Evolution Ornamental Mill
a 4 axis mill/ lathe/router
10 July 2007
Here she is in her final location. Cuter than a spotted pup laying under a red wagon!
I discovered www.mechmate.com which has free plans, active discussion group and a really nice machine. For anyone contemplating building your own I suggest using their plans. Laser cut parts of hard to build/crucial parts are available from group members.
Views from both ends
This is the Mechmate gantry. I still need to clean up the cabling.
Here you can see the AC outlet for the router and the dust collector. Voltage to the outlet is software controlled by using a solid state relay. A M3 command (start spindle) turns it on and M30 ( end program and rewind) turns it off. One interesting fact about solid state relays is that they need a load to activate. Since the router is electronically controlled it doesn't create a load until it starts. This caused some real head scratching as to why every thing worked with both plugged in but the router by it's self wouldn't start. When I don't have the DC plugged in I use a voltage tester that has a single LED and that is enough load to activate the solid state relay. I need to get the brush mounted on the dust collector foot. On the left is a limit switch which is activated by a spring loaded magnet mounted to the bottom of the X car. On all axis the driving pinion gear will run off the rack 1" after the limit switch should be sensed. This way if the switch is not sensed then the axis will not crash against the stop under power. All limit switches are normally close so if the wiring breaks the limit stop is activated.
Here you can see the spring with it's magnet just above the limit switch. The spring screws on to a left handed thread bolt welded to the bottom of the gantry so if it hits something it will bend not break. The spring is stiff enough so the magnet will not whip under acceleration or deceleration. The biggest profanity producer of the MechMate design is the rails. You either buy rails or make you own. Making your own is a several day dirty job unless you have a mill. Neither option appealed to me. First I tried 1/4" rod and that was a bust as I couldn't it straight enough. Next I tried 1/2" angle flipped over with the 90 degree up. I tack welded both ends and the stretched a fine wire from end to end . The wire gave me the straight line reference and the angle iron was weak enough that it was easy to align and tack weld every 6" yet has more than enough strength to support the gantry. This worked great except I couldn't do height adjustment so the rail had the same sag as the frame. So I spent the $250 USD to get the rails from Superior Bearing.
This is the 4 axis mill/lathe/router I built as a replacement for the Legacy 1800. I am using Mach 3 to drive the controller, repeatability of at least .01", Porter Cable 3 1/2 HP commercial router, router bed so it can operate as a CNC router with 20" by 129" capacity, thickness planner capability of 20" by 129", mill/lathe functionality of 24" by 10'+ and multiple wizards that are canned packages that will perform common operations such as roughing a 4 or 8 sided piece to round , turning the roughed piece to finished diameter and fluting. You enter the variables, length, initial diameter, finished diameter, number of flutes, etc and hit start. Rope and barley twists use the Magnate bits common to the Legacy and are a simple thread cutting operation. You enter clockwise or counter clockwise ( CW CCW), pitch and depth. Pitch can range from .0001" to 24" per revolution in .0001" increments. The difference between a lathe and a mill is it rotation of the stock. With a lathe the material is constantly rotating allowing only length and depth cutting and with a mill the stock is rotated as needed to do full 3D milling. Whether you are turning or milling is selected at startup. The hard part is the A (rotation) axis control because 1 degree of movement equals .2" on the surface of a 24" column. In order to engrave I expect that I will have to be within 1 minute ( 1/60 of a degree) of accuracy and this will probably include closed loop control of the stepper motor preloading of the gear train. I will add details so you can build your own. It came in about $5000.
Basic CNC Operations
G and M codes are used to control movement of the cutting fixture. These codes can be manually entered into a file or by taking a drawing from most CAD programs and running it through a post processor to generate the G and M codes. Post processors are machine controller specific because not all controllers use the came codes. There are Mach 3 post processors for most CAD packages and isn't any big deal and are usually free. Lazy Cam which is included with Mack 3 supports most CAD packages.
There are the important pieces. I am using a clone PC with 778 Mg of RAM, wireless keyboard and mouse and 2 parallel ports.. Mach 3 , http://www.machsupport.com/ , will only drive 4 motors per parallel port, stepper, servo or combination. Since I am using two motors for the Y axis I will have 5 total. Except for the A axis (rotation) all motors are 640 oz, 300 oz would probably work but I know 640 oz is more than capable of doing the job. PC is connected to home network and shares a color printer in the house and has cable internet access. Though defiantly frowned on by ArtSoft I ran a drilling test where the mill was drilling 6,912 holes, listened to music steaming of the Net and doing searches on the Net all at the same time and other than the mill slowing down occasionally there were no problems.
Mach 3 machine control software
Mach 3, http://www.machsupport.com/, Is really a fantastic piece of software. A full fledge 6 axis controller with all the bells and whistles for mills, lathes, plasma cutters, routers etc. It is written by CNC machinists originally for DIY machine builders but is so good that some CNC manufactures are going to it because it is better and cheaper than anything they develop. With over 20,000 copies running world wide and an active discussion group of 3500, bugs are rapidly found and usually fixed within 3 days. Why the bugs? Mach is constantly being improved and expanded. About every 2 months a lock down version is posted which has all known bugs fixed and they start on enhancements on that version. All upgrades are free! Price is $159.00 USD!
Machine design criteria
Speed versus cost/weight. Commercial machines of this size are multi ton monsters. They need the mass because of the tremendous force of 1000+ IPM ( inches per minute) movement and the torque of rotating the stock at speeds of up to 3000 RPM. They also run with accuracy of four plus decimal places. This results to their costs of 150K plus, plus, plus. I run a one man shop and there is no way I could afford the interest on one. My goal is to produce a machine that is affordable for a one man shop and if it takes 8 hours to do a 12" by 10' fluted column that is totally acceptable. Mine is running comfortable at 300 IPM which exceeds the speeds that I anticipate using. Rotation speeds may reach 100 RPM on smaller stock again the anticipated speed of less than 300 IPM will be the limiting factor. A 24" column will run at an anticipated speed of 5 RPM. Because of the low speed of rotation stock out of balance will not be a factor drastically reducing strength and weight needed. I need an accuracy of .01" which is easy to achieve and considered VERY sloppy in the CNC world. I am using a $325 Porter Cable router with manual speed control versus the $5000 spindles normally used. Presently I calculate that it will take four hours to do a 12" fluted column and as close as I can measure tolerances are within .01"
This is the POS gantry I designed which I replaced with the Mechmate gantry.
19 Sep 06
Ran a drill test of 96 by 72 holes a total of 6,912 holes. Total run time 2 hours. X, Y and Z axis appear to be working perfect. Interesting thing is I talked with a CNC shop and they said that their $200K machine would take 3 hours to run this job.
Playing around with VCarve and made this using a 60 degree V point. Edges are rough do to flex in gantry but that will be fixed soon.
Finally got the dust collector running. The 4" flex hose runs up to ceiling and across to a 650 CFM Grizzly DC mounted to the wall that discharges outside. Noise from DC is minimal but I need to muffle the router. I used the 4" E Chain for cables because I got it for $100. Would have preferred 2" but at that price I can live with it. Both router and DC are controlled by a solid state relay. At the start of a program I add M03 command ( turn spindle on CW) and this brings up the router and dust collector. When M30 (end program and rewind) is seen at end of program both are turned off.
8' column mounted. Ways, head stock and tail stock done, The ways are in the highest position for pieces up to12" in diameter. I am using the same concept as Legacy in that I will move the ways vertically for different diameter of stock. This will keep the Z axis travel to less than 6" and eliminating a lot of stress/flex problem of the original longer travel Z axis. There will be stops for 12", 18" and 24". Once the new gantry is in place I will align the ways to the gantry so that it is level in relation to the cutting tool. 5th Gecko drive mounted in control box.
This is the A axis gear train. The entire A axis assembly will raise and lower in 2" increments using a hydraulic jack mounted on the cross brace between the legs. It is shown in the highest position which will allow up to 10" diameter stock to be turned. Note the stops welded to inside of each leg. These stops were welded so that the Z axis has the same amount of travel on both sides. Once the A axis assembly is against the stops then the 2 bolts will mate to holes in the legs. The other end is done the same way. There are 4 more staggered hole in the plate for other positions. Each position will be squared to the Z axis. This way their will never need to be more than 6" of Z travel regardless of the size of material being turned. A axis is driven by a 1200 oz stepper. The gears are 9" and 2" in diameter so if my calculations are correct I will have 336 ft/lbs to turn the stock. The 9" gear uses a 1.25" wide belt which is wider than needed but that was what was locally available.
This shows both head and tail stock. Both are shown with the 4 independent jaw chucks installed. The tail stock has a live center with a #2 Morse taper and end of live centered is threaded so that the chuck can screw on. The head stock chuck can be replaced with a spur drive if needed. The ides is that a 3" by 3" by 1" mounting plate will be mounted in the center of the stock and then the 4 jaw will allow the stock to be centered. Note the yellow button under the shaft of the head stock. This is Hall effect homing switch. It will sense the bolt that is threaded into the shaft and this is the home position for the A axis.
Tail stock is 1.5" threaded stock with 2 nuts welded to plate and a locking nut. Underneath there is a .25" plate that tightens under ways with bolt on either side. The white pieces between the plate and the ways is UMHB ( the low friction stuff) so the tail stock slides easier.
Power control board for machine controller by Campbell Designs, http://www.campbelldesigns.com/. This is the power supply. It is set up for my mill and notice the extra standoffs and cable mounts still available. The power supply is shielded from the logics on the other side.
Logic side with the 4 Gecko controllers. Still room for 4 more Gecko controllers to be mounted. I really like the layout of this controller as there is minimum wiring, plenty of room for expansion and great shielding. By 1 September 2007 he should have a USB interface that will replace the printer ports.
This is the red oak end post that will be the main job for the machine. Here are some questions I have relating to doing this. If you have any suggestions/comments please email me. I need all the help I can get.
Now that I am down to getting the A axis functional I need to start preparing the drawings. I am building a 4-axis mill to do wood columns and other architectural products up to 24” in diameter and 12’ long.
The main job will doing stair end posts from red oak. The most challenging will be the transitions over .50” on Y from 5.75” square to 5.5” round and preventing tear out. Should I run as a mill or as a lathe? Either way I think I would want to run side cutting with a 0.50” or 3/8" straight cut bit so I am always cutting with the grain. Once the straight cut has done all it can there are still a some of detail work to be done and I think that a 0.50” 60 degree V will handle it. I am running Mach 3. The file will be in AutoCAD so lazy cam should have no problems with it. I will start with a depth of cut of 0.05".
- How is manual tool change handled?
- Now that I have the new tool installed and defined to Mach 3 how do I get it to do the places that the 0.50” straight cut couldn’t do?
- I would like make the last X number of passes as finish cuts (number unknown but suspect a cutting depth of 0.03” but number of passes and depth will take some experimentation). How is this done?
- How do I tell machine to side cut?
- There will be a 1" spigot left on the end of the piece so I can move the piece to a manual lathe for sanding and also could finish the areas that the cutter couldn't reach.
- Because of wood tear out I believe that the rotation speed during the cutting the transition will have to be slower. Am I going to have to manually edit this speed in the G code?
- Run time of the job is not very important as I have plenty that I can do while it is running but I would like to keep it less than one hour.
- Please send me any suggestions you have! I have only found 2 guys that are turning wood. One is using a V cutter like you would use on a metal lathe and the other is using a chain saw.
Parts list
20 degree rack at $23 for 6' sections they are 1/3 price of anyone else, McMaster Carr actually uses them Standard Steel Specialty Co 800-356-9232
4" X 50' flex hose www.peachtreeusa.com