Solid Carbide Thread Mills

Tapping is quicker for standard sizes in free-cutting materials. Thread milling wins when a broken tap would scrap an expensive part, in tough materials such as stainless, titanium and hardened steel, in blind holes where the thread has to run close to the bottom, and on large or unusual sizes. One thread mill cuts any diameter above its own size at the same pitch, and you adjust the thread fit with a tool offset instead of buying another tap. Our thread milling guide covers the comparison in full.

Yes, as long as the thread form and pitch are the same. A full-profile tool ground for 1.5 mm pitch Metric will cut M12 x 1.5, M16 x 1.5, M20 x 1.5 and any larger 1.5 mm pitch thread, because the diameter comes from the circular path in the program. It will not cut M12 x 1.75, which needs a 1.75 mm pitch tool. The smallest thread it can cut is set by its cutting diameter, which has to fit in the drilled hole. Partial-profile tools go further and cover a range of pitches.

It depends on the thread form. Carmex tools for Metric ISO, UN, MJ and UNJ are made for internal threads, with separate MT tools for external threads, because the root of a nut thread and a bolt thread is a different shape. Pipe-thread tools (BSP, BSPT, NPT, NPTF, NPS and NPSF), Whitworth, PG and the 60° and 55° partial-profile tools cut internal and external threads with the same cutter. Each product page says which it is.

Full-profile tools have several rows of teeth and cut the whole thread length in one 360° orbit, so they give the shortest cycle for production threads. Mini tools have a short cutting profile on a slim neck and follow a helical path along the full depth, which keeps cutting force low for small threads, deep threads and thin walls. Partial-profile tools cut only the flanks, so one tool covers several pitches with the same flank angle. Drill thread mills also make the hole.

With helical interpolation: the tool moves round a circle with G02 or G03 while Z moves one pitch per revolution. For a right-hand internal thread, climb milling means starting at the bottom and working up with G03; a left-hand thread reverses the direction. Use cutter radius compensation so you can adjust the fit with an offset, and allow for the feed at the tool centre being lower than at the cutting edge. The Carmex Tool Wizard gives the tool, cutting data and CNC program for your thread.

Not for most Carmex thread mills. The hand of the thread comes from the direction of the helical move, not the tool, so the same cutter makes right-hand and left-hand threads with a reversed program. Some series are made to run with the spindle in reverse (M04), and where that applies it is shown in the specification on the product page. Check it before you write the program.

Yes, with the right grade. Most Carmex thread mills use MT7, a sub-micron carbide with a TiAlN multi-layer coating, for general work in steel, stainless and cast iron up to about 45 HRC. For harder work, MTSH and MTH are made for steels up to 62 HRC, and MTH also cuts titanium and nickel alloys such as Inconel. FSH uses the MT3 grade with up to 7 flutes for up to 65 HRC, and DMTH drills and threads hardened parts in one tool.

The same tap-drill size you would use for tapping, which gives the thread's minor diameter: 8.5 mm for M10 x 1.5 and 10.2 mm for M12 x 1.75, for example. The thread mill's cutting diameter must be smaller than that hole, and its cutting length or reach must cover the thread depth. Drill thread mills (MTD, DMT and DMTH) make the hole themselves, so they need no pre-drilled hole.