Brace suitable for round parallel drill bits

[aesmith]

Hi,
I'm on the lookout for brace that can be used with modern round parallel drill bits. Even better if it can use square tapered as well, so I don't need to keep my existing brace.
Any particular types or models I should look for? I'm thinking old or at least second hand of course, but don't totally rule out new.
Thanks,

 

[ChaiLatte]

This comes close:

https://www.workshopheaven.com/ultimate-hand-brace-drill-3-jaw/
but the fundamental design limitations of a brace chuck mean it will not grip a round shank very well unless you use a Stilsons to tighten it.

If you want to grip a round item, the most practical way would be to buy a standard Jacobs chuck and a parallel arbor and then grind or machine the arbor so it has two square corners onto which the jaws of the standard brace chuck can engage to provide a mechanical drive (rather than just relying on the friction generated by the tightness of the brace chuck).

To give credit where it is due, please look here:

https://www.ukworkshop.co.uk/threads/brace-to-standard-three-jaw-chuck-adapter.98951/

 

[Sideways]

Modern auger bits have hex shanks that won't slip in a 3 jaw chuck.

Anything other than an auger or those adjustable diameter bits with a screw centre I assume need more speed to cut properly so are irrelevant to use in a brace.

 

[aesmith]

This comes close:
...
but the fundamental design limitations of a brace chuck mean it will not grip a round shank very well unless you use a Stilsons to tighten it.

If you want to grip a round item, the most practical way would be to buy a standard Jacobs chuck and a parallel arbor and then grind or machine the arbor so it has two square corners

Why do you say that the chuck on that brace won't grip a round bit?

 

[ChaiLatte]

Why do you say that the chuck on that brace won't grip a round bit?

Look at the machanical advantage you gain from a standard keyed Jacobs chuck - what is the gear ratio between the teeth on the key and the teeth on the pinion?

Similarly, look at how a keyless chuck on works - yes it is tightened by hand but again there is a lot of mechanical advantage being employed and keyless chucks are specifically designed to self-tighten.

A brace chuck relies on how tight you can grip the outside of the chuck and turn it. There is very little mechanical advantage to assist you, and the threads on which the chuck barrel run are generally quite coarse (fine threads = better mechaincal advantage). If you have perfected your hand grip by multiple watchings of the first series of Baywatch, it might work for you.

Note that none of the retailers who sell the item claim the three jaw or four jaw versions are specifically suitable for plain round shanks (see note here: Drilling by hand: Wheel Brace, Jaw Brace, Stock for Bits, Small Brace "Kuri Kuri" | FINE TOOLS "Less suitable for drill bits with round shanks, as these tend to slip under greater load"). As Sideways says, they sell the items to suit modern hex-shanked bits, which do not work well in a tradidtional two-jaw brace.