Laser-Cut Parts With Tapped and Countersunk Holes

What tapping and countersinking add to a laser-cut blank

A laser cuts the profile and plain through holes. A thread and a cone are separate operations: tapping cuts an internal thread in a hole drilled smaller than the thread’s major diameter (source 3), and a countersink is a conical hole that lets a flat-head screw sit flush with or below the surface (source 2). Both are second operations on the cut blank, and both are called out on the print by the fastener they serve, not by a hole diameter. A 5052-H32 bracket with four 1/4-20 tapped holes and two 82° countersinks for #10 flat heads is a typical print, quoted as one part rather than a blank plus add-ons.

The profile carries a laser tolerance, and the quote states the tolerance used (laser-cut tolerances explains it), while each thread and countersink follows its own callout. The quote covers the whole part, cut, tapped, countersunk, finished and inspected, from one piece up. Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each. How to order a part that also needs a reamed hole or a milled face is on laser-cut, tapped and machined as one order; the machining itself is the subject of secondary machining. This page is about the holes.

Sheet thickness, thread depth and when to use a nut

Depth is bounded by the sheet, and the arithmetic starts with the pitch. Threads per inch is the reciprocal of the pitch (source 1), so a 1/4-20 has a 0.050 in pitch: 0.125 in aluminum holds two and a half turns of thread, 0.250 in holds five, and 0.060 in barely more than one. Write the thread as "thru" or with a depth, and if the fastener is a set screw or a stud that must bottom, say so. Name the material and thickness on the print.

Thin sheet is where tapping runs out. Self-clinching fasteners exist to give strong threads in sheet too thin to be tapped (source 7). PennEngineering’s FAQ gives 0.030 in (0.76 mm) or 0.040 in (1 mm) as the general minimum sheet for its self-clinching fasteners, and asks for a panel that is ductile and softer than the fastener (source 9). When a print asks for a 1/4-20 in thin aluminum, the quote says how many threads the sheet leaves and asks whether a self-clinching nut, supplied and installed to the print, is acceptable instead. That route is covered on hardware insertion, and a screw, bolt or stud to the print is quoted on custom fasteners.

Pilot hole, tap drill and thread series

A tapped hole starts as a hole drilled smaller than the thread’s major diameter (source 3). Wikipedia’s Unified Thread Standard table (en.wikipedia.org/wiki/Unified_Thread_Standard) lists the tap drills: #43 for 4-40, #36 for 6-32, #29 for 8-32, #25 for 10-24, #21 for 10-32, #7 for 1/4-20, F for 5/16-18 and 5/16 in for 3/8-16 (source 1).

Call the thread by size and series on the print, such as 1/4-20 UNC; UNC is the coarse series and UNF the fine one (source 1). The quote sizes the pilot for the tap, and a drawn pilot diameter that disagrees with the thread callout is a question on the quote, not a guess. Heat-intensive cutting, laser cutting included, alters the base metal next to the cut (source 4). Call the thread on the print as the finished feature, never as a pilot diameter alone.

Countersinks, counterbores and chamfers: the callout

A countersink is called out by the fastener and its angle. Inch flat-head screws to the Unified Thread Standard most often have an 82° head, and ISO metric ones a 90° head (source 2), so the angle on the print is matched to the screw it seats. A counterbore is different: it makes a flat-bottomed hole, as for a socket-head capscrew (source 2). Other alloys and plastics quoted on request. Name the grade on the print.

Write the screw size, the angle, and either the top diameter or the depth: "#10-32 flat head, 82° CSK" with the diameter sized to the screw’s head reads without questions. A counterbore gets the diameter and depth for the head it clears, and a chamfer on a hole edge gets a size and angle. Holes close to a bend can distort when the bend forms (source 5), and a countersink is a hole too, so on a formed part the callout goes on the flat pattern where the bend line is visible, and the quote notes any feature close to a bend. Brackets that carry all of these features are on brackets and mounts.

Order of operations, inspection and what to send

Cut first, tap and countersink second, finish third. Anodizing grows the oxide down into the surface and out from it, about 2/3 in and 1/3 out for Type II and half and half for hardcoat by the Aluminum Anodizers Council’s rule of thumb (source 10), and small threaded holes may then bind and need chasing with a tap (source 8). For powder coating, threaded through holes are usually masked with silicone pull plugs, and blind holes with silicone plugs or stoppers (source 6). So the print says whether threads are masked or chased clean after the finish. A finish called out on the print is quoted with the part, and anodizing laser-cut aluminum ordered here is quoted with the cut parts; the finish hub explains what each finish does. 5052-H32 and 6061-T6 are covered on laser-cut aluminum. For inserted hardware, PennEngineering’s FAQ advises plating the panel first and then installing plated fasteners, or installing unplated fasteners and plating everything together (source 9).

Every part is inspected against your print before it ships. If a part doesn’t match the print, it’s remade or credited. A thread plug gauge for checking the tapped holes yourself is quoted as its own part on custom gauges. To get a quote, send the profile as a DXF or STEP and a PDF with thread size and depth, countersink angle and fastener, and the finish, and name the material and thickness on the print. A sketch, a new sample part or photos are enough to start, and the quote adds a CAD line for drawing it up. Any file type is accepted through the quote form, and the laser-cut parts hub lists every operation that can ride on the same order.

Sources

All accessed 4 October 2026. Where a figure here differs from your print, the print governs.

1. Wikipedia, “Unified Thread Standard”: en.wikipedia.org (tap drill table, TPI as the reciprocal of pitch, coarse and fine series).

2. Wikipedia, “Countersink”: en.wikipedia.org (definition, 82° and 90° angles by standard, counterbore compared).

3. Wikipedia, “Tap and die”: en.wikipedia.org (tap drill size, a hole drilled smaller than the tap’s major diameter, through and blind holes).

4. Wikipedia, “Heat-affected zone”: en.wikipedia.org (heat from welding or heat-intensive cutting alters the base metal next to the cut).

5. Gerald Davis, “Design tips for sheet metal: Bend relief, small holes, hole distortion near bends, and minimum flange widths”, The Fabricator, 25 October 2001: thefabricator.com (holes near a bend line distort).

6. Andrew Oniszczuk, EPSi, “How to Mask Common Part Features for Liquid and Powder Coating”, Products Finishing, 1 September 2017: pfonline.com/articles/how-to-mask-common-part-features-for-liquid-and-powder-coating (silicone pull plugs for through holes, plugs and stoppers for blind holes).

7. Skip Ross, PEM Fastening Systems, “Fastening in a Clinch”, Machine Design, 22 November 2001: machinedesign.com/archive/article/21815540/fastening-in-a-clinch (self-clinching fasteners give threads in sheet too thin to be tapped).

8. Wikipedia, “Anodizing”: en.wikipedia.org (oxide grows in and out by equal amounts, half the oxide thickness added per surface, small threaded holes may bind and need chasing with a tap).

9. PennEngineering, “FAQ”, PEM: pemnet.com/resources/faq/ (general minimum sheet of 0.030 in or 0.040 in for its self-clinching fasteners; a ductile panel softer than the fastener; plate the panel, then install plated fasteners, or install unplated fasteners and plate everything together). Plain text because the publisher sells fasteners.

10. Aluminum Anodizers Council, "A Conclusive FAQ Guide for Anodized Aluminum": anodizing.org/anodized-aluminum-faq/, no date shown (under nominal Type II conditions the rule of thumb is 2/3 in, 1/3 out; under hard coat, Type III, half in, half out).