Uncoated High Speed Cobalt drill in aluminum?

The degree angle at the front isn’t as important when it comes to aluminium. The smaller the angle the more aggressive the drill becomes. Eg if I had a high tensile bolt I would want a drill that is as sharp a point as I could get, like 90 or 60degrees. This is more to help break through surface skin quickly rather than have lots of engagement = friction = heat = work hardening the material and making it more difficult to drill.

When it comes to aluminium as a material any drill material will work (HSS, HSSE, Cobalt or carbide). The main problem as always is that aluminium being soft gives itself up for cutting very easily and is by nature very sticky. You are 100% correct with regard to built up edge. Surface condition of the drill bit is one factor that is very important. If a drill has a steam tempered finish (black) then this is enough for the aluminium to stick to and cause built up edge. Comparatively drills with a polished ground finish or have a coating are really good at preventing the material stick to the flutes of the drill.

The 2 main key factors that will help with drilling aluminium are flute angle and lubricant being used. A drill with a high rake/spiral flute is massively important to aluminium as it draws the cuttings away from the workpiece quickly therefore stopping it gumming up or clogging the flutes. Essentially it’s best for chip extraction whether drilling or milling. Drill flute depth is also critical for evacuation as more cuttings can fit in the diameter of the flute. Drills with high helixes like this are also referred to as worm pattern. Here is an example of a worm pattern drill with a gold coating: https://www.engineeringsupplies.co.uk/50mm-hss-e-goldex-jobber-drill-worm-pattern.html

With lubricant you shouldn’t use a standard cutting fluid or spray (and definitely not paste) as they are too thick and not viscous enough. These lubricants cause an obstruction for the chip evacuation and are more likely to clog the flutes. Best lubricants you can use are Paraffin or Templex cutting spray. In a worst case scenario WD40 is an ok alternative but still miles better than a standard cutting fluid.

In summary you need high helix angle drill with polished surface or with coating and using as light a lubricant as possible. Hope this helps :)

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