— FAQs —

What materials can SheetCNC cut? SheetCNC is designed to cut hardwood and softwood – including solid timbers, full-size birch ply, red-and-white ply, shuttering ply, and MDF including MR grade. SheetCNC can also cut many other materials including rigid PVC, polycarbonate, HIPS, HDPE, expanded PVC boards, and rigid foam sheets up to a thickness of 100mm. At the other end of the size scale we’ve used SheetCNC to etch and drill tiny double-sided electronic printed circuit boards. So if it’s timber or plastic and it fits on the machine bed, you can almost certainly cut it with SheetCNC.

What machining speeds and depths, realistically, can be used? Even when using low-cost economy carbide tooling, typical machining speeds in timber products are around 3000-5000mm/minute. For maximum precision the depth-of-cut should be limited to no more than 6mm per pass. But for rapid rough prototyping we’d use passes of 10mm – and sometimes more. Recommended maximum speed of rapids is 12000mm/minute to reduce risk of machine damage in case of accidentally driving the axes to limits. But higher speeds are attainable. Our more expert users run SheetCNC at 18000mm/minute rapids.

What size cutters are recommended? SheetCNC’s ER20 collet-chuck can accommodate up to a 13mm shank. But, typically, the largest cutter used on a large-format machine (except for facing jobs and 3D work) will be 1/4″ CED. Here’s a list of our go-to favourite cutters for use on SheetCNC:

  • Economy 6mm CED, 25mm CEL, carbide, single-flute upcutters. Ideal for cutting-out parts in 25mm boards. We run these at 3-10mm depth-per-pass, about 2000-5000mm/minute feedrate and around 0.15-0.25mm chipload in hardwood ply and MDF. Typically these cost £2-5 each. Longer CELs are available but those can be extremely noisy due to their reduced torsional stiffness.
  • Economy 1/8″ CED, 18mm CEL, carbide, single-flute upcutters. Good for prototyping parts from 18mm/15mm/12mm/9mm boards. Advantages over the 6mm cutters are that they are even cheaper (~90p each) and run even more quietly. We work these quite gently at 2-4mm depth-per-pass, about 4000mm/minute feedrate at 24000rpm. If these little cutters are pushed any harder they just snap. Longer CELs are available but their length makes them so fragile that they are virtually unusable.
  • Economy 1/8″ CED, 25mm CEL, carbide 2-flute downcutters. Superb cutters for slicing up thin plastics and thin ply which might otherwise snatch if cut with an upcutter. They also leave a very clean top surface on the cut. Somewhat stronger and stiffer than the 1-flute upcutters. Typically £3-5 each.
  • Economy 1.5mm CED, 10mm CEL, carbide 2-flute ball-ended upcutters. Great for shallow scribing of text onto parts at high cutting speeds. Typically £2-3 each.
  • Economy 0.2mm 10-degree carbide vee-cutters. We use these for etching the occasional printed circuit board (together with some 0.8mm dia carbide drills for the pin-holes). They’re even better at scribing onto ply and MDF than the 1.5mm cutters, but can’t handle more than about 400mm/minute feedrates. Typically ~50p each. At this price, assume the CED is only nominal.
  • Specialist 1/4″ CED mortice-style carbide compression cutters. Ideal for MFC (melamine-faced chipboard) and other jobs where a very fine surface finish is required on both top and bottom surfaces. Mortice-style cutters have shorter up-cut, allowing modest depths-of-cut to be used while still engaging the down-cut into the top surface during the first pass.
  • Jobber HSS twist-drills up to 6mm. Drilling in MDF and ply up to about 6mm dia is straightforward. Beyond that diameter the low rpm (and high torque) demanded by the drill-bit can’t be attained on the 2.2kW spindle. But, in any case, if larger holes are required they can simply be machined using a 6mm dia carbide cutter.
  • Jobber HSS twist-drills up to 13mm. We use these as budget reamers for any ultra-precise holes that are required in a job, after machining the hole deliberately undersize.
  • Facing cutter 25mm CED 3-flute. We use a Whiteside 6210 for rapid surfacing. A 6220 would work just as well but is costlier.
  • 2-flute ball-end cutters up to 13mm CED, for 3D work. We very rarely undertake 3D work ourselves so we’re not in a position to recommend specific 3D cutters. One of the limiting factors in 3D work is the availability of cutters sufficiently long to reach into the required pockets without the chuck fouling the workpiece. There is a trade-off between cutter rigidity and cutter CED – long, thin cutters being further constrained by the risk of overspeeding.

There is little benefit in using larger cutters for 2.5D timber work other than those listed above: cutting-out hardwood using large CEDs would only be likely to push the machine beyond its reasonable working limits resulting in either poor quality output or a failed job. Large, long cutters would be suitable mainly for 3D work and for 2.5D work in lighter materials, such as foam boards.

Can SheetCNC machine metals? The best short answer to that is… no. The full answer is that – if you already have a SheetCNC machine for cutting timber – then we wouldn’t discourage you from also experimenting with drilling – and making occasional light cuts – in aluminium and brass. (See our videos.) We have carried out a few very modest 2.5D metal machining jobs ourselves with SheetCNC. But, really, if machining metal is one of your reasons for buying a CNC machine then we wouldn’t recommend SheetCNC for you. By-and-large brass cuts quite well, and 6082T6 aluminium (which is usually 6mm+ thickness plate) can be machined too. Thinner aluminium – normally 5000-series – will bind badly without a constant flow of coolant, making it impractical to work on any CNC machine that doesn’t have a flood coolant facility. For cutting 6082, use a 2-flute HSS (not carbide) 6mm CED cutter at 8000rpm with a feedrate of 750mm/minute. Toolpaths must be designed carefully to limit depth-of-cut to no more than 1mm. Such a set-up will dry-cut 6082 without binding, provided that the workpiece is large enough to dissipate the heat. But even so, don’t expect to obtain anything like the usual fine tolerances that can be achieved in other materials. And do expect somewhat higher wear-and-tear on the machine’s mechanicals. So we’ll repeat what we said earlier: SheetCNC is not the machine to buy if you really need to be machining metal.

Can SheetCNC do 3D work? Yes. The new Mk3 version is fully capable of 3D work up to the limit of the Z-axis.

How much space does SheetCNC occupy? The full-sheet machine is 1.65m wide by 2.9m long. The half-sheet machine is 1.65m x 1.65m. In addition you’ll need space to move around the machine, plus a nearby shelf or small worktop area for the controller. Several of our customers have positioned their SheetCNC tight into the corner of a room, so that they have access to only two of its sides. This is not ideal but it is a workable option if space is limited.

What is SheetCNC built from? The structure is built from steel and 25mm MDF, with 25mm hardwood ply frame and bed. The axis rails are steel with ball-raced runners.

Why not plywood and aluminium – wouldn’t that be lighter and stronger? MDF is a remarkably precise engineering material to work with – far more dimensionally accurate than plywood. It also retains its shape better than plywood when subjected to the temperature and humidity changes expected in a typical shed. MDF’s precision allows us to design components which hold the machine’s runners at the very exact spacings needed to create a true and free-running assembly. Steel provides the stiffness required of such a large machine and offers much greater resistance to wear than aluminium when used for axis rails.

Suppose I want a vacuum-bed – can I do that? One of our factory machines is already equipped with a vac-bed. We use it for cutting materials which are too thin and flexible to hold onto the bed any other way. The construction of the vac-bed is very simple and we’re happy to share the design with any SheetCNC owner, FOC. All you’ll need to make your own full-size vac-bed is a 15mm sheet of MDF, some accurately-cut 20mm timbers, and – of course – a pretty serious vacuum pump. We’ve also made a smaller (A4 sized) vac-bed for holding printed circuit boards down while we etch them and that one can be powered by a vacuum cleaner.

How are the axes driven? The X and Y axes are driven by high-torque stepper motors acting on a high quality miniature chain drive. The Z axis is leadscrew driven.

Chain drive? Really? How accurate can that be? Do take a look at the videos at the bottom of this page! Our chain mechanism has been designed to offer an inherent chordal position error of less than 0.15mm – quite negligible when working with timber products. Better still, and unlike a leadscrew, chain suffers virtually no backlash error. And, unlike toothed belt, chain is extremely robust in a workshop environment. Chains don’t clog, won’t shred, aren’t prone to skipping, and won’t need constant cleaning to keep them free of cuttings. In short, chain is just about the perfect drive mechanism for a budget CNC machine. To see the accuracy that can be achieved by a well-designed chain-drive CNC machine, have a look at the images and videos of SheetCNC etching some tiny printed circuit boards. Even when using a 0.2mm cutter with 75% stepover, the cuts are precise and parallel, and the tiny 2mm lettering is perfectly formed. We can’t think of a better way to demonstrate the fantastic versatility of a chain-driven CNC.

Is SheetCNC noisy? No, not at all. SheetCNC’s spindle is water-cooled making the machine quite quiet.

Chordal Error

This is something we’re constantly asked about. Maybe it’s the fancy name that makes it stick in people’s minds? Anyway, here’s a video to show why it’s not an issue:

The video was filmed on a Mk3 SheetCNC which is about a year old and has seen some heavy use.
The machine has all-original mechanical parts, identical to those supplied in PembrokeshireCNC’s kit.

Backlash

Another popular question. Again, it’s really not an issue. Here’s the test: