SDS bits in traditional braces?

[Andy Kev.]

Out of curiosity, would a traditional brace be able to decently hold a bit with an SDS or SDS-2 shaft?

I ask because there are some decent looking bits with such shafts available. I presume that nobody manufactures a set of jaws with which one could adapt a brace.

 

[DoctorWibble]

Can't say I've tried but I'd guess not very well. At best you'd have alignment problems and the grooves in the bit might damage the jaws of your chuck. Crocodile jawed chucks might be encouraged to hold one well enough to get you out of a hole (!!) but universal jaws are a bit (!!!) more fragile and you'd risk ruining them.
You always could have a go at grinding a pair of brace jaws to fit. That might work though you'd likely burn through a few 50p car boot braces. And if you succeed you'd have an SDS only brace.
On a related point might be helpful for some to know that you can find adapters (try that German outfit Dieter Schmid's Fine Tools) that allow braces to drive various hex shanks and 3/8ths square sockets (Veritas do them too and one for 1/2 drive but shipping to Europe is expensive). Very handy things. Never seen an SDS chuck designed to fit into non SDS tools but they may exist in which case daisy chaining two adaptors could get you there albeit with some drive train rock and roll.

 

[Rorschach]

I made an adaptor that lets me use my SDS+ drill bits in a standard 13mm 3 jaw chuck. It's for my cordless hammer drill, works very nicely.

 

[AndyT]

Andy, now I'm back from my hols, I popped into the workshop and did some experiments.

If the brace is like the vast majority and has a single pair of "alligator" jaws, the answer is no. The corners aren't right on the bit and the diameter is too big.

But if you are lucky enough to have an old brace with a universal chuck, it's Yes.

This is a nice but rare brace by Peck Stowe and Wilcox which I wrote about here really-useful-brace-to-identify-t98439.html

And this is my favourite Stanley 144 with a four jaw chuck which fits really snugly

post1018706.html#p1018706

Both of these gripped SDS bits centrally, straight and firm.

I didn't go on to start drilling 8mm holes in masonry, but if they were auger bits it would have been practical to use them.

Sorry if this is a frustrating answer - it's a pity that chucks like these are not more common.

 

[Andy Kev.]

Andy, that is extremely interesting. So in principle the most likely solution (given the relative rarity of the first brace you illustrate) is to get a second hand brace with a four jaw chuck. I'll keep my eyes peeled.

And behold: https://www.fine-tools.com/bohr1.html

Dieter Schmid offers three four-jawed models, as hinted at by DoctorWibble above.

 

[DoctorWibble]

These old braces whether with universal jaws or the interlocking chuck (bugbears PSW) were designed to hold square tapered shanks and round bits only at a push. Arguably the ability to take round bits was something of a disingenuous marketing ploy. The interlocking chuck has a fixed square socket at the back to take the drive load and the jaws merely hold the bit in place. You shouldn't use bits which don't engage with the square socket. Universal jaws on the other hand have a smooth v-groove and some kind of parallel hinge to give a "better" grip of round shanks. The torque load is taken by the jaws themselves. That this didn't work too well is the reason makers developed expensive braces with complicated ball bearing chucks allowing a much tighter grip of round shanks.
Using braces to drive things they were not really designed to is one of the reasons many used examples have problems. The torque you can deliver with one is huge and just because a bit appears to fit nicely on the bench doesn't mean you're not going to damage it if you actually use it.
And remember SDS bits are grooved to accept a ball bearing drive and are made from modern very hard alloys likely much harder than the jaws in any old brace. If they slip they will chew up your brace far more effectively than any slipping round shanked bit ever could.
In short using an old brace to drive large SDS bits is akin to using your chisel to open a paint tin. A bad idea.

 

[Rorschach]

These old braces whether with universal jaws or the interlocking chuck (bugbears PSW) were designed to hold square tapered shanks and round bits only at a push. Arguably the ability to take round bits was something of a disingenuous marketing ploy. The interlocking chuck has a fixed square socket at the back to take the drive load and the jaws merely hold the bit in place. You shouldn't use bits which don't engage with the square socket. Universal jaws on the other hand have a smooth v-groove and some kind of parallel hinge to give a "better" grip of round shanks. The torque load is taken by the jaws themselves. That this didn't work too well is the reason makers developed expensive braces with complicated ball bearing chucks allowing a much tighter grip of round shanks.
Using braces to drive things they were not really designed to is one of the reasons many used examples have problems. The torque you can deliver with one is huge and just because a bit appears to fit nicely on the bench doesn't mean you're not going to damage it if you actually use it.
And remember SDS bits are grooved to accept a ball bearing drive and are made from modern very hard alloys likely much harder than the jaws in any old brace. If they slip they will chew up your brace far more effectively than any slipping round shanked bit ever could.
In short using an old brace to drive large SDS bits is akin to using your chisel to open a paint tin. A bad idea.

Some very good points here. When I made my adaptor I chose to make it from brass, which is soft enough to engage with the SDS shank without causing damage and engage with the jaws on the 3jaw chuck. If for some reason the bit should get stuck (never happened yet) then the adaptor is the only part that will be damaged.

 

[DoctorWibble]

Apologies Andy T, I confused you with Bugbear :shock:

 

[AndyT]

Apologies Andy T, I confused you with Bugbear :shock:

No worries - just remember which is the handsome one!

And don't fret about me wearing out any antique braces - I do have a selection of more suitable, non-SDS bits.