Right... this is my first attempt at a useful response to somebody. I am reasonably new to this so please feel free to disregard my points I will not be offended.
To remove confusion, I have taken the liberty of marking the axis on your drawing...
Different people refer to the three different axis as different things, so ive done this for the purpose of my post, if my comprehension of the axis's is wrong it doesnt matter because it will work for the purposes of this post.
Ok, for a start ... weight... in my opinion dont worry about it... forget it... make it as heavy as you can. Only places you need to worry about weight is the carry weight of the gantry. not the bed of anything that doesnt move...even then you dont need to worry about it that much. Your initial post you say wood and possibly aluminium... you need to decide because this will greatly effect your design......
lets assume you want to do aluminum... or even deep into wood.. if you don't now, you will once its working. So think strength!... stuff cant flex, they use big words on here like 'resonance' and 'inertia'. essentially it has to be ROCK SOLID!. So make sure you use the materials you have in the best way to make making the most of them to achieve the most strength.
Firstly, you need to ensure your bed is VERY well supported throughout (not just in certain areas) so id suggest some cross bracing of some description underneath whatever material you decide to use as your bed. (ive drawn some in yellow). Id also probably triangulate the walls of the bed. so perhaps mount the entire bed frame on a flat metal plate. so plate on the deck build your bed frame on that and bolt it to the bed frame? although it could be said the bed material that goes on the top will do this for you anyway.
next thing id look at is that gantry... the runners on the x rails look far far to close together? Ive marked in blue.. look at pretty much any of the other legged lifted gantry designs on here or on youtube... all of them have the gantry 'legs' triangulated to spread those bearings apart a bit... otherwise imagine you are milling a straight line right the way through a work peace... the miller will go in the workpeace and you will then attempt to drag that entire gantry forward.. with the present design you will see flex in those gantry legs... in actual fact what you will see is judder.. it will move forward a bit.. the gantry will flex back. the gantry will spring forward and then move forward a bit again... unless you widen the part I have marked in blue (do you agree?)
I hear the other points in relation to the thickness of the material., but Id say thats in-significant compared to the narrowness of those gantry legs. and how close the x bearings are together.... tall people have longer feet....
Y looks pretty good for now.
Z looks a bit long... (or the beds too low!) again. imagine the straight line scenario I explained above. imagine you have triangulated those legs to remove the flex... next thing thats going to flex is that long Z plate.
read through every one of the build threads.. submit some more ideas. Im still learning but I thought id make my comments as I know how pleased I am when I get a reply on my build thread!
Finally, you have obviously already bought the TB6560. So dont worry about that too much for now. just concentrate on the design of your frame. In time as you learn more and more you may decide to replace it. for a slightly different setup due to vulnerabilities this gear has because of the fact its working to its absolute limit just running the steppers. but like I say dont worry about that too much for now.
try google sketchup.. aka 'trimble' free. there are loads of tutorials all over the web.. and it has a 3d warehouse.. where you can type in your bar like RM1610 or whatever and it will be there on the screen and perfect measurements...
Last edited by kingcreaky; 12-12-2012 at 09:38 PM.
Ok guys... I'm gonna redesign this over the weekend and post iz back for further comments ;)
Guys... If I would use extruded aluminum profiles.. What size do you recomend? 40x40, 50x50, 40x80??
Could I use light versions of profiles? Weight of this is quite light, I'm not sure how stiff it is??
Not sure what size you should use so will leave that for someone with more experience but I would say definately don't use the light version of any aluminium extrusion, the wall thickness on them is not up to the job which would make the machine a lot less ridged.
King creaky is right, the gantry sides need to be wider at the base. it is too slender and will cause the bearings to bind under load. It looks like you are using on 100m block on each side? I would change that and use 2No. 50mm blocks and then space them at least 100mm apart. The 2 thirds rule is a good basis (300mm high so 200mm wide) You could reduce the spacing between the y axis rails and lower the assembly which would have the same effect.
The z axis could be improved by putting the rails on the z plate and the blocks on the y carriage. this would lower the c of g at full travel and more importantly make the z axis very strong in its top position. meaning that if you want to make cuts in tougher material you just need to raise the work piece on the bed to use the increased strength.
Using a large plate for the rail mounts is a waste and is just adding weight, this is were you can economise. 10mm plate could be used for the gantry sides providing you also used some triangulation, or added another pair of cross members behind the rail mounts to increase the lateral and torsional stability. If it was me I would use 10mm plate for the sides and then use 4 No. cross rails in ali extrusion,(the 2 back ones could be lightweight as the are for bracing not direct loading.
Finally I would swap the orientation of the Y axis lower rail so it is upside down and a mirror image of the top one. open bearings are weakest on the open side so as you have it the cutting force pushing up is acting against the weakest side of the of the top rail so it isn't being effectively used. By mounting them back to back they offer a better spread of load capacity and make the machine more rigid for the same components. I'm not say what you have done is wrong or wont work just offering a refinement that might make better use of your components.
Hope this helps and is just my opinion
Thanks guys for your inputs ...
In the meanwhile a lot has changed ...
When I realized that I'm gonna spend almost same amount of money on this machine and on machine 1500x750x300(effective travel will probably be around 1300x500x180) I switched to bigger size right away.
So I changed drivers and went for this - THB6064 special 1.1 description - around 45V, and 4.2 A.
Also I bought some aluminum to see and test ... It seems to me that 15x150mm should be stiff enough in combination with 40x40 and 40x80 aluminum extrusion. Extrusion I will use as "support" on x-axis (1500mm - I plan to use 40x80 extrusion) and y-axis(750 I plan using 40x40). On them I will mount rails.
I will also use SBR16 rails for all 3 axis, I'm thinking that this is also adding rigidity.
I will use Ross77 advice for z-axis cause it makes most sense to me also, also I'm thinking using 15mm thick aluminum for z-axis plate.
y-axis I will also design according to Ross77 comments putting rails vertically and opposite, lower facing down and upper facing up.
So gantry will be in 15x150 mm aluminum and 40x40 combined with 40x80 aluminium extrusion.
I'm guessing that this should prove to be stiff enough.
Also all ballscrews I'm gonna use are 1605 together with BK12/BF12 end support.
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