Thread: How much deflection to expect...
Cheers Geoffrey, nice of you to say so - perhaps a bit of a toy compared to some of the stuff these guys are building, but it's a toe in the ocean and it'll be fun getting to grips with the software and making it move!
You can think of the stiffness readings as spring constants, which can be combined as you would for springs. So in this situation you would have the same force applied to the spindle (i.e. Z-axis) and bed (i.e. X and Y axes), which is like having two springs in series - so to find the overall spring constant (i.e. stiffness), measure them both and use the following formula:
Then if is greater than 1000N/mm, you're in business. Unfortunately you can't really simplify that, but if one of the stiffness readings is significantly lower than the other (say 10*), then you can just use that as the overall stiffness wont be affected much by the other one.
Do it now.. it's the sort of thing that you'll get away with for a while, but will cause problems soon enough as it prematurely wears the bearings/nut.
Last edited by Jonathan; 14-01-2014 at 10:13 AM.
>If you dismantle the ballnut you'll probably find there's a ball in the wrong track, or bits of swarf in it.
Heh, no - I'll find myself on ebay looking for another one as it becomes clear that I'll never put it back together again..! That particular nut is very easy to get to as it sits directly under the table. Thanks for the tip re: bearing alignment. I did take my time putting it together and nipping things up progressively whilst moving the gantry from one end to the other. I'll have another look at it now. Despite the bit of binding when pushing the gantry by hand, it's still pretty easy to turn via the screw...
An update from the last couple of days, although I guess I ought to start a new build thread really - going a bit OT. I'll make it quick:
- Flipped the rubber - the protective flaps are working now - they look a bit kooky, but so long as they keep the worst off, I'm happy. Will also fit 'em to the table to protect X-running gear.
- Motors mounted and wired in (thanks to Clive S for the covers!)
- Monitor mounted to the frame and PC installed. Really nice having the DRO right next to the work-area.
- All gantries moving, a quick check of run-out along table X shows .07mm - the majority of which happens towards where the hint of binding was showing up - I'll whip the rails off and make sure there aren't any high-points.
All in all coming along quite nicely, still unconvinced by the clicky ball-nuts - I take it that they come pre-greased? Or should I squirt a bit more in..?
On my British made (Devon) machine I can get 1mm deflection at the collet with 1 finger pressure !!! That is why I plan a rebuild soon
BTW Wal - Your machine looks good, nice work !
Last edited by cropwell; 15-01-2014 at 11:41 PM.
Coming along nice and looking good. . .
If that screen is a touch screen then i'm not sure I'd have it that close to machine.?. . . . I wounce used a friends machine with a touch screen mounted next to machine but on a swivel head and while using the bloody thing kept Stopping, feedrate would change and all sorts of strange happenings.?? . . . Anyway after calling my mate's machine some nasty names and calling him over asking what the F'#k was happening he turned screen away and said try again.!!. . . . Yep flying chips where hitting it and changing feed over ride, feed hold etc. . . .Lol . . Was Very Funny.!!
>Yep flying chips where hitting it and changing feed over ride, feed hold etc. . . .
Hehe - nah, this isn't a touch-screen, although I ought to find some sort of cover for the keyboard - I can see those chips finding their way in between the keys.
Okay, I'll add a bit of grease - are there any tips on making sure that you don't over-pack the bearings?
Cheers guys, nearly there but loads left to do..!
Right, the build is nearing completion with homing and limits nearly all sorted, just need to machine me some new switch mounts - the ones on at the mo are rough fabricated jobs and I thought it would be cool for the machine to make nice ones for itself. Here's a vid of the mill cutting the switch mount profile shape into a block of semi-scrap 6082 I have lying about:
In the vid I’m using a 4mm square end-mill (2 flute) which is spinning at 12000rpm with the work feeding at 400mm/min. My initial depth of cut was 0.5mm with a 12.5% step-over. it’s a climb milling operation. Ignore the holes - they’re not part of the job, I used the plate to cut spacers from a while back… By and large, I'm pretty chuffed with how this test cut came out.
I've also had a go at perspex, which machines very well at the same settings as above (but with a faster feed-rate of 1200mm/min).
The other day I tried milling these switch mounts out of the ali that Apple use for their Mac Pro towers, which just shredded up like this:
I tried a few different feeds/spindle speeds, but to no avail. Earlier this evening I tried machining 'em using some old 3mm ali sheet that had been lying under my dads bench for probably the last 20-odd years, still no joy. Any recommendations on the grade of 3mm aluminium sheet I should be looking at for this kind of profile cut?
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