[ba99297]

Hi
My name is Vagelis and I am from Greece
I would like your advice and your opinion on the plans below.
Involving a cnc (1500mm x 1000mm) which
will runs with Yaskawa servo 400 watt (ordered and is on its way)
Supported drivers 20mm, ballscrews 16mm
Spindle 2,2 KW water cooled (I already have )

Now I am working on drafts of the skeleton
After reading a lot and saw a lot more I finally decided to use steel for chassis bridge, and restrict the use of aluminum only in Z (to become lighter)
Beyond that, as you'll see in the picture the long axis (Y) will have a length slightly less than 1500mm and the supported drivers will be screwd on I beam 120X60 mm
The two (right and left) will be joined by a plate of steel 10mm. To make the joints and set out distortions , each beam will be welded to a steel plate (blue in photo) with 6 holes (drilled oval) for fine adjustments.X axis (on which it moves Z) will put a rectangular beam 120X60 4 mm, which will be joined to the ends of the bridge in a corresponding manner. I would like your opinion mainly for this axis. As you can see at the photos the two supported rails drivers of X axes are not at the same plane , one "sees" in front and the other upwards. This gives me the ability to adjust the squareness of the spindle to the table.
Drivers in Z have distance (from center axis Khandro shaft about 175 mm) is it too;
Finally I would like your comment regarding a post I saw on cnc zone, where someone claimed that the weight (which most are trying to reduce as much as possible) finally is not an "enemy." He supports that the weight offers stability, reducing vibration and resonance as well as the fact that the tendency to fill the holes with machinery and cuttings to the ease finally beyond the aesthetic piece and do not offer anything substantial, however many times the " Slightly "works against robustness.
I would like to say to those who volunteered their opinion to remind them that the motors ( Yaskawa servo 400 watt ) have plenty ofo power for such a construction (I think), so any little excess weight not think to bring disaster.
Thank you for your time
Sorry for my bad english
I expect your advice
Vangelis

[ba99297]

Nobady?

[slimneill]

You are off to a good start with your design.

I'm of the opinion that if your motors and electronics can handle the weight and resulting inertia. Added mass is going to help give you a better final product by being more rigid, have less vibration and chatter will result in smoother cuts. If you go overboard and the bulk of the machine is too large for the scale of the motors and electronics then you are going notice a loss in performance and final product.

I’m not familiar with a stepper setup, but a rigid and study base is VERY important in terms of your machines final capability. You want it to be as rigid and sturdy as possible. It’s the foundation that everything else is being built on top of. It’s going to become your reference points for squareness and levelness. And if it’s not built strong enough to take a beating without moving, you will always be readjusting and aligning your various axes, based on a moving target. The base is the part that isn’t moving anywhere and the weight of it will not impact the motors or electronics at all. So build it strong and rigid, make sure that you can hit it with a hammer or a huge piece of material and it won’t budge or move on you and you will be thankful you spent the added money up front on a piece that at first glance isn’t very important. You have already made the conscious and smart move to use steel as much as possible. Don’t cheap out on a not so rigid and sturdy base. We used concrete to fix the X-axis rails on our build. It’s added weight and the steel doesn’t resonate nearly as loud as it use to when you hit it with a hammer. I’d add a lot of cross member supports to the base to help keep it square if that were my design.

With our build we originally planned to weld the whole thing together as much as possible, but then once we started welding the base we noticed how much shrinkage and warping still occurs even when you are trying to be very careful, instead we moved more towards, welding tabs and adjustment points to parts and then bolting the pieces together and using the required shims and locking nuts once its square, essentially removing the welding warpage from the equation prior to assembly and getting things square.

Is the squarness of the spindle to the table the only reason that the cross rails on the gantry are not in the same plane? I would think that having them in a two different planes will result in it being very difficult to a) get them both parallel and square to one another so that the Z-axis in truly vertical. And B) to fine tune the spindle squareness to the table. It would be easier to shim the spindle mounting base on the Z-axis in or out with respect to a perfectly square gantry and Z-axis then to rotate the whole z-axis and spindle assembly and result in the spindle plunging into the material at an angle every time the z-axis goes up or down. If your not careful any adjustment on or out on the rails will cause a rotation of the whole Z-axis and not just the spindle.

Sorry for the long winded response. Just my $0.02 from a rookie.

[ba99297]

Thank you very much for your answer
I have been waiting for many hour just for one answer to my post
The motors that i will use are 400 watt Yaskawa servo motors, and i am planning to connect them straight to the saft with no gear reduction
The have told me that such motors are strong enough for a 1000X1500 table
Does anybady have ay idea about how much gantry weight i can handle with that motors
In a few day i will post a new plan of my gantry. Isntead of one 120X60 4mm beam(green colour at the photos) i use two 80X80 4mm beams, any suggestions will help me
Thank you for your time

[slimneill]

I would reinforce any plate steel you use with some sort of a rib to prevent flexing,
Like in the image: http://i168.photobucket.com/albums/u.../CNC/cnc_5.jpg
think something similar to a piece of angle iron, it's will flex alot less then a flat plate. When a cantilever load is applied. Think diving board.

I think the base needs some additional cross bracing and support to prevent it from collapsing if hit on the corner.

[ba99297]

I would reinforce any plate steel you use with some sort of a rib to prevent flexing,
.................................................. ...
I think the base needs some additional cross bracing and support to prevent it from collapsing if hit on the corner.

Thanks for your answer.
I have in mind those two observations.
My plans need more work to be done.
I plan to use supported round rail 16mm for the 3 axis . Does anybaody know if 16mm are enough, or it will be needed 20mm. I also want to ask, if i use 10mm steel for the gantry side parts, how many mm should be the the bolt for the vertical joints between two parts of steel

Thanks for your time

[slimneill]

What do you plan to do with the machine? Cutting material, speeds etc?

How heavy do you thing the gantry is going to be on the rails?

How big is the spindle/router you plan to use?

They all factor into the loads and forces applied to the rails and uprights/

[ba99297]

Mostly i plan to cut wood, plastic, plexi glass, and if possible soft aluminium.
I know it is not easy
The spindle will be 2,2 kw watercooled
I suppose the gantry would be about 55 kg

gantry sides 2*12=24
gantry midle part 15
spindle 5
Z axis 3
gantry sides connetor 5
x, z motors 2
total 54 kg
This is an estimation i havent finished my plans yet

[ba99297]

Any other advice?