# Center Drills or Spotting Drills



## bluwolf (Oct 14, 2009)

In my limited experience with my 7x12 lathe I've always used HSS center drills. They've seemed to work fine. But I know there are spotting drills also. Does anyone have a preference and why?

Also, I assume (please correct me if I'm wrong) since I need carbide drills to drill stuff like SS and Ti, I would also need carbide center or spotting drills?

Thanks,
Mike


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## gadget_lover (Oct 14, 2009)

This wiki has a nice explaination.

http://en.wikipedia.org/wiki/Drill_bit#Center_drill_and_spotting_drill


I have a spotting drill permanently installed in a MT2 holder for my tailstock. It makes it super easy to start holes when I need it.

Daniel


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## precisionworks (Oct 14, 2009)

Center drills are designed to place a countersunk face in the end of a shaft, so that a live center or a dead center will exactly fit. Most motor shafts have "centers" drilled into them at the start of building the rotor. The shaft can then be removed from the first op lathe, taken to the second op lathe, and quickly be remounted without having to use an indicator. Centers are often drilled into both shaft ends so the shaft can be mounted on a cylinder grinder or some other operation.

The included angle of the center drill (directly after the drilling point) matches the include angle of a lathe center or grinder center, which is usually 60°. 

Spotting drills (or spotters) are short, rigid twist drills that have a very wide included angle, often greater than 140° - because some solid carbide twist drills are ground to 140°. Spotters also work if the drill point is the more standard 135° or 118°.

In a perfect world, center drills would be used only for drilling centers & spotters would be used as a starting point for accurate hole location. In a production machine shop both are used for hole location, and the spotter is most often seen in CNC equipment.


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## bluwolf (Oct 15, 2009)

gadget_lover said:


> This wiki has a nice explaination.
> 
> http://en.wikipedia.org/wiki/Drill_bit#Center_drill_and_spotting_drill
> 
> ...


 
Which would lead to my next question. What sizes do you use the most? I know which center drill sizes I've been using (incorrectly I now understand). What size do you have installed in the MT2 holder? And is that something you made up or is there another tool I'm inaware of for that specific purpose? And why not just a drill chuck?



precisionworks said:


> Center drills are designed to place a countersunk face in the end of a shaft, so that a live center or a dead center will exactly fit. Most motor shafts have "centers" drilled into them at the start of building the rotor. The shaft can then be removed from the first op lathe, taken to the second op lathe, and quickly be remounted without having to use an indicator. Centers are often drilled into both shaft ends so the shaft can be mounted on a cylinder grinder or some other operation.
> 
> The included angle of the center drill (directly after the drilling point) matches the include angle of a lathe center or grinder center, which is usually 60°.
> 
> ...


 
Excellent explanation. You guys are the best when it comes to newbs. The wiki had this to say in the explanation so I'm confused.

"Most modern solid-carbide drills should not be used in conjunction with a spot drill or a center drill. They are specifically designed to start their own hole. Usually, spot drilling will cause premature failure of the carbide drill and a certain loss of hole quality. If it is deemed necessary to chamfer a hole with a spot or center drill when a carbide drill is used, it is best practice to do so after the hole is drilled."

My original question was, since I have to buy carbide drills, I guess I guess I need carbide center dills which lead to the asking about spotting drills. But according to this I don't need carbide spotting drills. So what am I missing?

Mike


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## Rothrandir (Oct 15, 2009)

Depending on what you're doing, it may not be necessary at all to buy carbide drills.

I just finished a job running a #20 drill (about .160" diameter) 1.25" deep on 75 titanium 6al4v parts. I've run over 100 parts with the same cobalt drill (screw machine length) and have had no problems. This time I had to switch the drill out a few times (material issues?? not centered well enough???), but still not too bad for inexpensive drills.
I used a spot drill.

Of course this is with high pressure coolant and a decent peck cycle on a CNC lathe, where I can set the cut parameters very accurately. Doing so on a manual may have proved more challenging.

But the point remains I think...carbide may not be necessary. In fact it might not work as well.


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## Mirage_Man (Oct 15, 2009)

Rothrandir said:


> Of course this is with high pressure coolant and a decent peck cycle on a CNC lathe, where I can set the cut parameters very accurately. Doing so on a manual may have proved more challenging.



My experience is when using a HSS/cobalt drill on ti is that coolant is absolutely crucial to get any life at all out of the drill. They will burn up in very short order without it. I have yet to run coolant on my new lathe. I just haven't really wanted to deal with the mess. So lately I've been using solid carbide drills on ti stock. They last much longer and can be run at higher speeds and feeds. Of course I when I say "feeds" I'm referring to manually feeding with the tail stock. After all the ti I've drilled I've gotten a pretty good "feel" for it. Only problem is solid carbide drills are expensive. Having them re-sharpened locally helps keep the cost down on the life of a drill though. If people only knew how much tooling costs to make the stuff we do . 

That brings up another point, re-sharpening. I tried the Drill Doctor on my cobalt drills and IMHO was a total waste of time. It works fine for smaller diameters but I found it an exercise in futility on the larger ones. My advice if you need to sharpen a lot of drills is invest in a real sharpening set-up or do like I have and find a local sharpening shop. My guy sharpens my drills and end mills to unbelievable edges. I would venture to say at least as good as new if not better. But depending on where you live you may not be lucky enough to have a shop like that.


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## precisionworks (Oct 15, 2009)

As stated, cobalt will work *with coolant* (even plain old HSS will work with coolant & speeds plus feeds that will put you to sleep). Carbide is the plan if you need to either run dry or use Tap Magic applied to the drill - which is what I do. Drill in a short distance (peck), withdraw the drill & brush off chips, squirt Tap Magic into the hole & on the drill flutes, and peck again.



> Drill Doctor on my cobalt drills and IMHO was a total waste of time.


You need the Darex V390, which is awesome on cobalt. I have the V290 which does well on everything but cobalt.



> Most modern solid-carbide drills should not be used in conjunction with a spot drill or a center drill.


The only problem with Wiki is that some information is not updated. As long as the spotter has an included angle the same as (or slightly greater than) the drill point, you are ready to go. Almost all indexable spotters today are greater than 140° - usually 144° - because they are designed to be used with carbide tooling.

Carbide tooling is always nice on Ti, SS, AR plate, etc. But a billion holes have been drilled through the toughest metals with HSS at 25 sfpm with a mist bottle :thumbsup:


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## gadget_lover (Oct 15, 2009)

bluwolf said:


> What size do you have installed in the MT2 holder? And is that something you made up or is there another tool I'm unaware of for that specific purpose? And why not just a drill chuck?



It's a 1/4 inch spotting drill, with (IIRC ) 140 degree point. 

Th holder is a blank MT2 arbor from Little machine shop. http://littlemachineshop.com/products/product_view.php?ProductID=2394&category= They were on sale, so I picked up a couple. I drilled it for a tight fit and added a set screw for good measure.

Why not a drill chuck? First, All the drill chucks I own are cheap and do not always hold the bit exactly on center. Second, it's a hassle to swap in the chuck, then fit the drill, then change to the other drill. Third, the center drill is used more than any other single bit in my lathe.

Daniel


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## bluwolf (Oct 15, 2009)

Mirage_Man said:


> I have yet to run coolant on my new lathe. I just haven't really wanted to deal with the mess.


 
I don't have the lathe yet. But I already bought one of those misters like Will got. I'm hoping that will be a good compromise between brushing or squrting it on and flooding my garage with coolant. Any opinion on whetehr it will work with Ti?



precisionworks said:


> You need the Darex V390, which is awesome on cobalt. I have the V290 which does well on everything but cobalt.
> 
> The only problem with Wiki is that some information is not updated. As long as the spotter has an included angle the same as (or slightly greater than) the drill point, you are ready to go. Almost all indexable spotters today are greater than 140° - usually 144° - because they are designed to be used with carbide tooling.
> 
> Carbide tooling is always nice on Ti, SS, AR plate, etc. But a billion holes have been drilled through the toughest metals with HSS at 25 sfpm with a mist bottle :thumbsup:


 
Wow. I just looked at the price of one of those V390s. I think I'll try to find a good sharpening shop

That's why I asked about the Wiki quote. It didn't seem to agree with anything I had read anywhere else.

Right now the stuff I would be doing in Ti is pretty specific. Basically, it will be drilling about a 1/2" through hole, around 3" deep in a 5/8" piece of rod. It sounds like the best route to go is to buy the carbide tooling I need, spotting drill, drill bits, and reamers, to accomplish this specific task, right?



gadget_lover said:


> It's a 1/4 inch spotting drill, with (IIRC ) 140 degree point.
> 
> Th holder is a blank MT2 arbor from Little machine shop. http://littlemachineshop.com/products/product_view.php?ProductID=2394&category= They were on sale, so I picked up a couple. I drilled it for a tight fit and added a set screw for good measure.
> 
> ...


 
Thanks Daniel. I could have used a couple of those at one time or another. I was just too lazy to go looking for them at the time.

Mike


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## PhotonFanatic (Oct 15, 2009)

bluwolf said:


> . . .
> 
> Right now the stuff I would be doing in Ti is pretty specific. Basically, it will be drilling about a 1/2" through hole, around 3" deep in a 5/8" piece of rod. It sounds like the best route to go is to buy the carbide tooling I need, spotting drill, drill bits, and reamers, to accomplish this specific task, right?
> 
> ...



You might want to check out tubing since you are fairly close to some of the thicker walled Ti tubing that is out there.

I wouldn't bother reaming, unless you've got some real tight tolerances to meet--a good boring bar will get you a very nice finish.

I'd also skip the spot drill if you are going to a 1/2" hole--a good 140-degree coated carbide drill(s) is all you really need.


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## precisionworks (Oct 15, 2009)

> You might want to check out tubing since you are fairly close


+1

You'll pay less for material & have much less machine time (and tooling wear) if you can start with tubing.



> Wow. I just looked at the price of one of those V390s.


My V290 was around $450, new in box on eBay, which qualifies as a great buy. But it will not thin cobalt twist drills. That is the problem with cobalt - the body is so thick & heavy (web thickness) that the point must be thinned or it will not drill. Hand thinning the web is not hard once you do a few (hundred )

A less expensive drill grinder is the Lisle 91000, which I use mostly for larger twist drills as it goes up to 1 1/4". Simple as can be, built heavy, and sharpens most any drill quickly. That was also an eBay purchase, seems like $300 or so, new in box.

http://www.lislecorp.com/grinder_index.cfm

There's one currently on eBay and it looks brand new: http://cgi.ebay.com/Lisle-model-910...emQQptZLH_DefaultDomain_0?hash=item439ad08b8b


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## bluwolf (Oct 16, 2009)

PhotonFanatic said:


> You might want to check out tubing since you are fairly close to some of the thicker walled Ti tubing that is out there.
> 
> I wouldn't bother reaming, unless you've got some real tight tolerances to meet--a good boring bar will get you a very nice finish.
> 
> I'd also skip the spot drill if you are going to a 1/2" hole--a good 140-degree coated carbide drill(s) is all you really need.


 
All good advice. But I had a peek on ebay and unless I searched wrong or something I didn't see any Ti tubing that fit the bill. Also, I only saw one listing that specifically said the tubing was seamless.

Maybe if I was more specific it would be helpful. I make pens. The Ti would be the tubes and parts press into the ends. Do you think that I could bore close enough for a press fit or should I ream?



precisionworks said:


> The only problem with Wiki is that some information is not updated. As long as the spotter has an included angle the same as (or slightly greater than) the drill point, you are ready to go. Almost all indexable spotters today are greater than 140° - usually 144° - because they are designed to be used with carbide tooling.


 
So armed with this bit of info I scamper off to look on ebay for some spotting drills. There were a bunch of 90 and 120 degree drills also. These are the ones to stay away from? And what is their purpose for being a different angle point?

Mike


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## PhotonFanatic (Oct 16, 2009)

bluwolf said:


> All good advice. But I had a peek on ebay and unless I searched wrong or something I didn't see any Ti tubing that fit the bill. Also, I only saw one listing that specifically said the tubing was seamless.
> 
> Maybe if I was more specific it would be helpful. I make pens. The Ti would be the tubes and parts press into the ends. Do you think that I could bore close enough for a press fit or should I ream?
> . . .
> Mike



Titanium Joe has some 5/8" 3AL-2.5V seamless tubing with a wall thickness of .054", making the ID .517"; price is only $1.59/foot.

You should be able to press fit into a bored hole with no problem.


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## Mirage_Man (Oct 16, 2009)

bluwolf said:


> I don't have the lathe yet. But I already bought one of those misters like Will got. I'm hoping that will be a good compromise between brushing or squrting it on and flooding my garage with coolant. Any opinion on whetehr it will work with Ti?



I don't see any reason why it wouldn't work on ti.


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## bluwolf (Oct 16, 2009)

PhotonFanatic said:


> Titanium Joe has some 5/8" 3AL-2.5V seamless tubing with a wall thickness of .054", making the ID .517"; price is only $1.59/foot.
> 
> You should be able to press fit into a bored hole with no problem.


 
Thank you. I will look into that. The numbers I was using were approximate just to illustrate what I'm trying to do. I haven't actually taken accurate dimensions of what it is I need. And that would save a TON of drilling and boring, not to mention wear and tear on the tooling. But I do have a piece of solid rod Ti 12" long. And I really do want to learn how to machine it correctly for the experience. If I can find the right tubing I'll practice on the rod first.



Mirage_Man said:


> I don't see any reason why it wouldn't work on ti.


 
Brian, thanks for that. It's all pretty scary when you don't have a clue what you're doing.

Mike


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## bluwolf (Oct 16, 2009)

I just looked at the tubing at Ti Joe's after taking dimensions of the I.Ds and O.Ds that I need. I need .513 od and .378 id on one and .564 od and .458 id on the other. The .550 with .230 would work for the smaller tube. But to get .564 I'd have to start with .625 tube and none of them have enough wall thickness to get me below .458. Looks like I'd have to drill and bore the bigger tube at least.

Oh, and the tube is $1.59 an inch, wow.

Mike


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