This is a story about an all steel, 2000 x 1300 x 250 mm work area CNC router, where nuts and bolts replace weldments.
The idea is quite simple and the concept is not new and has been tested and verified to work on a small steel design. I decided to scale it up to 10mm steel sheets.
But my goal was not only to remove the need of welding, but also to integrate a linear shaft support so that round supported rails can be made cheaper. Almost all parts will be plasma cut from 10mm steel sheets. A few parts, like the Z axis moving plate and the ball nut attachment plates will be cut from 15mm steel sheets to reduce binding or avoid bracing. Linear rails are standard 20mm stainless steel shafts. and will be welded to the supports (I haven't found a way to fix them using nuts and bolts that would fit with my design, and I don't believe it would be a good way to do it).
Here are a few renders of the complete Z axis design (calculated weight is 9kg without spindle):
Complete Z axis.
Inside the frame.
This image shows the steel bolt and nut connection, plus the integrated linear shaft support. You can also see how the connections affect the part by cutting the shape of the bolt and nut, and adding joints on both sides of the bolt. I actually made smart components that achieve this. I have a few different versions and sizes for the connections:
- simple: cuts the shape of the bolt and nut
- single: cuts the shape of the bolt and nut + a "tooth" on one side (sizes are small, medium or large)
- double: cuts the shape of the bolt and nut + a "tooth" on both sides (sizes are small, medium or large)
All cuts have a play of .1mm. Bolts are M10 x 35mm with matching nut (standard, grade or pitch don't really matter as there aren't any tapped holes).
Back of the Z moving plate with balll nut support. All made from 15mm steel sheet.
Y: 28kg without gantry sides and without Z
Z: 9kg without spindle
X: SBR20UU + SFU2010 2000mm
Y: SBR20UU + SFU1610 1300mm
Z: SBR20UU + SFU1605 500mm (because it came with supports and couplers, and was cheaper than shorter lengths)
Linear motion electronics:
X: 2 x Nema 23 425oz/in driven by 2 x Leadshine AM882
Y: 1 x Nema 23 450oz/in driven by Leadshine AM882
Z: 1 x Nema 23 425oz/in driven by Leadshine AM882
2.2kw water cooled + VFD
Basic 5 axis board, 4 limit switches, with Mach3 support, from BuildYourCNC.
DIY unregulated 70V 10A, following Boyan and Clive advices.
Where I got the parts:
- Ballscrews + nuts + end supports + couplers are from AliExpress seller Kevin Ho at ROB BEARING AND MECHANICAL PARTS. Contact him if you need custom lengths (that's what I did).
- Nema 23 425oz/in + breakout board are from buildyourcnc.com 3 axis Nema 23 electronics kit (I purchased them 4 years ago).
- Nema 23 450oz/in is from a random seller on AliExpress.
- spindle kit is originally from another AliExpress seller but I found the shipping price too high, so I asked Kevin Ho (the guy from whom I bought the ballscrews) if he could get the kit for me with a better price and he gave me a $60 discount (this is calculated using kit price on August 18th of 2015, which is the day I am writing these lines).
- AM882 drives are from here. Be careful to make orders with maximum THREE drives or you'll pay for shipping. I did an order of three and another of one.
- SBR blocks are from here. Again, be careful to make orders of maximum TWO packs, or you'll pay for shipping. I did an order of two and another of one.
- spindle kit
- 3 nema 23 couplers (made a mistake by ordering 8mm couplers instead of 6.35, so had to re-order).
Solidworks 2014 SP2
Windows 7 Home Basic
Eight year old HP Pavilion DV6500, 2GB RAM, small NVIDIA graphics chipset
Your input is welcome and very valuable to me ! I will make the DXF files when done modeling the entire machine, and when most of you will agree with the general design. Plus, there's no hurry to get the parts, as the company I work with will have them cut in the next 24 hours after they receive the files.
Special thanks to Boyan Silyavski, Clive S, toomast, all members that have answered my questions, and all members that contribute to this amazing forum.
I will start the design of the gantry tomorrow. I am too tired of clicking the Solidworks "rebuild" button for today.
Last edited by eurikain; 20-08-2015 at 12:36 PM.
It's certainly impressive I can see a lot of work has gone into this.
I do worry about the straightness of the steel to get an accurate machine. May I ask why you have not gone with square profile rails? I look forward to watching this develop. ..Clive..Clive
Thanks ! Yes, you are right, probably more than 30 hours of modeling so far, because I went through several designs, and had never used SW before, so I had to learn everything from zero ! But now I've got most of it figured out :D Great program to work with, though sometimes a bit frustrating.
project I linked in my original post, they got a .1 play on joints, 0 play on holes (that's what I've got), and they cut the plates on a .001 accuracy machine, so plays were correct when cut. The machine that will cut my parts has more than .001mm so I'm not really worried about cut straightness. if all edges, joints, teeth and pockets are cut straight I wouldn't see how there could be any straightness error :/ Where would they come from ? Are you talking about the steel straightness itself ? May be I can ask them to surface the sheets from which they cut the parts on both sides ? Would that be a fix ?
Last edited by eurikain; 19-08-2015 at 12:58 PM.
I've used TBR20's on my build and they work well etc. BUT, if I was building it again I'd use profile rail. Why? Rigidity (my rails aren't really long enough for this to be an issue for me) and ease of maintenance. Have a look at the attached pic:
The bearing housing in the block will work it's way loose from time to time despite the top and side grub screws that are meant to hold it in place (you can only nip 'em up so far before the unit binds). Once the bearing housing has loosened it will, over time, rotate and eventually the sharp corners of the cylinder will scrape along the rail supports. This isn't a catastrophe, nor should it lead to a catastrophic failure, but it's an annoyance that'll cost you time and an extra thing to watch out for. No biggie for a hobbyist like myself, but if downtime's something you want to avoid then do yourself a favour and buy profile rails...!
Hi Wal, and thanks for the input :)
I appreciate the advice ! Though I think I won't worry much about this as this is my first build and as I don't intend to machine things that often (I'm still a student and the machine will only be accessible on weekends). I went with SBR rails because in my humble opinion replacing a $5 SBR block every so often is not such a problem :) The machine design is done so that you can take it easily apart whenever you want and put it back together without loosing starigthness, rigidity or anything, as steel won't move when mounting / unmounting.
May be in a later version of this machine I will switch to profile rails and HWIN blocks though :)
Last edited by eurikain; 19-08-2015 at 01:53 PM.
That's fair enough. Just thought I'd give you a heads up. Best of luck with the build!
Hey mates ! (hahahahaha for those of you who will get it)
I spent yesterday modeling the Y axis. Today I will make the gantry sides to fix the Y axis, fix its motor, and connect Y and Z if I have the time.
Here is a render of the Y axis with a section view (calculated weight is 28kg):
Last edited by eurikain; 20-08-2015 at 09:17 AM.
Looking at your renders - in reality, your rails will be supported along their entire length, won't they? Not at intervals, like you've got them in the images..?
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