Spot Drill Life = 0

[PaulR]

I bought a 3mm solid carbide 90° spotting drill for steel which arrived yesterday but on very first use one of the lips broke off. This was on mild steel with the drill press set to a medium speed. I didn't use any oil thinking that such a small dimple wouldn't need it. Is this likely to have been the problem or maybe I made the spot a bit too big/deep (maybe 1mm across)?

[Jasonb]

I've HSS ones that have been going for several years on the manual machines and been using a 4mm carbide one on the manual mill where I also do all my drilling for the last year or so. I don't bother to lubricate the spot drills as it is such a small amount cut. The 3mm and 6mm carbide ones I use on the CNC are also fine after several years and tend to run a lot faster than the manual ones and again mostly dry..

Size of spot was fine or could be larger depending on what size drill was to follow

Were you trying to locate it in a punch mark? if the alignment was not right then that may have caused the hip. They are better used into bare metal so suit the lathe or mill more than a drill press unless you have away to locate the hole. Run at your bench drills highest speed as I doubt that is above what the drill can run at for the spot drill. Lastly if you have some runout on the drill press the carbide won't like that.

[ShopShoe]

I echo what Jason says above.

My spotting drills are also HSS and are lasting well on manual machines.

I have some carbide tooling, but have come to notice that it often cracks, chips, or breaks under less-than-perfect conditions. I don't think I could only have carbide (or only have HSS). I have to have a mix of tools for different situations.

I did early-on learn that the use of a spotting drill takes away the need for center-punching. If you must center-punch, it must be a good punch mark or it will stress one side of the tool more than another. (Having said that, I must say that I do sometimes use punch-marking, but it depends on the project and the material.)

ShopShoe

[Dave Otto]

A drill press really lacks the rigidity to be using carbide tooling.

Dave

[rklopp]

Dave O's got it. A drill press does not have practically any lateral stiffness. The rack hand feed has zero axial stiffness. Of course, the cutter may not have been the best, either, but even the best carbide spotter should not be used on a drill press. Carbide spotters can chip even in CNCs if the approach to the solid surface is wrong. After all, the cutting speed at the center is zero, which is totally sub-optimal, and stresses right at the center tip are very high.

[PaulR]

I've HSS ones that have been going for several years on the manual machines and been using a 4mm carbide one on the manual mill where I also do all my drilling for the last year or so. I don't bother to lubricate the spot drills as it is such a small amount cut. The 3mm and 6mm carbide ones I use on the CNC are also fine after several years and tend to run a lot faster than the manual ones and again mostly dry..

Size of spot was fine or could be larger depending on what size drill was to follow

Were you trying to locate it in a punch mark? if the alignment was not right then that may have caused the hip. They are better used into bare metal so suit the lathe or mill more than a drill press unless you have away to locate the hole. Run at your bench drills highest speed as I doubt that is above what the drill can run at for the spot drill. Lastly if you have some runout on the drill press the carbide won't like that.

Cheers Jason. It was into bare metal not a punched dimple. I haven't checked runout of the drill press but I'm pretty sure there will be a fairly significant amount. As I mentioned I had the belt in the middle position so speed was probably nowhere near high enough.

[PaulR]

I echo what Jason says above.

My spotting drills are also HSS and are lasting well on manual machines.

I have some carbide tooling, but have come to notice that it often cracks, chips, or breaks under less-than-perfect conditions. I don't think I could only have carbide (or only have HSS). I have to have a mix of tools for different situations.

I did early-on learn that the use of a spotting drill takes away the need for center-punching. If you must center-punch, it must be a good punch mark or it will stress one side of the tool more than another. (Having said that, I must say that I do sometimes use punch-marking, but it depends on the project and the material.)

ShopShoe

Thank you, looks like HSS is probably the way to go for me.

[PaulR]

Dave O's got it. A drill press does not have practically any lateral stiffness. The rack hand feed has zero axial stiffness. Of course, the cutter may not have been the best, either, but even the best carbide spotter should not be used on a drill press. Carbide spotters can chip even in CNCs if the approach to the solid surface is wrong. After all, the cutting speed at the center is zero, which is totally sub-optimal, and stresses right at the center tip are very high.

Thank you, all useful information and no doubt some contributing factors in there.

[petertha]

I distinctly remember going through 2 4mm center drills in quick succession on my lathe before realizing my tailstock was out. My bad. Not by much, but enough to snap the the center drill pip off real quick. The smaller the cutting tools, or more delicate the cutting surfaces, the quicker things go awry. If your spindle / bearings / drill chuck jaws are worn or otherwise not gripping the tool concentrically or axially to the rotating axis, that is likely the problem. HSS is more forgiving, but its not really dealing with the problem. You may be seeing swarf but chances are high its not the correct profile cut & misalignment is stressing the tool. I would make use of your broken shank, which is generally very accurate OD. Put it into the chuck & put a dial test indicator on it. Up near the jaws & down the shank. Release & regrip in a few different positions. See what it's telling you. You can get some very high quality carbide tooling from typical Asian suppliers in many different geometries for reasonable cost. I think we are benefitting by its industrial use predominance. HSS is great but its also seems to be getting harder to source. Good luck.

[john mills]

if that is a carbide spot drill it could be run as fast as your machine will go   even with hss it can be run fast if there is any thing loose it will chip.
i run them flat out even on a machine i used that had a 10000rpm spindle
john

[PaulR]

@petertha @john mills
Thank you. When I get 5 minutes I'll check the chuck with a DTI but I think it'll be bad. I also need to pay more attention to drill speed.

[Mike R]

I've broken the tip on a few 90° carbide ones as well.   90° tips are more fragile than the regular 118° or 135° tips on drills. 
Also, as many others said, the drill press isn't going to be friendly to carbide due to lack of rigidity and / or movement in the column etc.
HSS is perfectly capable in mild steel, will definitely be a more durable choice for drill press work. Alternatively, look at 120° tip spotting drills, they will be much more robust at their tips.

[PaulR]

I've broken the tip on a few 90° carbide ones as well.   90° tips are more fragile than the regular 118° or 135° tips on drills. 
Also, as many others said, the drill press isn't going to be friendly to carbide due to lack of rigidity and / or movement in the column etc.
HSS is perfectly capable in mild steel, will definitely be a more durable choice for drill press work. Alternatively, look at 120° tip spotting drills, they will be much more robust at their tips.

Thanks Mike, I've made a mental note of that. I think for now I'll stick with centre punch marks when using the drill press as there's most definitely lateral movement in the spindle.