measuring a bunch of miscellaneous screws.


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