[silyavski]

Hi,
Time goes by and soon will need a bigger and stronger machine. Before half an year i spend quite time designing my next one. I called it Simple CNC as i like simple things. Now decided to follow with my project. I will redesign it again for the sake of refreshing my memory and checking the suppliers stock. Nevertheless i would like to be an open project so i will share the plans.

About the design:

notes:
1. I live in EU so all measures in mm
2. construction: 180x80x4 mm main profile and 40x40x3 mm reinforcing profile, 10mm steel plates/at the gantry sides
3. workable area 1300x1300 mm
4. 3 rack and pinion drives from CNCrouterparts nema 34 and ballscrew at Z
5. HSK LY20HL rails from Automation overstock / i have to ckeck if there are still available
6. 12cm z depth and total 18cm workable Z when spindle moved to upper position
7. 2KW water cooled spindle
8. Sill haven't calculated the exact weight but it will be around 200kg, so it should be quite stable

My purpose with this machine:
1. stable, simple and relatively cheap machine
2. truly universal - suitable for fast woodworking,serious aluminum routing and apart of that even for removable plasma bead. Good enough to accept and cut half of standard panel /as sold in EU/
3. precise

will update regularly the drawings/ Sketchup/

When i say cheap i mean cheap. the iron itself is like 200 euros. And the guides i believe were like 800 shipped to Spain. Lucky you who live in USA.

So , how do you see it from engineering point of view?

The point discussing it here is to have a free universal design anybody could build and scale if longer machine needed. I will leave the design as table top as even if i build a 3m long one it would be like this, for the sake of portability/ i don't own my house/. Thanks for reading

hi res pictures and the current sketchup file:

http://theyatagan.com/storage/Simple%20CNC/

[henningda]

Hi,
can't really comment from an engineering point of view. I've only built a CNC out of MDF earlier and was planning to do one made of slotted aluminium. Now that I saw your design I was kinda inspired to attempt in steel.

Just wanted to say I'm very interested in seeing how this progresses. Please keep us updated!

Maybe a stupid question, but what is the purpose of the two profiles on the underside of the table?

[dmalicky]

Nice clean design. As you probably know, it's challenging to design a long moving gantry to do heavy cuts in aluminum (very stiff), and also do fast cuts in wood (not too heavy). Some thoughts from a mech engr view...

- It's smart that you made the z depth shallow -- machine stiffness at the tool is proportional to the inverse square of the z height ( 1 / z_height^2 ).
- The tubular cross-member for the gantry is a good choice. For the 1300 length, 180x80 is probably on the small side for serious aluminum work. The 4'x8' commercial machines are in the ballpark of 200x200, I think. I'd delete the "ladder" pattern on the back and increase the main tube to at least 180x120 (to be both stiff and light, go for the biggest cross section with the thinnest wall). That will be much more effective, and less welding will keep it straighter. And it's simpler.
- The gantry tube will need some internal bulkheads to keep the cross-section from distorting into a parallelogram (from cutting loads in the long direction). The gantry uprights do that at the ends, but bulkheads are also needed spaced down the length. I've done some FEA modeling on a similar design and found just 2 internal bulkheads improved the stiffness at the tool by about 3x. To attach, some small rosette welds should minimize distortion, or use epoxy and bolts.
- It's good you made the main rails a little above the cutting table. I think that's optimum as it's in between both the CG of the gantry and the tool tip forces, to minimize both of their lever arms.
- The gantry uprights could probably use more stiffness in the lateral direction.
Keep up the good work!

[silyavski]

Hi, sorry, a lot of work these weeks.
Ok.

Nice clean design. As you probably know, it's challenging to design a long moving gantry to do heavy cuts in aluminum (very stiff), and also do fast cuts in wood (not too heavy). Some thoughts from a mech engr view...

-Quite a challenge:violin:

- It's smart that you made the z depth shallow -- machine stiffness at the tool is proportional to the inverse square of the z height ( 1 / z_height^2 ).
- The tubular cross-member for the gantry is a good choice. For the 1300 length, 180x80 is probably on the small side for serious aluminum work. The 4'x8' commercial machines are in the ballpark of 200x200, I think. I'd delete the "ladder" pattern on the back and increase the main tube to at least 180x120 (to be both stiff and light, go for the biggest cross section with the thinnest wall). That will be much more effective, and less welding will keep it straighter. And it's simpler.
- The gantry tube will need some internal bulkheads to keep the cross-section from distorting into a parallelogram (from cutting loads in the long direction). The gantry uprights do that at the ends, but bulkheads are also needed spaced down the length. I've done some FEA modeling on a similar design and found just 2 internal bulkheads improved the stiffness at the tool by about 3x. To attach, some small rosette welds should minimize distortion, or use epoxy and bolts.
- It's good you made the main rails a little above the cutting table. I think that's optimum as it's in between both the CG of the gantry and the tool tip forces, to minimize both of their lever arms.
- The gantry uprights could probably use more stiffness in the lateral direction.
Keep up the good work!

- the thing is that they sell the tubes 6 meter long, that is why i calculated everything to be 6m long or multiplied. So mentally i was stuck with the gantry made from the same profile and reinforced
- I also believe that sectioned reinforcement will be much more stronger than bigger gantry and not to forget vibration proof. if i use one bigger square tube the wall thickness will be 5+5=10mm , and now is 4+4 + 3+3+3+3= 20. So the gantry is like made from 10mm walls. Furthermore i will use big motors with 2:1 or 3:1 reducers so actually i investigated quite a bit and there will be no problem filling that gantry with something/ cement, gel, epoxy or whatever to make it stiffer and heavier.

PS. Possibly at the back of the gantry there will be housed something and further covered with bolted steel plates which will make it unbendable in Z direction. I am a fan of spreading the forces and balancing them with sectors instead of big whole piece. When i think of rectangular tubes, i am more worried from twist not straight bend, thats why the reinforcements, they make more thick overall corners compared to a single profile, hence less prone to twisting. Correct me if i am wrong.

what do you mean internal bulkheads? can you please explain me better?

Hi,
can't really comment from an engineering point of view. I've only built a CNC out of MDF earlier and was planning to do one made of slotted aluminium. Now that I saw your design I was kinda inspired to attempt in steel.

Just wanted to say I'm very interested in seeing how this progresses. Please keep us updated!

Maybe a stupid question, but what is the purpose of the two profiles on the underside of the table?

The table base that holds everything together and prevents bending in all directions. It makes , how to explain, the forces act on sectors instead of the whole length. Something like spreading the eventual leverage.

[ukracer]

Hi,
Time goes by and soon will need a bigger and stronger machine. Before half an year i spend quite time designing my next one. I called it Simple CNC as i like simple things. Now decided to follow with my project. I will redesign it again for the sake of refreshing my memory and checking the suppliers stock. Nevertheless i would like to be an open project so i will share the plans.

Is there an update on your project mate??

[silyavski]

Is there an update on your project mate??

i revised the plans and still checking on the prices of rails.

it is quite tempting to start building it right now, but..$$$. So i decided first to source and buy the rails. The drawing can be adjusted with some mm but not if soldered before buying the rails.


The main doubt is 3m or 1.5m long. If longer i should go with supported round rails TBR25 or similar. I have a plan for the 3m version with round rails if sb is interested