Well I've made some progress in the past month. After weeks of waiting I finally took delivery on the drip tray. Probably overpaid too, at least it came out looking nice, that is until I unleashed my welding talents (or lack thereof). I went with 0.06" steel sheet since it also needs to support a full enclosure which is still
tbd. Might just throw together some PVC pipes and shower curtain, I really want to get this thing running soon! Rustoleum primer and enamel was used on the frame and mill. Seemed to scratch off pretty easy with just a fingernail, so I tried 1 part appliance epoxy on the drip tray. A little better but still can scratch it with a fingernail. Should've gone with a 2 part epoxy. Oh yeah, the epoxy granite filling went well for the base of the mill. That sucker is solid now, around 350lbs. I'll have to take pictures and explain the process when I fill the Z column later. Figured its a good idea to wait until after placement on the base while I can still lift it myself. Getting the filled Y column in the drip tray was no simple task. As you can see, its way more fun to rig up levers and blocks to lift a few hundred pounds rather than buy an engine hoist. That's how they built the pyramids. Or maybe it was aliens. Didn't want to wait on them though so I went with blocks and levers.
You may also now notice there are 4 blocks on the Y rails rather than the original 2. I was mulling mwood3's question on 1 blocks per rail and messing around with a 6" vise on the table. The whole thing just looked wonky and after a quick calculation with machining forces and comparing to bearing ratings, it seemed certain conditions would get dangerously close to the bearings max moment. Fortunately I was perusing ebay and serendipitously discovered another set of NSK bearings! Their mounting height is a little shorter and will require some standoff plates but this allows me to take the Z bearings and put them on the Y. In order to not lose the10" Y goal I bastardized 2 bearings by removing the end caps and sandwiched them together so that their balls now recirculate through both bearings. This saves me nearly 2" off ball return tubes and thus giga-bearing is born! Probably destroyed the P4 rating since the balls are individually sized for each track but wont be noticeable due to the limitations of the ballscrews. They still slide smoothly which is what concerned me most. I also machined a new saddle plate to bolt the X and Y axis together. This will connect to the old saddle plate still attached to the X axis, making life so much easier when it comes time to combine the X and Y since now I dont have to turn bolts in confined spaces. The only drawbacks I can see is a loss of 0.75" of Z travel due to the extra saddle plate, and the stiction of 4 heavily preloaded bearings is up to 80lbs. May have to turn on backlash compensation in Mach3 since I doubt the cheap chinese ballscrews have the rigidity to push 80lbs without deforming several thousandths. Speaking of, I've also begun overhauling the ballscrew bearing ends.
While the ballscrews and nuts themselves are satisfactory, the cheap pieces of Chinese garbage bearing ends need some serious rework. The rubber seals are so tight on the shafts that they actually start smoking when turning quickly. Off with their seals! Next, all 3 needed nearly 0.025" of shims between the outer bearing race and housing endcap. The one housing that wasnt a press fit would let the bearings float that amount, which shows up as backlash. That's alot of backlash! Lastly, since these AC bearings are not duplex pairs, I decided to shim between the inner races to take out any additional backlash. I managed to destroy 2 sets of AC bearings pressing them off the shaft and out of the housing. Probably more my fault for not having a proper press, but at $6 a replacement from VXB.com its no huge loss. To shim the one good set left I placed arbor spacers (complements of McMaster) between the inner races until the outer races just barely grazed eachother under finger pressure, and then added another 0.001" shim for good measure. This set required 0.006" of shim, though I didnt notice that amount of backlash before due to the press fits probably helping to offset the races some. Could use a little more but I'm hesitant the ABEC1 tolerances would survive heavy preload for long. You can see the super high tech test rig. With the shimming it's getting 0.0015" movement from ~80lbs thrust. Tis all for now, waiting on some boxes with parts to continue. Then I can attempt squaring Y and Z columns once axis are reassembled.
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Originally Posted by Zach_G
Well I've made some progress in the past month. After weeks of waiting I finally took delivery on the drip tray. Probably overpaid too, at least it came out looking nice, that is until I unleashed my welding talents (or lack thereof). I went with 0.06" steel sheet since it also needs to support a full enclosure which is still tbd. Might just throw together some PVC pipes and shower curtain, I really want to get this thing running soon! Rustoleum primer and enamel was used on the frame and mill. Seemed to scratch off pretty easy with just a fingernail, so I tried 1 part appliance epoxy on the drip tray. A little better but still can scratch it with a fingernail. Should've gone with a 2 part epoxy. Oh yeah, the epoxy granite filling went well for the base of the mill. That sucker is solid now, around 350lbs. I'll have to take pictures and explain the process when I fill the Z column later. Figured its a good idea to wait until after placement on the base while I can still lift it myself. Getting the filled Y column in the drip tray was no simple task. As you can see, its way more fun to rig up levers and blocks to lift a few hundred pounds rather than buy an engine hoist. That's how they built the pyramids. Or maybe it was aliens. Didn't want to wait on them though so I went with blocks and levers.
