HMT's 10 steps to halve the price of your hole broaching

Posted by Piers Crane on

 Here are the most effective ways to increase the productivity and reduce costs for magnet hole broaching. 

1. Still using HSS annular broach cutters? Making the switch to Carbidemax TCT cutters will see your cost per hole go down dramatically.

Up to 4X longer life per cuttter. In 12mm structural steel, HSS cutters will average 100 holes before the teeth are blunted to the point of compromise. A Carbidemax TCT broach cutter will cut in the region of 400 holes. With the Carbidemax 40 range only costing £1 per 1mm diameter (example, 18 x 40mm cutter costs £18) There is no longer any cost downside to purchasing the higher quality TCT cutters.

4X fewer cutter changes and reduced breakage rate. A cutter change will normally take around 1 minute, and often a lot longer than that, so again the job is being completed quicker and cheaper. Not having another cutter out on site can cost a day's work for a site team sometimes, and this will be 4X less likely to happen if they are using Carbidemax TCT instead of basic HSS annular broach cutters.

15% Faster Cut. You will be paying an operator to cut the hole. With the faster cutting speed the job is not only completed quicker but your labour costs have decreased by 15% during the drilling time.

2. Centre Punch

Especially for smaller diameters of broach cutters like 12-16mm, it is highly advised to set a strong centre dot with a centre punch. Align the tip of the pilot pin exactly with this centre dot. This will give a easier start to the cut, which will reduce the wear on the teeth and give a longer overall cutting life. This is most critical on the smaller diameters already noted, but advisable on all sizes of broach cutters as well as Carbidemax holesaws

3. Ventilate deeper holes during the cut

For any holes to be made in metal thickness greater than 25mm, it is recommended to follow these steps. Also, if a greater resistance or chattering in the cut is felt. This may be down to work hardening or a harder inclusion in the material. Note. Do not turn off the magnet during this process, to make sure the drill remains in exactly the same position.

  • A. Exit the hole while the cutter is turning
  • B. Remove as much swarf and chips as possible
  • C. Fill the cut in progress with lubrication oil
  • D. Start the machine and enter the cut again with the cutter turning
  • E. Repeat as necessary when chips build up in the cut again.

4. Slides

Most magnet drills work on a rack system with adjustable slides. These are designed to wear over time and normally will have grub screw adjustment to tighten these up again. Test the magnet drill by winding the motor up to the top of the slides and let go. if it slides down quickly it is too lose and needs tightening up to the point it can support the weight of the motor without holding the handles. If a slides are too loose, the cutters can be banged onto the surface of the metal at the start of the cut, damaging the cutting teeth. Also the cutter will be shaking and not cutting true, cutting too much metal. Slides should be checked and tightened up on a monthly basis, or weekly if it is intensive use on large or deep holes. It's advisable to have magnet drills serviced at least once a year, as they get a tough life.

5. Lubrication

HMT advises continuous cooling during the entire hole cut. The larger and deeper the cut, the more critical the application of coolant. Watch the chips to make sure they do not start to turn blue or discoloured with heat. Specialist coatings are available for cutters if there is a special application where coolant is not allowed, e.g. in a high purity environment.
  • A. Horizontal down drilling - Soluble oil applied either through the arbor if possible or by spray bottle to the cutting face
  • B. Positional and overheard drilling. Depending on the application use a good quality spray lubricant or cutting paste to ensure the cut does not run dry.

6. Check the Magnet hold

If the magnet is not holding at full power, the downward pressure of the cut will start to lift the drill away from the surface of the material. This will cause issues as the cut angle will not be true, and cutters can break, or the cut will take longer. In the worst case scenario the magnet hold can release.

Reasons why the magnet may not be holding at full power, and suggested fixes, are listed here.

  • A. Thin material. Steel below 10mm will not give enough magnet hold. Consider using a permanent magnet magdrill or clamping a thicker plate to the work surface. VacBase can also be used.
  • B. Swarf and chips between the magnet and the material. Take some time to clean the magnet and surface before starting a new hole. The MagWand cleaning tool can make this easier
  • C. Excess paint or rust on the working surface Clean and prepare the working surface of the metal to be drilled. Alternatively a new plate can be clamped on, or a VacBase used.
  • D. Stainless or Non-ferrous materials that are non-magnetic VacBase can be used in these applications. Alternatively a portable drilling solution can be specced, like Carbidemax Holesaws in a drill chuck.

7. Optimise machine speed for the cutter

Each different size of broach cutter has a different optimum cutting speed. Check the speed of your magnet drills to see how this compares to the RPM that the machine is set to. Often we find operators using variable speed machines that are set too fast or too slow for the size of cutter being used. Also bear in mind that Carbidemax TCT Broach Cutters can safely be run at pro-rata twice the speed of the equivalent size of HSS broach cutters, which gives a 15% faster cut (on average) . If you would like assistance to work out the best settings to use, please send the following information. Speed and recommended RPM data is available on request.

  • A. Size and number of holes needed
  • B. Thickness of metal
  • C. Type of metal
  • D. Positioning (eg horizontal down, overhead vertical up)
  • E. Access (are there access issues which will limit the size or type of the machine that can be used)

8. Stack Cutting multiple layers

One issue that adds time and expense to the job is when multiple layers of material are needed to be broached, so the cutter has to pass through different layers, creating a new 'slug' each time. With a standard cutter, this slug will become stuck if the cutter is not withdrawn after each layer and the slug removed. This is because the normal teeth shape on a cutter results in an inverted 'Top-Hat' shape of slug, and the teeth are not designed to keep on cutting another layer. The Carbidemax Stack Laminate cutters are designed with a special teeth geometry

9. Feed and pressure during the cut.

To maximise the life of the broach cutter, it is highly recommended to apply the feed very slowly and cautiously during the first 1mm of cut. Once regular swarf chips are appearing then apply normal feed pressure. This will significantly extend the life of the cutter. If insufficient feed/pressure is applied, the teeth will rub instead of cut, generating too much heat and risking work hardening. Also if too much feed/pressure is applied by leaning on or extending the handles, the same will apply. This will show in blue or discoloured swarf and chips. The right feed/pressure is being applied when continuous swarf is coming from the cut, and it is a clean silver colour.

10. Access & using the right machine.

The operator will normally try to complete the hole cutting task with the machine to hand, which is understandable. However, often this is not the best machine for the job in terms of speed or capacity. Now that specialist machines are readily available to hire, it is often more cost effective for fabricators to hire the best unit for the job. An example of this is in tight access applications, where a low profile, (right angle) magnet drill is only needed occasionally, or larger cutters and countersinks that have a slow recommended RPM. Hiring the correct machine will often result it better life from the consumables, and a quicker completion of the task.


Older Post Newer Post


Scroll To Top