No they are not at all final, they're still crap
Look at the distance from the tool tip to the bearings above. 3 miles is too much.
Find a good solid cardboard box. Remove front and back. Try standing something on top.
When you figure out how to stop it collapsing, go back to your router drawing and try again.
21-04-2013 #12No they are not at all final, they're still crap
I would agree that the gantry sides are way to slender. You either need to reduce the height of the y axis or thicken up the side plates with some of that profile section. Having now seen the whole design I would reiterate my earlier comment about increasing the distance between the y axiz rails as that will reduce the torsional force on the gantry sides and also give a better ratio of supported to unsupported plate (not sure if that's the best way to describe it?)
The Z axis is way to complicated , get rid of all the blocks and wedging plates. i.e. make the bottom plate as one piece that bolts to the bearing and is also the spindle mount. Do the same with the top plate and make it bolt to the bearing and be the ball screw mount. this will make it lighter, stronger and much easier to build.
Keep at it, as its worth getting right before you start building.
OK I give up and have deleted all drawings to start again, But before I start with a new drawing please can you send a quick sketch of your cnc or a picture as I did not under stand what you mean about the bottom plate as one piece that bolts to the bearing and is also the spindle mount, Remember I have no machining ability so I will be buying the aluminium cut from the supplier at 20mm thick and cut to size as I am disabled and could not hacksaw 20mm thick aluminium plate. But I do have a drill press. I Have been copying some designs but have been adding some extra bracing etc. So now I have a blank screen on my computer and before I start again it would be nice to see your CNC or where to find your build to give me some help in the design.
There is no set way of doing this, best way depends on what you have to work with and what you are trying to achieve.
The newbie mistake is guessing that at some nebulous time in the future you will want the gantry to clear 6".
In the real world you do 99% of your cutting in the bottom 1" because that is the length of your average router bit.
Get it wrong and 99% of your cutting is done at full tool extension and the machine tries to shake itself to bits.
Q1: What height does your gantry need to clear?
Having designed and working with a machine with the C style gantry I would strongly suggest IF possible to move the C so that the Screw is behind it to protect the screw from swarf (I have to clean mine often). While you really do need to increase the rigidity of the gantry supports, that can be done a couple of different methods.
1) go to extrusion for the gantry sides (the solution used on my machine)
2) Increase thickness and add full running ribs to add even more rigidity
3) Increase thickness even more then above and add partial supports to help transfer force to the plate you use for the x axis rails
I would not only go through the build logs here but also go to places like , shopbot, CAMaster, MultiCAM, and a few others and look at those machines and their designs. One of the items about hobby CNC machines is they are often over built. It is not a bad thing but it can add to the expenses without reason. The use needs to be taken into account in the design. Building a machine that can cut steel for doing MDF is over kill and funds used poorly.
Good luck with the design and keep posting, don't mind the gruff from any of the folks here, it is normal and you just take on the information and let the rest go.
Apologies if my comments seem harsh, I am only trying to help you make your machine as strong as possible and easier to build.
My Machine is still on the drawing board and is way different from yours anyway. if I get time I will sketch some thing out for you.
I've attached a design I started 4 years ago but abandoned as I needed a stronger machine, you might be able to adapt afew bits. The z axis has the one piece top and bottom plate I was talking about and also the raised x axis rails might suit your design as it makes the gantry shorter and still gives a good depth of cut. Its not a finished design so I know its not perfect.
That can be done, however you need to be careful not to have the ballscrew far from the Y-rails and spindle, otherwise the stiffness of the axis will be greatly reduced.
Here is my new drawings for my 1100mm X 700mm X 300mm CNC, the only thing that I kept was the bed, everything is new from there.
I lowered the height of the gantry the Z axis from 125mm to 55mm (that's back to the height that I had my very first drawing) from the bed that should let me put a thin mdf board as a sacrificial board. The travel in the Z axis is 110mm.
The gantry sides are made out of two 20mm thick plate aluminium which will be bonded and bolted together, the first one is solid the second one will be lightened. The Z axis will also use 20mm plate aluminium. The backing on the Y axis is 12mm plate aluminium bolted to Aluminium Profile Extrusion. And the X axis can easily be stiffened buy adding more Extrusion to the Bed if needed.
Thanks for letting me see your drawings, and I have seen this design before and dismissed it as being to difficult to build. The welding part is easy but to make it accurate would mean a lot of shimming, as you know welding one side of the metal joint twists the steel one way and when you weld the other side of the joint it will pull it back again. I am not longer able to Cut and grinding steel due to now being disabled. But I do like the Z axis and I would like to see a photo of your machine.
Last edited by Bush Flyer; 26-04-2013 at 11:23 AM.
A quick thought!
Flip the 'Y' axis (top to bottom) arrangement over and add another plate to the back to mount the ballnut and you will always have a nice clean screwIf the nagging gets really bad......Get a bigger shed:naughty:
Looks good mate. are you happier with this as well?
Whilst myself and others could carry on making suggestions to tweek if further I think you have got to the point of a build-able machine, without going into calcs you have gone as far as you can.
The only point I would make and it is minor and that is that you might need to add additional support to the top of the X axis bearings to stop them opening up due to the weight of gantry, placing the rails and bearings on their side will improve load capacity but some of the cheaper bearing holders can give and open up the bearing.
I apologise for misleading you with the table distance as I presumed you meant with the z axis at the top of its travel. I see from your drawing you are talking about it a full extension.
I have seen this design before and dismissed it as being to difficult to build
The welding part is easy but to make it accurate would mean a lot of shimming, as you know welding one side of the metal joint twists the steel one way and when you weld the other side of the joint it will pull it back again
I never got around to building it so no photos I'm afraid.
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