Tips for Proper Use

Carbide Tool

Always choose a milling cutter which is suitable for the material which you process. Please notice our extensive descriptions of the tools and their fields of application in this catalogue. Withstand the temptation to use a tool which you have at your fingertips incidentally.

If your material should not be listed, please classify it according to its machinability (hardness). When working on brass for instance, you should rather orient on the parameters of aluminium than on those of stainless steel, whereas when working on construction steel, you should rather orient on stainless steel than on aluminium. Following, you'll find more tips for choosing and using our carbide tools and diamond tools.

You can also use the opportunity of our personal tool advisory service via phone or e-mail. If we should give you advice concerning the machining parameters, please provide us with the following information:

  • type of the material (with data sheet, where necessary)
  • the maximum thickness which you want to process
  • your intended tool diameter
  • basic information concerning your machine (manufacturer and model, rotational speed of the spindle and its power, how do you fix the workpieces?)

If you have already machined this kind of material, which tool do you use currently and what are your parameter settings? Finally, what are the problems?

Setting the machining parameters

In order to set the optimal values for lowering speed, dipping depth, feed rate and rotational speed, a number of factors are important:

  • what material is the workpiece made of
  • how is the workpiece fixed
  • type of coolant/lubricant
  • power/maximum rotational speed of the spindle
  • minimum/maximum feed rate of the CNC milling machine
  • stiffness of the machine

As there is a large number of parameters which influence each other, it is not possible to provide you with generalities concerning the machining parameters. Instead we would like to give you miscellaneous directions which points deserve closer attention. In any case you have to observe all safety and protective regulations of the machine.

When you set the operational parameters, you should approach from the safe side, so you should choose at first for most materials a lower lowering speed, dipping depth and feed rate - but keep up the rotational speed. During the milling process, you can further optimise the results by carefully changing the parameters. When machining plastics, please note that feed rates and rotational speeds which are too slow may lead to a melting of the material.

Dipping depth

dipping depth into different kinds of materials
Schematic illustration of the dipping depth into different kinds of materials from rigid foam over plastics and aluminium up to stainless steel. With increasing hardness of the material, the spiral of the flute becomes flatter and the cutting edge becomes shorter.

The dipping depth depends on the power of your spindle, i. e. only if your spindle has a sufficient power reserve, you may actually set the maximum dipping depth. In case of doubt: When you mill deeper slots it is better to remove in more steps less material than too much at once. Usually, it is also more economic to mill a slot in several steps with less dipping depth and at higher rates of feed than at once and accordingly slower. General guidelines for the relationship of dipping depth and cutting edge diameter:

  • rigid foam: up to 5-fold diameter
  • plastics (acrylic, etc.): up to 2-fold diameter
  • aluminium: up to 0.5-fold diameter
  • steel: up to 0.3-fold diameter
  • stainless steel: up to 0.2-fold diameter

Please observe also the load display of the spindle controller, especially when you are working with bigger tool diameters on difficult to machine materials like stainless steel. It should not exceed a load of 80 %, if possible. So you should approach the specified dipping depth only stepwise and always watch your spindle load.

Choice of the milling direction

milling in the counter direction
While milling in the counter direction, the tool moves against the material. While milling in the same direction, the tool moves with the material.

Contrary to the circumstances on heavy machining centres, the quality of both edges of the milled slot will never be exactly the same when you work on lighter milling machines. While milling in the counter direction, the tool moves – relatively regarded – against the material. The chip size becomes increasingly bigger towards the middle.

While milling in the same direction, the milling cutter moves with the material; the chip size is reduced again until the exit of the cutting edge from the material. The cutting edge runs in the counter direction as well as in most parts of the same direction against massive material. However, immediately before the exit, there is not much material left. So the last bit will often be rather torn off instead of being cleanly cut. Therefore the counter direction becomes smoother than the same direction.

However, this effect varies strongly with the characteristics of the material, the geometry and sharpness of the milling cutter and the machining parameters. Thus we recommend to mill internal contours clockwise and external contours counter-clockwise.

Cooling the cutting edge of the tool

For working on most kinds of materials it is necessary – or at least recommended – to cool the cutting edge of the tool with air or lubricant. This improves the surface quality and prolongs the endurance of the tool.

If cooling is not possible, the recommended minimum values for rotational speed should be adhered to; the feed rate, however, should not be set too slow. In this case, the heat dissipation will be made by the chips, otherwise you will risk that the material scorches.

Recommended coolants/lubricants:

  • plastics/acrylic
    dry processing with chip extraction or cooling with compressed air
  • aluminium
    spray lubricant ALU-N or minimum quantity lubricant WST 20
  • steel/stainless steel
    emulsion of spray lubricant AquaTec® and water or minimum quantity lubricant WST 20. For manual application also cutting oil spray Alpha 93

What to do in case of problems?

  • If especially plastics should melt, the reason may be that the tool advances too slow and produces too much heat. Please reduce the rotational speed and increase the feed rate at the same time.
  • If a milling cutter should become plugged, usually the chips have not been discharged quick enough. In such a case, the dipping depth and/or the feed rate have to be reduced. It may also help to use a different tool. Please note the hints on the number of cutting edges of milling cutters.
  • When working on critical materials like extruded acrylic, milling cutters with polished flute have proven to be well suitable. Here the chips can hardly stick to the cutting edge.
  • In case of a burr formation, you should increase the cooling. It could possibly become necessary to make also an additional finishing pass. Another possibility would be to increase the feed rate and to reduce rotational speed and removal rate at the same time.
  • If a tool breaks rather frequently, the removal rate is too high or the true running of the spindle is not exact enough. Please reduce in such a case the feed rate and/or the dipping depth and exchange the collet chuck for test reasons.
  • In case that your controller does not have a look-ahead function (point-to-point or look-ahead of just one vector), you should stay below the calculated maximum feed rate, especially when performing fine engraving works. For instance, if you engrave small fonts which consist of numerous little vectors, the machine always has to accelerate and slow down strongly again. Even if the controller calculates one vector in advance (e. g. vhf CNC 450), it cannot accelerate in a curve to maximum speed because each next but one vector will be “in the dark”. You have a similar situation when you drive with your car in the fog, when you can only see from one guiding pole to the next. So an optimum velocity along the path (as is the case with CNC 550 – 980) can not be achieved. The bearings of the machine and the tool will be exposed to strong forces due to the strong acceleration and brake applications. On top of that, the machine can “overshoot” due to the mass inertia. This effect becomes obvious in a bucking of the machine which leads to results that are worse on the whole. The speed advantage can be neglected. Please interrupt the output process as soon as the machine starts bucking and restart it at reduced speed.
  • If your CNC milling machine permits only lower rates of feed than it would be possible according to tool and material data (please note also the above-mentioned remarks concerning fine engraving works), you should reduce feed rate and rotational speed accordingly.