Messages

11

Show"N"Tell ( What you have made with your CNC machine.) / Re: My first attempts at laser engraving.

« on: June 26, 2009, 03:11:37 AM »

A CO2 laser at the right power / feed produces an optically clear polished finish.

All forms of mechanical cutting require flame polishing to replicate this.

12

Show"N"Tell ( What you have made with your CNC machine.) / Re: My first attempts at laser engraving.

« on: June 25, 2009, 12:06:21 PM »

Guys, different types of laser produce different wavelengths, and you need to select the right wavelength for the material in question, eg a wavelength that is absorbed.

Invisible IR from a CO2 laser is ideal for cutting / marking acrylic, marking glass, cutting / marking wood, leather, etc etc...

Here in the UK you can buy *********e chinese aircooled CO2 lasers for around 250 quid for 25 watts, just add a neon sign transformer and some fans and you're good to go, for a couple of thousand hours.

Pukka sealed for life and lasts for 5k 10k CO2 hours laser cost more, as do water cooled.

Coherent and Synrad both make visible spectrum diode lasers in the multi watt range, (as well as CO2) not so good at cutting transparent materials or metals... quite expensive because you end up needing a quality PSU that can deliver 100 amperes at 2.0 volts, exactly for even a moderately powered beam...

CO2 is a lot more versatile, you can cut metal with it, just a question of power.

As a rule of thumb, you get about 2 watts of power per inch of tube, think on this if planning on mounting the tube in the Z axis, if not, if planning on using flying optics, good luck to you on the precision front.... think about it.

A 25 watt CO2 laser will slowly cut clean through 10 mm acrylic, a 100 watt will cut eighth inch steel plate.

CO2 laser basically operate at RF, so you can switch them on and off very, very, very fast, which can be useful.

==========================

Now, everyone talks about eye safety, and this is true, even a 1 watt laser focused by the eye lens on the retina will permanently blind you before your brain even begins the blink reaction, and thats a visible laser, IR is even worse, except IR flashback can be very easy prevented by using an IR opaque medium, like acrylic or pilkington glass, this is how greenhouses work after all

HOWEVER

Permanent blindness is not the issue.

I emailed tweakie about this, a laser essentially creates a high energy plasma cloud of chemical elements from the substance being lasered, and all sorts of rubbers and plastics and other materials start giving off clouds of extremely toxic and / or carcinogenic compounds like benzine, phosgene, arsenic, chlorine etc etc etc...

Laser cut steel creates clouds of micron sized rust

Laser cut stainless steel creates clouds of very nasty heavy metals like chromium etc that once absorbed the body can never rid itself of...

As I said to tweakie it would probably be healthier to hand my small son a lit cigar than to let him be in the same room as a cutting or engraving laser, even if he was wearing a welding mask...

CO2 lasers are a lot like gas axes, they have a jet of gas (often just dry clean air) shooting out the same nozzle as the beam, and the gas jet is what really does the cutting, the laser just melts.

Essentially the difference between a 25 watt CO2 laser and a 100 watt CO2 laser is that any job the 25 watt one can do, the 100 watt can do at 4 times the feed. However, but there is a lower limit for each material and job, and that limit is the ability to punch through fast enough to have minimal deflection and to move fast enough to have minimal heat going anywhere except the desired spot.

====================

DO NOT BUY 150 mW laser diodes for big bucks, every single old CD burner has one in it with a lens, for free... DVD burners nearer 200 mW.

a suitable hole bored longwise in a CPU heatsink and fan is good for cooling, and long life on diodes is good cooling, good power (within limits), soft start and stop

Forget visible light diode lasers unless you want to run a light show, invisible IR is where it is at for delivered energy, but requires slightly special optics, not just ordinary glass lenses.

====================

If you're serious about it a 25 watt CO2 tube, neon sign transformer and tube cooling is dead simple, and actually works out a lot cheaper per watt than a 150/250 mW diode bought new, plus PSU, etc, and optics are affordable, and a clean air supply for the jet, just watch out for the 22kvolts and the instant blindness or instant 3rd degree burns, but you be able to cut most organics and plastics up to 10mm thick slowly, and engrave most plastics, glass, and organics and even metal (after pre treating) quite fast indeed.

HTH etc

cheers

13

Share Your GCode / CNC "rackmount" pizza box server plans for MiniITX mobo, PSU and dual 3.5" HD

« on: June 25, 2009, 05:36:08 AM »

From the included readme1st
=====================

Bare bones "rackmount" format computer case.

This is 99% of everything you need to build a basic "rackmount" format or "pizza box" format computer case, based upon the excellent Via Epia MiniITX format boards.

This design allows for the MiniITX mobo, MiniITX PSU, and two 3.5" hard disks all to be mounted in a robust case with EXCELLENT noise cancellation properties and EXCELLENT airflow through the case.

In the drawings the mobo, PSU and 80mm fans are all represented by simple boxes outlining their maximum dimensions, so within this framework you can for example rotate the 170 x 170 mm mobo 90 degrees, or decide if this is the front or the back of the finished case, as you choose. I would recommend against rearrangement of the component positions though.

Design notes.

1/
All construction is from 10 mm thick acrylic, you decide if you want clear, coloured, smoked, whatever.
Building this case from acrylic should cost no more than £25 (UK pounds) in materials.
Acrylic is strong, a good electrical insulator, a good sound insulator, and unfortunately for a computer case also a good thermal insulator.

2/
The air flow through the case is managed by two cheap generic 80mm case fans (though I would STRONGLY recomment you buy two decent 80mm fans from http://www.dorothybradbury.co.uk/, I suggest two NMB-MAT RB-80-L at £8.45 each) with flow in series between the two should one fail, the air flow path is in by the motherboard, across the motherboard, where it is directed by the air dam into the first hard disk caddy.

In this caddy air flow over BOTH important surfaces of the hard disk, before going around and then cooling both surfaces of the second hard disk in its caddy.

From here the air passes through the PSU, through the fans and out the case.
Despite the lower power consumption of Epia boards, you could fit a more powerful MiniITX board, as this design addresses one of the biggest weaknesses of the ATX design, in that every single major component has forced and channeled positive air flow.

The design of the channels and the order in which flow happens is optimised to dissipate any mechanical noise inside the case, and not to carry it out through the vents. Fan noise will be minimal.

3/
Cabling and wiring.

I've left basic parts of the canvas blank, such as the square cut out for the motherboard I/O panel, the air entry, the air exhaust, and the PSU mains plug.

I have left these blank because this way you can make slight alterations to suit yourself, if it was me I would for example strip the casing off the PSU and run it naked (quite safe in an acrylic box) for better air flow, and solder in a IEC socket mounted directly on the rear panel, I'd also recess the mobo 10mm and fit a front air entry filter next to the I/O panel cut out, and I would direct the exhaust air out the rear, this way I'd have a "pizza box" with the mains cable at the rear and all the I/O and air filter at the front.

Pay particular attention to passing the hard disk data and power cables for the second hard disk through the internal air dam, you want enough room to pass the cables but not a big void to short circuit the air flow, the first hard disk is easy, but watch cables don't block air flow, use rounded IDE or SATA, you do not need the second hard disk.

Also pay attention to the ATX power cables through the air dam to the mobo, you also want a snug fit that doesn't cost you air flow.

4/
General construction and assembly.

Mobo mounts can be drilled and tapped straight into the base. Ditto PSU

Fan carriers are dead simple, just two sheets with angled recesses to hold the fans snug, make it a nice push fit for the fans, if you buy Dorothy Bradbury quality cans fit then and then glue the fan assembly into place permanently, make sure the two fans both work together, not against each other.

Hard disk carriers are slightly different between disk 1 and disk 2, disk 1 carrier has an extra bit of air dam. Hard disks go centrally to allow air flow over both sides of the disk, just drill and tap for hard disk mounting screws, AFTER you make sure you have the hard disks the right way around for the data and power cables, eg data and power cable ends pointing towards the PSU.

Recess hard disk mounting screws into sides of carriers, You can secure hard disks + caddies from below with recessed screws.

Even if you only fit one hard disk, make both caddies, they also serve as air ducts.

I'd make the base and four sides, and leave the lid as a separate item screwed on with recessed screws.

The nice thing about this is you can see in, so you can see if cruft had made it past the air filter and is clogging, or you can see status LED's etc etc etc.

In theory, apart from the fan carrier recesses, the mobo I/O, the air entry and exhaust, and the IEC socket, you could make this entire thing with no CNC machning at all, just cut the acrylic to size (or buy it cut to size) and drill and tap or glue where needed.

However, there is a lot of scope for some nice CNC work to make this a really, really nice piece of kit.

5/
Notes

As it stands this design is 444 mm wide, 350 mm deep and 75 mm high, it is only the 10mm thickness of the construction material that stops it being 1U, but nevertheless is is a pleasing dimension, and due to the internal structures such as the air dams, fan carriers and hard disk caddies it is literally strong enough to stand on.

THINK THRICE, MEASURE TWICE, CUT ONCE is very much the motto here, if you end up with problems or things not fitting or working out extremely neatly and effectively then you simply were not careful enough, or you decided to alter something for no good reason.

Glue the four box sides and base together.

Glue the hard disk caddies together.

Glue the air dam together.

If you buy Dorothy Bradbury fans and check orientation glue the fan carrier in place

DO NOT GLUE ANYTHING ELSE, use countersunk fasteners, and do not glue these things until you have offered up and done any required machining, eg front and rear panels require air vents and I/O, air dam requires cable notches.

6/
Finally, this design. like all my stuff, is released under the GPL V2.0


7/
Zip file contains Rhino .3dm files, autocad .dxf (CAM metric) and images, everything you need.



25th June 2009

14

Share Your GCode / CNC kids toy project..

« on: June 24, 2009, 11:50:22 AM »

Kids toy 01.

The kids toy is basically two piece of 10 mm thick acrylic put together with a channel on the inner faces.

The oil filled channel allows the ball bearings to slowly follow the path down by gravity vs viscocity, speed varies according to slope, slow on the slant and faster through the curves, when done just flip it like an egg timer.

Essentially you have a round section ball bearing in a square section channel, ball bearing diameter should be as close as possible to channel width, but just under. You know how your mill cuts so make allowances as required.

e.g. buy your bearings FIRST and measure them.

Acrylic adhesive doesn't actually glue, it welds, so when done you have a very strong and very safe container that won't leak.

Cut the two parts out.

Tap the 4mm holes to 5mm.

Flame polish the channel and outside edges.

Assemble it with the bearings and fasteners. NOT THE OIL OR GLUE.

Check it all works, e.g. bearings run from top to bottom and back again and that the two surfaces mate well.

Tap the breather to 3 or 4 mm whatever you prefer.

Split, leave bearings in, use enough adhesive around the edges and fastener holes to make a 100% seal, but not so much that it squeezes into the channel and buggers up the channel.

Set is aside to cure for a hour.

Add oil using the small breather at one end until full, plug breather with grub screw and thread sealant, set aside to cure.


1/ Two pieces of acrylic 300 mm x 150 mm x 10 mm.

2/ Sixteen off 5 mm dia by 15 or 20 mm long cap screws (15mm if you countersink the heads) Plus one 3 or 4 mm grub screw.

3/ Three or four 10mm diameter ball bearings

4/ Acrylic adhesive

5/ Small bottle of baby oil.

Job's a good un.

Any queries contact me direct.

Included .jpg screenshot, .3dm Rhino drawings, exported .stl files, and Mashcam generated .nc files using a 3mm diameter end mill.
Suggest around 75 mm/min feed per 1,000 spindle rpm if you feed over ride.

NOTA BENE

Have included TWO sets of .nc toolpaths

The standard set uses a single 3mm dia end mill to do everything.

The other set has "* 6mm.nc" names and uses a 6mm dia end mill, much faster but does not include the 16 fastener holes, ONLY does the channel.

You choose.

24th June 2009.

John

Kids toy zip contains everything, 1.9 MB

15

General Mach Discussion / Re: Phantom Limit Switch Events

« on: June 23, 2009, 02:20:27 PM »

The one thing I forgot that also counts.

Your stepper controllers, PSUs and breakout board all REQUIRE forced air cooling, I run a couple of standard PC 80mm fans @ 12 volts on exhaust at the top of my cabinet, if I turn them off I get random limit switch events after about 15 minutes.

16

General Mach Discussion / Phantom Limit Switch Events

« on: June 23, 2009, 08:44:18 AM »

By this I mean when you get a "limit switch triggered" message and everything stops, but no limit switches have been physically triggered.

I've been playing with this for some months now, applying the scientific method.

I tried all the usual scenarios, from really cheap and crap single core conductor with crimped spade terminals wiring all the limit switches in series, right up to grounded high quality shielded cable soldered on to the limit switches.

In between I have played with all the debounce settings too, even setting them as high as 20,000.

I have even played with all the possible earthing methods between machine tool, computer, parallel port breakout card, you name it.

To be sure, ALL these variables had some effect, as indeed did other devices on the same mains circuit switching in and out, and indeed the various routings and separations of various cables.

However, attach an oscilloscope to the limit switch circuit and suddenly things become clearer, especially when you set things back to the bad scenarios rather than the "that seems to be working fine now" scenarios.

Sit there with your eyes glued to the scope screen and every single phantom limit switch event is mirrored by a spike in the noise shown on the oscilloscope waveform.

N.B. I have not been able to determine from mere observation where this noise is coming from, for all I know it could be the neighbours mobile phone or the workshop computer wireless network card, there was no obvious trigger such as "there goes the compressor" or "I just started the lathe motor inverter."

I think that all this investigative work is important, other wise you have "cures" that work for me, but not for you, e.g. raising debounce to 3,000, because all these cures are in effect lucky guesses that mask the problem, rather than curing it. I wasn't content with fixing it for me, I wanted to fix it for everyone, including me on my next machine, or after I move this one, or after I add another tool to the workshop, etc etc.

The definitive cure is to purchase a single 0.1 uF (micro-farad) polyester capacitor (electrolytics are no good as they have +ve and -ve preferences) and attach it across the two limit switch wires close to where they join the parallel port breakout board.

Here in the UK you can buy them individually from Maplins for 13p each.

I would not go any smaller than 0.1 uF initially, nor would I go bigger, too big will dump too much current when the limit switches actually close, but you could buy three or four 0.1 uF and parallel them up one by one to test if required.

Instantly I had to increase the gain on the oscilloscope by 10x to see the same noise spikes, and even then they were significantly reduced and much more rounded with shallower slopes.

As far as curing the phantom limit switch problem goes I was able to set everything back to "worst" case scenarios with minimal debounce and the phantom limit switch problem appears to have been totally eliminated.

Given that this is a potential cure that costs the price of a cigarette, is easy to test (just clip the cap across the wires with two croc clip test leads) and doesn't require altering anything else, I would suggest you try it out as a FIRST resort rather than last, if you have phantom limit switch issues.

HTH etc

17

Share Your GCode / CNC coolant tank project

« on: December 22, 2008, 08:36:20 AM »

This is quite a simple one, make a 400 x 320 x 120 mm coolant tank from acrylic and a generic aquarium pump, maybe 25 quids worth of acrylic and very simple machining, could even be done manually with no issues, 3mm end mill is all you need.

As usual, all primitives in dxf and an html to explain what's what.

This one contains an extra warning at the end of the docs, electrictricity + water + machine tools = rust  and / or electrocution.

njoy

18

General Mach Discussion / Re: Opinions on use of ancient computers to run Mach3

« on: December 21, 2008, 04:02:14 PM »

I don't know the ins and outs of Mach3 code, but I do know it isn't "just another app" sat on top of the OS, instead it uses in effect fake realtime code, which is going to bypass any BIOS aware OS code that is for example stepping the CPU clock.

But, all these "green" features are simple to disable in BIOS anyway in every desktop I've ever seen.

I just can't get my head around why people would (given the effective free cost of an old desktop or server box) insist on using a laptop though, which would have a far greater level of such tricks to be disabled, even assuming all of them could....

for example good luck downloading and flashing the "OEM" BIOS onto a dell laptop (instead of the dell BIOS)

Mind you, I have had this (I/O flexibility) conversations with vaxen / PDP-11 owners, who just couldn't understand how our megahertz cpus with astonishing 4 megs of RAM couldn't hold a candle to what their PDPs could do in a few k....

19

General Mach Discussion / Re: Opinions on use of ancient computers to run Mach3

« on: December 21, 2008, 11:03:58 AM »

Two points.

1/ It is stupid to even consider power saving on a PC that is controlling a machine tool complete with spindle motors and steppers / servos and associated power supplies.

2/ The modern Core 2 Quad, eg Q6600 series, are remarkable for anyone coming from Pentium4, in every way, though completely unnecessary unless your workshop PC also does duty as your CAD/CAM pc.

The thing that we are really talking about here is the actual electronic component and PCB construction quality of older pukka kit versus modern consumer grade kit, and there really is very little comparison.

On a closely related subject
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=71
this is the guy who tests actual PC PSUs...

I can't tell you how many transient computer errors we cured over the years by simply swapping out apparently working within parameters at first glace cheapo PSU's.

20

General Mach Discussion / Re: Opinions on use of ancient computers to run Mach3

« on: December 20, 2008, 08:25:00 AM »

If you're into the investigating OS usage bit have  ago with Quickslice which gives a graphic display of cpu usage by process.

http://www.microsoft.com/downloads/details.aspx?FamilyID=6247BB76-13C5-4E0E-B800-53DC1B84A94C&displaylang=en

direct link to executable

http://download.microsoft.com/download/win2000platform/qslice/1.00.0.1/nt5/en-us/qslice_setup.exe