Larger drills bits on a smaller lathe

brandon428

H-M Supporter - Silver Member
H-M Supporter - Silver Member
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Nov 15, 2020
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138
Hi all,

I realized yesterday that over the years I've collected enough tooling where I now have several ways to drill holes between 1/2" to 1" on my smaller 9" lathe with a MT2 tailstock. More specifically, I have a handful of sizes with MT2 shanks, S&D bits, straight shanks, etc. Wondering what other people do.

Couple of arguably reasonable options:
- Jacobs 14N chuck with 1/2" shank S&D
- Jacobs 14N/18N chuck with 1/2" shank S&D for up to 3/4" bits plus 3/4" shank S&D up to 1" bits
- Jacobs 20N chuck with straight shanks
- MT2 bits from 1/2" to 3/4" plus MT3 to MT2 adapter with MT3 bits from 3/4" to 1"

Some combinations of the above? Any of the above others might consider crazy talk?
 
it’s not a huge lathe, but I have a Jacobs 20N on an MT3, goes up to 1”.
 
I'm not sure what my biggest drill bit is, but I think it's only 7/8 mt2... After that I bore.. I have an SB9 so things get dicey with large bits... they have a habit of either spinning in the tail stock, or making the chuck extremely hard to take off, so boring is easier on the lathe.
 
Above 1/2", I only use MT drills up to 1" and bore from there. Less chance of spinning a big drill in the tailstock ram.
 
Eric, is the idea that the lathe dog will quickly hit the carriage if it spins to minimize the damage?
 
I'm not sure what my biggest drill bit is, but I think it's only 7/8 mt2... After that I bore.. I have an SB9 so things get dicey with large bits... they have a habit of either spinning in the tail stock, or making the chuck extremely hard to take off, so boring is easier on the lathe.

I have an SB9 too. Except for 1" specifically, MT2's don't go that much above 3/4". I also always bore if I'm going bigger than 1".
 
The other real question would be "what is the horsepower of the lathe?". I wouldn't try to push a drill larger than 3/4 inch unless you have a full horsepower.
 
Really? I have an SB9 with a 1/2HP motor. I have used drills above 3/4" many times, and while I run slower, haven't run into issues.
 
Brandon428, yes, if you have a gearbox or a pully system to reduce RPMs (acting as a torque multiplier), you can push a higher diameter. For those without this advantage (ones that use variable speed motors), they will find this limit realistic.
 
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