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Messages - Stonemull

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1
Aliexpress.com / Re: Mini CNC
« on: August 22, 2017, 11:46:37 AM »
Its a lot of fun and a good way to learn CNC tooling, mine has never had, or ever will, have a lase fitted to it so can't help you there. I can't see why fitting a laser to it would cause issues though. What problems did they have .. and what 'knife' are you talking about ?

Wood or softer materials are fine, force on the Z axis causes the X rods to flex, due to the flex you want to make sure your cutting direction is correct, use climb milling instead of conventional, or else the tool chatter is nasty. It has trouble with regulatr milling cutters on aluminium,

The things I bought it for are learning, pcb drilling (which it does a great job of, seeing how usable pcb engraving is (jury is still out) and simply cause I like tools, I wanted one.

If you don't want to do metal, even soft metal,  these things work fine. Spindle speed is a bit low, i measured it at around 8500rpm. Ability to do 20000 would be nice.
I bought some tunsten carbide cutting bits suitable for dremels, had better luck with aluminium than milling bits, attached is a photo showing some manual operations on a chunk of aluminium, I found a 0.1mm x 3mm cut prodyuced results but its barely doable. Honestly, it is out of its league but I coukd in an emergency use it to clean up a part I guess.

Accuracy is quite good, I have been cutting pcb tracks at 0.05mm deep with a 0.1mm engraving bit, you can repeat the gcode and it follows the same cut.

I am yet to try 3d carving a piece of wood much, I have used it to cut a couple of stencils for the plasma cutter, but not tried an actual wood carving yet. It is next up on the cards after I get some work done.

2
Projects / Re: My Rotary Axis
« on: August 19, 2017, 06:54:46 PM »
Vector mode too, can't do that on mine due to backlash in output gearing, it looks like your settings are incorrect though .. a bit squished on the rotary axis.


3
Projects / Re: My Rotary Axis
« on: August 19, 2017, 07:31:53 AM »
That'll get 'er done.

4
Projects / Re: PCB photoresist film exposure
« on: August 17, 2017, 07:22:15 PM »
It does work well with good peroxide, using it here I have to use 2 parts peroxide to 1 hcl and it still takes 1.5 hours with agitation..pharmacy peroxide has stabilisers added.
Also I assume you ae discarding the solution after a while ? there is no need.
Does it turn green or start off green ? You can achieve the same thing without any peroxide by using an air bubbler.
Australian muriatic or peroxide, not sure which, seems to have iron contaminants, mine goes brown instantly if I mix them, that is just the hcl from a hardware store..


5
Trouble Shooting / Useful Troubleshooting Diagram
« on: August 16, 2017, 11:05:55 PM »
hopefully helps someone.

6
Projects / Re: PCB photoresist film exposure
« on: August 16, 2017, 11:00:32 PM »
Problem is, I simply cannot get cheap peroxide, I have only 2 options currently, 3% or 6% at $5 per 100ml from a pharmacy, it seems to hardly do anything sonetimes. Or 5 litres of 50% from a chemical supply house $50, I think, they do not sell single litres as the bottles tend to outgas and explode.
50% will catch fire if it touches wood or paper, I just don't want a big bottle of it lying around.

So I am currently using hydrochloric acid (muriatic acid 35%) ... added some peroxide and copper to get the reaction started, bubble air through it, after a few hours it eats the copper and eventually turns from brown to green (copper chloride) it now eats copper damn fast, just need to use an air bubbler to give it ixygen, no more need for H202 .. the chemistry gets stronger over time and you need to dilute it with more acid or just water depending on its pH.

Reflections arent a problem, the beam will never head straight back up in the exact direction and spread, it will never make it back through the lens system, a laser works by bouncing light to and fro, so even if 100% of it made it back it would likely interfere with the laser phase and upset the lasing function.
Think of how the lens system operates and what a reflection spread would be, multi lens systems like telescopes etc do not work well backwards, they expand the light instead of focusing it.

7
Other Software / Re: T2Laser Software
« on: August 12, 2017, 01:21:57 AM »
This does not relate to australia post, I have had things take 10 days to go 55km from brisbane yet stuff from china in less time than that.

8
Projects / Re: My Rotary Axis
« on: August 08, 2017, 10:53:59 PM »
They are not as bad accuracy wise as that, have a look at limit switch testing and you will find tests giving 10-15 micron repeatability, (0.015mm) on each axis. That would be a well setup machine obviously but even low cost steppers, reasonable belts and a solid frame will result in far better than 0.05mm resolution reliably.

Stl's are a problem. in that they don't do circles, or squares for that matter, everything is a triangle mesh no matter the shape of the model. So all the holes are polygonal and the number of segments change depending on size (and CAD program settings), this is one area where openscad shines as the $fn variable tells the renderer and stl generator how many segments to generate, I usually design with fn= 12 and then use fn = 100 for small holes, it means a render that was produced in 5 seconds originally may now take 10 minutes, but you only do it for the final output.

Since everything the printer gets is straight lines in 2 axii's linearity should not be an issue either.

By far the largest error is the actual deposition process itself, you are smearing a viscous, sticky liquid ontop of other plastic at fairly high speed, just having the end of the nozzle dirty can affect quality if you want perfection. Then like I said, filament drag, temperatures, speed, fan rates, filament variations, vibration  etc etc etc all have some effect.


9
Projects / Re: Self balancing robot
« on: August 08, 2017, 07:48:15 PM »
Mdf base has been discarded, it was too heavy, was falling apart, single bearing up front meant axle wobbled, so designed a central spar that the old bits mount to but rotated the electronics and flipped the rear axle assembly around.
It was supposed to have battery under slung and I designed the length to suit but found of course the front axle hits it, so jow I need to put sides on it and mount the battery up top.
Apart from that pretty happy with its new shape.


10
Projects / Re: My Rotary Axis
« on: August 08, 2017, 03:08:36 PM »
When you drew the holes did you take into account the nozzle size?

If you are using a .4 nozzle then you have to open the "hole" .4diameter, .2 radius. The slicer programs do not use any type of "tool size" compensation. Even then the bottom layer will be off as it is purposely mashed into the bed for better adhesion.

This should help you get more accurate hole sizes.

I am about 95% sure this is incorrect, slic3r has settings for extrusion width for first layer and then other layers. Cura has settings for different sections, infill, skin, support etc.
This affects how soread apart the lines are and obviously, their position.

Also, looking in the wrong place to calibrate, you need to look at the machine settings first, for instance my latest machine had steps/mm on the X and Y set to 81 when it should be 80.
My guess is they did that to compensate for PLA thrinking 0.5% but it is the wrong way to go about it, scale the print in the slicer by 0.5% if you have to, the X shoukd move 80mm if you tell it to, not 81mm.

You adjust the machine so it does what the slicervis telling it first, then toy with settings in the slicer to get the results you want, that is the point of calibration.


edit: the new central spar for my robot chassis just completed actually (2:45 print), the 2 bearings are 11mm outside diameter and are a push fit with a vice but can then be removed by hand, the central bush for the bearing to 6mm bolt needed rework, the outside is 8mm and I shoukd have designed it 8.2 to cope with shrink, it is a tiny bit loose in the bearing, the 6mm centre hole I had to drill out to fit over the bolt, the bit next to it is what was removed. A trick for drilling pla to not tear it up is to operate the drill backwards, then it will remove much thinner amounts of material.



11
Projects / Re: My Rotary Axis
« on: August 08, 2017, 01:22:36 AM »
That is pretty accurate, a correctly calibrated printer should produce the correct size holes, however even temperature will affect them.
The slicer might put the nozzle in the correct spot but as it extrudes hot plastic and draws a small circle it drags the filament inwards towards the centre. Lowering temperature and speed on articles with small holes can help.

Personally if I want a hole for a 3mm bolt I print it 3.5mm, 2.5mm for a tapped hole.

12
Projects / Re: My Rotary Axis
« on: August 07, 2017, 10:30:34 PM »
Its a known. fact that all cool things are made with orange PLA.
So I have no doubt it will be awesome.
I am guessing you intend to raise the bottom of the object up and maintain the same focus height ?

13
General Questions / Re: New Chinese GRBL board spotted
« on: August 06, 2017, 10:21:33 PM »
I can verify the optocouplers are not just for show :)

Thanks for mentioning them, reminds me that yes, i do have one of these boards somewhere and I bought it to CNC control my plasma cutter, figured it woukd be noisy and I might need the isolation. only issue is that I just hunted for it and still can't find it..

One downsiide if the optos I have read is that grbl no longer is the determining factor on pulse speed, the optos slow it down somewhat. As low as 10khz reliably  (down from 30khz) though i have not verfied it, it could come down the brand of opto used.

Good review, pretty much my thoughts on it too.

14
Custom Size Frames / Re: Little CNC mill
« on: August 06, 2017, 10:00:11 PM »
Reviewing the design again, I see that the bolt with the wingnut is pulled up against the bottom of the T-slot wings. The other pivot bolt, at least in the machine too world pushes against the top of the table, not the bottom of the slot.

Clamps are better to use this way, thanks for the comment.


These arrived today, I figured more cutting edges the better at the fairly low spindle speed, these work great on mdf and useable on aluminium, not much good as end mills but if you can use lift milling on the edges it has reasonable cutting speed. Only doing 0.25mm cut depth and around 100mm/min feed it was cutting a 4mm vertical surface. So slow and needs thinking to get the cutting direction, feed rates etc correct but doable on aluminium.
Not something I want to do much, just good to know it is possible.

http://s.aliexpress.com/3iAruuI3


Edit just a note: these will not clamp up in the standard 3.125mm collet, you need a 3mm one, luckily I have the 1mm to 7mm in 0.5mm set now.




15
Projects / Re: Self balancing robot
« on: August 06, 2017, 09:18:11 AM »
Turns out the stepper vibration was just resonance, around 10000mm/min causes issues but the galue is different for each motor.
Made a mount for the OLED, i2c distribution and magnetometer, swapped out the generic adjustable buck module for a proper 5A ESC and redid the motor wiring and a few other bits and pieces.

Ran some numbers and found I was way under guessing grbl, I know it copes with 30000 steps per second so with 16 microsteps and my 100mm diameter wheels (10.18 steps/mm) it works out 176000 mm/min (10+ km/h)  Thats flying ! So here it is at that speed on the coffee table, 10 metre run, lots of torque too, ramped up the motor current a bit so it will have no issues doing this on the floor .. shortly.

http://youtu.be/nB818NhLutE

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