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20-08-2010 #1
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20-08-2010 #2
Hi Johnathan
personally I wouldn't go for that length of travel on unsupported rail. The calculation you need is for a cantilevered beam, just you have it mounted vertically. As a rule of thumb I look at third points, so for a cantilever of 400mm you would need a 1200mm rail with the mounts 800mm apart. (not very feasible)
If this is a router then I guess this will then be mounted on a y axis gantry and needs moving as well so overall weight will be an issue. Is there a reason you need such a long z or could you just change the bed height
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21-08-2010 #3
600mm is about as much as is practical allready. I read somewhere a rule of 2:1, i.e. if the bearings are 200mm apart then it's acceptable to have the force (of the cutter) 400mm away.
Yes it's a gantry router. I can think of things I'd like to make which need that long a Z, maybe not quite 400mm but close enough.
With regards to accelerating the mass of big Z axis/gantry I should be ok as on the X-axis I'm using two 3Nm steppers @ 70V for the and spinning the nuts, not the screws. The nut is currently held between two tapered roller bearings with a pulley in between.
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21-08-2010 #4600mm is about as much as is practical allready. I read somewhere a rule of 2:1, i.e. if the bearings are 200mm apart then it's acceptable to have the force (of the cutter) 400mm away.
The thing to remember is that all machine design is a compromise, and as such it will be designed for a specific task, if you need 400mm of travel then you will have to put up flex and vibration at certian points and reduce feeds and speeds accordingly.
The other point is that it will only be as good as the weakest bit....theres no point in have expensive powerful motors and drives and then using unsupported rail... it just dosnt make sense.
I hope I dont seem negative or put you off but rather offered some pointers to another route.
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21-08-2010 #5
I've just checked the Igus datasheet and that is indeed the case.
I've already got the expensive powerful motors and drivers on my milling machine. I intending to use those motors on the router and put some 1 Nm ones I've got lying around on the router.
On the contrary - you're not putting me off, yet!
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21-08-2010 #6
Did you save the transformer out the microwave ?
John S -
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21-08-2010 #7
The microwave itself didn't catch fire - sorry I exaggerated a little there. Still it was pretty big flames! So yes the microwave still works fine.
I do have a couple of microwave transformers. I did take the 2KV secondary out of one with the intention of rewinding it for my stepper motors, however I got a toroid cheap on eBay so I left it.
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21-08-2010 #8Did you save the transformer out the microwave ?
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21-08-2010 #9
Based on a point load I get 0.07mm deflection with the two 20mm unsupported rails and the 150mm bearing spacing in the drawing. I'm not sure how to calculate the torsional deflection...this is getting a bit beyond what I've just done at school and I'm too tired to start reading up now so I'll leave it for tomorrow!
I'm happy for anyone to make a valuable contribution :)
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21-08-2010 #10this is getting a bit beyond what I've just done at school and I'm too tired to start reading up now so I'll leave it for tomorrow!
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