Even an accurately-ground drill bit is no substitute for a reamer.
I agree completely, but for different reasons.
The hole for a bearing will never be accurate unless an accurate hole is drill in the first place. If we are talking utra-high precision here, then the hole should be drilled and reamed with a CNC machine. However, if we are just talking about a hobbyist who just needs to install a couple bearings without being ultra high precision, then the ground drill bit should do the job.
The pilot will ultimately determine the inner dimension, and as long as the drilled hole is within a press fit range, the bearing should install just fine.
CNC isn't necessary, a manual milling machine or lathe with a milling attachment will do. I get very accurate results with my little Taig lathe and milling attachment.
A drill bit cuts only on the end -- not on the sides.
Earlier this year I cut the heck out one of my fingers with the flutes (or whatever they're called) of a large drill bit. Pretty sharp edge/s for something that doesn't cut.
[Apply direct pressure... and try to not think about it.]
I sympathize, PJ. I've never gone more than a couple weeks without injury when using power tools. You'd think I'd learn eventually. 'Probably oughta wear Kevlar mittens and a helmet whenever I go into my shop.
But, seriously, the flutes of a drill bit are not cutting edges for materials other than human flesh. Try enlarging a hole by applying lateral pressure to a drill that's rotating in the hole it drilled. You can't do it. With an endmill or reamer, though, it's a different story.
While modifying a drill bit this morning, I remembered this comment:
But, seriously, the flutes of a drill bit are not cutting edges for materials other than human flesh. Try enlarging a hole by applying lateral pressure to a drill that's rotating in the hole it drilled. You can't do it. With an endmill or reamer, though, it's a different story.
I must say that I respectfully disagree. By reducing a portion of the diameter of a drill bit through a grinding process, thus creating a step bit, the second step which is no longer associated with the cutting tip, consisting mainly of fluting, is quite capable of boring a hole.
.. By reducing a portion of the diameter of a drill bit through a grinding process, thus creating a step bit, the second step which is no longer associated with the cutting tip, consisting mainly of fluting, is quite capable of boring a hole....
As I've understood it, the reason the flutes are sharpened is only so they can cut through any chips that might form and get stuck between the hole and the flute. The flute edges, by themselves, make terrible milling bits. But from the sound of it, Bruce, you've just made yourself one of these:
But from the sound of it, Bruce, you've just made yourself one of these:
Exactly, that is a step bit, but by machining it myself through a grinding process, the sharp edges of the fluting on the smaller diameter have been removed.
I have been installing bearings and bushings with a pilot kit from Harbor Freight for years. or I am I missing something. I was a machinest for 25 years. There is some good info here. If anybody really wants to know the proper technique for press fitting bushings and bearings read machinerys hand book.
When the drill is ground, the larger diameter portion does then engage like a cutter, just not laterally, and it's cutting surface is significantly diminished from the potential a drill has otherwise. For small steps, this works, but heat can be a problem with the cutting surface at the step.
Comments
I agree completely, but for different reasons.
The hole for a bearing will never be accurate unless an accurate hole is drill in the first place. If we are talking utra-high precision here, then the hole should be drilled and reamed with a CNC machine. However, if we are just talking about a hobbyist who just needs to install a couple bearings without being ultra high precision, then the ground drill bit should do the job.
The pilot will ultimately determine the inner dimension, and as long as the drilled hole is within a press fit range, the bearing should install just fine.
Bruce
Earlier this year I cut the heck out one of my fingers with the flutes (or whatever they're called) of a large drill bit. Pretty sharp edge/s for something that doesn't cut.
[Apply direct pressure... and try to not think about it.]
But, seriously, the flutes of a drill bit are not cutting edges for materials other than human flesh. Try enlarging a hole by applying lateral pressure to a drill that's rotating in the hole it drilled. You can't do it. With an endmill or reamer, though, it's a different story.
-Phil
While modifying a drill bit this morning, I remembered this comment:
I must say that I respectfully disagree. By reducing a portion of the diameter of a drill bit through a grinding process, thus creating a step bit, the second step which is no longer associated with the cutting tip, consisting mainly of fluting, is quite capable of boring a hole.
Bruce
As I've understood it, the reason the flutes are sharpened is only so they can cut through any chips that might form and get stuck between the hole and the flute. The flute edges, by themselves, make terrible milling bits. But from the sound of it, Bruce, you've just made yourself one of these:
Exactly, that is a step bit, but by machining it myself through a grinding process, the sharp edges of the fluting on the smaller diameter have been removed.
Evan
When the drill is ground, the larger diameter portion does then engage like a cutter, just not laterally, and it's cutting surface is significantly diminished from the potential a drill has otherwise. For small steps, this works, but heat can be a problem with the cutting surface at the step.