This guide provides some basic rules and tips for successfully producing forms using the rotary broaching process.
Rotary broaching requires two components: a rotary broach tool holder and a broach. Rotary broaching can be performed in almost any turning center: lathe (manual or CNC) or mill. The only difference is that in a lathe the tool holder is stationary and the part is turning whereas in a mill, the rotary broach tool holder is rotated in the machine spindle and the part is stationary.

The Poliangolar tool holders have completely sealed bearings. Therefore, there is no need for constant greasing.
Poliangolar tool holders are completely adjustment-free. Alignment between the rotary broach to the centre of the workpiece is extremely important. Broken rotary broaches or uneven form configuration can result from improperly centered broaching. As long as the toolholder block on your turret (or machine spindle on a mill) is centered with your workpiece, simply insert the tool holder and clamp it down.

Fluids play a minor role in rotary broaching being, generally, a low heat operation. However, the use of cutting oil is recommended as an alternative conventional water-based coolant.

Pre-turning the diameter of the workpiece is required for external broaching.
The pre-turned diameter must be smaller than the major diameter of the broach.
It is recommended to turn the workpiece diameter to the smallest allowable diameter so the broach will clear on the major diameter. Allowing for more clearance will reduce the required broaching pressure and increase tool life.

A back chamfer or undercut will allow swarf to break cleanly.

With difficult machining, it may be useful to use tools with a specific coating, which a specific coating, which in most cases can be TIN-PVD. The use of one of these coatings is recommended as the tools become more resistant to the heat produced by the machining and to wear and as a result extend their life.
The TIN-PVD coating reduces wear and the tendency for seizing and produces an anti-adherent effect during machining, and is recommended for soft materials such as aluminium alloys.
The Poly x Inox coating can also support grater thermal loads and better results have been obtained when machining abrasive (superalloys, cast iron) and harder (steel alloys, stainless steel and titanium) materials.

The most frequent causes of breakage or chipping of the tool edges are:

• Imperfect coaxiality with the part to be machined, in this case the tool is not damaged when it penetrates the pre-hole but in the succesive return phase, when the bending action due to the imperfect centering stops.
• Insufficient pre-hole depth therefore the material removed during machining, and which is pushed downwards, does not permit the tool to reach the preset depth and therefore the edges are stronlgy strained against the build bottom.
• Twisting of the machining when the pulling lever is not used, and also in this case the breakage occurs when returning, as the edges are located in a different position than when machining started.

When machining square profile keep in mind that the quantity of material to be removed is more than double the amount for a hexagonal slot, for this reason the machine is stressed more, therefore these procedures normally require a very rigid and powerful machine.
When possible, and especially with a square greather than 20mm, a few masures can be implemented:

• The pre-hole must always be as large as possible.
• If the square section (S) must have four complete surfaces, the quality of material to be removed can be reduced by first making small holes (d) in correspondence of the four edges and then the central pre-hole (D).
• When possible round of the edges in order to remove the sharp edge, which is the most fragile point of the tool and also the section that tends to break or chip first. In this way, most of the material is removed and the slot can be made, also quicker, and with a better finish.

Of course, the same considerations apply to large sized hexagonal slots (usually above 30mm).
Taking the above into consideration, any polygonal slot can be machined such a stellar, grooved or involute, always providing that the quality of material to be removed lies within the permitted limits of the machine or machning times.