Thread: Gantry design and FEA analysis
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25-04-2020 #1
Tip: if you can add some bits of bar to stiffen your Z-plate (i.e. turn it into a channel section) you will do better cost for cost than a flat plate. For example a 10mm plate 180mm wide with some 30 x 15 bar fixed down the edges is about 2.5x as stiff front to back as a piece of 20mm plate 180mm wide - go simulate it if you want to. I mention this because you generally end up with some space between the front and back z plates due to having to accommodate the carriages, ballscrew etc., so why not put something useful in there. The front (moving part) of the z-axis maybe isn't such an issue as the z rails will stiffen that.
PS If you want 0.1mm accuracy, you will likely need to design for static deflection figures rather better than that - remember that cutting metal produces a lot of vibration which can mess things up.
PPS what FEA package are you using? looks good.Last edited by Voicecoil; 26-04-2020 at 11:16 PM.
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03-05-2020 #2
Do you mean like this ?
The FEA software is Fusion 360, it is really nice once you get used to it. What kind of ballpark figures should I be looking at for in the deflection analysis ? At the moment I'm not actually taking figures as real world numbers, but more to compare the deltas between different designs.
Originally Posted by routercnc
Originally Posted by routercnc
Originally Posted by Kitwin
Originally Posted by Boyan Silyavski
Originally Posted by Boyan Silyavski
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03-05-2020 #3
You are overestimating my skill and ability! I used a cheap stick welder I bought online which is the only welder I have ever actually used. The pieces were clamped together with C-clamps and vice-grips and if I remember correctly I used a couple of pieces of wood as braces to keep the pieces as flat as possible. I don't have a welding table so worked on the gravel path outside my shed. I clamped everything as tightly as I could before I began and didn't undo any of the clamps until it was finished. Having spent the last couple of days properly aligning this machine for the first time I can say how pleasantly surprised I am with the result of my first attempt at welding. It's needed some shims to get everything level and parallel but has turned out very well I think. The important thing is to think about how you will make your design adjustable, where you will need to have joints that can take shims for alignment and how you will access those joints when the machine is complete without taking half of it to bits again.
An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.
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03-05-2020 #4
Thanks for the advice, yes I think the joints and adjustability becomes really important- so many choices!
Originally Posted by Voicecoil
That does seem like a great idea to add rigidity
I think I've read a few times that it's better to have the guide blocks fixed and the linear rails moving down on the Z axis- I've also seen this quite a few times on builds, apologies if this is not what you mean by saying ('best to have the Hiwin rails fix directly onto the plate')
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04-05-2020 #5An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.
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03-05-2020 #6
Not really, I'm pretty sure it would be best to have the Hiwin rails fix directly onto the plate (which will add some rigidity already, especially with the extra stiffness of steel, so would be worth adding into you simulation) I was meaning maybe either side of the ballscrew (assuming there's enough clearance) or even on the front either side of the spindle mount if there's space. Just trying to help you add some cheap rigidity :-)
The FEA software is Fusion 360, it is really nice once you get used to it. What kind of ballpark figures should I be looking at for in the deflection analysis ? At the moment I'm not actually taking figures as real world numbers, but more to compare the deltas between different designs.
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