As this is my first post here, let me start by saying that I have never built a CNC machine before and other than a general college course on CNC/machining and reading this forum/CNCZone, I have had very little experience with either CNC or machining so hope you guys can keep me right
Following the advice given to others on here, I started reading through the build logs section of this forum and found a few designs I liked and also many handy tips that should help me along the way. I think I am now at the stage where I can start this build log to develop the design and hopefully soon start building! Please see following summary of the design:
- Machine profiles out of Wood/MDF
- Aluminium work ranging from machining profiles from plate and also machining blocks for which typical maximum total cutting depths are around 30mm
- Able to do some detailed work with both wood and aluminium like the Aztec calendar posted here
I understand that one machine cant suit all materials/requirements and so I will be more than happy if the machine is slow at cutting wood but is also strong/stiff enough to machine aluminium.
The attached is what I drew up based on what has been designed and seemed to work for others on this forum, the guts of it being based on Noplace's design and gantry on Ivars design.
- Cutting Area approx 750 x 400 x 100
- 2.2kW Chinese Water cooled spindle
- Rails are HGR20 on all axis (dimensions: 1000mm/600mm/300mm ) with wider type carriages on the X axis only
- Ball screws are 1050mm 1610 (double) on X Axis, 650mm 1610 (single) on Y Axis and 250mm 1605 (single) on Z Axis
- Motors are 3x NEMA 23 3.1Nm. One motor has been used with a belt drive for the double screws on the X Axis based on JAZCNC's setup here. This is mainly because I will be using LinuxCNC and have heard it doesn't support slaved motors.
- Frame design, Z-axis motor and ball screw covers are also based on JAZCNC's design here. Frame is from 50 x 50 steel box section with larger sections being 100 x 50 (3 or 4mm thick). Side plates on the gantry are 10mm thick steel and all other plates including Z-Axis assembly and X-axis support bearing support plates are 20mm thick aluminium.
Some initial Questions -
1. Am I heading in the right direction with this setup or does it make more sense to look at something different?
2. Will 4x M8 bolts supported by the aluminium blocks tapped 15mm on each side of the gantry be enough to support the full gantry? Would it be better to make the supports from steel and weld the gantry box section to this with holes in the box section to get access to the carriage bolts?
3. What is the recommended thickness for the gantry box section? I will be using 3 of 4mm for the frame.
4. I have seen mention of Bearing spacing/aspect ratio on the forum so from the model, measurements taken between the inside of rail blocks and inside of rails are as follows:
X Axis - 42.74mm between blocks, 680mm between rails
Y Axis (Gantry) - 40.50mm between blocks, 150mm between rails
Z Axis - 30mm between blocks, 130mm between rails
Will this be OK or is adjustment of these dimensions required?
5. Is compressed air a requirement for when machining Ali? If so, I will need to build a compressor into my budget.
I haven't ordered anything yet as this is my first build and know for sure that I have cocked up on something somewhere! So I look forward to all the comments/guidance you guys can provide.
Last edited by examorph; 04-01-2016 at 12:43 AM.
Erm i think you should look at your Frame section size in the model because it looks too large to be 50mm and out of proportion. This can affect how things fit so worth putting write now.
As for the rest then it's mostly there with just a few exceptions.
You need ends on Gantry to help stiffen the gantry up.
Brace the ballnut Drop bracket on the Gantry ballscrew and try to keep the Drop brackets on the Slaved axis to shortest possible length.
Put some short legs on it or adjustable feet it will make setup easier.
1 x 3Nm motor driving two screws with belts will struggle so I'd think about using larger motor. 6nm would be better but unfortunatly this means nema 34 and plenty of volts. Idealy Mains voltage drives.
Or other option is to use higher pitch 20mm and gear it 2:1. This will double your torque and lower the actual ballscrew speed so reducing chance of whip and resonance but will give roughly the same speed as 10mm pitch.
Material thickness then 4 mm for steel box and if Gantry is Ali then thick has possible idealy 10mm.
Yes Air is required for cutting ali properly mainly to clear chips and stop re-cutting.
Hi Examorph and welcome to the forum. Its nice to see that you have done a lot of research into this and I think you will do well.
I would not buy any electronics etc until you are well on the way with the build as no doubt things will change with time. I notice you are going with Liniuxcnc you are correct that it is not easy to slave with it although some have done it with extra electronics (but not for the feint hearted). Will you be going down the Mesa route ie 5i25 and 7i76 cards.
Good luck with the build and has been said all questions are good even the dumb one's as they will save you a lot of time and money.
Last edited by Clive S; 04-01-2016 at 08:17 AM...Clive
The Y axis front plate looks like it is a long way from the front of the gantry, perhaps 20mm or so? This reduces the stiffness for no real reason. I would aim for a gap of 5mm or so depending on how accurate you think you can make everything / flatness of gantry section.
Also the X axis connection down to the ballnut looks a bit less stiff than it could be. Can it be optimised a bit more? Maybe raising the ballscrews a bit in Z and mounting the ballnut to the [I]underside of the X axis bearing plate (bolting in the Z direction instead of Y direction). I think I would use another spacer / packer piece under the bearing plate to avoid raising the ballnut too much and creating a problem attaching the bearings and steppers into the frame at each end. You may even be able to mount the ballscrews closer to the sides of the frame (in Y) which all helps.
Thanks everyone for the comments, please see below revised design showing modifications are per your suggestions (I think ).
Still need to figure out some of the finer details for fittings, positions, etc but think it will be OK for initial review.
JAZZCNC - I checked and checked again and its definitely 50x50mm box section drawn in SolidWorks all to scale (although spindle might be out as this was a copy/paste job ). Might look off because of the machine being quite small compared to others (750 x 400 x 100 cutting area).
The ends on the gantry are welded and don't go all the way as I wasn't too sure how else to get access to the bolts. Gantry is all steel, would 4mm box section for this be OK also?
To confirm, as the size of the machine is fairly small, would it still need the 20mm pitch screws or larger motor for the X-Axis or can it do without? If needed, are they 2020 ball screws?
Clive S - Sorry I have never heard of the mesa route before and still after reading up on it I have no clue does the 7i76 replace the BoB and 5i25 act as some sort of motion controller?
RouterCNC - Simplest way I could think of pulling up the X Axis screws was just to stick it onto some box section and weld wherever it needed to be as well as using a 5mm aluminium spacer to help align things as suggested, will this do the job?
Thanks again for the comments and guidance guys.
Last edited by examorph; 06-01-2016 at 01:14 AM.
06-01-2016 #6Clive S - Sorry I have never heard of the mesa route before and still after reading up on it I have no clue does the 7i76 replace the BoB and 5i25 act as some sort of motion controller?
This is where you can get them in Europe http://eusurplus.com/index.php?route...tegory&path=63.
Basically the 5i25 is the card that goes into a pci slot in the PC (Linuxcnc is a real-time op system and does the motion controller stuff) and the 7i76 is the BOB for all the input/outputs etc...Clive
Thanks for explaining this to me Clive. Reason for LinuxCNC was really just because it was free, but after looking at the boards it may end up being cheaper and easier just buying a Mach 3 License and one of these boards.
I updated the design slightly to raise the Y Axis ball screw by sitting it on some box section, similar to the X Axis (not sure if it would be stiffer buying wider box section and turning it 90 degrees or maybe also taller and having it sit at the base of the 'L' ?). Another reason for doing this was that I found on kincreaky's build log that Chai could supply these so I added them to all 3 axis and will get them with the rails/screws as it will save shipping.
This also gives me enough space to go with a belt to drive the gantry screw which might be better?
I remember reading somewhere that 25mm end machining is recommended when using pulleys, will this be enough in my case or do I need more?
The X axis bearing connection looks better now. For info you can buy ballnut mounts off e-bay which are longer than the one you have drawn so give a bigger footprint and are stiffer. They are connected by 4 bolts, not 2 which is better.
On the Y axis the 2 ways of mounting the ballscrews you have drawn are probably similar in stiffness so go for what seems most practical to make - but how will you mount that box section end-on? You mention turning it around which would be better.
Last edited by examorph; 07-01-2016 at 10:52 PM.
Examorth The board that you linked is the pmdx Is an excellent BOB but for the best results it will need a motion controller like say the Ethernet smooth stepper as the PP on pc's these day are flaky to say the least. There will be more support on this forum with Mach3. Good luck with the build...Clive
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