HSS Drill bits vs Brad Point Drill bit.

[Toecutter]

Ok, so I bought some decent HSS drill bits and Brad point bits for pilot hole accuracy. (I find HSS are not great for precise guidance in larger sizes)

The Brad points seem to drill bigger than the HSS of the same size. I tried 2 and its a good 0.5 of a mm bigger. Both were 12mm bits

Is this normal?

 

[RobinBHM]

I would expect the brad points to be spot on to size, do they measure right with a vernier / caliper?

 

[Toecutter]

I would expect the brad points to be spot on to size, do they measure right with a vernier / caliper?

I don't have one to hand. Even a 12mm brad is making a wider diameter than 12.5mm HSS. Its going through MDF btw.

 

[RobinBHM]

Is this free hand drilling or in a pillar drill?

Generally I find HSS bits drill rather oversize holes in wood as they wonder a bit. The brad point bits have an outer scribe which keeps them quite true when freehand drilling.

If you try and push the drill bit by hand into a drilled hole, that will tell if the hole is enlarging whilst being drilled or the bit itself is oversize. It almost sounds like the drill bit is 1/2" which is 12.7mm

 

[Toecutter]

Is this free hand drilling or in a pillar drill?

Generally I find HSS bits drill rather oversize holes in wood as they wonder a bit. The brad point bits have an outer scribe which keeps them quite true when freehand drilling.

If you try and push the drill bit by hand into a drilled hole, that will tell if the hole is enlarging whilst being drilled or the bit itself is oversize. It almost sounds like the drill bit is 1/2" which is 12.7mm

Its a pillar drill. I drilled a 12.5mm brad point hole, then put a 12.5 hss in and it wiggles quite a bit. Tried 3 brad points and they all do it.

Maybe its a bad batch.

 

[Steve Maskery]

The usual reason for drills drilling oversize is that the centre point is not central. But for several new drills to behave like that is puzzling, I grant you. The other possibility that would make sense is if they were actually Imperial 1/2" rather than metric. It's difficult to know without seeing them, unfortunately.

 

[Tortion-Stephen]

As above, my experience of brad point is that they are usually spot on. For ordinary twist drills, split point ones usually wander less and drill straighter as you don't have essentially a static point in the middle that needs to compress to clear the hole. That said, if you're using a drill press and there is runout of the chuck/arbour/both you're not going to get a decent hole anyhow; I saw a Clarke Metalworker Drill press with over 1mm of runout!

 

[DiscoStu]

I know you tried the HSS in the hole drilled by the brad point, but I wonder if you have tried drilling with the HSS? Did that produce the correct size or was that oversized? If oversized as well then could it be the pillar drill has a small amount of movement in it.


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[Hemsby]

Does the 12mm have a reduced shank diameter :?: