19mm Bench dogs - 20mm or 3/4" hole?

[billw]

Yes, I am aware there is under 1mm in this whole shebang. However I don't want to do this wrong so....bench dogs/pups seem to come most commonly in 19mm sizing, at least the ones I've found and yes I am partial to Veritas kit. I have to drill the corresponding holes and I just want to check whether there's actually any reason why a 20mm auger/flat bit isn't perfectly fine or are there some 19mm bench accessories that really need the tightness of a 3/4" hole?

 

[AndyT]

I mostly use blacksmith-made holdfasts, but also have a Veritas bench pup and their discontinued longer benchtop clamp thing I have forgotten the name of but which fits into two holes.
I used a 3/4" auger bit to make all the holes and they all work fine whatever goes into them. The Veritas bits don't need an extra-snug hole. The bench pup/dog has a big wire spring down the side and the other thing has an expanding cone plug, so either would be fine in a slightly bigger 20mm hole.

 

[sammy.se]

Are you making an MFT, or adding dog holes to a more conventional bench?
I made an MFT using a template. My dogs are exactly 20.0mm, and fit snugly into 20mm holes. 1mm on an MFT means a large margin of error.
My MFT - created with a template - is about 1mm out per metre, which I think is rubbish :-( next time I will buy a CNC'd MFT. I still use the MFT for clamping etc, but I cant rely on it for square cuts, unfortunately.

 

[spb]

The answer will depend on exactly which bits of kit you've got, as they use different mechanisms to stay put in the hole. The Veritas stuff is designed for 3/4" so obviously that's the size to go for given a choice, but if you've got a 20mm bit already and no 19, then just drill a whole in a piece of scrap the same thickness as your benchtop and see whether you're happy with how the various pieces hold in it. As Andy said, the Veritas dogs have springs to help them stay put even in a loose hole, but holdfast or other clamping device might not do so well.

On the Veritas note, their planing stop doesn't have those springs, so would rattle a bit in an oversized hole. Whether that's an issue is a matter of taste.

 

[billw]

Are you making an MFT, or adding dog holes to a more conventional bench?

Dog holes into a conventional bench.

 

[Droogs]

If you plan to use traditional holdfasts then 20mm hole with a minimum depth of 2" thick top in order for them to work smoothly, 3/4" hole for bench dogs

 

[samhay]

I find the Veritas wonder Dog quite a tight fit in a 3/4 hole, so expect 20mm will be fine.
But as others have said, it is an easy experiment to try in a piece of scrap.

p.s. my holdfasts like a slightly smaller hole, so you may have to compromise.
And now edited for typos.

 

[Bm101]

I have a couple of Simon James holdfast in 19 mm holes. Perfect. I also have a (used) veritas wonder dog that only fits a 20 mm hole. I cut the wire off.
I use it as a clamp in the one 20 mm drilled hole on my worktop. The holdfasts work fine in the 20 mm hole but I don't want to redrill all the dog holes to 20 mm just to suit the veritas dog which rarely gets used tbh compared to the versatility of the holdfasts.

 

[billw]

Simple things like testing on a piece of scrap are the sort of things I’d actually never think of unless I read it here.

In this instance it’ll only be benchdogs, so it sounds like 3/4” is the better bet.

 

[Chris Hawkins]

I use a metric 20mm MFT (created using Parf MK 2 guide system) - I find the Veritas 3/4" bench dogs unusable in these holes. Hope that helps.

 

[sometimewoodworker]

Simple things like testing on a piece of scrap are the sort of things I’d actually never think of unless I read it here.

In this instance it’ll only be benchdogs, so it sounds like 3/4” is the better bet.

if everything you are going to use is ¾ then you need a ¾“ bit as ¾“ is 19.05mm so a 19mm bit can easily be too small.

3/4“ items are mostly terrible in 20mm holes.

I've standardised on 20mm as I can pad out the very few ¾“ things with tape.

 

[billw]

One 3/4" auger bit duly ordered. This would be so much easier if the Americans (and Canadians) went metric, which might be problematic since most of them get confused by the 24-hour clock.

 

[Eshmiel]

One 3/4" auger bit duly ordered. This would be so much easier if the Americans (and Canadians) went metric, which might be problematic since most of them get confused by the 24-hour clock.

And much else! Table saw design, for example. There are other things evidencing a Great Confusion in that land. Many other things.

On the other hand, it's pretty queer in Blighty these days.

I blame Mrs Thatcher (and the Kennedys).

Myself, I have been confused since birth - more and more as the Unavoidable Event at the other end of this peculiar thing called life approaches.

I blame John Logie Baird.

Eshmiel

 

[nybroc]

Yes, I am aware there is under 1mm in this whole shebang. However I don't want to do this wrong so....bench dogs/pups seem to come most commonly in 19mm sizing, at least the ones I've found and yes I am partial to Veritas kit. I have to drill the corresponding holes and I just want to check whether there's actually any reason why a 20mm auger/flat bit isn't perfectly fine or are there some 19mm bench accessories that really need the tightness of a 3/4" hole?

I suspect there is a tendency to over exaggerate the need for perpindicular holes or the exact diameter of the hole. I knocked up my first diy holdfast this morning. It is made from 600mm long 16mm diameter mild steel round bar. I used cold bending to get the shape of the holdfast, no heat at all. I put the 16mm bar in a small metalwork vice. I used a tube I had to hand. It came from an old Rayburn cooker, the chrome finish 'handle bar' at the front. Roughly 25mm diameter (1" ?) and a metre long. Very thin tube walls which I thought might buckle but no hint of the tube becoming misshapen. Dead easy to use. The bench is over 100 years old and a wreck so I didn't mind if the holes made a mess of the 3" bench top. I didn't have a drill of the recommended size, 18mm. The nearest I had was a 20mm forstner so I gave it a try with a cordless drill. The hole wanders at the bottom by about 1/8" inch. The first time I bent the bar I got the dimensions wrong with insufficient bar to go fully down the hole. So I left the small bend for the pad and straightened the major bend, again with the tube. Didn't get it perfectly straight. The end result after I had re-bent the major bend is a holdfast who's appearance is quite scruffy. Nothing at all like the posh ones that are £30 or £50 each. But the functionality of mine is every bit as good if not better. The price for each, around £3 to £4 each. This assumes you already have the metalwork vice and the piece of steel tube. Now I know how to do it I could knock one up in ten minutes. RESULT!