Announcement: Welcome to TRB-CNC Routing

My name is Tom. I recently purchased and built a medium sized CNC routing table. I’ve now discovered I can easily share the wonders of CNC routing with a few of the masses. If you’re one of those masses, put on your creative thinking cap and keep reading.Gantry and table front view

Below is a short introduction to CNC and my specific machine. The picture to the right shows the basic table with X, Y and Z axes. The router bit is inside the black brush thing. In the photo you can see the top of the router motor sticking out from the “Dust Shoe”, the thing with the black brushes on the bottom. The dust shoe has a long hose to clean up cuttings as they are cut. This is important so they do not interfere with the action of the bit. Too much waste material can hinder cutting action and result in inaccurate cuts. Behind the router on the back side of the Z axis bar is the “lead screw”.

Anti Backlash Nut

A typical Anti Backlash Nut

The lead screw is a long round threaded rod with carefully calibrated threads cut into it. The lead screw is driven around directly by a stepper motor (not in picture) that, when turned, moves the entire router and Z axis bar up and down. The lead screw mounts to the Z axis via an “Acme Nut” also known as an “anti backlash nut”. The nut has spring loaded threads that grip the threaded rod but will give gracefully if overpowered such as if the Z axis jams or goes haywire and tries to cut a hole to China. You can also see the gantry risers in red and the large aluminum bar mounted to it going across the table to the other side, also in red. This represents the X axis. On the front of the X axis is a flat steel bar upon which the X axis rides. If you look carefully in the photo you can see the long gear track that mounts on the back side of the X axis. This long gear track is used to drive the X axis from left to right using a Pinion Gear. This type of drive system is called “Rack and Pinion” or R&P drive. A Rack and Pinion drive system is rugged, relatively common making parts easy to find, and very accurate. It makes the job of calibrating the motor turns to actual movement very easy and very linear over its entire movement. R&P drives do not generally require any special corrections along either axis like some ball screw devices require. This rack and pinion drive is the same system used to steer your car. When you turn the steering wheel you are turning a pinion gear down between the front wheels. This pinion gear rides on a long gear attached to both wheels. Turning the steering wheel turns the pinion gear, moves the gear (AKA “rack”) and then the wheels so the car does not try to climb trees or run over people.

View from control panel, a laptop PC.

View from control panel, a laptop PC.

This next image shows the machine from the operators point of view. You can clearly see the Laptop PC and mouse I use to drive the motor controller. Behind the PC is the “moving gantry”. You can also see a large wire chain mounted on the back of the X axis (left to right movement) and a second wire chain running to the top of the Z axis (up and down movement). This gives you a good idea how large a parts can be cut on this machine. This machine is perfect for hobby sized personal projects, small to medium sized engravings, small to medium 3D carvings, small to medium pattern cutout and just about anything else you can think of.

What is a CNC Router?

My machine table is just over 25″ wide and just over 49″ long. In a pinch I can cut parts up to 25″x49″ inches but normally I’m limited to 24″x48″ without special setup. The term CNC stands for :”Computer Numeric Control“. CNC machines come in many different types and sizes. My machine is a moving gantry CNC router. A moving gantry CNC is a large square frame with a gantry mounted across the table. The gantry has a router mounted on it that can be moved up and down in relation to the table top to control the router bit. It can also be moved left and right to laterally drag the bit through the material, cutting as it moves. In addition the gantry “trolley” moves the entire horizontal motion mechanism including the router on a steel track from one end of the table to the other. This gives it the ability to cut in 3 different directions at once. The cut point, or “quill” as the router bit is sometimes called moves up and down, left and right and forward and backwards in relation to the fixed table beneath it. That’s why it’s called a moving gantry router. The 3 different directions of motion make this a 3 axis CNC router. It’s one of the most common types of routers used today. There are, however, many other types as well. Some have a fixed router position and a moving table. Others are capable of rotating the router at an angle to the table giving it an additional axis of rotation. Still others have a lathe chuck that can rotate a piece of round stock for cutting legs or other round or roundish parts and some have a separate motor attachment called an “indexer” that allow it to cut normally flat carvings into the surface of round objects. An indexer can be used for such things as cutting text into the side of a large bowl, or adding decorative touches to a wheel. The indexer temporarily replaces the Y axis (forward and backwards) movement with a rotating motor capable of holding and indexing the part such that flat engravings and carvings can be cut on a round surface. I may eventually invest in an indexer once I get more experience.

How does a router cut sideways?

Downspiral cnc router bits

Downspiral cnc router bits

It may seem easy to visualize a twisting bit like a drill bit but router bits are not simple drill bits. In fact with few exceptions, the router will not even mount a regular drill bit. There are cases where a simple drill bit can be used but generally speaking a router uses very specific specially designed cutting bits. A drill bit has a sharp edge on the tip and only on the tip. The twisting flutes on most drill bits are not even sharpened and if pushed sideways into material will not cut at all. With enough force the bit will just break.

Commonly used CNC bits

Commonly used CNC routing bits

The twisting flutes up the sides of a drill bit are there to carry away the chips or strips of material the tip has cut away from the bottom of the hole. They are not intended to do much cutting. If you’ve ever tried to cut sideways with a regular drill you know what I mean. Router bits have similar names but that’s where the similarity ends. Router bits come in literally thousands, even tens of thousands of different shapes, sizes, types, directions of rotation and length. Each of these dimensions need to be taken into account when choosing a bit for a specific task. This is all important information and must be taken into account when deciding how, or even if, a particular routing program can be run on the desired material.

How does a CNC know what to do?

CNC machines, like any generic computing device, require programming. The term CNC means “Computer Numeric Control” and was first written as just “NC” meaning “Numeric Control” since the very first automated cutter used punch cards to make cuts. Later when the computer became available the extra term was added to denote the difference between a straight NC machine and a CNC driven by some kind of computing device. CNC machines began their proliferation in the late 60’s and early 70’s. By the mid 80’s they were becoming increasingly common and today are as common as the automobile. Since the CNC machine requires programming, where does that programming come from? If you are the part designer it comes from you. It comes in the form of a drawing you may have made in a CAD program, or it may come from a simple hand-drawn diagram. In either case it must eventually be imported into an appropriate intermediate program and converted into “Machine” code. In this case it’s called a toolpath and it’s written in “G-code”. G-code is the language of the CNC machine. Whether it be a 20′ square custom door cutting machine or a simple 12″ table top engraver it will still require G-code to make it go.

What can I make with a CNC router?

A CNC router can be used to cut materials both soft and hard. From simple Styrofoam or foam board to aluminum, brass, even steel. Cutting steel and aluminum requires special bits, slower cut speeds, lubrication and usually much slower bit rotation speed. Metals also require cooling and  lubrication while cutting. A CNC that cuts metals usually has a “mister”. A mister is a spray nozzle that keeps the part being cut as well as the bit that’s cutting bathed in some kind of lubrication. Since the lubrication is a liquid it also requires a way to control it which means a solid table with a collection tub or some other way to collect spent mist. I do not currently have a mist maker installed and at present have no plans to install one. Cutting mild steel, aluminum, brass, ceramics and other hard materials requires special attachments that are both expensive to purchase and to maintain. For that reason I don’t have them installed but If you have a metal cutting job and you’re insistent enough it could happen.

CNC routers can be used to make a myriad of objects from a simple flat cut board to a series of complex curves, angles, circles, flutes, straight cuts and arcs to form nearly any shape you can imagine. One of the most common uses for CNC today is to make custom Signs. Start with a piece of wood, add a decorative, representative background, add your Company Name, a Logo, your company slogan and even add extras like a 3D relief carving representing our business. Vectric Software has a Sign Gallery showing actual signs that were made using a machine just like mine. Have an idea but aren’t sure it can be done? Shoot me an email and I’ll find out.

Recently it’s even become possible to engrave a photograph into a solid piece of material to create a memory that will truly live forever. Because the CNC router has been around for so long, ways to cut even the most complex of objects have been researched and perfected and can be copied and applied to many different materials. One of the easiest examples is cutting a single piece picture frame. In the past, traditional wooden picture frames were made from 4 discrete pieces of material, usually with an angled corner. Now, however, that same frame can be cut from a single large piece of wood. Add some decorative edging, add a decorative curve or two and round the outside edge and you can have a custom picture frame made from a single piece of your favorite wood. No corner seams, no staples, no glue, just one beautiful frame to aid in displaying your favorite image or painting. Other favorite items include custom wooden boxes. A CNC can carve out the inside of a block of Oak, Cherry, Pine, Poplar or even Mahogany to form a seamless, single piece wooden box. A second piece off the same block can be carefully cut to make a custom matching box top, complete with custom engraving in the form of lettering, special designs, even a photo rendering. And because the wood came from the same block, the grain will match perfectly between the box and the box top. For more CNC routing examples, search the internet or take a look at Vectric Software Web Site.

Hopefully this has given you a general idea who I am here at TRB CNC. If you have questions feel free to leave a comment.

 

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