CNC Shark

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The CNC Shark

Description

The CNC Shark, or "Shark," is a CNC router. The Shark's website describes it as "designed for routing all types of wood, routing or engraving plastics, and even etching or cutting tile..." CNC means Computer Numerical Control. Software on a PC controls the Shark via its USB interface. It contains a Bosch Colt palm router, which spins at 16000 to 35000 RPM (selectable manually by a dial on the top).

The Shark works much like the Handibot and its bigger sibling ShopBot.

Travel: X: 24" Y: 13" Z: 4.5" (Note our X and Y are switched, relative to the manufacturer's recommended setup. Our X is the long dimension, currently parallel to the front edge of the bench.)

Location

The Shark is set up on the bench on the south wall of the wood shop area. This is just to your left as you enter the wood shop from the classroom or multi-purpose room. The computer that controls it sits on the shelf above it.

Training

As with other sophisticated and expensive power tools at Xerocraft, you must be trained on the Shark before you may operate it without supervision. If you're not yet trained, a trained user can supervise your use of the machine. At present, those who know the Shark include Adam H, Andrew, and (as he admits, to a lesser extent) Liam G. Mike R is also familiar with the Vectric authoring tool Vcarve Pro, which is like Aspire (which is installed on the PC that controls the Shark) and with the Handibot (which works quite similarly). (Other members who know the Handibot could also provide useful background information. These include Connor B, David L, and others.)

The Shark retails for almost $3000 (not including the actual router, which costs over $100, or the bit, which may cost anywhere from $12 to $50) and the Shark at Xerocraft is on loan from a private individual. This only underscores the Xerocraft policy requiring that you be trained on a tool before you operate it.

Some dangers of improper use include:

  1. injury to people and things, by a flying bit, due to incorrect torque in tightening the collet or a damaged collet
  2. injury to people and things, by a flying work piece, due to incorrect programming, incorrect X/Y orientation, incorrect jigging/fixturing, or inadequate clamping
  3. damage to stepper motors by running beyond their limits, or by running over the clamps
  4. damage to router (bearings will wear faster and runout will increase)
  5. damage to the bit (chipping or dulling e.g. by running over clamps or cutting at wrong speed)
  6. damage to the collet (by over-tightening)
  7. damage to clamps (notice the marks on one of the blue Rockler clamps from a previous collision)

Please watch the Xerocraft web site for class announcements. When you do see a class there, you'll be able to see its date, time, instructor, maximum class size, and whether you need to RSVP.

Bits

The Shark's extra bits are kept in a clear plastic flat hinged box. To the right of the attached computer's UPS, you'll the wrenches you need to change bits. They fit the Bosch Colt router's shaft (10mm) and collet (17mm).

The included router has a 1/4" collet. It accepts bits with 1/4" shaft.

Some of the CNC-appropriate bits that we have include a 1/2" 90-degree V bit, a two-fluted 1/4" spiral upcut and downcut, four-fluted 1/4" spiral (can't remember whether up or down cut, TBD), 1/4" ball nose, 1/8" ball nose, and one-fluted 1/8" end mill.

These bits also work with the Handibot.

You may wish to bring your own bit if you want a sharp one, and it might be good manners to do so if you plan to do a lot of cutting. Good router bits may cost up to $30-50 each, but some are available for closer to $10-15. (Connor suggested looking on Amazon.)

Carbide bits are recommended. They "do not really get dull," as Connor mentions, but still they can begin to cut more slowly if a residue builds up on them. The residue (often brown or black and gummy) can be removed with Crud Cutter or with Shout. Both are in the white wire rack on the door of the cleaning closet just north of the kitchen sink.

Choose your bits for your project. For carving text into signs, a V bit may be useful. For much other 2D and 3D work, you may want a 1/4" spiral (up or down cut) for roughing and a smaller (e.g. 1/8") bit for finishing. (With the Shark, it's pretty easy to change bits while leaving your work piece jigged/fixtured.) If you need a round-over bit, be sure to get one meant for point cutting, plunge, or CNC. Another type, meant for manual operation, has a guide bushing that makes it wider and thus not compatible with tool paths generated for the Shark.

When installing bits:

  1. Inspect and clean the collet (see Proper Colleting and Collet Maintenance in CNC Routing)
  2. Use appropriate torque. Bosch told Liam G "finger-tight and then one-eighth turn." [As of 9/22/2015 they've promised to send him a specific torque in inch-pounds.] However, as of this writing (9/28/2015 )the collet in the Shark at Xerocraft has been over-tightened previously, with the consequence that it now does not grip the bit adequately unless tightened to that same excessive degree. Liam G suggests you make sure to try on a test piece to make sure your bit doesn't slip. If it slips up and stops cutting, press E-stop, turn router off on its switch, tighten collet further, and re-start your job.
  3. Fixture your work piece so that the bit can reach as low (in the negative Z direction) as you need it to. This may mean raising your work piece up, if you just installed a shorter bit.

There's another option for bits, though it may not work totally reliably: With a 1/4" to 1/8" adapter bushing or reducing sleeve or a 1/8" collet, you may be able to use bits with 1/8" shaft, such as those for a Dremel rotary tool. (Xerocraft may have an adapter bushing/sleeve somewhere, but as of 12/19 Liam has not seen it yet.)

Feeds and Speeds

"Feeds and Speeds" refer to feed rates and spindle speeds, and they vary with the material and the bit. They also depend on the rigidity of the machine.

The router's spindle speed is not under software control. Even though the software we use lets us select a speed, this is ignored. A red dial on top of the router sets the speed. Settings 1 through 6 set speeds of 16,000 to 35,000 RPM, respectively. Set a speed recommended by a "feeds and speeds" chart or calculator, linked below in the References section.

The feed rate is the rate at which the router's bit traverses the material in the X or Y dimension. (Plunge rate is the rate at which the router's bit plunges down into the material, in the Z dimension.)

Rules of thumb:

  1. First test on a piece of scrap material.
  2. If you get burning or melting, try a faster feed rate.
  3. If you get big splinters or chips, the machine vibrates, or your work piece vibrates or comes loose despite having clamped it tightly, try a slower feed rate or (if that would cause burning or melting) a shallower pass depth.

Materials

So far, Xerocrafters have cut mainly wood (solid and MDF particle board) on the Shark. Polycarbonate has been cut successfully also. Other plastics are possible, as are thin brass and aluminum. If you want to cut anything other than wood, please get supervision from a Xerocrafter with experience with these materials, even though you've taken the class. This is both to protect both you and the machine and to improve your odds of success.

On 12/12/2015, a team of three CNC Shark class students cut a slot in a flat bar of aluminum (about 1/8" thick) using a 4-fluted 1/4" bit. They bolted the aluminum directly to the slots in the bed. They used a spray cutting fluid or coolant borrowed from the metal shop. They spread aluminum foil to protect the bed from being saturated with oily cutting fluid. The feed rate was calculated initially from the feeds and speeds calculator linked below. It had to be reduced to about 50% of that to stop the machine and work piece from vibrating heavily. (The CNC Shark is not the most rigid machine, which limits the speed compared to machines for which the calculator was designed.) They also used an air compressor to blow the chips away (toward the wall). The slot came out okay. (The edges were a little rough and should be sanded.)

Further advice on cutting aluminum may be found here and here.

Software

There are two main kinds of software relevant to the Shark:

1. Its proprietary Control Panel software, which imports gcode and controls the actual machine. This is installed on the computer above the Shark and registered to the Shark's serial number.

2. Authoring tools. Installed on the Shark's attached computer are Aspire and Cut3D, both by Vectric, who also supplies the authoring tools bundled with the Handibot and its large cousin the Shopbot. These all generate gcode (to control the machine) based on your design. Aspire can import 2D vector art in DXF, DWG, EPS, AI (Adobe Illustrator), or SKP (Sketchup) formats. It can also import "3D mesh files created in other CAD software such as Rhino, SolidWorks, AutoCAD, Silo, MOI, Blender, SketchUp etc." The file formats are STL, 3D DXF, OBJ, 3DS, VRML, 3DM, and SKP. Cut3D imports only STL files.

A free trial of Cut3D doesn't expire. It will preview how your model would be cut 1-sided, 2-sided, or 4-sided. It will even let you save the configurations you make within it. But it won't save any gcode. A free trial of Aspire also don't expire, and will preview your model, but it won't let you save anything at all, not even the configuration.

For some models, cutting a 3D model from an STL file can be a quicker alternative to 3D printing. For example, a model that might take 7.5 hours to print on one of Xerocraft's 3D printers might complete in about 1-2 hours on the Shark.

At the same time, Cut3D may generate a toolpath that takes much longer than one that you could create in Aspire. This is because Cut3D insists on covering every point in the X-Y plane.

Issues

We are keeping a list of Shark issues/deficits and are working to fix them:

1. (Fixed by 9/18/2015 after noticing on 9/12/2015) On the attached PC, the Shark's control program's registration had expired. We had to download the current version before it would register itself. It's version 1.6 and is registered now. Its registration is derived from the serial number of the specific CNC Shark attached, so please do not use this Shark to register software on other computers.

2. There is a "stutter" in in the X axis. You may notice it making more noise when moving in the X axis than in the Y. This may persist until we replace the X-axis stepper motor. Until then, the damage may slightly limit precision.

3. The Shark can suffer damage (i.e. to stepper motors) if the tool reaches the limit of any of the 3 axes (X, Y, or Z). This may be prevented by adding limit switches, if practical. Looks like probably limit switches could be used only in a limited fashion at best, e.g. to cut the power, to simulate a keypress or a mouse-click to hit the E-stop.

4. The improvised clamps' carriage bolt heads don't catch easily in the bed's t-slots. One must, at the last, reach under the bed to hold the bolt heads while tightening the wing nuts. (Update 12/19: David bought T-slot bolts, but Liam took them to exchange for longer ones. Liam hasn't done this yet. Shame on him!)

5. X and Y axes are switched, relative to the product specifications given on the manufacturer's web site. In other words, in our Shark, the X axis is the longer one, which currently is oriented parallel to the front edge of the bench.

6. The collet has been over-tightened in the past and deformed. After that, the nominally correct torque did not suffice. (It costs about $7 to replace and as of 9/28 a new one is on order.) Update 12/5: A new collet was received by early October. Update 12/19: The new collet is at least slightly deformed, in that it doesn't have enough spring to grip the bit when the nut is loosened.

7. (12/5/2015) Lately the black Lenovo computer attached to the Shark has been acting up: refusing to boot, asking to re-install Windows, or not letting certain programs open any files. We are looking into this. Update 12/19: The PC seems better after we blew out the dust from inside.

8. The attached computer occasionally chimes the sounds that indicate the disconnection and connection of a USB device. It seems that power cycling the Shark's control box fixes this. The switch is on the back at the left side.

Manuals

Resources