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10-10-2012 #21
That would be very tricky to do as the box section is 60mm and the rail base plates are 65mm.......unless i've completely misunderstood. I'd have to mount somthing to the side and offset by 2.5 mm. Tricky but doable.....
There's no way im going to be able to bend the box section. I'd expect the ali back plate to bend before the steel. However they do "look" straight.
Right so that sounds like the ballnut mount is upright mounted against the Z upright and runs between the Y box section beams. I had i laying on it side poking out the back. The rail base plates would be approx 330mm apart if the mount is 200mm. What could you get the ballnut mount down to?
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10-10-2012 #22
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11-10-2012 #23
The SBR25 rail base is 55mm wide unless I'm missing something?
We're only talking small fractions of a milimeter which doesn't require that much force. Both will bend a little bit...
About 160mm if you're happy being limited to only using 1:1 or 1:2 ratio without changing the belt. Don't quote me on that though as I need to draw it first!
It would be fine with 1/2" thick plate, but that doesn't really change the conclusion as it's still expensive.
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11-10-2012 #24
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22-10-2012 #25
Due to a change in plan i've settled on a 1200mm for both X and Y. Ill be using 2 lengths of 60mm box section on a back plate with sbr25 rails to form the Y axis. Y is mounted on the X bearings near enough at the mid-point of the Y bearings. I've not drawn them in yet but ill put some diagonal pieces in to support the Y uprights against the X bearing plates.
Would taking the Y uprights below X bearings and box section and linking up with the opposite side of the X bearing plates offer significant more support to the X bearings?
Y bearings appear to be a little out of position. Everytime i move 1 bearing, they all move! I must have grouped them somehow. Going on the bearing blocks are 65mm i have a 20mm space between the 2 which make 150mm from one end to the other on each Y rail. Is this spacing sufficient?
Is it best to drive Y on the main Z back plate or can i use the shorter Z back plate? I'd like to protect the Y screw from any debris.
Attachment 7198
Cheers
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14-03-2013 #26
Just a quickie in prep for building a PSU. I've got 5 MA860 drivers rated at 7.2A each driving 3.1nm steppers.
When I come to use all 5 stepper they wont all be maxed out at once. What rating of transformer should i be looking for?
I'm looking at 1200VA 2x50 at 12A each. Wire the output in parallel and get 24A. Yes this is below 7.2x5 but would i ever exceed that machining wood/composites/Ali?
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15-03-2013 #27
Bit of a hand waving explanation here, but in short...The the motor coils are rated for 2.1A, and you'll put them in parallel so 4.2A per motor. Due to them not drawing anywhere near full power most of the time, you can design for about 2/3rds of that, so 2/3*4.2*5=14A. 50V, so P=50*14=700W. So you need the nearest size transformer, or combination of transformers above that rating - so most likely 800VA. Plus some capacitors and a rectifier. I've currently got a 500VA and 325VA to power 5 or 6 of those motors.
Last edited by Jonathan; 15-03-2013 at 12:14 AM.
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15-03-2013 #28
With reference to the section marked in bold, you simply cannot make such a sweeping statement, ive just welded my complete 7x4 and i used my dual dial guages one the gantry was clamped and ready to weld and there is no diference in the distorsion after welding or certainly no more than there was before the welding. If you weld it in the correct fashion and you have used a jig to hold the pieces, then it is fine. I will admit that if you use a 2mil rod on an old stick welder crank up the amps and weld 2mm box together you will have problems but a modern mig used to tack the items together before finishing the welding of it turns out fine, im not saying Its better than Ali, just that if care is taken during the welding of steel box no more surfacing and leveling will be required than before you welded it. Obviosly when mounting the rails onto the gantry you will have to do some remedial leveling work but its just not difficult, I will show you how ive done mine in the next week or so and it certaily ticks the 0.05 accuracy box you mention with ease
RickAlways bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
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15-03-2013 #29
Ah the ruddy motor windings! New i was missing something. Ta
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15-03-2013 #30
Even before welding, it's questionable whether steel box section is accurate enough to mount round rails on opposite faces, so no matter how good the welding is it's not a good plan. It certainly wouldn't work for profile rails without further machining or shimming.
How do you know?
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