What is minimum hole size?
Minimum hole size (or minimum hole diameter) is the smallest hole a laser can cut cleanly in a given material and thickness. The safe rule of thumb is a hole no smaller than the material thickness, though a well-tuned fibre laser can often go to about half that on thin sheet.
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What does minimum hole size mean in fabrication?
Every hole starts with a pierce, and the beam then has to cut a tight circle while heat builds up in a small area. Below a certain size, the hole comes out tapered, rough or out of round, fills with dross, or doesn't cut through at all.
The limit depends on the material, thickness, machine and assist gas:
- 1x material thickness is the safe default. In 6 mm (1/4 in) plate, plan for holes of 6 mm or more.
- On thin sheet, a fibre laser cutting with nitrogen can often manage about 0.5x thickness.
- Thick plate cut with oxygen usually needs more than 1x, because heat builds up in the small circle.
- Narrow slots and cut-outs follow the same rule as holes.
How is minimum hole size used?
Estimators check hole sizes against thickness when a job is quoted, and programmers check again when it's nested. A hole below the limit is either marked with an etched centre point on the laser and drilled to size afterwards, or changed on the drawing after a conversation with the customer.
Tapped holes are where this comes up most. An M6 thread needs a 5 mm tap drill hole, and a 1/4-20 UNC thread needs about 5.1 mm (a #7 drill). In 3 mm sheet that's fine to laser cut. In 8 mm (5/16 in) plate it's below 1x thickness, so it's usually drilled.
Why does minimum hole size matter?
A hole that's too small for the thickness can fail on the machine, so the part gets re-cut or finished another way. A hole near the limit can be tapered or rough enough to cause trouble with fasteners or tapping. Neither problem shows on the drawing.
Small holes also take more time than their size suggests. Each one needs its own pierce, and holes below a set diameter are cut at a slower fine feed rate, so a plate full of small holes takes much longer than its cut length suggests.
Small holes in thick plate
Laser-cut holes in thick plate aren't perfectly parallel. The hole tends to be slightly wider at one face than the other, which matters for holes that take a press-fit pin, a bearing or a close-fitting bolt. Those holes are often cut undersize and then reamed or drilled to finish.
Many shops record a small hole limit for each thickness in their cutting parameters, along with the diameter below which the fine feed rate applies. Writing these down once saves every estimator from relearning them.
Minimum hole size and quoting
The quote is the cheapest place to catch an undersized hole. Spotted then, the drilling can be priced or the drawing changed. Spotted at the machine, it means rework and a phone call to the customer. Tempus Tools lets you set a small holes limit for each thickness and shows a warning on the part when a hole falls below it. Holes under the fine speed diameter are priced at the fine cutting rate and pierce time you set, so small features are charged at the speed they really cut.
Related terms
Price the drilling and tapping with the cut
Holes too small to laser cut get drilled and tapped instead. Tempus Tools prices drilling, tapping and countersinking as secondary processes on the same quote, and warns you when a hole is below the small hole limit you've set.
FAQs
What is the minimum hole size for laser cutting?
As a safe rule, no smaller than the material thickness. A well-tuned fibre laser on thin sheet can often cut holes about half the thickness, while thick plate cut with oxygen may need holes larger than the thickness.
What is the smallest hole you can laser cut in 3 mm steel?
Plan on 3 mm (1/8 in) as the safe minimum. Many fibre lasers cutting with nitrogen can manage about 1.5 to 2 mm, but check with the shop that will cut it.
What happens if a hole is too small?
It can come out tapered, rough or out of round, fill with dross, or fail to cut through. It then has to be re-cut or drilled.
Can you laser cut tapped holes?
The tap drill hole can be laser cut if it's above the minimum hole size for the thickness, and the thread is then tapped as a separate step. Below the limit, the hole is drilled instead.
Does minimum hole size change with thickness?
Yes. The thicker the material, the larger the smallest hole that can be cut cleanly.