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Page 5 ADD-ONS
Fig. 35 Above shows the zeroing probe set, the design of which includes the device and some mods to Mach3 I got off the net from a person called "erniebro" - Thanks, Ernie! The way it works is when you have the origin located on the material to be routed (X=0, Y=0), you clamp the material onto the table, and place the plastic device with the copper pipe close to that location. At the bottom of the copper pipe is a crosshair, scribed onto the plexiglass, that allows you to locate that point with good precision. Once in place, you jog the router bit over this pipe, and lower it part way into the pipe. You then click on a button on the Mach screen, which causes the bit to move forward and back, electrically touching the pipe on both sides, and then Mach knows where halfway is, and then it moves the bit right and left, until touching and then it knows exactly where the center of the pipe is. It then positions the bit above the pipe, right over X=0 and Y=0. You then remove the plastic piece and place the aluminum strip to cover the origin point. Clicking on another screen button causes the bit to lower until it touches the aluminum strip, at which point it knows exactily where the surface of the material starts (Z=0) plus the thickness of the aluminum strip (.125 inch). It then raises the bit half an inch, and Voila! - your machine has aligned its X,Y, and Z axis with the origin of the material, regardless of where it was clamped to the table. Unfortunately, the Bosch Colt is double-insulated, which means the bit or collet does not make electrical contact with the table frame, so a large alligator type clip on the collet is needed to complete the circuit. The hold-down clamps you see in the movie and on the edges of Fig. 35 are some I got at HF on sale for cheap, and they work great.
Fig. 36 Figure 36 shows some of the pieces that were cut out in Fig. 32, as well as how they snap together to form the cable chain on the left. This will keep my cables out of the way while the router is working. Above is the dial indicator attached to the router mount. This allowed me to measure table tilt relative to the X and Y axies. Lengthwise there is a 100 thousandths difference from one end to the other, and about 40 thousandths across. Not too bad for the lack of precision instruments used when I built the table bed. At this point, I have two choices - by placing some layered shims under the plywood base, I can even up the table, or I can just put a sacrifice board on the table and run an end mill across the whole surface at a constant depth, making it flat with respect to the router bit. I think I will even up the base with shims, making it easy to replace the sacrifice board when needed.
Fig. 37 Above is a very useful and cheap add-on. You may often want to be looking closely at the bit while you position it, which is awkward with the keyboard. Here, a game controller is used as a pendant, which allows you to get close while positioning and keep your keyboard away from the dust. (A plastic keyboard cover might be a good idea, but I haven't gotten one yet - they make one for just about any keyboard design.) If you browse goodwill stores or look on Craigslist, etc. you can often find this kind of game controller for next to nothing - brand new they are $20. Most of these work by plugging in to a USB - make sure you get the software with it or can download it from the manufacturer. This software translates the movement of the game controller switches to keystokes you can assign with the software. So, if Mach 3 wants the page up and page down keys to move the Z axis, you just assign those keys to two of the buttons on the game controller, and then do the same for the X and Y axis.
Fig. 38 In Figure 35, the device to zero the Z axis relies on an alligator clip onto the router collet, and a 1/8 inch srtip of aluminum. One time I was using this, the router bit didn't stop when it made contact, but kept bearing down. Luckily, I was right next to the Estop switch, but it ruined the tip on a V bit before I could hit it. I chalked it up to my own carelessness, and was careful from then on. However, when it happened a second time, and ruined another bit, I was not a happy camper. Initially I thought that it was due to a bad connection at the collet, but I have since learned that others have seen the problem, so I have reported it. (Note from later: I've since learned that the software mods (mentioned at the top of this page) for the probe has a bug in it that allows for the occasional hangup. I've since repaired the bugs, but I've stayed with the solution below for the Z axis since it is just as easy to use, but doesn't risk killing a bit.) The winter 2009 issue of Digital Machinist magazine had an interesting answer to the problem. The one I built shown above is a bit different than the all-steel one shown in the magazine - it is made from aluminum scraps left over from building the gantry, but it seems to work just fine. This is practical due to the availablity of accurate $10 dial indicators from Harbor Freight. The way this works is that you lower the router bit until the dial indicator reaches zero. This occurs when the rocker bar is parallel. Then, just like before, Mach 3 has the offset height of the device specified and now knows where the surface is and sets that to zero. To calibrate it after it's built, the rocker bar had a piece of 1/2 inch material placed under both sides of the pivot, ensuring the bar was parallel, and the dial face was then set to zero. Then, a milling bit is lowered at the far end of the bar until the indicator read zero. The bit was then immdediately moved to cut a block of material. The height of the resulting cut was measured with a caliper and recorded and specified to Mach 3's offset. From then on, I just lower the bit until the dial reads zero, and click - it's done. Although one can attempt to make this height be equal to some round number, like 1.000 inch to so, there really isn't any need as long as you accurately know what the true height is when the pivot arm is parallel. Below is the back of the gauge.
Fig. 39 Ok, its now 6 months down the road from first cut, and several emails have asked for some more details. Your mileage may vary, but here are some lessons I've learned: 1. Budget for software. Although the cool part of this build (IMHO, of course) is the simultaneous control of 3 motors and the mechanical complexity involved -- in the end it is primarily a software animal. There are some good freebie programs you can use, but they are usually not as in depth as the more expensive ones, especially in the CAM area. You will need a control program (this talks to the stepper, usually through an interface connected to the computer's parallel port), a CAM program (which generates toolpaths from CAD drawings) and something that allows CAD drawings to be created and manipulated. This can be either a CAD package (like Autocad, Alibre, Rhino, etc. which can sometime contain a CAM module as well) or some of the CAM products have enough CAD capability built in that you may not need anything more extensive. Many CAD programs are now more concerned with collaboration (i.e., how do you have many engineers, modifiying part drawings all at the same time, designing the same machine) than in drawing capabilities. Also, their user interface development can be trapped by their own history. In general, the more you spend on the software, the more you will be able to do with your machine. So, the point where you really have to face the question "What do I want to do with it?" is when buying the software. For all of the vendors below, you can download and play with trial versions and read their manuals and watch their tutorials. Take advantage of that, and browse their user forums. Usually the forums on the vendor's website are more in depth than the vendor dedicated ones on CNCzone, but it sometimes pays to visit both once in a while. Herewith are the ones I use, and heartily recommend: Mach3 - Very nice, extensive control of your motors. (Its primary competitor, EMC, is a freebie for Linux, but I haven't tried it - Mach 3 was highly recommended and I had a Windows machine that was networked, so I went with it. EMC used to be hard to get running, but I have heard it has improved greatly and I have friends who think highly of it.) Mach 3 is very well documented, has many add-ons, and very flexible. If you go to many other types of automated machines (like CNC mills or lathes), you won't have to learn a new control package. There is so much there that I am sure I have yet to fully take advantage of it all. Do take advantage of some add-ons you find in the Mach3 forum on CNCzone. $175. Cambam - nice, simple 2D package, great for cutting parts from a 2d drawing. It's pretty new, so important features are still being added all the time and documentation is slim. $149. They offer a bundle of Cambam and Mach3 for $315, which is what I bought, and I think it was a great place to get started making things. VCarve Pro - Really a pleasure to learn and use. Great support on their forum. You can be productive pretty quickly with this package. I can scan in an image off a printed page, and make a carving out of it pretty quickly with this. $599. If you are really thinking about doing some sculpting in what is sometimes called 2.5D (It takes a machine with more than 3 axies to do true 3D) you should look at Aspire, which allows sculpting and 2 rail sweeps. I attended a Vectric user group meeting in Dallas in November 2009 as a newbie, but really felt I left as a raw but well informed intermediate user. Well worth the travel and registration costs. Additionally, I use Illustrator if I have any extensive drawing work to do (I already had it) and sometimes Inkscape (a freebie) as well. Photo2sketch (also a freebie) is sometimes a good starting point if working from a photo, depending on the photo subject. 2. You are going to need a good dust collection system, depending on the material being cut. Most plastics give off relatively large chunks of swarf, so they are not much of a problem. Wood varies all over the map, but some are definitely worse than others, especially the hard, dense woods like bloodwood. MDF is just horrible. This stuff will hurt you, so don't ignore it. I have seen some systems address this by placing a big airtight box over the whole table, but you still have to clean it all up when the cut is done, which involves you putting your face into the dust when vacuuming it. I think a dust shoe that collects the dust at point of generation does the best job. Search CNCzone and YouTube for "dust collection" to see what others have done. Use your CNC table to make it. Unless you are looking forward to buying lots and lots of filters for your vacuum source, get or make a cyclone - they work great. You can find ones that fit over a 5 gallon bucket, and they collect an amazing amount of dust, not just the bigger particles. 3. Oddly enough, after using this machine and building some projects with it, I have completely changed the way I think about it and making parts. I now think about using a toolpath to cut the final size of a wooden object, when just using a table saw would have been simpler before. After being so concerned about the limitations of the machine with respect to speed, accuracy, repeatability, etc. I have come to the realization that I am the real limitation of this machine - whatever I can imagine, layout, figure out how to tell my CAD program, etc. are the true limits to this machine. A rather sobering thought. For a sample project adventure click here. Hope you found some of the info on this site useful. Thanks for viewing! |
