Slanted holes

Lo-Fi said:
Could be a few things. What machine are you using? Some drill presses are not so sturdy and can flex.
You're also allowing errors to creep in by going up in small increments. Best practice is to have the pilot hole just big enough for the chisel point on the largest drill. When shaving off 1mm, particularly in ali, the larger drills are liable to grab and wander. In this case, 4mm then straight to 8mm should be pretty good
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I quite agree with this post, best practice would be to use a spotting drill and then go to the full size drill; using small drills to start the hole invites wandering, the full size drill is much more rigid than all the other drills used.
 
No doubt I am mis-understanding the problem but would starting the hole with an end mill create a horizontal plain for the center drill to locate the final through hole more accurately and help eliminate deflection?
Have a good day!
Ray
 
T Bredehoft said:
Square end mills, when used for spotting leave a 'flat spot' that is slightly HIGH in the center, they're sharpened so only the tip cuts when moving horizontally. I wouldn't think starting a hole with one would be of any advantage.
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I think this would depend on the angle. If the angle is steep enough, the OD of the spotting drill will make contact first and the hole will likely move off center. I always created a flat spot on the work with an end mill in this situation.
Robert
 
I find that using stub drills that have shorter lengths in comparison with their diameters, so even choking them up into the drill chuck as far as possible will have somewhat less chance of bending while drilling. A rigid machine holding the drill also keeps things from bending under the load. Properly ground drills that are sharp and have the proper geometry in their grinds are always better. If the cut is forced, it is likely to drill in a different direction than desired.
 
I feed in horizontally with an endmill then spot drill. I then go to the biggest factory grind I have for the hole. I use the big (final size)
drill last because all my big drills have been sharpened by me which means the webs are all over the place. I need to have that web clear for a true hole.
 
Work on your drill sharpening technique. Both cutting edges need to be the same length and the same angle for the drill to cut properly. If you do not have a drill sharpening gauge get one. To properly sharpen a drill by hand demands patience which I am sadly lacking.
 
Illinoyance said:
Work on your drill sharpening technique. Both cutting edges need to be the same length and the same angle for the drill to cut properly. If you do not have a drill sharpening gauge get one. To properly sharpen a drill by hand demands patience which I am sadly lacking.
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Yeah, me too. Add to that arthritis and some parts missing from left hand and you have a formula for poor drill sharpening.
 
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