#qi-hardware IRC log for Wednesday, 2013-12-25

whitequarkroh, wpwrak_: what do you think of this CNC machine? http://www.mydiycnc.com/the%20design04:52
whitequarkor this one: http://www.ebay.com/itm/CNC-3020T-DESKTOP-ROUTER-ENGRAVER-ENGRAVING-DRILLING-MILLING-MACHINE-NEW-p8-/20072179877305:22
DocScrutinizer05>>Shipping: $399.00<< WTF?12:48
whitequarkDocScrutinizer05: doesn't matter, there are others selling the same machine with sane shipping price12:49
DocScrutinizer050.05mm precision sounds good, if that's true12:55
DocScrutinizer05particularly spindle motor axial often is a problem12:56
DocScrutinizer05when the mill axis has 0.1mm room to move up when under pressure and come down again while slowly milling too deep into the workpiece, you got a pretty nasty problem12:57
DocScrutinizer05you *might* be able to cure this by simply rotating the whole contraption upside down12:58
DocScrutinizer05but obviously you mustn't have slackness in any other of the parts then12:59
DocScrutinizer05well, in any of the parts that get pushed up by mill engaging to the workpiece12:59
DocScrutinizer05the pricetag for that thing sounds reasonable, when it's not a flimsy scam13:01
DocScrutinizer05however please ask roh who seems to have some RL experience with those sorts of machines13:01
whitequarkDocScrutinizer05: I've seen several people on the net who bought this machine13:02
whitequarkthe general consensus seems to be that its mechanics are up to the task13:02
DocScrutinizer05maybe a good idea to check by google what they are doing, and then asking them what they think about it13:03
whitequarkno need, the guy already described it in the blog: http://makerflux.com/projects/my-new-cnc-router13:03
DocScrutinizer05for an artist interested in milling tiny angel figurines from wood, the machine may be perfect while still completely unsuited for e.g. PCB milling13:04
DocScrutinizer05(not saying it actually _is_ not suited for PCB)13:05
whitequarkmain two complaints seem to be shitty wiring (I can cope with that), and the fact it requires a hardware parallel port13:05
DocScrutinizer05I don't know the machine13:05
whitequark(the controller is *incredibly* dumb)13:05
DocScrutinizer05no problem either :-P13:05
whitequarkeither buy an old PC or use a micro to reimplement half of the control logic13:06
DocScrutinizer05actually that's better than the controller being incredibly fubar13:06
DocScrutinizer05huh? use a usb-parallel adapter13:06
whitequarkI suspect the controller is done entirely of 74HC series or something like that13:06
whitequarkDocScrutinizer05: doesn't cut it. timings are off13:06
whitequarkwith HW LPT port it even requires Linux RT, the regular one won't work13:07
DocScrutinizer05errrr- ummmm13:07
DocScrutinizer05prolly a job for a beagleboard or sth like that then13:07
whitequarkan atmega would suffice :p13:07
whitequarkbut, yes.13:08
whitequarkit's not a problem for me either13:08
DocScrutinizer05or simply abuse an old injet printer's control logic ;-P13:08
whitequarkthat actually sounds much more complicated13:09
DocScrutinizer05yeah, it is13:09
DocScrutinizer05but it shows what grunt in MCU you need13:09
DocScrutinizer05I can't think how a USB is too slow13:10
whitequarkI think it's more the fact that it doesn't have guaranteed latency that's a problem13:10
whitequarkwell, not with interrupt transfer, which USB-LPT adapters use13:10
whitequark"You also need to be aware that there are not limit switches, and the system is open loop in design. The spindle speed control is manual, which is not too bad for a tool this small."13:11
DocScrutinizer05even when you control the steppers PWM by bitbanging the parallel port's IOs, it still should easily do the maybe 5kHz with a precision of 8bit timing13:11
whitequarkI'm not sure how bad is that13:11
DocScrutinizer05aka phase modulation13:11
DocScrutinizer05and requirement for RT-linux is basically nonsense. The developer just never heard of kernel drivers13:12
DocScrutinizer05and high precision timers13:12
DocScrutinizer05and IRQ13:13
whitequarkit uses linuxcnc, not its own software13:13
DocScrutinizer05yeah, and that got developed by a noob I guess13:13
DocScrutinizer05of course you can't implement a PWM phase controlled stepper controller as a userland process13:14
DocScrutinizer05but honestly, 480Mb/s USB2.0 speed should suffice to control a USB<->parallel converter pretty tightly13:17
whitequarkthat's really more about latency than bandwidth13:17
DocScrutinizer05latency is a function of bandwidth13:18
DocScrutinizer05and actually latency here is irrelevant unless this whole concept depends on meaningless IRQ events generated by the CNC-controller13:18
whitequarkseems like it uses one input pin13:19
DocScrutinizer05you could introduce a delay in propagation of control signals from PC to parallel port, in the range of hours or days, and nothing would change13:19
whitequarkah, that's just the big stop button. so... no idea why it needs realtime13:19
whitequarkmore reviews: http://www.mycockpit.org/forums/showthread.php?t=21625&s=eb6502d9f23c55f0468a93d9c1a9e425&p=112943&viewfull=1#post11294313:21
DocScrutinizer05and the latency in USB seems like 1s * (2*8bit) / 480E6bit/s13:21
whitequarkokay, okay, I don't know13:22
DocScrutinizer05which is still pretty sufficinetly short in my book13:22
whitequarkI've seen someone write that it doesn't work with USB-LPT13:22
whitequarkmaybe it's hands.drv13:22
DocScrutinizer05sure it doesn't work with USB-LPT since the whole program is a userland program that not even has access to direct USB13:23
whitequarkthe critter seems good enough for the cost overall... so waiting for what roh says13:23
DocScrutinizer05it's amazing the whole thing works at all - even with using RT-linux13:23
DocScrutinizer05you regularly want to implemet the complete bitbanging on a kernel driver level13:24
DocScrutinizer05and that driver of course won't use libusb ;-P13:24
DocScrutinizer05it however easily can use USB OHCI directly13:25
DocScrutinizer05EHCI whatever13:25
whitequark... I don't think so13:25
whitequarkEHCI is nontrivial to use13:26
whitequarkand why would you want to reimplement it anyway13:26
DocScrutinizer05I nevertheless think the whole software is written in c# and no idea about kernel level drivers13:26
DocScrutinizer05thus they reverted to RT-linux and cranked up the scheduling for the process so it never gets preempted13:27
DocScrutinizer05and probably do direct bitbanging to the parallel port13:27
DocScrutinizer05from userland13:27
whitequarkI'll just make sure that the first board I do with it would drive it from USB13:28
whitequarkand that will end the question :p13:28
whitequarkthen I'd want to replicate atusb/atbens reliably, that would be a good test of the machine13:29
Action: DocScrutinizer05 just idly wonders how they made libmomo behave under RT-linux13:29
whitequarkunrelated: I also bought a roll of this: http://www.ebay.com/itm/Dry-Film-Solder-Mask-Roll-of-12-in-x-42-5-in-bigger-lenght-by-request-/161140135802?pt=LH_DefaultDomain_0&hash=item2584b3577a13:30
whitequarkwonder how well it will work13:30
DocScrutinizer05OT: Cree has really awesome LED products13:32
whitequarkas well as several types of photoresist... I just want to go and properly test and document all the convenient (absolutely no screwing with toner) ways of making PCBs I know13:32
whitequarkand figure out which ones work best13:32
DocScrutinizer05a white HighVoltage LED with Ufwd=23V13:32
whitequarkhuh, 23V13:32
DocScrutinizer05yeah! :-D13:32
whitequarkdo they have several junctions on the same crystal?13:32
whitequarkor what?13:32
DocScrutinizer05a 10W 5*5mm LED13:32
DocScrutinizer05don't ask me how they do it, they say SC^3[TM] technology13:33
DocScrutinizer05I found a few really nice things at cree.com13:34
DocScrutinizer05the 10W LED is ~5EUR at digikey13:34
DocScrutinizer05oops nope13:34
whitequarktalking about LEDs: I want to use this http://www.ebay.com/itm/231121837688?ssPageName=STRK:MEBIDX:IT&_trksid=p3984.m1426.l2649 for exposing the resist/mask13:35
whitequarkseems I could make it distributed (spatially) better than with lamps13:36
whitequarkmore even13:36
whitequarkthat strip eats 24W, at 30% efficiency it's 8W of UV... more than enough for quick exposure13:37
DocScrutinizer05my comment? generally you prefer a small concentrated light source for contact exposures of any kind14:09
DocScrutinizer05ideally you'd have uniform parallel beams of light, from a light source infinitely far away14:10
DocScrutinizer05the next best thing is a huge uniformly shining surface that has no minima and maxima14:11
DocScrutinizer05so you achieve uniform exposure across the complete PCB even when the distance between light source and PCB is relatively short, like in the sub-meter range14:12
whitequarkDocScrutinizer05: well, my thoughts were that 300 leds evenly distributed over surface is better than 2-4 lamps14:14
DocScrutinizer05I'd dare to give a rule of thumb which is: the distance between light source and exposed object needs to be 10 times plus the size of the largest structure found in the lightsource itself14:14
DocScrutinizer05so when your LED's are spaced at 1 inch, you should move away the lamp at least 10 inch from the PCB14:15
whitequarkmakes sense14:16
DocScrutinizer05and of course your area of observation in the lamp is at least large enough so a point at edge of PCB "sees" the same when looking up, like a point in center of PCB14:17
DocScrutinizer05means your lamp area has to be significantly *larger* than the PCB14:17
whitequarkyes, that was my issue with my previous lamp. it was pretty tiny, about 15cmx4cm14:18
whitequarkmaybe 20cm14:18
DocScrutinizer05or much much smaller ;-)14:18
DocScrutinizer05anyway, the size of the complete lamp also counts when checking for "largest structure seen inside the light source"14:20
DocScrutinizer05unless the lamp#s size is way larger than the PCB14:20
DocScrutinizer05it's all about unifirm exposure aka brightness the lamp creates on PCB surface14:21
DocScrutinizer05and human eye is a pretty poor probing tool here, it doesn't notice */ 2 14:21
DocScrutinizer05photo resistive damn sure does14:22
whitequarkI wonder if I could verify it with the photoresist itself14:22
whitequarklike, expose it for five seconds, then develop... will it shed uniformly or not14:22
DocScrutinizer05sounds feasible14:22
DocScrutinizer05I'm just thinking of 4 mirrors forming an endless mirroring of original lamp14:23
whitequarkthat sounds weird14:24
DocScrutinizer05but they need to be pretty good14:24
DocScrutinizer05nah, that's not weird, that's simply a 4 walls enclosing the PCB and lamp setup14:24
DocScrutinizer05so close to the lamp area from each of the 4 sides that when looking up to the lamp the PCB 'sees' and enless uniform area of one true and multiple mirrored lamps in all directions14:26
DocScrutinizer05ideally gapless14:26
whitequarkthanks, I'll consider this14:27
DocScrutinizer05get 4 mirrors 30*80cm, build a square tube from them. then place your LEDs evenly spaced all over the one open end of the tube. Place your PCB into center of the plane of the other open end14:28
DocScrutinizer05sounds complex but actually is pretty trivial14:28
whitequarkyeah I got it14:29
DocScrutinizer05except for the mirrors themselves which need to reflect UV light14:29
DocScrutinizer05usual mirrors don't14:29
whitequarkmetal foil?14:29
whitequarkeg thin Al foil14:29
DocScrutinizer05alu foild maybe14:29
whitequarkover say plexiglas14:29
whitequarkafaik plexiglas is UV-transparent14:30
whitequarkatleast it very much seemed to be transparent to me, seeing as the resist got exposed through it14:30
DocScrutinizer05why not expose the alu foil directly14:30
whitequarkit's not mechanically stable14:30
DocScrutinizer05place it on top of some stable surface, like plexi or wood or steel14:31
DocScrutinizer05use sticky or glue to fix it14:31
whitequarkah, right, I could just flip the plexiglas base14:31
whitequarkso the foil would reflect UV directly14:31
whitequarkas a bonus point it will shield whatever else there is in my room from UV14:32
DocScrutinizer05pretty convenient exposure chamber14:32
whitequarknot sure how much degradation would there be from occasional firing of ~10W lamp, but still14:33
DocScrutinizer05you could place a small hole on top between all the UV LEDs to peep inside, and a few red or maybe yellow LEDs for convenient illumination for human inspection14:35
DocScrutinizer05and when you anna go fancy, you can even have a small string pulling up a mask that covers the PCB and protects it from any ambient UV while handling14:36
DocScrutinizer05ooh, nope, as that would pretty much spil the mirror cabinet#s properties14:37
DocScrutinizer05you could use a black plastic foil sheet to cover the PCB, and you pull up and out of the tower this whole plastic sheet with a string, through a hole (same hole used for peeping)14:38
DocScrutinizer05sheet like "cloth"14:39
DocScrutinizer05easily pull it out through a tiny hole14:39
DocScrutinizer05since it folds up and slips through the hole14:39
wpwrak_it's always interesting what the body craves after a night of drinking. today, not just water but sugared water14:44
DocScrutinizer05then for 'calibrating' you prepare a mask that has ... "40" "20" "10" "5" ..., place it in your chamber and cover it by a black sheet that comes out under the morror so you can pull it away step by step. Then you  pull the cover until 40 is seen and uncovered and expose for 40s, then pull cover wurther until 20 is seen and expose for 20s. Then develop and see which number looks best. Let's ay it's the "10" then your optimum exposure 14:47
DocScrutinizer05time is 10+5+2+114:47
DocScrutinizer05when your numbers been like 1 2 5 10 20 50 100 200 50014:49
DocScrutinizer05or you use 1 2 4 8 16 32, and expose "1" for one second, and everything N >1 for N/2 seconds14:52
wpwrak_whitequark: (cnc mill) looks nice. having the table split is a little unfriendly but the rest looks good14:52
wpwrak_that was about the second one. details are little hard to see for the first one14:54
wpwrak_DocScrutinizer05: USB imposes its frame timing. it's completely unsuitable for this type of basically GPIO control15:04
wpwrak_(10 W LED) it seems to be more like 2 W for continuous use, 2.9 V * 700 mA. the 3 A seem to be just pulse current. e.g., for a camera flash15:15
DocScrutinizer05wpwrak_: I think that statement is a tad too oversimplified15:18
DocScrutinizer05re USB15:19
DocScrutinizer05it would largely depend on timing of that frames15:19
DocScrutinizer05given those USB2parallel coverters easily handle GDI printers which often are no less stupid regarding in-device embedded intelligence and the amount of timing the host PC is supposed to provide for driving the GDI printer...15:21
DocScrutinizer05(10W) nope, 3A/10W is coninuous operation15:21
DocScrutinizer05700mA is just the test current15:22
DocScrutinizer05for which color, efficientcy, forward voltage etc is rated15:22
DocScrutinizer05you however need to take care about proper heatsink15:23
DocScrutinizer05and I'm a tad lost there since I wonder how much of the power you feed to the LED is converted to light and which fraction actually dissipated for heating up the chip15:24
wpwrak_(usb) frame timing is 1 ms at least up to full-speed. they have slightly finer granularity at higher speeds but i don't know how much finer. maybe 4x or so on high-speed.15:25
wpwrak_so this means that, e.g., if you do something like read a register (not the case in a cnc mill, but just to give an example), it takes 1-2 ms: 0-1 ms to send the read command and 1 ms to get the result.15:27
DocScrutinizer05on highspeed that should be faster15:28
wpwrak_yes, it's faster because you have, i think they're called microframes15:29
DocScrutinizer05the whole communication probably can be done streaming data words to the USB->parallel latch15:30
DocScrutinizer05and even when not, 4k/s new values appearing on parallel output seem fine grained enough a timimg to drive a stepper motor, even by PWM15:31
wpwrak_(microframe) it's even 8x, so 8 kHz15:33
DocScrutinizer05I think for driving stepper motors you need Ft of some 100Hz15:34
DocScrutinizer05so we have a headroom of at least factor 20 here15:35
DocScrutinizer05for multiplexing 3 motors via one 8bit (10bit) parallel15:35
wpwrak_lemme calculate ... 2500 mm/min, hmm, doesn't say what resolution. let's assume 0.05 / 1615:35
wpwrak_that would be 13.3 kHz. that may be close enough15:36
DocScrutinizer05where from you take that factor 16? for PWM?15:37
wpwrak_not sure if pulse timing also matters, though. it might. e.g., it's not just stop and go but you try to accelerate the motor gradually. so you'd vary the frequency.15:37
wpwrak_from "16 subdivided driving down"15:38
DocScrutinizer05that's however on a *completely* different scale15:38
wpwrak_and knowing that for example my mill has a 62 um resolution.15:38
DocScrutinizer05we're talking about that CNC3020 though, and that has precision of 0.05mm15:40
DocScrutinizer05I guess precision >= resolution here15:40
wpwrak_yeah, could be. 30 um would be 500 um/1615:46
wpwrak_err, sorry, confused :)15:46
wpwrak_50 um repeat, 30 um resolution. okay. surprisingly close15:47
DocScrutinizer05wpwrak_: btw your calculation missing a tiny detail: for full speed moving you don't to fraktions of a step on a stepper motor15:48
DocScrutinizer05you operate the motor at full steps at maximum operation frequency15:48
DocScrutinizer05you do fracion steps only for smooth *slow* movements or for positioning netween two steps15:49
DocScrutinizer05so your factor 16 isn't relevant here15:49
DocScrutinizer05and that makes my statement about factor 20 headroom look pretty good, eh?15:50
wpwrak_want: http://www.youtube.com/watch?v=xZOiNdkJ8SU15:50
wpwrak_dear china, please make a USD 500 mill like that ;-)15:53
wpwrak_(steps) yeah, not sure how that fractional steps vs. full steps thing works15:57
wpwrak_phew. 36 C. getting a little hot today ...16:00
wpwrak_may be the hottest day the second half of this year16:01
DocScrutinizer05the fractional step thing works by giving (e.g.) 20% of current to phase-1 and 80% to phase-2, so the axis magnet positions on 1/5 of the angle between that phase-1 and phase-2 position16:10
DocScrutinizer05the sequence is kinda like: 1; 1&2; 2; 2&-1; -1; -1&-2; -2; -2&1; 1...16:14
DocScrutinizer05you can position between any of those 8 full steps by applying fractions of 100% current to either of both phases16:16
DocScrutinizer05aka coils16:16
DocScrutinizer05aka electromagnets16:16
wpwrak_oh, even analog regulation. fancy.16:17
DocScrutinizer05PWM usually, yeah16:17
DocScrutinizer05obvously you usually got a multiple of 8 steps per 360° rotation on most stepper motors16:20
DocScrutinizer05up to 360 or more16:20
DocScrutinizer05for full speed you often even skip intermediate steps and do "full step" 1, 2, -1, -2, 1...16:23
DocScrutinizer05while the 8 step mode is calling the additional 4 steps half steps iirc16:23
DocScrutinizer05sorry it's like 10 years since I last looked into that stuff16:24
DocScrutinizer05hmm, the control box specs say "G Code" -> http://en.wikipedia.org/wiki/G-code16:27
DocScrutinizer05this however might mean the software "API" on the windows computer16:30
wpwrak_hehe, yeah. i think they also mention mach on the windows side16:33
DocScrutinizer05AWESOME! http://www.jinlantrade.com/ebay/3020t/CNCusermanual.doc16:34
DocScrutinizer05>>After installing the Mach 3, on the desktop, there will occur 3 icon as follows:  XXXXXX  Notice: do not open them, please restart your PC at first (if you open the software not restart PC,it need uninstall fully and reinstall it) <<16:38
DocScrutinizer05see "Engine Configuration... Prts & Pins"16:42
DocScrutinizer05>>Kernel: 25000Hz<<16:44
DocScrutinizer05according to 2nd window "Ports & Pins" Mach3 doesn't do half steps, and particularly no step fractions16:46
DocScrutinizer05looks like lowest level interface for a pretty standards hardware stepper controller: direction and step signal16:47
DocScrutinizer05so the controller box of the 3020 has 3 stepper controller chips I'd guess16:48
DocScrutinizer05via USB according to what you wrote, we can make the motor do 8k steps per second16:50
DocScrutinizer05and that's it. the only problem with this limitation is that stepper motor can't go faster than that, and the 'noise' that's particularly relevant when moving two axis concurrently is determined by the jitter in that 8k timeframe16:52
DocScrutinizer05I can't see the motors mechanically following any such jitter16:52
DocScrutinizer05axis magnet's inertia is a pretty good lowpass filter16:53
DocScrutinizer05which also means the timing of the controller must not jitter so much that motor skips a step16:54
DocScrutinizer05all this can get handled by simply not moving the motors at maximum speed16:55
DocScrutinizer05I don't see any basic showstoppers for a USB<->parallel converter16:56
DocScrutinizer05I think on windows some of those (rather their drivers) can even fake a IO port number that the driver is listening to, to emulate a built-in parallel interface16:57
dos1most of usb<->parallel converters (especially the cheaper ones) won't work - usually they're just emulating the printer interface17:01
DocScrutinizer05I also just thought the Mach3 *might* use a definiton of doing fractional steps by applying PWM to the direction signal17:06
DocScrutinizer05I never heard of sth like that in hw controller chips, but it would be pretty obvious a way to implement fractional steps17:07
dos1hmm http://www-user.tu-chemnitz.de/~heha/bastelecke/Rund%20um%20den%20PC/USB2LPT/faq.en.htm17:09
dos1Q9 is interesting17:09
DocScrutinizer05ooh, "microstepping" not "fractional stepping"17:14
DocScrutinizer05dos1: *excellent* find! :-)17:26
whitequarkreading backlog17:31
whitequarkwpwrak_: (good one) you mean the one from ebay?17:33
whitequarkDocScrutinizer05: (1-2-5-10) yeah, figured, that's how I did it in the past17:34
whitequark(heatsink) for a self-adhesive LED strip with three hundred LEDs? how on earth are you suggesting to do that?17:34
whitequarkwpwrak_, DocScrutinizer05: (pulse control) from the screenshots it seems that it has one Step and one Direction pin per axis17:36
whitequarkoh, you found that already17:36
DocScrutinizer05see http://www-user.tu-chemnitz.de/~heha/bastelecke/Rund um den PC/USB2LPT/ for a adapter that might "just work2 for you17:36
Action: DocScrutinizer05 hates it when fools add spaces to URLs17:37
Action: whitequark is looking at http://www-user.tu-chemnitz.de/~heha/bastelecke/Rund%20um%20den%20PC/USB2LPT/ul-17.en.htm17:38
whitequarkI think I can manage to assemble that myself, even17:38
whitequarkdo they have any in stock? doesn't look like there's been made a lot of them17:39
whitequarkok, doesn't seem that anyone sells complete devices at all17:42
dos1DocScrutinizer05: I was looking for some usb<->lpt converter while working on that drawing robot - finally gave up and used some old laptop with integrated lpt to control it :D17:47
whitequarkand the chip is EOL17:47
whitequarknot stocked even17:47
DocScrutinizer05whitequark: it's a DIY thing17:47
whitequarkdos1: wow, a laptop with LPT. I don't think I've ever seen one17:47
whitequarkDocScrutinizer05: figured17:47
dos1whitequark: http://www.tholt.com/images/toshtop.jpg something like that17:48
dos1maybe even same model, looks similar17:48
whitequarkdos1: that's a murder weapon, not a laptop :]17:49
dos1hehe :D17:49
DocScrutinizer05dang, seems we think alike, eh?17:50
DocScrutinizer05didn't notice >>[2013-12-25 18:48:46] <dos1> whitequark: http://www.tholt.com/images/toshtop.jpg something like that<<17:50
DocScrutinizer05since I been searching ebay ;-)17:50
whitequarkoh, there's a replacement for that EOL'd cypress chip17:51
DocScrutinizer05and whitequark, *my* link is a murder weapon17:51
whitequarkDocScrutinizer05: sure sure. *writes down to never ever screw with joerg*17:52
DocScrutinizer05yeah, particularly since I have the somewhat even heavier CF-2917:52
DocScrutinizer05http://www.ebay.com/itm/BLACK-TOUGHBOOK-CF-29-TOUCHSCREEN-Panasonic-laptop-Military-Police-RCMP-SWAT-/181286146497?pt=Laptops_Nov05&hash=item2a357f11c1 LOL17:54
DocScrutinizer05lol @ part of the URL17:55
DocScrutinizer05though... WTF is RCMP?17:55
whitequark56K modem...17:56
DocScrutinizer05hehe, yeah, a funny relic in CF-2917:59
DocScrutinizer05dos1: yeah, quite impressive. I also seen videos of divers operating CF-29 under water :-)18:03
DocScrutinizer05though I don't recommend doing that "at home", the seals pretty often are _not_ 100% water tight18:03
DocScrutinizer05anyway I guess when you get that 3020 CNC, you should get a dedicated PC for it right away, and better get one with parallel interface18:05
DocScrutinizer05shouldn't cost you more than max 15% on top of the price for the CNC18:06
whitequark"when" already :p18:06
whitequark15%? pretty sure I can find one for free18:06
whitequarkthere's *tons* of old hardware lying around18:07
DocScrutinizer05I really like that 3020 thing, for that pricetag18:08
DocScrutinizer05almost temped to get one for me18:09
whitequarkhuh! guess that's a good thing18:09
Action: whitequark opens local ebay clone and sorts by price, asc18:10
DocScrutinizer05swapping/adding the mill motor for/with a "printer" would make for a nice combined 3D-printer&mill, for really nifty hybrid stuff to build18:10
whitequark"pentium 100mhz, will give away for a liter of juice"18:10
whitequarkDocScrutinizer05: hm, that is a very interesting idea18:10
DocScrutinizer05duh! using a fibreoptic and focusing lens I guess you could do UV-curing for 3D printing *inside* a resin bath18:13
whitequarkcan you even send resin by mail?18:14
whitequarkI doubt I can buy it here18:14
DocScrutinizer05I have no clue which type of resin or other chemical would be used for conventional 3D light-curing printing18:15
whitequarkapparently bisphenol-A based epoxy. eww.18:16
whitequarkI'm not sure I want to touch that at all18:16
DocScrutinizer05you are not supposed to _eat_ it :-D18:16
whitequarkoh, it's not nearly as bad as pure phenol. okay then18:17
whitequarkstill... I don't need a 55-gal drum of stuff18:17
DocScrutinizer05I wonder if you could do useful printing with a modified hotglue gun as print head18:18
DocScrutinizer05could result in quite unique elasic objects18:19
whitequarkI'm not sure they fit my definition of "useful"18:19
whitequarkalthough they are sure unique. unique in their complete lack of applications?18:19
DocScrutinizer05well, there might be *some* applications18:19
DocScrutinizer05when usually you'd use silicon-rubber18:20
DocScrutinizer05e.g protective sleeves18:20
whitequarkyeah you can't really buy uv-curing resin here. it's either super-expensive specific stuff (special glues, dental, etc) or gigantic amounts from china or wherever18:20
DocScrutinizer05contact the fabber scene18:21
DocScrutinizer05they must have such stuff around18:21
DocScrutinizer053D printer18:22
whitequarksure, there could be about three guys in entire RU doing that18:22
DocScrutinizer05duh! weird18:22
whitequarkit's a very expensive hobby18:22
whitequarkwith $100/l resins? no way18:23
DocScrutinizer05I thought particularly russian guys should be very interested in that sort of "let's see what can get done"18:23
whitequarkthey are. but with docs mainly in english, expensive hard-to-obtain resins with possible customs complications... very few people are going to go through that18:24
DocScrutinizer05hmm, yet another weird idea: use a inkjet printhead to spit droplets of hardener into the 2 components resin bath18:24
whitequark1) afaik printerheads are very finely tuned to the specific consistency of ink18:25
whitequark2) you think it would harden fast enough? not sure18:25
whitequark(1) so the hardener wouldn't properly "boil out" or maybe will just flow through18:25
DocScrutinizer05instead of epoxy "resin" you could go experimental and see what soluble glass gets you18:26
whitequarksoluble glass? O_o18:26
whitequarkohhhh sodium silicate. I think it's sold here as glue18:26
DocScrutinizer05that liquid based on silicon18:26
DocScrutinizer05sodium silcate18:27
whitequarkyou can add ethyl alcohol to it, it'll form a weird substance with nonlinear properties18:27
DocScrutinizer05it hardens with some other chemical18:27
DocScrutinizer05actually a number of other chemicals. Probably all metal salts18:27
whitequarkat long timespans it flows. at medium it acts elastically (kinda like shitty rubber). at short it shatters in shards18:27
DocScrutinizer05plus some acids prolly18:27
whitequarkpoor man's http://en.wikipedia.org/wiki/Silly_putty18:28
whitequarkDocScrutinizer05: not sure about mechanical properties of the result18:28
DocScrutinizer05me neither18:29
whitequarksounds like it would be fragile and/or weak18:29
DocScrutinizer05well, that's a good start to do some experiments, no?18:29
whitequarkyep, why not18:29
whitequarkhm, it hardens because metal silicates form18:31
whitequarkso that'll require a ton of metal salts18:31
DocScrutinizer05quite possible, though i know it also hardens in free air, that's why it's been used to write on bottles with it18:32
DocScrutinizer05maybe by the carbon from CO2 ?18:32
whitequarkyup, also evaporation of water18:33
DocScrutinizer05well, it's not water soluble once it hardened18:33
whitequarkoh, it's not? I misremember then18:33
DocScrutinizer05afaik not18:33
DocScrutinizer05I think I heard it's been used for permanent writing on glass bottles18:34
DocScrutinizer05mixed with chalk or some other pigment18:34
whitequarkhere it's used as a shitty paper glue18:34
whitequarklike really shitty, it's really weak18:34
DocScrutinizer05it doesn't really glue at all18:35
DocScrutinizer05about as much as salt water18:35
DocScrutinizer05but it seems to even kinda mix with the glass of the bottles18:35
DocScrutinizer05I dunno, just wild guessing here18:36
whitequarkeh? how'd that happen18:36
DocScrutinizer05I can't think of a substance that simply dries to a chrystaline form to really stick on glass bottles18:37
DocScrutinizer05there must be more to it than just some shit drying18:37
whitequarkvan der waals forces can be quite high with glass18:37
DocScrutinizer05and glass is also silica18:37
whitequarkthat uv curing epoxy is apparently used for gluing legs to glass tabletops18:37
whitequarkand it sure as hell doesn't mix with glass... it's pure organic18:38
whitequarkmaybe the similar composition helps it somehow. I don't think they mix though18:38
DocScrutinizer05the UV hardening acrylate glue I told wpwrak_ about18:38
whitequarkyes, that's about the only thing I can find references to in russian18:38
DocScrutinizer05not mix literally, for sure18:38
DocScrutinizer05nothing _mixes_ with glass18:39
DocScrutinizer05but some substances act on the surface of glass. E.G alkali substances tend to etch glass suface smooth18:40
whitequarkI believe alkalis do dissolve glass, very slowly18:41
DocScrutinizer05that's why it's dangerous to boil alkali stuff in glass pots, it may "explode" since there's no micro-scrs left in glas for the steam bubbles to build on it18:41
whitequarkapparently pH>=9 is needed18:43
whitequarkwhich isn't all that high18:43
whitequarkthat's... 0.0022% solution of NaOH, if I remember anything from my chemistry courses18:48
DocScrutinizer05>>Molten NaOH eats glass, as will a 50% boiling solution of NaOH; though at a lower rate. Doesn't touch stainless steel though. This is a well tried process for de-enamelling sheet iron articles which cannot be shot-blasted<<18:48
whitequarkI guess that would just work extemely slowly18:48
DocScrutinizer05when it's well tried, then I gather it works in finite amount of time18:49
whitequarkah, the old thermodynamics vs kinetics18:56
whitequarkthermodynamically, you're a cloud of hot gas and a pinch of ashes18:56
whitequarkkinetically, not quite so :p18:56
whitequarkhttp://en.wikipedia.org/wiki/File:Na_(Sodium).jpg <- imagine throwing one of those in water. mmmmm18:58
larsc_better back up first20:10
lekernel"disposal of sodium"20:30
wpwrak_just flush it down the toilet ;-)20:59
larsc_put it in some coating that slowly dissolves and flush it down the toilet21:04
wpwrak_yeah, sugar-coat it :)21:04
wpwrak_that may actually be the perfect crime - all evidence will self-destruct by the time someone gets to examine it ;-)21:05
lekernelof course, someone had to do it21:13
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