View Full Version : Would this concept work?

17-06-2015, 10:22 PM
Hello again. Just been playing around with an idea in sketchup, probably not that good but think it will help me understand the do's and don'ts from your observations if that's o.k. The drawing is utterly carp, I've only used sketchup for a hour or so. That's my excuse anyway. ha ha.

I want a cutting area of at least 600mmx900x200mm. I think this design should easily do it? I would also like to run the 2 ball screws (1610 1.2m) on pulleys under the bed with 1 stepper to keep them clean and out of sight to make a tidier looking machine also. Is this o.k to do or wont it work that well?

The dimensions of the drawing are approx. 1.35mx0.9m. The height from the bottom of the frame is 490mm. I would use 120mmx60mmx3mm for the main frame and top of gantry. I would use 80x40 for the lower section of the gantry that is connected to the ball screws.

Any help would be much appreciated. Thanks


17-06-2015, 10:27 PM
I would also add 80x40mm supports in the middle of the frame just above the ball screws.

Gantry = around 24.2kg

Frame = 53.6kg

18-06-2015, 02:30 PM
Personally I would mounted the ballscrews on the outside of the bed side-frames and drive the base of the gantry legs directly.

This will give a much stiffer gantry drive system, allows you to fill the middle with a nice stiff bed cross members, and allows all of the bed frame to sit on the table (rather than feet at the corners top raise it).

As drawn it's a lot of work and somewhat of a performance compromise 'just to hide the drive mechanism'. If you are worried about swarf on the screws there are brush solutions possible (see a recent machine built by Dean). But on the outside of the gantry sides is reasonably protected anyway.

You can still drive from a single motor by mounting it sticking out of the rear cross member with an arrangement of belts.

Boyan Silyavski
18-06-2015, 05:24 PM
I agree with that. Though the screws inside seem a good idea at first and even the connecting plate could be made quite stiff, there are some small details to be considered.
-tightening the motor belts and later visually inspecting them constantly. Ones inside it would be difficult to notice something is not right
-adjusting all that contraption, once the machine is heavy
-screws outside are almost at the ideal height for cutting with very short to none arm, to drive the gantry, once inside the arm becomes big, needs additional strengthening which may lead to need for Servo motors due to too heavy gantry

In short- all could be done but on a first build i would aim for simplicity, proven designs, easy to adjust. raising the sides of the table is not ok if you are in a production workshop and need a machine to lift heavy plates to the table. All else is a preferred design, shorter to none gantry legs and additional dust protection. Its proven, dust will not go on screw even without vacuum cleaner.

18-06-2015, 06:43 PM
Thanks for the informative replies. So running a couple of long belts on the outside shouldn't be a problem? I would probably use self tensioners if that'd work? I will check out Deans cnc, cheers.

Yea, I thought about access to the pulley after I did the drawing, haha. Not good. Could put a Perspex plate across the back where no cutting is going to take place, but whats the point. Could put some nice neon lights in there too,haha. :)

Would the top section of the gantry work O.K? As its easy to do, just 5 pieces of 120mmx60mm box section. Looks a bit crude but would add extra 8mm steel plate to support the top too.

Will keep checking other peoples designs as I agree with you guys by making a tried and tested cnc.

I've also seen your project 1 silyavski. Wow that looks like a beast! Very nice. But looks too expensive and heavy for what I want, also I don't think I'd be able to make something like that. Really want to keep the whole cnc less than 100kg.