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Twist Drill Angle with Center Drills vs Spotting Drills
- Thread starter wildo
- Start date
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- Dec 20, 2012
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- 9,422
True, true.
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- May 16, 2016
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These spotting drills that you speak of are a mystery to me, I don't believe I've ever heard of them before, never seen one, and certainly never used one. When I did my apprenticeship in the early 60's we were taught to pick up a center spot with a center drill, but only drill the point in, do not drill deep enough to start the 60deg taper for running a center in. the drill with a number of drills getting larger each time up to 1/64th smaller than the required hole, then finish the hole with an on size drill with the corners slightly knocked off. only using a reamer if super accuracy was required. Larger holes requiring high accuracy were normally bored anyway. Thus pilot holes were all the go. most of our work was in annealed tool steel, maybe something to do with it. I don't remember any problems with chatter or out of round holes.
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- Jul 2, 2014
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I very rarely have any trouble with drilling holes when using a mill or a lathe, and I imagine that other rigid machines would be about the same. Almost all the troubles I have ever had in drilling have been hand held or on my 17" floor model Enco drill press. If I do things the correct way, without cheating to save time, it works fine. If I get lazy, then occasionally I have real trouble, sometimes making nasty holes and occasionally ruining an otherwise nice part. I think the fact that this thread is now up to 44 posts says that others might have also had issues with drilling "simple" round holes to the correct size and in the correct location. It is great that we can all learn and share on these forums...
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- Nov 16, 2016
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- 38
Spotting drills may by useful on small mills with round column. Spotting drill is shorter than standard drill but longer than center drill - maybe not much but sometimes enough to let you use standard drill or reamer without moving the table and loosing position after spotting.
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- Nov 18, 2012
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- 1,352
Well I have been doing quite a bit of drilling, tapping and relocating holes accurately. Sizes are for 4-40 and 6-32 cap screws.
I am drilling and milling on my tricked out JET drill press. Using the #5 centre drill tip only has worked extremely well. The bit seems to snug right in without any wobble or digging in.
As a hobbyist I have been using centre drills for spotting for over 40 years. So far my take is that with my equipment the spotting drill or in this case the tip of the large centre drill is a lot better...so far.
And this is a bit of an aside, but I also learned on this great forum the difference between spiral point and spiral flute taps and have been using the spiral point on this project in aluminum. What a huge difference compared with straight flute. Just cuts right through with no having to back up and break the chips.
David
I am drilling and milling on my tricked out JET drill press. Using the #5 centre drill tip only has worked extremely well. The bit seems to snug right in without any wobble or digging in.
As a hobbyist I have been using centre drills for spotting for over 40 years. So far my take is that with my equipment the spotting drill or in this case the tip of the large centre drill is a lot better...so far.
And this is a bit of an aside, but I also learned on this great forum the difference between spiral point and spiral flute taps and have been using the spiral point on this project in aluminum. What a huge difference compared with straight flute. Just cuts right through with no having to back up and break the chips.
David
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- Dec 20, 2012
- Messages
- 9,422
I like form taps in aluminum - stronger, cleaner threads and NO chips.
- Joined
- Dec 20, 2012
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- 9,422
I've been thinking about this subject and I think it comes down to this: use what works for you. You can use a center drill, spotting drill or just the drill. I don't think anyone is saying you have to use only a spotting drill to drill a hole, or that using a center drill is wrong. I suspect all of us are capable of testing these drills for ourselves and coming to our own conclusions.
The value of this thread is that we have been able to share what a spotting drill is, what it is used for and how to choose one.
The value of this thread is that we have been able to share what a spotting drill is, what it is used for and how to choose one.
- Joined
- Jul 2, 2014
- Messages
- 7,594
I recently bought some USA made cobalt, 135 degree, split point, screw machine (stub) length drills. Got a dozen each of 1/4 and 3/8" diameters, new and in the original sealed packaging, for less than $1 each, free shipping on eBay. I have given some away to my buddies, but I probably still have a lifetime supply of them on hand. I can use these as spotting drills, and they are split point so they do not need a center punch mark when using them on the mill with 90 degree smooth surfaces. I can also use them to start holes accurately in work on the lathe. The split points are also very useful on small center punch marks, even for hand held drill motors.