Locating A Part To Be Drilled On Center. ?

WesPete66 said:
Thanks to all for the replies!
Actually I was looking at the v-blocks recently, the ones with the groove cut in the bottom that lets you align a drill bit to the slot. Are those worth the money? It's gotta be better than what I have now..
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kd4gij has the right idea. If instead you put a 90 degree (45 each side) tool in your drill press spindle, you can push it down into the v-block and hold it there until the v-block is tightened to the table. Change to a center drill, carefully peck a tiny hole and then open it to just under the diameter of the center drill tip only, no shoulder or main cutter entering the work at all. Now change to your drill and make the hole.
 
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Bob Korves said:
kd4gij has the right idea. If instead you put a 90 degree (45 each side) tool in your drill press spindle, you can push it down into the v-block and hold it there until the v-block is tightened to the table. Change to a center drill, carefully peck a tiny hole and then open it to just under the diameter of the center drill tip only, no shoulder or main cutter entering the work at all. Now change to your drill and make the hole.
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Spotting drills are 90 Deg. and designed specifically for spotting drilled holes, why would anyone change to a center drill for spotting holes? Center drills are for creating lathe centers, spotting drills are for starting holes for the twist drill to follow, these are not the same thing.
 
Wreck™Wreck said:
Spotting drills are 90 Deg. and designed specifically for spotting drilled holes, why would anyone change to a center drill for spotting holes? Center drills are for creating lathe centers, spotting drills are for starting holes for the twist drill to follow, these are not the same thing.
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I am assuming the main drill has a 118 degree point angle here. The starting tip of the center drill is ground at 120 degrees. The spotting/center drill should have a LARGER angle than the drill that follows for it to follow with proper guidance, not walking around as the cutting lips make contact with a 90 degree hole part way out on the cutting lips, which leads to chatter and poor following. The chisel point of the larger drill should be first to contact the work in the starter hole and start cutting, with the cutting lips taking over the job from the center outward, not starting by taking notches from some random points on the cutting lips. In this way the starter hole is truly guiding the drill.

Using the 60 degree main cutting portion of a center drill to make a starting hole for a drill is a really poor idea, even worse than the 90 degree spotting drill, but it is very commonly done. Using the parallel bore caused by the entire tip of the center drill penetrating the work is not quite as bad, but still wrong, and is also sometimes done in error.

Again, the only way a starting drill can facilitate centering of the drill and locating where the drill should follow is for the included angle of the starting/spotting drill to be slightly larger than the drill which will follow. That would mean a 120 degree spotting drill for a 118 degree drill to follow, and a 140 degree spotting drill for a 135 degree drill to follow.

I understand quite well that what I am posting here is not common practice. If you disagree with it, please explain to me why it is wrong.

Specifically, in the case of starting a hole in a curved surface, which is what the OP was trying to do, the center drill is a pretty good choice because it is extremely rigid, has a 120 degree starting angle, and can leave a small, well centered starting hole if pecked lightly and carefully, avoiding the need for milling the curved surface flat first, which would be probably be best for higher precision work. A spotting drill has a larger chisel point and is also less rigid than the center drill is, and is therefore more likely to walk off the curved surface.

Does that make sense? It has worked well for me...
 
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All Good Ideas!

Here are a couple of others. I made up some V blocks for the drill press by welding two pieces of angle to a piece of 1/4" flat plate. You can size thwe angle to meet your needs. The one improvement that I would make would be to make the base plate larger for more convenient clamping.

Another way to make an "emergency" V block is to clamp two pieces of pipe together with two Vise Grips. V Block .JPGE-V Block .JPG
 
even a pair of dowel pins could be held together and clamped or set in a vise as well, i'd imagine-
 
Depending on your indicator, you can use it. Bring your part up to touch the drill bit, set indicator, tap to move part (half diameter plus half drill bit). If yu only have a 'finger' or test indicator, be a little tougher, but doable. Great ideas above as well.
 
One thing that doesn't get mentioned very often is to be sure the cut off tool is perpendicular to the work. Doing this and following these suggestions has improved my cut off work a great deal.
Have a good day!
Ray
 
I touch off 1 side with an edge finder then dial in center. Then center drill to diameter of the drill I am going to use. The center drill to diameter will help the drill stay on center.
 
I'm in the middle of making cutter blocks for small diameter stock. I will use 1" hex and square stock, drill/bore and ream
for diameters dead center and use a set screw to hold stock. Now, I can just turn the block on the flats and get my holes or flats
on the opposite side or with hex stock, at different points. For cross holes, you can drill holes on the flats of the square stock
90 degrees opposed or any other configuration one wants. Or, you can make bushings so one can use different size drill bits with the square or hex cutter blocks.

Cutting a small flat with end mill on round stock before drill the hole helps to keep the drill from wandering.
The idea came to me from reading Guy Lautards BSR books.
 
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