Drilling holes in steel

[bcp]

I often see instructions for large holes that say to gradually increase drill bit sizes to reach your target size. For example, "For a 5/8 hole, drill 1/4, 3/8, 1/2, then 5/8." I used to do this but often ended up with chipped corners on large bits.

Then I tried the less often recommended method of drilling about a 1/8 pilot hole before using the final size bit. The small pilot hole lets the large bit cut without having to force the non-cutting center portion through the steel, and the full width of the cutting edge is used instead of just the corners. This works better for me.

How do you do it?

Bruce

 

[frugalangler]

I often see instructions for large holes that say to gradually increase drill bit sizes to reach your target size. For example, "For a 5/8 hole, drill 1/4, 3/8, 1/2, then 5/8." I used to do this but often ended up with chipped corners on large bits.

Then I tried the less often recommended method of drilling about a 1/8 pilot hole before using the final size bit. The small pilot hole lets the large bit cut without having to force the non-cutting center portion through the steel, and the full width of the cutting edge is used instead of just the corners. This works better for me.

How do you do it?

Bruce

I use:
the less often recommended method of drilling about a 1/8 pilot hole before using the final size bit. The small pilot hole lets the large bit cut without having to force the non-cutting center portion through the steel. This I consider a BIG center-punch to keep the large bit from wandering and starting to cut.

 

[CalG]

The BEST is to drill with a pilot that just equals the center web of the final drill bit to follow.
nothing wrong with an 1/8th inch for most work, but if you need to poke an inch and a quarter hole through 3.4 inch plate, a larger pilot will help. Creeping up on a hole is foolish, especially in thin stock. Grabby and you end up with a tri-lobe hole. FOOLISH, I don't know where such nonsense originates.

Here is a tip when drilling thicker stock. Set the pilot drill dept to just NOT break through the far side of the material. Then Fill the pilot with your choice of cutting oil or wax. There will always be some lube available where it's needed and all won't be carried away with the swarf like when the lube is brushed on from above. (Do that too if drilling is heavy).

 

[Curly351]

If drilling with a press and the bit is sharpened correctly 3/4 would work with no pilot, how ever if drilling by hand you will definitely will need a pilot hole.

 

[Spanner]

The BEST is to drill with a pilot that just equals the center web of the final drill bit to follow.
nothing wrong with an 1/8th inch for most work, but if you need to poke an inch and a quarter hole through 3.4 inch plate, a larger pilot will help. Creeping up on a hole is foolish, especially in thin stock. Grabby and you end up with a tri-lobe hole. FOOLISH, I don't know where such nonsense originates.

Here is a tip when drilling thicker stock. Set the pilot drill dept to just NOT break through the far side of the material. Then Fill the pilot with your choice of cutting oil or wax. There will always be some lube available where it's needed and all won't be carried away with the swarf like when the lube is brushed on from above. (Do that too if drilling is heavy).

Great tip Cal!

Yes. Small pilot followed by final full-size drill.
The split-point (four facet) drills are great and work well in the smaller sizes (up to 8mm imo) for a single pass drilling.

For drilling the key is down-pressure. Insufficient pressure on the drill allows the drill bit to skitter around and not cut properly. Ideally you want to see spiral twirls of swarf curling away from the hole. The average home-owner is unable to maintain sufficient down-pressure to make this happen. Overheating of drill bits is common as a result.

A Drill Press enables weight to be applied and the bit to cut correctly, creating swarf.

Funny how a two-spiral drill bit creates a tri-lobal hole when it grabs and skitters. Funny 'peculiar', not funny 'haha'.

 

[franklin2]

I often see instructions for large holes that say to gradually increase drill bit sizes to reach your target size. For example, "For a 5/8 hole, drill 1/4, 3/8, 1/2, then 5/8." I used to do this but often ended up with chipped corners on large bits.

Then I tried the less often recommended method of drilling about a 1/8 pilot hole before using the final size bit. The small pilot hole lets the large bit cut without having to force the non-cutting center portion through the steel, and the full width of the cutting edge is used instead of just the corners. This works better for me.

How do you do it?

Bruce

The 1/2" in the above example is too close to the final 5/8 size. That does tend to chip the outer portion of the 5/8 bit(or whatever size you are using). I agree with what someone else said, the last pilot hole drilled should put you somewhere in the center of the final size drill bit cutting area. I don't drill all those pilot holes either, I am in too much of a hurry. For the 5/8 example I would start with the 3/8 and then go to the 5/8, done.

 

[mark in portugal]

It depends on available tools, material to be cut, degree of accuracy required.

I have a heavy drill press and use it whenever possible. I have used a handheld drill for a 1" hole through steel, but I didn't like it. I had a 3' handle on it and someone holding that so it couldn't torque away from me.

Even with the drill press, there's a limit. for 30mm [1-1/4"] holes through heavy plate, I drill 9/16" [ish] first because my machine can't handle the torque of the bit otherwise.

When the bits are new and factory sharpened, they cut fairly straight but after hand held re-sharpening mine usually cut tapered holes. A final pass with a slightly larger bit [even if unevenly sharpened] solves the problem.

 

[chim]

A pilot 1/3 the size of the final hole works OK for me.

 

[jenkinsph]

I bought these drills for my present project to drill for bushings mounted in box tubing with 1/4" wall. Works well with less torque needed to turn them. Bought these in 1 3/8" down to 7/8" sizes very satisfied with the results after using these to drill holes in tubing and flat bar. These will cut up to 1" deep but other depths are available.

This is the 1" size.

 

[Big Barn]

I bought these drills for my present project to drill for bushings mounted in box tubing with 1/4" wall. Works well with less torque needed to turn them. Bought these in 1 3/8" down to 7/8" sizes very satisfied with the results after using these to drill holes in tubing and flat bar. These will cut up to 1" deep but other depths are available.

This is the 1" size.

I have that style also. I use mine mostly for under 10 ga.



Terry