Alexandre Guimar=E3es wrote: > > Hi everyone, has anyone built a home made > > CNC pick and place machine to do SMD work? >=20 > I have the first one built from printer parts and it works but I am > going for the second one with real guides. > The design I will be using > as the base for my new machine can be seen at > http://groups.yahoo.com/group/Homebrew_PCBs/files/Dscn0329.jpg . Nice picture, ouch it's 1.4Mb though... You seem to be getting some sag in the middle of the gantry, you could add a cross brace or box section to the gantry and one supported rail would be a big improvement compared to the 2 unsupported rails. :o) > It is not > worth it, in my opnion and by some experience trying, to use old printe > parts for it. It is cheap enough to make one with the proper mechanical > parts. You can use simple plastic nuts to drive the screws. The only > problems is that you will need access to a mill and a lathe to make the > screws with the proper advance characteristics. You need a screw with b= ig > advance to make the table move fast. I already have some large rugged (all metal) printer chassis, good toothed belts. My current rig gets 6rps x 56mm =3D 336mm/sec, and my stepper drivers are PIC based, giving 8 microsteps, ie 1600 usteps/rev and 28 microsteps to the mm. So it has good power, high speed and 1/28th mm resolution is fine for 0805 SMD stuff. With a microstep driver most belt driven printers will perform this well. Mine has been lugging a 2.5kg load (head) back and forth at 300mm/sec with never a missed step. A pick and place head should weigh less than that. > I prefer using the machine to put solder paste and then the compone= nts > and use the toaster oven method. You do not need any glue !! Even if yo= u use > components on both sides of the board you do not need glue at all. The > solder cauldron will probably not work, the glue could melt and the > components will not like all that heat on them. I can assure you that t= he > toster oven works great. I have more than 3000 boards on the streets do= ne > that way with no returns caused by bad soldering ! Yep, oven was my first idea. I'm currently doing solder paste by hand, and toaster oven. But, after some tests it is a LOT slower than glue and dip technique. Modern VCRs are made this way, they use a heatproof red glue spot, pick and place SMD, then wave or dip solder the board. Soldering takes about 4 seconds, even with my crude test attempts. That's much faster and easier than in a toaster oven. You don't need paste, which is expensive and goes off, and it's easier to build a glue applicator than a paste one as glue flows better. I'm really interested in what your doing, but if i'm going to build from scratch I still think glue and dip is going to be better. > The problems I have not adequately solved yet are how to control th= e Z > axis of the machine cheaply and how to take the components out of the r= olls. > The Z can be controlled by a hobby servo motor and the components might= be > taken from the rolls by using the Z axis vacumm pen pulling the roll an= d > getting the component afterwards. I have not tried that yet. Please tel= l me > if you have a better idea on this areas. I have a suggestion here. Get the parts loose, not on rolls. Sprinkle them on a white tray, then use a cheap video camera into the PC and just get the picker to identify the part orientation and pick it up. You only need a video still capture board, a cheap mono one, some VERY easy image reconition stuff which you can get off the net from the robot soccer guys. I think you could use a mechanical tweezer and rotary head, just sprinkle the parts and let it do the rest. Gluing parts holds then very secure if the board goes through other processes before soldering, like having some larger parts added to the board by hand. Gluing is also safer for double sided boards?? So do you have any pictures of the "old ugly" unit you are actually using now? I would love to see it. :o) -Roman -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.