Big CNC

The Big CNC is a custom CNC router designed and built by Danny Miller. It has a maximum cutting area of 5' by 8'

Max Z height is approx 7.5" from nut to spoilboard, but this does vary as spoilboard is added or removed. Note that the max usable stock height will typically need room for your bit to go on top of it

Spindle 3KW digitally-controlled VFD using an ER20 collet system. Manual bit changes, no ATC.

LinuxCNC control system

Z-height may be set by wireless toolsetter provided, or eyeballing it

CAM postprocessor should be "LinuxCNC", and not an ATC version. If nonarcs is an option, this is recommended over the arc option, but arcs will work. LinuxCNC used to be called "EMC2" long ago, "EMC2" postprocessors should work.

Cuts wood, plywood, plastic, many other materials. It is also capable of cutting nonferrous (aluminum, copper, brass) sheet metal and nonferrous billets (thick blocks of metal stock) with proper feedrates and compressed air nozzle. The compressed air nozzle will drive chips out of the cutting area so they are not re-cut by the bit and provide some cooling. For billets, while the CNC router may be capable of it, the Tormach is more capable as it is stiffer, lower RPM, and equipped with flood coolant.

CANNOT CUT STEEL. Steel requires coolant which is not compatible with the MDF bed. Steel can create red-hot chips and sparks which can start a dust collector fire, a very dangerous situation.

Members must complete the Big CNC Class before using this tool

Checklist

Before I Start

• Make sure rail travel is free of obstructions such as vacuum carts
• Switch on the two power outlets
• Wear Glasses and Closed Shoes
• Fix your work to the table (nylon nails, screws, double sided tape)
• Mount the bit
• Unrack & Home
• Switch on Dust Collection

When I'm done

• Shutdown the two power outlets.
• put wrenches, bolt, thingy back in the box in the CNC cabinet.
• Clean up the remaining dust.

Tooling

Users must bring their own bits. All CNC routing bits should be carbide, not HSS (High Speed Steel). HSS will not damage anything but the performance on wood, plywood, plastics, etc is poor.

An RCK-2249 surfacing/rabbeting bit is provided in the cabinet. This is an excellent choice for surfacing lumber slabs (live edge table) and pocketing. The 2 cutters on bottom of the bit plane the surface for a smooth face. It is 1-1/2" and uses two different types of carbide inserts which you will want to bring along with screws if you want to get the best quality cut. Larger diameter bits typically do not produce as good a finish, as any tram error (the spindle not being perfectly perpendicular to the surface) tilts the circle the bit makes which creates a slight scalloping of the surface and this requires more sanding to smooth out.

https://www.toolstoday.com/v-11847-rc-2249.html

The Diamond-Like Carbon inserts RCK-70-DLC and AMA-12-DLC are the best choice for surfacing lumber. This bit CANNOT PLUNGE it must approach the work from the side.

Places to get bits in town

Sparktech in Round Rock has a very comprehensive range of carbide tooling appropriate for CNC routing http://www.sparktechinc.com/

Easiest shopping is through eBay, most inventory is listed. Select "local pickup", check out, drive to Sparktech

• Sparktech's ebay store is CarbidePlus aka OliverToolCompany, username is DrillMan1 https://www.ebay.com/str/carbideplus?_trksid=p2047675.m3561.l2563
• Woodcraft (limited range). Note that most hand routing bits are not appropriate for CNC
• Dixie Tool Crib https://www.dixie-tool.com/

Online

• Amazon
• eBay
• https://www.toolstoday.com/

Full ER20 collet system provided in Inch and Metric. However, they are communal and prone to wear which adds runout and reduces the hold, and you may wish to get your own collets so you know the condition. Collets are generally cheap, the Techniks brand is consistently higher quality for about $15-$20 collet. In practice the majority of carbide tooling is 1/8", 1/4", and 3/8", so that may be the only Techniks collets you need to get. The ER20 nut is provided and generally does not have wear issues so it is not necessary to bring your own.

https://www.amazon.com/s?k=techniks+collet+ER20&ref=nb_sb_noss

Videos explaining differences of upcut, downcut, and compression bits on wood.

https://www.youtube.com/watch?v=seAmL6mtqgM

Those are the 3 most basic types. There are many other types

• straight mill
• ball mill
• taper mill (various ball dia, taper length, taper angle)
• v-carve (various angles and diameter)
• surfacing bits

Within a type, there are variations in:

• flute count
• flute geometry
• flue length
• flute diameter
• shank length/diameter
• coatings (DLC, Spektra) reduce friction, cut slightly cooler, and last longer
• Some bits have replaceable carbide insert cutting edges.

Conventional drill bits can be chucked in the ER20 system. Please use the tightest collet available, which may mean selecting a metric. Any slippage between collet and tool will generally damage the collet.

Holddown methods

All work needs a holddown solution. We need to avoid embedding metal into the MDF bed as this will break the bit when the spoilboard is resurfaced.

A Raptor air nailer firing nylon polymer nails is provided, along with the special-purpose Raptor F15 polymer nails. This is only to be used for CNC, and must NEVER be loaded with metal nails.

The polymer nails are approx 1.25" long and effective on plywood and MDF up to 1/2" thick. It is possible to do 3/4" but this leaves little left to actually go into the spoilboard. Some hard lumber or plastics may be too hard and the nail will break before penetrating.

Polymer nails will be broken off and left in the MDF bed at the end of your job. This is acceptable, the surfacing bit will slice right through them.

Metal nails are entirely prohibited

Steel screws are an option. Only high quality screws should be used- Kreg Pocket Jig screws are the best option. Spax screws are also acceptable. Cheap drywall screws are not acceptable, as they are very prone to break in the spoilboard. Screws generally require predrilling to avoid engaging the threads in the stock or splitting the stock. It is often possible to predrill with the CNC itself without a holddown if the stock is large enough.

If you DO break a steel screw off in the bed, please circle the problem with a black Sharpie on the bed itself. We will extract it before resurfacing but we need to know where it is before the bit finds it.

Video explaining tape-and-superglue holddown method. No holes are made in your stock, and no glue soaks into your stock either if done properly. The blue painters' tape adhesive is the only thing on the bottom of your stock and should release completely when done.

It is a very secure hold yet 100% removable with no marks on your stock at the end. In general you should use secondary spoilboard as shown, nailed or screwed to the machine's spoilboard. It is possible to skip this and put tape on the machine spoilboard directly, but rough MDF does not tape well and we need to avoid glue seeping from the sides onto the spoilboard as well.

https://www.youtube.com/watch?v=gTUAAm0DFOQ

This is also a great option for holding down live edge slabs which have no place for a screw hole that would mar the final surface appearance. In this case you might only tape-and-superglue 4 corners selectively onto some plywood or MDF tabs while off the CNC router bed, then nail or screw the tabs to the spoilboard to secure the slab.

Resources

• Class Notes
• Introduction to Vectric CNC
• VCarve Tutorials
• LinuxCNC Tutorials (video)

Maintenance

This tool is owned by Danny Miller and hosted at Asmbly for members to use. Please contact the workshop committee if maintenance is required.