The Drill Dilemma: How to Choose the Right Drill Type

Imagine you’re standing in front of your machine, blueprint in hand, knowing that every hole you drill needs to be spot-on. The clock is ticking, the material isn’t forgiving, and the pressure to deliver a perfect part is mounting. Drilling might seem straightforward—until you’re battling tight tolerances, stubborn materials, and the relentless demand for efficiency. The right drill doesn’t just cut a hole; it dictates cycle time, tool life, and part quality. Get it wrong, and you’re looking at scrap, costly rework, or worse—a halted production line.

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With so many options on the market, how do you know if you’re using the best tool for the job? Let’s break it down and explore three primary categories of drills: indexable insert drills, replaceable tip drills, and solid carbide drills. Each has its place, and knowing which to choose can mean the difference between smooth sailing and a frustrating scrap pile.

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Hi

I am wondering if there is a quick and precise way of drilling on a sloped surface.

We manufacture hex nuts. We have some customers asking for nuts that have a through-hole drilled across two flats.

In essence we are drilling onto an EN36 steel surface sloped at 30 degrees to the vertical.


The drill diameter is 2.5mm

The drill depth is 10.5mm

I am wondering if I should make some sort of drill guide for this. Or perhaps I should come down with flat bottomed end mill, to produce a flat on either side of the hole, then drill it?

Some sort of solid carbide drill should do the job as it will need to be a 5D type, so 12.5mm length.

I need to be able to do this in a repeatable manner, for about pieces without breaking too many drills because they're about £20 each.

Any help would be appreciated. I do a job like that a couple times a year. I use a flat bottom endmill the same size as the thru hole to start a flat surface, then the same size ballmill to give the drill point something to follow.

I used to break drills randomly until I added the ballmill. 303 stainless, .062 holes.
I had to eff around with my peck depth so the drill wouldn't break on the exit side.

Already being done in large qty's there is a Jig made for them:
Heinrich Adjustable Cross-Hole Drill Jig Hand Operated - 905 - Penn Tool Co., Inc

Looks like this fixture only goes across the flats. OP wants to drill through one corner, a much harder thing.

I've done this before, made a drill guide. It was still touchy. If I were to do it again I would probably use an endmill to make a flat, then drill.

Regards.

Mike

Looks like this fixture only goes across the flats. OP wants to drill through one corner, a much harder thing.

I've done this before, made a drill guide. It was still touchy. If I were to do it again I would probably use an endmill to make a flat, then drill.

Regards.

Mike

No, you make the drill bushing bottom to fit, and adjust the location accordingly. You might make a bushing jig the angles and fits close to the part angle
and perhaps try a drill with an end mill point grind.

No, I have never tried this.

the drill with having a thinner web so not being as strong as an end mill, but with having an Od circular land so to position better to hole and bushing center.

and yes a special point would be an extra cost.

it is not uncommon that a Parabolic drill has a thicker web. You use something like this Safety Wire Nut & Bolt Jig Kit - Imperial

FWIW I shudder to thing how many 000's I've done over the years using such jigs, ....just take it very gently when starting the hole, sorta let the drill lips cut their way in first - oh and it's hard on drills, so buy plenty and don't bother with anything fancy dancy.

FWIW 2 - Once you've dialled yourself in, it'll take you longer to change the part than drill the hole.

You use something like this Safety Wire Nut & Bolt Jig Kit - Imperial

FWIW I shudder to thing how many 000's I've done over the years using such jigs, ....just take it very gently when starting the hole, sorta let the drill lips cut their way in first - oh and it's hard on drills, so buy plenty and don't bother with anything fancy dancy.

FWIW 2 - Once you've dialled yourself in, it'll take you longer to change the part than drill the hole.

Cheaper is better eh ?

Within reason?? very much so Doug (ordinary general decent'' HSS jobbers will do fine) it's the last sort of job on earth I'd use carbide drills for.

I was referring to the fixture, not the drills.

Your is "quick and dirty" and the linked I show is more versatile, and has a replaceable standard drill bushing for much longer life.

Within reason?? very much so Doug (ordinary general decent'' HSS jobbers will do fine) it's the last sort of job on earth I'd use carbide drills for.

He says they manufacture them. To me that says they're already setup in a CNC machine (guessing). Adding 2 operations with a spot and a drill that are done in a CNC controlled, precise, repeatable manner, adding a few seconds to a part inside the machine seems more efficient and likely cheaper than a 2nd op with a homemade or store bought jig on a drill press. But maybe that's just me. Given a good machine, and coolant through the tool, or at least some high pressure coolant, I'd wager you could get through of these on 1, maybe 2 drills. The drills are about $120 each. How much time did you save over breaking 6x $20 drills and the handling time to do of them on a drill press or knee mill?

I could be way off here, but those're my thoughts.

He says they manufacture them. To me that says they're already setup in a CNC machine (guessing). Adding 2 operations with a spot and a drill that are done in a CNC controlled, precise, repeatable manner, adding a few seconds to a part inside the machine seems more efficient and likely cheaper than a 2nd op with a homemade or store bought jig on a drill press. But maybe that's just me. Given a good machine, and coolant through the tool, or at least some high pressure coolant, I'd wager you could get through of these on 1, maybe 2 drills. The drills are about $120 each. How much time did you save over breaking 6x $20 drills and the handling time to do of them on a drill press or knee mill?

I could be way off here, but those're my thoughts.

Good thoughts Glasshopper me ole china, it really comes down to process requirements. I think I go with the fixture, maybe not the one you buy but you could make one pretty fast to hold 'x' number in a vise. The real problem with CNC is opening the GD door. 2 vises 10 per vise and you are making these with a 50 cent drill

Yes if I was doing one or two I would spot it with a carbide endmill and drill with a regular drill

I do a job like that a couple times a year. I use a flat bottom endmill the same size as the thru hole to start a flat surface, then the same size ballmill to give the drill point something to follow.

I used to break drills randomly until I added the ballmill. 303 stainless, .062 holes.
I had to eff around with my peck depth so the drill wouldn't break on the exit side.

Can one go straight to ball end mill ?