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Hi Eddy
I thought if I used either of the others the ballscrew could go at the back? (behind the gantry beam...or should it be as close to y axis rails as possible?)
It is the dimensional accuracy that is tempting me with the aluminium section... one less thing to think/worry about, and a 15kg saving on weight cant hurt... or will the extra mass help with damping?
would a bolted aluminium gantry be stiff enough for light aluminium/brass work?
The ball screw on my machine is behind an L shaped gantry and it works fine. I fitted a plate to the front, it's all bolted and glued and I think it's stiff enough to cut aluminium okay. There are other designs on the forum more suited to metal, silyavski for example has a nice design; http://www.mycncuk.com/threads/6457-...9577#post59577
I don't know if you saw this, if you are doing calculations, it's a pity more people didn't contribute;
http://www.mycncuk.com/threads/7155-...6572#post56572
yes I saw both of those, and like both designs, I spent several weeks reading various design/build threads before I started, but for a first build I am finding is a bit much to remember everything
will have another read of silyavski's post... my concern there is welding introducing unwanted distortion but think I might be able to come up with a suitable compromise :nevreness:
gantry based on 200x100 RHS, pretty much all bolted.... this has the benefit of simplicity, which I always like, no need to weld any of the joints, just weld in bolting plates to the ends, only drawback is closeness of y axis rails hence the layout
can I use hiwin rails in this configuration?
Yes you can use Hiwin rails vertical or horizontal, just make sure you can get them lined up exactly in both planes.
Don't stress over the gantry weight you'll be ok upto 80Kg with 2 motors using the correct pitch, motors,drives,voltage etc.
Regards the gantry then again don't stress. Any of the designs you have showed will be more than strong enough but the last one will be by far the easiest to make.
Most of the Steel based Gantry's your are seeing on the forum at the minute are hugely over engineered and quite unnecesserily so in my experience considering the relatively small 2.2Kw spindles they are using on them. Whether that be wood or Aluminium they are cutting.!
I mostly build small/medium routers using much smaller aluminium profile arranged in an L shape which I'm sure you have seen on the forum and they easily handle cutting woods soft or hard and light duty aluminium work. So I can assure you at this size your design using 200x100 RHS is still OTT for just cutting woods.
My larger 4x4 and 8x4 router design uses 120x80 in the L shape arrangment and it also easily handles any cutting forces that a 2.2kw spindle can throw it's way. At your width this would be ideal and massively strong for your needs and very easy to build.
So please don't get caught up in all the Hysteria and paranoia regards strength that seems to be sweeping the forum at the minute.! IT'S NOT NEEDED FOLKS.!!
Your design so far is fine and I'd only make a few changes to the design and Eddy as mentioned them both.
Don't let the diagonals meet in the centre if welding as there is too much heat generated in one spot.
Thou I don't agree about diagonals not going into corners.? Your better having the corner to corner rather than in the middle of a tube as there will be less pulling forces trying to bend the tube. But in both cases it's a not a big deal and much better than none at all.
Forget round type rail it's junk and profiled rail from China as come down so much in price it's not worth not using them.
Don't get too wrapped up in the design your nearly there, you have a good proven design that will easily fullfill your needs just iron out the small details and get building.
Good luck.!
Thanks Jazz :peaceful:
I did/do wonder about the requisite stiffness, but as I have no practical experience in this field I have to read, listen and assess as best I can... I am on a few photography forums and the nit picking arguments about lens quality etc is the same sort of thing I think... sometimes best just getting on with it and having fun rather than worrying about the tiniest improvements.
will make the changes to the frame in final ( hahaha who am I kidding... it will change up to the day building starts ) draft ... lots of stuff to learn/ work out how it goes together yet...but some of the builds here have really given me ideas... and tripled the original guestimate LOL
still plodding on... a question about the best stepper position for x & Y axis... is it better to connect directly or use timing belts? Obviously Z seems better belt driven but it does not have to deal with so much mass/inertia and helps to move the COG back towards the centre of the gantry ( at least that's how I am thinking?)
Use belts, they dampen resonance, and if need be, you can change the gear ratio later on by making one pulley larger than the other.
15 or 25 mm belts? What is the "rule" for minimum radius on pulleys for this kind of application