CNC Tapping Speeds and Feeds Calculator

The feed rates, speeds, taps, etc. Is all specific for each thread; they are not things you can fudge. If you need to tap threads on a CNC machine, you have to get them right, because if you dont, youll break taps, make oversize holes, etc. The spindle just goes where you tell it to go and doesnt compensate at all. Make sure your numbers is right before you start the cycle because getting them slightly wrong means broken taps or oversize hole.

From there, the rest of the math starts with surface speed, or the velocity at which the diameter of the tap is spinning as it cuts into the wall of the hole. This will be expressed in feet per minute and picked from a table according to the material being cut. Titanium has slower speeds, since you dont want to work harden it and have your taps break off.

Set the right speed and feed for tapping

Aluminum can run faster. From that number, you plug it into a common formula to convert to revolutions per minute. Then you multiple this figure by the pitch (or distance) of the thread, because you need the machine to pull the tap the correct distance for every revolution.

This way, it wont eat up the hole or cause issue. There’s a whole bunch of little units to convert so a calculation program takes care of it for you, and the machine doesnt have to wait around while you fiddle with numbers. The recommended settings change with Tap geometry: With a Spiral-Point tap, you can go slightly faster in Through Holes as chips are directed forward.

With a Spiral-flute variety, they draw up on the chips. Also note that they do nicely in Blind Pockets but need to be used conservativey in terms of speed. And then there’s the Roll-forming tap; which displaces rather than cuts the metal; so it runs at higher speeds in Ductile materials but not well in Cast Iron.

The bottom line is that choosing the wrong tap style raises Cutting Forces and results in defective part. So choose tap style by Material Category and Hole Depth. The second calculation is material properties plus the source of the liquids used to cut it.

A common mistake is that you can use the same cutting fluids on everything. While mild steel will cut well with conventional tapping fluid, stainless steel hardens rapidly when worked and needs to be heavily lubricated while also running at half the speed factor. Mist delivery vs. Flood application doesnt seem like much of a distinction.

But using flood actually lifts away chips better and lightens tap load. Remember that removing the chips has a direct impact on tool life. Because small taps less than a quarter inch have fragile shanks, you want to add an even greater safety margin and run them slower.

Bottom clearance of blind holes is a function of depth and reversal allowance. This means there has to be enough room in the hole for accumulated chips, the tap chamfer, and the synchronizing reversal action. Too little clearance results in increased cutting forces as it pulls out.

Too much clearance prolongs cycle time. Therefore, you’ll calculate this dimension with consideration of feed rate used and the depth of the hole, since the machine requires some fixed distance to reverse direction before it binds. Baseline values is listed in reference guides which may be adjusted once youve tested samples of parts.

The practical effect of your speed setting is how it will affect cycle time. Each small decrease in RPMs will add a few seconds to each hole and those few seconds can quickly turn into minutes when you are producing several hundred holes. The other side of speed is tool longevity.

Higher speeds mean shorter tool life and more unexpected stoppages. So you take your calculation as a starting point but then you pay attention to what happens during the machining process. If something changes in the machine like a little vibration or if the cycle seems to run longer than expected, time to tweak the numbers.

When it comes to different operations, there are some standard starting points called reference tables. These tables tell us what drills to use with which tap size when forming threads or cutting them. The tables detail the liquids we should use on tough metals.

And they tell us generally that a cut tap can be used at a higher speed than a roll tap in a given material. In other words, you use the table to get out of the danger zone without having to go too far off base because you dont have test data for the particular material. And they allow us to compare like materials if we dont have the test data for a certain material.

The key to successful tapping is knowing what the material can take and what your equipment will do. Lock the feed rate to the thread pitch and match the surface speed to the workpiece. Then use a safety factor that matches your willingness to lose a tap.

Keep those parameters consistent through like jobs and things stay under control. Lastly check the tap condition and thread quality at the end of every job. This assures continued life in the tools, less scrap, and allows you to keep the machine going uninterrupted.