Last week my motherboard in the little computer I was going to use died. I guess when the power supply blew it took out the motherboard as well. It seems the RAM and CPU are still good so I picked up a AsRock socket 478 motherboard new for $52. In cut a old desktop case in half front to back and installed the board and power supply. Reinstalled XP and everything seems to work good. I am going to scavenge parts out of the old SFF computer to hold the CD-ROM, hard drive, and smart card reader.
I am also looking into installing flood coolant. The base of the machine was originally designed to be used as a sump. I had some worries as the copper air line leading to the air assisted ball screw. I pulled off the cover off the base and stuck my digital camera in there and took a couple blind photos. I found that they has driller right through the wall of the sump. Ouch. And not only only one hole but three! I raised and locked the knee and removed the knee ballscrew. I yanked the old copper line cleaned out the holes with some spray degreaser. I then used some rubber well nuts and installed them in place with a bunch of silicone and tightened them up. I let them sit a while and then put a nice layer of silicone over that. I dont think coolant will get through that!
Since I had the ballscrew cylinder apart I took it apart since I had been hearing air leaking. I found the piston had came loose from the rod/screw and air was escaping through it. I totally cleaned the ballscrew and found aluminum chips in the nut so I pulled that apart as well. The nut is pretty worn. Looks like it will need replacing eventually. I cleaned it out and reloaded the balls and reassembled everything. I added a thin ship between the inner races of the angular contact bearing of the nut/pulley to increase the preload and to compensate for wear. I replaced the air fitting on the bottom to the pushlock type poly line connector and drilled holes to bring the air line out the side of the base along the side to the regulator in back. It moves smoother without all the chips in in the screw nut!
Got a little more done on the mill this weekend. The replacement scale for the one I crushed came in on friday. I picked up a similar model and was able to use my old long scale with the new reader head. The only difference was the new head output in ttl quadrature instead of the sinusoidal quadrature that the old head output in . Plus the new head was a fixed 10X mulitplication out. This gives me 50800 divisions per inch over the old 25400. A little overkill...
Not wanting to cut up cables I made a jumper that connects between the header connectors in the Heidenhain interpolator boxes. Works good. Though when I went o home the X axis would randomly stop thinking it hit the home switch. Eventually I figured out there was some crosstalk from the encoder on the X axis that was tripping the X home input. I moved the input to the other parallel port and the problem disappeared.
I found out Mach cannot stop a spindle at a certain location. No big deal. So I just went with doing normal closed loop spindle control. Initially I tried using the keyence sensors to sense the edges of the fan blades but the pulse time was just too short. I then made a 4 sector encoder wheel in corel and glued it to the fan on the spindle motor. I still could not get a stable signal into mach. It would work fine up to about 1000 rpm and then loose the signal from the sensor. I initially though it was the Opto22 input module that I used to interface to the 5v logic could not handle the rise/fall times. I put a scope on the output of the Opto22 and found I was getting a good signal out. It turns out that again I was getting some crosstalk. This time from the step signal going to my VFD control. It was scrambling the signal going into the computer. I moved it to the other parallel port card and now I have a stable signal to the computer. I ran the spindle calibration routine sucessfully and enabled closed loop spindle control. Now if I put a load on the spindle it will compensate and maintain spindle speed. The next trick is to make a pickoff right off the quill. This way I dont have to do any calculations for ratios due to different selection in the varidrive.
My current plan to do this is to cut out a disc out of 1/4" aluminum and drill a hole radially through the edge and insert one of the fiber sensors. I will then make up a linear encoder strip which I will wrap around the quill for a 2 or 4 segment encoder. The disc with the sensor will mount to the quill cap. If this works I will make a more permanent encoder strip or may just paint it right on the quill.
Next project is to make up a drip/chip tray for the base for when I start to use flood coolant. I have a electrical panel cover from an old promass board loader that is almost perfect for that. I marked it out last night and will take the plasma cutter to it tonight and make it fit. I have a couple holes to plug up when some of the controls were also.
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