Shopbot and Tormak
Device Manufacturers
- ShopBot website - The classic CNC wood router in our woodshop. Tabletop to 4x8. Shopbot Alpha is 4x4 foot.
- Iconic CNC website - Midsize CNC routers
Maker Nexus Equipment
ShopBot Alpha
The Maker Nexus woodshop has a ShopBot PRSstandard 48-48 with an effective work area of 48" x 48" for cutting soft materials such as wood and plastic. The shop has chucks for mounting 1/8", 1/4", 3/8", or 1/2" tools. There is no automatic tool changer. Spindle speed must be adjusted manually. Jog speed must be no more than 4 ips or the machine will lose position.
Safety considerations
There are more safety considerations than what's listed here. But these are some things we have learned:
Hazards from dust
- Use the dust shoe or ShopVac to keep clearing dust away: Don't stick a brush or a stick in the path of the router spindle, use a vacuum to keep clearing the area instead.
- Wear a mask: The ShopBot throws a lot of dust and chips into the air, so wear a mask to avoid breathing in this stuff. Also, the router bit may heat and char the outside edges of some wood (or pockets) so you don't want to inhale smoky ash.
Hazards from fire
- Peck drill holes, use upcut bits: It's highly recommended to do "peck drilling" where the spindle retracts the router bit every depth pass to ensure clearing out the wood chips. Also, use upcut bits to remove chips faster. If chips become packed down into the hole, they can very quickly smoke due to friction.
Hazards from metal in the bed
- Be absolutely sure to check for metal in the bed: If you are carving through your material, be very careful to know the path of the carve so it doesn't bump into a screw that's snapped off.
- Clean out your work holding screws: When you are done, be sure to remove your screws. If you snap off a screw, still try to remove it from the bed with some pliers. Call for help from the MOD if necessary.
Hazards from metal in your work
- We only permit brass screws as work holding: If you are screwing something into the bed we only permit brass screws because they will be less likely to damage the router bit or the ShopBot spindle. Hitting a screw during a cut will still deflect the spindle which will leave you a bad carve.
Hazards from an uneven bed
- The bed isn't flat: Over time, the bed will become less flat. Many of us use a "spoil board" or "sacrificial board" under our work for a few reasons:
- Carving through the material will only hit your sacrificial board: Which means you know there won't be any weird screws or other hidden channels to deflect the router bit
- Your board is flat: Because it has less bumps and ridges it should provide for a more even carve
- Level your spoilboard: You can surface your own spoilboard using the CNC itself so it is flat relative to the machine, especially if you use the same spoilboard and same location on the bed
- Repeated work holding: If you have repeated operations, this means you can reuse your work holding screw holes, or you can have other fasteners to pinch the work to your spoilboard
Maintenance
Tuning the PRS Gantry
Main instructions on the ShopBot Blog:
- The blog cautions against loosening the gussets which may cause further alignment issues because they were manufactured using specialized jigs that have precise alignment
Tormak
(Not available.)
Software
To prepare your design for cutting you need to create "tool paths" for the target machine. There are 3 steps to using the CNC. 1) generate some vector-based designs. Any drawing program on any platform will do. 2) Import those into something to specify tool paths (cutting and shaping moves). 3) Export the actual GCODE cut file that will drive the CNC.
In software you define the material your part will be cut from, the tools (bits) you will be using, and the speeds and feeds for each tool.
- V-Carve is software provided by ShopBot to create tool paths. In your design software save a 2D file as .dxf and then import into V-Carve. Now in V-Carve specify your tool paths - tool selections, speeds, feeds, etc. Finally, create the cut file.
- V-Carve has a free limited feature version that members can run at home to prepare their files. V-Carve is a Windows program but members routinely run it on a Mac using Parallels or Virtual Box.
- We have one copy of the full featured version at Maker Nexus that members can use to generate their GCODE cut files.
- Maker Nexus has made several videos on using v-carve.
- Fusion 360 can create toolpaths and GCODE. However in the free version of Fusion 360 all the rapid moves (G00) are converted to G01 which is slower. So your cut file will take longer to run if you create it with the free version of Fusion 360. If cutting on the Shopbot, you can press (Shift + "." = >) to speed up the Feed Rates. This is an incentive to upgrade to a paid version of Fusion 360.
Techniques
ShopBot specific tips can be found at ShopBot tips.
Speeds and Feeds
Wikipedia has a good page on speeds and feeds. In particular, you can get the cutting speeds for many materials using a high speed steel cutter. http://en.wikipedia.org/wiki/Speeds_and_feeds Missing from the Wikipedia table is Wood. The Cutting Speed for a soft wood, such as pine, is 1000 feet per minute.
There is a recommended speeds and feeds calculator at http://www.custompartnet.com/calculator ... d-and-feed The calculator needs Feed per Tooth. We were told to use the following values:
- Aluminum: 1/100th the bit diameter
- Wood: 1/50th the bit diameter
- Foam: 0.1
Plunge speed should be about 1/3 the feed rate.
Most router bit specs have feed recommendations. Amana router bits also specify the material type. They have bits for wood, plastic, stone, metal, etc.
Problems when cutting
If your wood part smokes, then either increase the feed rate or slow the spindle RPM. If you hear screeching, they you are feeding to fast - or too slow. Try slowing the feedrate first. If that doesn't work, then increase the feed rate a bit.
Spoilboards/sacrificial boards
Having your own "bed on the bed" really helps to make a clean cut, especially if you are cutting through your material. (It's OK to cut through to the bed a little, but the bed is so uneven sometimes your parts just break off.) Many of us use a small piece of MDF or 1/2" plywood as a board, and we Z-zero off of the board.
Some big advantages of your own spoilboard:
- It's flatter. Your board is likely in better shape than the shared bed.
- You can build a jig on it. You can glue down other pieces of wood to make a repeatable jig that can hold your materials without having to drill your materials
- Pro tip: Carve the rails of your jig with the ShopBot! Yes, after you affix some rails (and make them a little bigger), load a straight bit and run a program that carves the rails straight. If you put your spoilboard back in the same position all the time then you can make programs that carve off of your known rail sizing.
- e.g. Amy likes making a 20"x20" spoilboard and gluing 3/4" plywood rails on it, then mill the rails down to 40mm thickness. Thus with the X/Y being zeroed off of the prox switches, any material will always have its leftmost X edge being at 40mm.
Supplies
Bits
The shop keeps a few bits on hand for classes and for resurfacing the spoil board but you should purchase your own bits to avoid damaging the shop's tools and ensure consistent results for your projects.
The more flutes a bit has, the more heat it generates. Typical flutes for materials:
- Plastic: 2
- Wood: 1 or 2
- Aluminum: 2
- Steel: 4
CNC router bits are different from handheld router bits. They are driven through material by a rigid gantry whereas handheld router bits follow a path using a guide bearing. Be sure to buy the right kind of bit.
Dan-Mar Tools is a good source of bits 907 American Street, San Carlos, CA 94070 Phone:(650) 591-2651For cutting pink foam, Matthew had a four inch long bit that was about 0.5 inch in diameter. The flutes were almost like a rasp on it. He said it would just rip thought the foam at very high speed. Great for a roughing pass.
You can also purchase bits online from Amazon and other retailers. Carbide bits last longer than high speed steel but are much more expensive and brittle (don't drop them!). Some manufacturers offer complementary sets of bits at a modest discount to get your collection started, such as MakerMade, Whiteside, and Freud.
Materials
Pink Foam
I bought 4x8 sheets of two-inch thick pink foam insulation at Home Depot. Not every HD carried it. The sheets where scored half way through every 18 inches. This material cut extremely well. I sprayed the finished piece with shellack. For a more spooky effect I sprayed it with gray paint and the material started to dissolve away a bit.
