Project Logs

Collapse

• Additional optional z plate for Chinese 300W spindle

  Kert • 01/28/2016 at 10:53 • 0 comments

  I added a secondary optional Z axis plate with a hole patter for the Chinese 52 mm diameter 300W 48V ER11 collect 3000 to 12000 rpm spindle. This plate was added into the 6mm kerf compensated nesting autocad file. As a result the plate got 20mm larger reducing the potential Z axis movement range by 20mm. The mounting pattern for the spindle is 20x70mm hole patter taking M6 bolts. On the picture the yellow stuff is "behind" the z axis plate and the red thing is this new optional spindle mount.

• DRV8825 heatsinks

  Kert • 01/23/2016 at 12:12 • 0 comments

  I have ordered few more bits and pieces which will take about 4 to 6 weeks to arrive from china. Few more stepper motors and I decided to give a try to arduino as a preliminary driver for the machine. Back when I was looking into it it was not looking like particularly capable or even outstandingly economic way of driving a cnc machine but over the past 8-9 months it seems something has happened. When just browsing around ebay I stumbled upon an arduino uno clone for something silly cheap - like 3 or 4 EUR or so and I had seen some mentioning of an arduino based thing called grbl. So after reading about it a bit it did not seem too bad at all. So I now have an Arduino Uno clone, CNC shield 3.0 and three more stepper motor drivers based on DRV8825 driver ship incoming. I do already have also parallel port based components sitting in a box so I guess I can try out them both eventually. Ideally I might be able to wire everything up in such a way that I can switch between driving the machine with parallel port and with arduino just by flipping a switch.

  The stepper motors I ended up ordering for X and Y axes (some Nema 17 size pretty long things claiming to deliver 50 N.cm) seem to requite current in the range where these stepper motor drivers will need some heat-sinks to not shut down because of thermal protection kicking in.

  Heatsinks advertised online for these drivers are really small aluminium things claiming to be 11x11x5 mm in size. Because I tend to water cool my GPU's in my PC's I do have various VRM heatsinks sitting around so I plan to use some of these on the driver boards. They seem to be cheaper (when bought as a pack of 10) and a bit more capable than the ones advertised in the net specifically for these drivers. Only problem might be the size. Might have to arrange also some kind of fan over these.

  It seems there is more or less exactly 11 mm between the legs of the driver board and they seem to be sticking slightly higher than the chip itself. While the copper one I have have dimensions of 11,5 x 13,5 x 5 mm and the aluminum one is about 13x14x6 mm in size. Will see once the stuff arrives and I get around trying if I can actually at last make some kind of stepper motor to move - if there is a problem I can always file one edge of the heat-sink down a bit. At the moment I have only one DRV8825 based driver for testing purposes which I was thinking of hooking up to a parallel port interface based board, only problem with that is that my second PC which does have a parallel port is in use at the moment for other purposes and it is inconvenient to test those things at that location where it is at the moment.

  Overall I'm pretty busy at least until end of March so it is unlikely that I get anything done in immediate future. Just the right time to do the orders and wait for the stuff to arrive.

• Huh, it's been a while

  Kert • 01/18/2016 at 09:26 • 0 comments

  Well - I have been rather busy for the past summer, autumn and winter and to be honest I am still rather busy. Anyway I got around to updating the components list at last - this is just the mechanical components (no steppers or electronics) for time being. I do think about this project more or less regularly but lack the sufficient free time to do any significant enough progress worth mentioning in this log. Perhaps I'll get around visiting the laser cutter at last in a month or two with the pile of acrylic sheets sitting under my desk and staring me accusingly.

  I'll see if I can upload also the cutting patterns in here if anyone else feels like giving it a try. If I can then there will be two versions of the patterns - one without any kerf compensation and another set with kerf compensation of about 0.42mm (which is the kerf width of the Chinese 80w CO2 laser ctter present in the makerlab which I can access). The sheets are 400x600mm (which is the working area of that laser cutter) in nesting.

• Linear bearings

  Kert • 04/18/2015 at 11:23 • 0 comments

  16mm linear bearings arrived at last. That should be all the mechanical components from China which I needed for the frame assembly. What I am at the moment chronically short of is free time. Progress is kind of slow if I can spare less than few hours per week for the time being on this project. I have not forgotten about this DIY cnc dream of mine and expect to be able to finish it, just not as fast as I initially hoped to. If any of you want the drawings before I get around to doing the prototype physically feel free to send me a message and I'll upload them somewhere. Current plan is to upload the drawings somewhere once I have made the first prototype and made sure that all that looks ok on digital canvas does so also in the harsh reality which can be a bit less forgiving than ones imagination ;)

• Some more components arrived

  Kert • 03/28/2015 at 12:28 • 0 comments

  It seems some of the packets from China have made it faster than I anticipated.

  However, as noted, I'm a bit too busy atm to do anything with these other than be happy that the packets have made it. Already packing bags and will be sitting on a plane soon. Presumably should be able to dedicate a bit more quality time for this project in few weeks when things have settled down a bit again.

• Some delays

  Kert • 03/26/2015 at 08:58 • 0 comments

  I have not forgotten about this project. Just have been busy with work and will be so at least until mid April. Have a conference to attend and as it usually goes things get busy.

  On the more positive side - anti backlash nuts arrived today and I'm expecting to see the linear bearings to arrive as well within few weeks. The makerlab I was planning to use for laser cutting is a bit behind the schedule, as far as I'm aware, with getting back up and running after moving into a larger building but should also be fully functional soon.

• Overbudget :(

  Kert • 03/02/2015 at 09:19 • 0 comments

  Seems that I am going overbudget. The initial goal was for doing this "undrer 300 EUR" but the material costs before laser cutting will be pushing me up to 325. With the laser fees added I'm hoping to fit within ~350 EUR for the machine with the pen, dremel-mill and USB microscope. A good enough power laser diode + driver would (will?) add extra ~50 EUR to that.

  The material I ordered is about 1.5 m^2 of 6mm plexiglass and 0.85 m^2 of 2mm plexiglass. With the additional cutting fees and VAT this will cost me 95 EUR. Plexi is more expensive than I thought it would be.

  6mm (manual) nesting. 5x 600x400mm and 2x 100x1000mm pieces. There is some spare space which I intend to fill before heading out to cut that stuff out.

  2mm nesting. 3x 600x400 mm was the minimum reasonable quantity so I will have plenty of spare 2mm plexi for making the electronics boxes and other nonstructural components.

  Detailed quote for plexiglass (in Estonian).

  1. 6mm Plexiglas XT kirgas 3050x2050mm 1.46 m2 39.00 56.78

  602x402mm 5tk, 1000x100mm 2tk

  2. 2mm Plexiglas XT kirgas 3050x2050mm 0.83 m2 14.00 11.65

  602x402mm 3tk

  3. Saagimisteenus 1.00 tk 10.00 10.00

  Kokku 78.43 EUR

  Käibemaks 20% 15.69 EUR

  Kokku tasumiseks 94.12 EUR

• Home/limit switches, electronics mounting.

  Kert • 02/21/2015 at 13:08 • 0 comments

  Got around to thinking through the electronics, cable management and what to do about sensors. For X and Y both home and limit sensors are not a problem, for Z-axis I'll probably go with just a home sensor and skip the bottom limit switch - or use something more conservative with space. Current plan is to use inductive sensors - now plexi is not particularly conductive ;) so I will have to glue a little spacer or nut into the locations where the switches are to trigger them.

  There are now a little extra plates under the stepper motors - just in case, as apparently finding long enough M3 bolts can be quite problematic. The basic idea with cable management is that drivers will be located as close to the motors as reasonable, so I will have to route only power and guidance signals to the moving parts of the machine. I do not know yet the exact dimensions of the electronic components so I have provided small mounting holes for boxes in which electronics will be sitting. For cable chain support the intention is to use 30x30 mm L shaped piece of sufficient legth on one side of machine. Similar solution will be used behind the gantry providing signal to the Z-axis. Optionally a compressed air supply can go also through the cable chain (6mm OD 4mm ID hose, ok for up to 4 bar) although I suspect it would be far easier to just hang it down from somewhere above the machine. The 220V power cable for the Dremel (Actually mine is called Combitool 160) will be hanging from above .. somehow. As I am not all keen on putting that through the cable chain as that way it would be rather hard to remove the tool if needed.

  And few more details as well

  Cable chain. I am still thinking if I will use M3 bolt or a similar size blind rivet for attaching that L shaped profile.

  Yellow highlight hole is for inductive sensor and red highlight holes are for putting the box with electronics there. Once the test components arrive and I get around figuring out the exact size of that box.

  Meaning of colors is the same in this figure as it was in the previous one. Z axis top plate.

  X-axis front plate, meaning of the colors same as above.

  So whats next - exporting the component drawings and noting down how many pieces of each will I need, kerf compensation of the components. Nesting them by hand into a 600x400 mm chunks (as I'm not immediately aware of a good nesting program) and then ... then it will be a time to order the materials and after that a cutting time. When the makerlab where I can access the lasers opens in new location early in March.

• Kerf (laser cut width) compensation

  Kert • 02/19/2015 at 17:49 • 2 comments

  Apparently the laser in the Markerlab I'm intending to use uses only and only Chinese closed source control program (with English menus ofc) and a side effect of that is that no kind of G-Code or anything similar access is exposed. Which would be ok, if the laser control soft would have ability to cut with kerf compensation - which it does not apparently. Which leaves only the "hard way" of doing it - by providing CAD drawings with the cut width compensation taken into account.

  Obviously this would be damn tedious if doing it one offset at a time and prone to lapses of attention and human errors. What follows is a description how to minimize errors (at least in the plan in my head currently) in that process and partly automate it (Autocad, in my case but most others that can take LISP macros should work somewhat similarly)

  (1) Export your flat pattern as a 2D drawing. I am using Autodesk Inventor ability to move the drawing in the export process to positive quadrant of X-Y plane and replacing all lines with closed polylines. But practically all CAD programs should be capable of doing something like that. With some additional post-processing might be needed for making all existing lines into closed ploylines and for getting rid of overlapping lines (which would cause the laser to burn that line as many times as many overlapping lines you have). Outer profile and inner profiles in different layers for me and only lines to be cut on the drawing.

  NOTE: Circles remain circles and are not converted to polyline (for me). They must be converted afterwards which is not a straightforward process in Autocad. This: http://forums.autodesk.com/t5/visual-lisp-autolisp-and-general/circle-to-polyline-circular-polyline-to-circle/td-p/3036078 LISP macro can be used for that and seems to work well for that purpose. Load it, select circle and issue "C2P" command from command line and the magic happens making it a polyline.

  (2) A neat LISP macro: http://www.realerthanreal.com/autolisp/offsetmultiplepolylines.lsp is capable of offsetting all selected CLOSED polylines either inwards or outwards by the same offset value (that is why I had to convert regular circles to polyline circles). Obviously mine are all closed lines. I intend to cut them, after-all with a laser. You can call that command by issuing command "OffsetMultiplePolylines" from command line.

  (2a) All INNER profiles will be offset inwards by half of your laser cut line width. The big bonus part is that you can select them all at once and offset them all at once avoiding errors (assuming you manage to select them all, that is why mine are on different layer, I enable only that layer, select all and offset them all, then enable outer profile and offset that separately, that one can be done with a regular offset if its already a single polyline).

  (2b) OUTSIDE profile will be offset outwards by half of the laser cut line width.

  Loading a macro in Autocad can be found Tools/AutoLISP/Load Application... After loading the macro it can be called from command line like regular Autocad commands.

  Top - part before above described kerf compensation process, below after the kerf compensation process. Cut line width is 0.45 mm (based on measuring it roughly in the test parts) meaning the offset is 0.225 mm. If in doubt better under-estimate it than over estimate, I think. Then the holes will be a little larger than intended but if a bolt does not go through a hole if you overstimate compensation it might be an hassle). Now for such a tiny part this is easy, it would be probably even easier to do it just by regular offset deleting previous lines as you go from one side to another. But for a larger part with all the little cutouts, holes for various stuff and so on a manual process would need rather heavy concentration to not miss anything and to not apply offset somewhere twice.

  At least that is the plan so far. We'll see if this will actually work in practice as well when I get around to exporting the flat...

  Read more »

• Z-axis compensation

  Kert • 02/18/2015 at 20:04 • 0 comments

  Good news, it seems. I started digging around to see if it is possible to compensate for z-axis deflection/bend through in my intended software which is linuxcnc and it seems this is theoretically possible:

  "The probekins kins module is a trivkins module with optional Z correction. By default, probekins behaves like the trivkins module.

  The purpose of probekins is to aid milling slightly warped workpiece surfaces, or deal with a machine imprecision, like for instance when milling a PCB when the board is not ideally horizontal after clamping, or slightly bent or warped. The idea is to probe the actual surface at several points covering the whole milling area, and generate Z correction values from the probed values by interpolating between neighbouring points."

  From: http://wiki.linuxcnc.org/cgi-bin/wiki.pl?ProbeKins

  Seems good enough for a start although this particular one seems to be using a linear interpolation. Anyway that means that I will not worry too much about the z-axis bend through for now as long as that is not large enough to cause other issues like, for example, stuck leadscrews or excessive wobble.

View all 18 project logs