The optimum speed for a given diameter of core barrel will be different when used in asphalt than it is when used in concrete.

Speeds and feeds

Asphalt 6 metres/sec.

Concrete 3 metres/sec.

for example:-

If you are drilling a 107mm diameter core barrel through concrete you would need the following calculations for optimum coring performance. A 107mm barrel circumference is 335.98mm  (π x Diameter). We know that 1m = 1000mm. So with one complete rotation of the barrel we know that it will travel 335.98mm, but we need to be traveling at 3m (3000mm) and at every second for concrete. 3000mm divided by 335.98mm = 8.929102922 which we can round off to 9 so the barrel needs to be rotated just slightly less than 9 times in order to travel 3000mm (3m) and every second if we want the best performance in concrete. We also know that theres 60 second in 1 min, and we need to be able to rotate the 107mm diameter barrel 9 times every second. 60 x 9 = 540. So the optimum for this 107mm barrel in concrete is 540 RPM .

Our Magnum 5+ Handheld Hydraulic core drill is perfect as it runs a 600 RPM at 20/ltrs per min

If the core bit is rotated too quickly the core bit will stop cutting after the barrel has reached a depth of more than 50mm. The core barrel stops cutting because whilst the diamonds have fractured down the matrix surface material (segment bond) has not worn away, so the new layer of diamonds have not been exposed to the cutting surface. This is known as 'Glazing".

A nicely ‘Dressed’ segment

A nicely dressed diamond segment showing diamonds standing proud of the matrix with supporting tails of metal behind each diamond. NB The tails will point opposite to the direction to rotation.

A badly ‘Glazed’ segment

A segment showing only a few diamonds standing proud of the surface. Most of the remaining diamonds are not proud and therefore not cutting.