So the big question is what do I need to build a CNC...? Looking at the web, its clear that there are just as many ways of building a CNC, as there are people interrested in this, so what I basically did was to look for what parts that were available for me, and build from those.
Quickly I discovered that getting parts from Denmark were vertually impossible, because there simply is no market for used CNC parts here..., so I turned to Ebay, and found a huge selection of usable CNC parts, just waiting for me.
To be able to dimention the CNC frame, I need to seek out the vital parts that need to go on the frame, this beeing:
- Lead Screws (XYZ) - Linear Bearings (XYZ) - Milling head with ER16 Collet.
Leadscrew / Ballscrews
So I started looking at leadscrews/Ballscrews, and came across this great offer. A set of 3 spindles including thrust bearings at both ends, only a spacer and a nut missing, but Ill manage (-:
These lead screws will set the physical limits of the milling machine.
(Used lead screws from Malaysia, purchased on eBay - No Problems)
You might have notised that the pitch on these screws quite high (20mm pr. rotation) which by some persons will be considered very steep, and I agree and thinks it will be torture for the motors to try to drive these screws, resulting in loss of steps, and therefore unusable results. Therefore I investigated the possiblity of a reduction between the stepper motor and the spindle, and I managed to find a way to do a 4:1 reduction with tooth belts. In addition to reducing my motor to spindle ratio, I also eliminated another common problem in DIY CNC world, which is resonance. As the motors work, they make a horrible loud noise when beeing run directly on the spindles, so many use some kind of rubber bridge on the axis to isolate the motors harsh movents from the spindles just slightly.
The motors that followed the kit were 305 oz/in motors with a step degree of 1.8, which give a perfect 200 degrees pr. rotation. If I were to run the motors directly on the spindles, it would give me a resolution of 20mm/200 steps = 0,1 mm pr step (1:1 microstepping mode.). So when I build the 4:1 reduction, Ill have 0.025 mm resolution which will be more than enough for me at this first CNC build. If I find that I need more reolution, the kit from hobbycnc is able to run in the following microstepping modes: 1/1, 1/2, 1/4, 1/8, and 1/16. So in theory, my resolution could be 0,0015625 mm pr Step - But this is way beond the precision of this CNC anyway. And when you increase the stepping division, you are giving up power of the motor.
The Linear bearings were also found on Ebay, and was found after the leadscres were recieved, because if all the leadscrew length is to be used, its important to find the correct linear bearing. This is naturally because you need to have 2 bearing blocks spaced on each bearing rail. The further apart, the more stable the construction will be.
2 at the top, these are the linear bearings for the Z-axis
The long bearings at the bottom are the X-Axis bearings.
Im only missing the Y-axis bearing, I found one that are 21" 5/8, in length which is just perfect... However the Danish Post service has much to be desired.. Still not arrived after 15 Days in Denmark...
Ordered it the 29 Jan 2008, and today its 05 Mar 2008... And they are still not here... But I have the tracking number, so I know they are not lost.... I guess...
This is how I obtained the 4:1 belt reduction. I located an Amarican dealer of alu. tooth belt pulleys and belts. Im impressed about the quality - but they didnt come cheap either!!! but unfortunately were my only option. - The shipping were the most expensive!
Belts and pulleys.
As for the milling head, I ordered everything for this from an existing product: the Taig milling machines has an exceptional good milling head, and you can get it with ER16 collet, which is a standard. So finding milling bits (Pro or hobby) will not be a problem.
Peatol Machine 19 Knightlow Rd. Harborne Birmingham B17 8PS England 011-441-21-429-1015 "www.peatol.com" -> They dont have email, so you will have to grab your phone...
And these are the parts I recieved:
2 x ER16 standard collets in 2 different sizes, perfect to start up with.
The milling head with pulley, dovetail mounting plate and motor mounting plate, and the motor including the pulley and drive belt..
The motor os 220 VAC. 0.18 KW. 1390 RPM.
The above items makes it so much easier to build the CNC, as it is off the shelve items, and spares can be purchased. And the mounting system is easy and the ER16 headstock is commonly available, so there will be no problem finding different tools for this collet system.
If in need to do so, the headstock can be removed from the dovetail mounting post, and placed horisontally, and the ER16 collet removed and replaced with a chuck off the shelve, and you have a Taig lathe...
If the result of the CNC turns out good, Ill add the 4´th axis to the CNC, which will be a second horisontal headstock controlled by a gear reduced stepper motor. this way its possible to make parts that were vertually impossible on the 3 axis machine.
Building the frame is about to be realised. I have recently discovered the very potent and extreamly easy Google Sketchup 3D drawing program, and therefore made a 3D model of all the components I have collected till now, and se how I would visualize the CNC at current stage.
Please not that the drawing is not finished, as I dont know the extual dimentions of the Y axis as I dont have them yet.. But they will come. - And the gantry will be mounted where it is now. it will be more to the center..
Please ask if you would like the Sketchup file (.skp), and have a look through the 3D drawing your self.
First G-code controlled moves.. making a simple square in mid air..
Yes, the first cut was done today in Aluminium, I recieved the endmills I ordered from Ebay, and they a 4 flutes endmills.
The result of the first cuts, sorry about the focus, but the camera is not good at taking pictures of objects close to the lens. I think the result os ok, but my final verdict will come when I have a solid metal plate as X-Plane, instead of the 10mm wood board that I currently have!!! but it cuts, and its the wood that gives way when I turn up the speed of the axis.. Enjoy:
Yes I know its not much, but its only the 10mm cut at the end of the bar. (-:
Some tests with weight on the X plane: in the first video im running with velocity of 153 mm/2 and an acceleration of 500 mm/s^2. The load on the x-plane is from a solid cast iron flat + sulid metal fixture (21Kg) and 2 weights waying each 5 kg (10Kg) so that is in total of 31 Kg. (Not coundig the plane, metal wise and the linear bearing trains.)
Second video I didnt write down the data, but its probably not far from the above - Using EMC Stepconf program to cycle the plane
X - Axis frame.
The frame tubes have been recieved, and I just got the angle brackets, so I can start to weld up the X-frame:
Finished welding on the brackets.to the top tubes.
Using a polished solid table plate as "true flat surface" on top of the metal "true flat" you see above. This is because I dont have a "true flat surface" of this size, so Ill have to do with what I have. It actually turned out ok, but the final trimming will be done when the linear bearings is going to be mounted.
Making threads to hold the x-axis thrust bearing, and making the motor mount, to also accomodate belt tention adjustment.
Next will be mounting the linear bearings. The top of the x-frame will not be machined to true flat due to its size, but instead the linear bearings will be mounted on nuts that is individually welded on to the frame, so the linear bearings will be tightent on to these nuts. The nuts are adjusted and alligned carefulle before welding. This will come soon... But first the moving x-surface needs to be made and mounted on the rail trains.
Making connectors for each motor on a front plate for easy and controllable access.
Y - Axis frame
This is the Raw Y-frame mounted on the X frame, just for measure and checking for compatinility. It seems perfect for holding the Z axis.
Preparinng the Y-Axis rails by fitting small welding pads with thread in it on each rail hole. onec fittec it wil be layed down on the frame, and spot welded and checked.. and finally wielded firm on all pads.
Trying the Z-axis on the Y-frame, nd se if it fits.. it fits perfectly..
Trying the complete Y-frame on the X-axis, Please note the mounting brackets at the bottom of the Y frame to add stiffness to the mounting point, but also to make the hight adjustable if needed some time in the future..
Z - Axis frame
So the frame will be made up over a set of box tubes, that is very solid, and light. this will be rigid enough for the Z-Axis.
The box tubes is cut out to hold the top and bottom ends - 16 M6 threads were cut to make the frame rigid.. The hole at the top til hold the ballscrew.
The structure assembled.
Mounting the linear bearings, and a bearing clamp for the leadscrew end support. On the backside you can se the holes that is used to access the screws for mounting the linear bearing.
Here you see where the limit switchedis going to be placed. They are not mounted, because from now on this item is going to be carried areound and trial fitted many places, and those fragile plastic switches breaks first time I place the Z axis on its back.. will first be mounted when the Z axis has a Y axis to go on to.
Fully extracted upwards.(The CNC motor is mounted at the top of the Z-axis)
Fully stretched downwards.(The CNC motor is mounted at the top of the Z-axis)
The total Z-axis including the 220V motor and the part that needs to be static on the Yaxis weighs about 14 Kg. From the feel of moving the motor when the toothbelt is on, I dont think it will be a problem to move the Z-axis up and down - if it does I have some good ideas to how to eliminate this.
Ofcource there will be some minor things to do like brackets for the motor power connector so it will not wave around, and wire guides for the switches etc., but this will come at the final part of assembly.
Sorry for having cheated, but I have already assempled the kit.
The kit is a "Solder yourself" kit, that comes nicely in bags with EVERYTHING you need for building the controller except the transformer and the box and connectors. Everything included, even heatscrink tubes for the wires.
The kit is purchased from www.hobbycnc.com, and you have several option of motor strength (yes the motors are included also), and number of axis. I choose a 3 axis kit with 305 oz/in motors. (I did prepare my box for a forth exis, as you can purchase the extra axis components seperately.)
These are the 305 oz/in stepper motors that are included in the kit. (The timing belt pulleus attached to the shafts are not included.) kit was assempled in no time, and worked straight away.
As I currently dont have a working CNC, I can not reveal its performance, but it does seem very potent when the motors are spinning like mad on the table beeing run from a test G-code program.
This is a trial of the HobbyCNC motors and the board beeing controlled by the freeware TurboCNC (DOS)... Working on getting emc2/ubuntu up and running.
Read more about the kit here: http://www.mibot.com/hobbycnc/driver.php (Email me to report bad link)