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by Peter Brett - October 2005
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Two Hole New Designs
I admit that I find their demonstrations persuasive, if not conclusive.
Also, whenever I have had a Marcrist diamond cutting product to try out, I have never been short of builders willing to “borrow” them from me once the reviews are completed. That sort of speaks for itself.
By the time you read this two new types of core bits will have been launched by Marcrist in the UK. Designated the DCU750 series and the DCU550 series they have between them many design innovations that are the result of continuing development and design improvements. In fact, both series have patents applied for.
I will start with the DCU550 series, because it has some new features that I found intriguing on a more “normal” looking core bit.
I have always found Marcrist core bits to be well engineered, and this series is no exception. They run very true and the screwed adaptor is robust and cleanly made. It would probably take a very dedicated and pernickety user to examine the detailed differences between the DCU 550 and run of the mill bits, but they are significant and allow a fast start and smooth finish to cutting jobs.
The segments on the core bits are first of all “raked”, meaning that the leading edge of each segment is slightly higher than the trailing edge. Since less initial contact with the surface to be cut means that there is less initial friction, the cut is able to be established quickly. After watching Mark Essex, Marcrist’s Northern Regional Sales Manager, start drilling a core in an engineering brick with seemingly no effort, I expected to experience at least a bit of difficulty as the segments found their cutting trail.
OK, so I didn’t make it look as easy as he did, but I didn&Mac226;t struggle at all. The core bit was extremely well behaved during the starting phase, and then I just needed to hold it in place with some downward pressure to finish the hole.
The second innovation to consider is that top edges of the segments are shaped like inverted rooftops. A sharper edge here creates a smaller friction area for starting a cut. And logically it follows that a sharper leading edge will make it easier for the thicker cutting edge that follows behind. Rather like drilling a small hole in a hard piece of steel and the enlarging it by drilling a bigger one. By then relieving the cutting edge with a subtle chamfer and a concave bulge, making a space, the dust created can be whisked away if you are lucky enough to have dust extraction. This also allows the final core to be coaxed out of the bit with very little effort. After drilling several cores in some of the hardest grade industrial bricks I have ever seen and a 30mm thick piece of granite, the cutting edges had not lost their profiles and the diamonds, were, if anything, standing out more visibly. It is clear to me that there was a great deal more use to be got out of these core bits.
Since I hope to be moving house soon, and with a list of improvements to be made on the new house growing by the day, I intend to hold onto my test samples!
The DCU750 series has a different design intention behind it. It is aimed at increasing the speed of cutting of the average core bit by between 30% and 50%. To achieve this, the designers have come up with a serrated diamond coated edge that really does have a very good initial bite. There is more than a passing resemblance to a row of sharks teeth! Like the DCU550 series, it too is very easy to start, and unlike some others, Marcrist’s core bits don’t seem to need guide bits. After the initial excitement it becomes a bit “boring”, because all you have to do then is apply pressure to finish the hole. Timed demonstrations have borne out Marcrist’s claims about the speed of cut.
But longevity is also an issue. Usually diamond segments that cut faster tend to wear quicker, and this is the trade-off that most users expect. By making the actual diamond containing segments deeper, (a full 8.5mm) a longer service life is assured. With a similar double concave design to the 550 series, de-coring is easier too.
Both the 550 and 750 series of core bits are available in sizes from 22mm to 162 mm. This covers the range for most domestic and industrial plumbing, and I bet that the average plumber doesn’t have to drill cores in engineering bricks or granite. Most face bricks and breeze blocks would succumb to these core bits without much struggle.
One of the things that I find slightly mystifying, and yet also encouraging, is that Marcrist offers a money back guarantee with these core bits. Some marketing people would cringe at the potential risk, and yet Ian Bannister of Marcrist tells me that they have very few end users taking up this offer when Marcrist has offered it on other products because the customers are usually totally satisfied. Personally, I like the fact that Marcrist is a privately owned UK company that exports 50% of its production. Marcrist shows that producing diamond based cutting and drilling tools in an expensive western business environment can be done, and that quality and value for money can go hand in hand.
Independent Review by Peter Brett
Airstream Communications