Concrete is made of sand, rocks, fine particles, and rebar held together by cement. You can't cut chips out of a rock with a cutting edge, but you can break off chips by hammering it. So to drill it, the bit has to pound it until it breaks, then crush the pieces into dust that will evacuate through the flutes. So the optimum bit for concrete is a soft steel shank (so it's not brittle, because it's gonna take a pounding) with something very hard, tough, and especially not brittle at the business end, for example tungsten carbide in a softer metal matrix. The shape doesn't need a cutting edge, it's more like a chisel.

Some metals - you're most likely to encounter steel, especially stainless - are harder than (some) bulk concrete. Aluminium and copper are considerably softer.

It is absolutely possible to drill concrete without using tungsten carbide. People carved stone for centuries with bronze or steel chisels and a hammer. But these tools get blunt quickly. Carbide just lasts a lot longer.

Exactly why is the metal drilling bit not suitable for drilling into masonry as well so we end up with two different types of drill bits?

There's a type of tool that works on pretty much anything: diamond. It's very hard, therefore very brittle, so the whole tool is not made of diamond. Instead, diamond dust is deposited on the edge. It abrades off material, pretty much like sandpaper.

Drywall is pretty soft, and it's possible to drill it with steel bits easily. However it contains very hard particles which will abrade off the cutting edge, so that drill bit will no longer cut steel.

The machine executed a perfect 3D parallel cut on the opposite face of the neck, also, I have tried this process four times and the error is exactly the same each time. So no, it's extremely unlikely my machine is skipping steps, the error would be inconsistent.

Its extremely unlikely that the code itself is causing the issue, its very common however to have problems on stepper-motor/hobby type machines.

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Drill bits for metal use sharp edges to cut chips. If the bit is well sharpened, you can get nice continuous chips. The bit material has to be harder than the workpiece in order to cut it, and it also has to hold an edge. However, harder materials tend to be more brittle, which means the higher quality bits cut better but are also easy to break if you're not careful.

Hardness is a different story; I had to look at several sites to find comparisons. Mohs in the hardness scale for minerals. But in many decades of hardness testing of metals , I have never seen Mohs used for steel . But it is on the net. Very brief summary: cold rolled ( most common steel) is Mohs 4 ( most other metals and stainless will be lower). Steel knife blade is Mohs 6. Sand/quartz is Mohs 7. Limestone ( common concrete aggregate ) is Mohs 4. So in very general terms the hardness of concrete and cold rolled steel are about the same ( Mohs 4).

I've been looking at the problem forensically today and it appears that it's an issue with the Z-axis direction control; rather than gliding down into the cut, it's moving upwards. All ops thereafter are off axis.This would mean that there's a problem with the controller S/W (Mach 4) or the controller board. However, both of these perform perfectly apart from this particular strategy. I have informed the relevant vendors accordingly.In the meantime, I have replaced the 3D parallel strategy with a 3D pocket and I'll run the machine again tomorrow.

I have found that there are two different type of drill bits for the concrete/bricks and metal. Metal is so much harder than concrete and bricks. Therefore, from logic I would expect that the drill bit used to cut metal will have an easier time drilling into the wall. However, I have found that this is not recommended. In other words, only the masonry bit should be used for masonry. I have been told that using the metal drilling bit for masonry will actually damage the bit overtime or cause faster wear.

Bits designed for hammer-action on masonry are shaped differently. This is the main mode of drilling, where the tip bashes material from the bulk, and the flutes transport it out of the hole. In contrast cutting metal (or wood, or plastic) you're actually cutting. One needs to be strong, and is tapered to concentrate force, the other needs to be sharp. You'll see a similar difference between a cold chisel and a woodworking chisel.

Many metal-drilling bits are marginal for steel anyway - OK if you can get the job done fast, but if you're doing enough that they heat up, they'll blunt quickly. These are often used on wood and plastic as well. For small holes in brick, mortar, and plaster (softer building materials), an old metal drill bit will actually work quite well, without hammer action - but it will get even blunter fast.

Rock is crushed and scrapped; metals are cut. One bit type can not do both, generally. There is a range of harness and toughness in tungsten carbides so the carbide in a masonry bit is different from one in a steel cutting bit or a cutting tool in something like a lathe.

I'm using the 3D Parallel strategy to clear out material from a guitar neck model. I zero the Z-axis at the bottom of the material and run the machine.At some point the machine starts cutting fresh air so I stop the process. When I return the bit to XYZ zero, the Z axis has somehow gained 6.1mm from it's original zero position.

its actually very common for it to repeat the error of lost steps. There will be one line where it accelerates too fast, the controller is over buffered, or there is a mechanical issue at one node along your linear motion system. It could even be something overheating, and of course that will show up at the same location as it takes the same amount of time for the heat to rise.

But it's not the bulk you're interested in - it's the worst case components of that bulk. The aggregates in concrete can be really rather hard, and are more abrasive than the smooth surface you get in steel.

So a diamond core drill will make holes into pretty much anything, but it is a very slow process and it makes a lot of heat, so it needs to be water cooled... not the most practical when you want to hang a picture frame. It will also make holes through tile without fracturing it, which is nice.