It's going to be incredibly slow with 5mm pitch ballscrews.
Hi,
I share with you my design of a CNC router. Quite classical, I tried to optimize the ratio working area vs footprint.
Characterictics and Specs:
- main purpose is woodworking, plastic and a bit of aluminium
- dimension 1700x1250
- working area : 1380x920x225
- I left an opened space on the front to be able to fix vertical pieces and machining the side edge (especially for woodworking)
- SFU2005 ballscrew on all axis (1100mm for X, 2x 1500mm for Y and 350mm for Z)
- HGR20 + HG20CA rails & blocks on all axis (1200mm for X, 1700mm for Y and 400mm for Z)
- 4 NEMA34 closed loop (5NM / 6A / 2.2mH) 1 motor per axis except on the Y axis (2 motors)
- 4 HBS86H motoro drivers
- 4 350W 60 VDC power supply (1 per motor)
- 2.2KW spindle (4 ceramic bearing) with VFD (380V both VFD and spindle)
- Double shielded cable for Spindle power
- All others cables (stepper motor, encoder, proximity sensor) are simple shielded
- UC300ETH motion control + UBB1 breaking board and UCCNC software
- Spindle will be controlled by RS485
- 24VDC and 5VDC power supply for motion controller board and proximuty sensor
- 2 inductive proximity sensors per axis (home + limit) + on additionnal on the Y for homeing and self squaring gantry
- 8020 aluminium extrusion based :
- Gantry : 80x160
- Gantry post : 80x80
- Y : 80x120
- the base is made with 3 80x80 and 4 80x40
- the legs are 80x80
- All aluminium plates are 20mm thick
- All the main construction is built on aluminium
- All "accessory" parts and "cosmetic parts" are 3d printed (PETG). There parts are splits to be printed on a "classical" 3d printer (Prusa Mk3s)
For provision : enough space in the control box to add a 5th power supply + driver for a futur rotary axis
Some design choices:
0. All motors are fixed using motor braket with C5 bearing :
1. On the Y axis, the motors and ball screw and below to gain some space on the side
2. I decided to get bigger rails and profiles on the Y axis compared to the ball screw to get approximatively yjr same size than ball screw + motor bracket + motor. By this way i can get longer base for the gantry support
3. I placed the X motor on the back of the gantry to balance it a bit
4. I screwed 2 plates on the sides of the Z plate to enforce it
I've a question : the gantry post are inspired by the AVID CNC (copied ) I also use the 'interface piece' between the posts and the grantry beam, but, to be honest, with understandy the advantage over a simple fasterner
This is quite common, but i will use plywood first hoping having enough rigidity to mill aluminium replacement parts.
I've attached some rendering of the actual design
Similar Threads:
It's going to be incredibly slow with 5mm pitch ballscrews.
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
It looks rugged.Have you done a preliminary weight estimate to see if your floor is strong enough?If your understanding of the CAM side of the process is as advanced a your ability with the CAD side,you should be set to crank out parts quite soon.
I'm afraid I'm not... I've just started to discover and learn the CAM side... I foreseen a lot of failed parts and broken bits
For the weight, the floor is not a big deal. But I'm a bit concern about the overal weight of the gantry (and its inertia) : i estimate the gantry weight around 65kg
Hi Vodka - The gantry screw you have speced can push out over 500kg of force. The small arm you have connecting the drive to the saddle will bend quite easily, plus it will deflect quite easily giving you poor accuracy. cheers Peter
I guess something like that should be better :
- the arm tight to the ball screw nut is shorter and stronger with a triangle shape : I keep two small aera parallel to the nut: i will use them as reference for my proximity sensors (limit + and limit-/home)
- the bend radius of the dragchain can be bigger
I also think about adjustements
For Spindle trimming, i though putting a small adjustement scew on a side of the spindle bracket, having one bracket fixation hole quite fit as pivot point, and the 3 others quite loose for the adjustement. But this is for the trimming on the X plane .... what about the Y plane ? any idea / suggestion ?
Another question about scew : typiccaly, the DIN912 screw, is it better to use stainless stell or Zn ?
Maybe attach the spindle mount on a longer vertical plate then use shims to the top or bottom as required. Pop/beer cans or whatever that doesn't compress a lot.
Here are some renders on the updated design, taking in account your feedbacks
Thanks guys
Hi V0 - go straight across with the bracket 1) you pay for the material you cut out so its $$$ in the bin 2) its stiffer if its straight 3) its easy for you to do (if your cutting it say with hand tools) or cheaper if its straight but mainly 2) its stiffer which is really important... Peter
Actually, I've thought about that .... there are here and there some "spacers" and I would use the wasted material to machine these little pieces
But you were right guys, this version bracket is way more stiffer.
When i moved the motor/ball screw on top, my concern was : what about the gravity center (and therefore, the inertia of the gantry) ..i'm a bit affraid of vibrations
Hi V0 - Minimising the stack height of the Z is tough on this sort of machine. The answer is rigidity. It doesn't really matter where the CG is as long as your structure is stiff enough. Take advantage of all available space to make every element as big as possible. Geometry is your friend. for a 1.25 increase in size you double the rigidity so look at every part and make it as big as possible. Take advantage of height as this does not impact the foot print of the machine. Keep at it... Peter
edit
since you are making plate parts I'd consider making a plate gantry. Gives you more opportunities for geometry and stiffness. Construction sections are not stiff for their size or weight. see attached...
Last edited by peteeng; 03-03-2021 at 02:47 AM.
He means constructing a gantry out of plates (not extrusions)
The 8020 / quick construction extrusions lose a lot of stiffness by having channels in the outsides.
Hi V0 - You also mentioned vibration. In another thread there was a lot of work done tracking down vibrations to the small free edges in construction extrusions and the thin free ends. Although convenient these extrusions have a lot of negatives... Now's the time to sort through these issues. Making prototype parts from ply is a great idea... Every part must be reviewed and you have to ask the Q can it be stiffer? eg the bracket attached...Using plate the gantry can be twice as stiff yet the same weight as the construction extrusion....You can still make parts shapely or attractive but not at the cost of stiffness...Peter
Its fine to use extrusions if that's what you want to do. But you will build a better machine from plate and std extrusions then using construction extrusions. Another issue with these is cutting the ends square. In CAD your ends are perfect in reality its quite hard to cut them square so they bolt together square. A few threads cover that as well.... Keep at it...
here's a very good plate machine for ideas
Last edited by peteeng; 03-03-2021 at 05:25 AM.
Laminating ply with aluminum? Attractive, low cost, and functional. I'm definitely considering this for my build.
I'm not especially ocnerned about squareness of the end except for the gantry side.
The post is screw on the sliding plate, then the 90° angled bracket are also screwed. and finally, the side plate because I need access to screw that fixes the gantry beam. ... It will be quite hard to proceed, and once it will be possible to check the splindle trim error in the XY plane (back and forth), it will be very hard to adjust it
This is probably why the posts on avid cnc are only fixed on the side plate