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| Brushless DC Motor Spindle by c raynerd |
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| raynerd:
Cheers Peter. I`m going to put my hands up here and say I`m useless! My grub screws always slip. I`m guessing here, but I think the grub screw on the original shaft is M4 ish. So would you drill 4mm so the grub goes into the shaft or just shallow mark so that it is essentially sitting on a flat? I`ve filed flats before and my grub screw always ends up slipping and I don`t understand why since in theory, it can`t!! Chris |
| Bluechip:
Chris What's on the end of your grub-screws ?? A point ?? The cup/knurled cup/dog point hold a lot better. Particularly the latter if you do a small hole to accept the end. You can , if you have enough room, stick a second screw on top of the first, as a 'lock-grub-screw'. ie. two short instead of one long one. If you are going to put two in different places, the second goes at 90 deg. For some reason shaft retaining collars / gears etc. on machines are always like that. Why, I don't know. IIRC there was some explanation given in the ME postbag section decades ago. Why grub-screws anyway? If it's permanent, poke a taper pin in the wretched thing, or even a roll-pin. Taper for preference. BC |
| John Rudd:
Thought I'd chip in with a couple of things...... Is your power supply capable of being current limited? Brushless motors can draw a fair amount... I'd stick with the single grub screw...If you stall the motor (potentially this could happen) you will either burn out the speed controller if the power supply isnt limited or may damage the motor windings... :zap: It makes sense to have a 'weak link' so to speak.. If I'm talking rubbish just ignore me.... :scratch: |
| raynerd:
Hi guys, just updating this thread as I`ve not had much time to do so recently. I stripped and rebuilt the spindle and while doing so, I took some pictures: Here are all the bits. You`ll notice the surface marks where the bearings were skipping on the previous built due to not enough tension and slight misalignment. I hope this is now stopped!? You can see the thust bearing on the shaft up need the head of the chuck. The bearings are separated by a number of washers which will compress to apply tension to the bearings. Bottom half of the motor is screwed up: And the bell slid on the shaft with a grub screw tightening this up. There is now a flat milled onto the shaft: It is working well so far. I`d love to know how it would perform as a tool holder grinding spindle on the lathe! According the my hall effect sensor and Mach3 - I can get 10,100rpm max speed. Chris |
| raynerd:
Just to bump this back to the top as I`m hijacking Erics CNC build thread with comments on the spindle. As John has mentioned in his post above, I am having issues with the power supply. It works fine for wood and plastic, but starts stalling on other harder materials. I`ve cut brass and ally, but the cuts are so small it is almost impossible unless the material is thin. I was told the ATX probably wouldn`t do. Swarfing - I know you said to tie two ATX supplies together, problem is, I already have 2 tied together to run my cnc machine steppers so that would be 4 in total! Rather than going to the trouble of trying to find two more, I think one of these cheap Chinese made 12v supplies will be OK. What sort of current will this spindle be trying to pull? As John said, I`m guessing if I allow it to pull too much current it will burn itself out! Chris |
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