Laser Cut Parts (Bits from Bytes)

For me the cost of the meterial is being eclipsed by the time I am spending
re-tightening a screw that you can only get at after disassebling half the machine only to break the part and have to glue it back together or replace it.

I am seriously considering putting some super glue on the screws to stop them undoing themslves. Of course as soon as I do this I will probably find that I have put the part on backwards .......

I love the idea of aluminum annodised in cool colours.

And yes as soon as the system is up and running there is a long list of parts that will need to be created and replaced. Actually I am thinking of building a second reprap out of ABS. Basically using the laser cut reprap as a Reprap - boot.

Hopefully the pain will soon be over and I will have my reprap working as god intended.


regards

Stephen

Steel or Aluminium would be very expensive Acrylic was choosen for its ease of cutting I do appreciate that it gives no warning of impending failure & for that reason we have switched to Hi Impact Acylic this can still be broken but does show stress lines first, We might also do the diagonal ties out of Acetal as this is very resiliant.

As for bolts coming loose which ones? I thought you could get to most even when assembled. If they do need locking try a thread lock compound as these come in various degrees of permanance go for a holding type not complete locking.

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Ian
[www.bitsfrombytes.com]

The bolts coming loose are due to my fear of breaking the acrylic by tightening them too much and breaking something. (I only have so much glue).

Incidently how much would it cost extra for Aluminium?

regards

Stephen

Most cordless drills come with a torque setting and can be used to tighten bolts. Thus they can be used to tighten just the right amount. Maybe someone knows the correct setting?

I not sure of the extra for Aluminium but steel would be the cheapest metal option to cut but very expensive to ship, I think the steel option would be in the

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Ian
[www.bitsfrombytes.com]

Quote

rigidness (is that a word?)

I think I'd go for 'rigidity' myself. It gets about two orders of magnitude more hits on google, so I guess thats some support for it

... then i would recommend black POM-sheets as ideal material - black for good absorbing laser-energy and it have exellent specs for wear and rigidity ...

I'm milling all my micro-grippers with solid-state hinges, mechanical parts and all other stuff (see in my posts about "Han Solo") from POM.

The only parts i milled from Nylon were the big triangles in my Tripod-toy - it's more 'soft' when milling and isn't so exact in the final diameters because of higher elasticity too.

PVC wouldn't be so good for laser-cutting because of the highly acidic and toxic fumes ...

Viktor

Greetings all,

Would Polycarbonate (e.g. Lexan) work for laser cutting?
It's available in black as well as clear, and is *much* more rugged than other plastics. It (Lex) costs a little more than acrylic, but is very tough stuff, and very difficult to break by tightening fasteners. My impression is that the cutting and shipping dominate the costs, so using a more durable material might be an attractive option. I believe the density is similar to that of acrylic. (Most plastics are close to a specific gravity of 1.4.)

-- Larry

I found while assembling the corner blocks that measuring the distances between the two plates allowed for getting the bolts tight but not breaking anything.'generally' the plates could be pulled down to 7.7mm without harm, but I'm being a bit cautious and have mine a 7.8mm at the moment. (8mm would be the gap size with no flex, as that's the diameter of the rods).

>Most cordless drills come with a torque setting and can be used to tighten bolts. Thus they can be used to tighten just the right amount. Maybe someone knows the correct setting?

Tried it, setting 1, the lowest setting on my drill/driver (makita with 16ish torque settings) is too much by a large margin. I'm sure torque wrenches/screw-drivers must exist for these low torque levels which is good as I don't think at this level humans are very acurate on their own.

I know that measuring the bow of the parts works, but repeatedly going around with a caliper is quite a tedious way of doing it. Something like holding a straight edge against the piece and jugging it by the gap or more easily by how much the straight edge can be rocked might work.

Check out one of my entries in the builders blog. I took a couple of pieces of 8mm stock and used them as temporary spacers when tightening the corners. It worked well for me.

HMMM

Still think aluminum is a good way to go. Worked for Macarno.

Ian you have a Bronze, Silver and Gold option what about a
aluminum version - pick up only?

(Yes I would consider travelling all the way to the UK from Australia. I could see my mum on the way. Although I don't know what customs would make of it.)

Also I get the feeling that as long as the parts were general purpose enough it would be worth while disassebling the Dawin to make the next version of reprap with aluminum. After all reuseing something is better than recycling.

A Macarno reprap system? won't be long till it upgrades itself!
But that is the point isn't it?

Grin

Stephen

... maybe aluminium- or iron- casting moulding for the complexer parts?

We had som discussions about lost-cast-moulding: - reprap the parents from plastic or wax (or mould wax-copies), make sand-waterglass-moulds, sinter/burn the moulds or simply pour the fluid metal through the wax-object ...

Viktor

I will look into a aluminum price. would you want all parts or just the ones more prone to breaking?

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Ian
[www.bitsfrombytes.com]

spcmicro:

That looks a lot simpler for getting alignment right, but how do you judge the 'tightness' of the bolts?

I would appreciate any advice on getting the laser-cut extruder to work. I am using HDPE at 240 degrees and I think this temperature is correct as I have checked it at room temperature and 100 degrees. Earlier, when the extruder was leaking, only 20% came out through the nozzle but the filament was being driven by the screw feed and I made a reasonable first attempt at the 'minimug'. Now I have fixed the leak, the extruder runs for maybe 10 seconds and then the drive starts skidding and once it has cut a groove in the filament, I have to take out the filament and cut off the spoiled section to get it started again. I have found that the pressure springs on the roller do not supply enough pressure to drive the filament through the nozzle and so I have to compress them to solid to get any extrusion. The extruder speed is currently set at 150. I wonder if I am trying to drive too fast but at '100' the motor tends to stall.

Any suggestions would be appreciated, especially the settings being used for successful operation of this extruder.

I've been able to extrude HDPE at 200 extruder motor speed/240c extruder temp with the bfb lasercut extruder, after making the following modifications:

I sanded down the connection points where the drive gear subassembly joins with the main plate/top plate (step 3 in the Extruder Assembly pdf) so that there is an angle on all the connection points. Basically the main plate side is lower than the top plate side, so that the drive screw is closer to the filament channel at the bottom of the main plate/top plate subassembly. I sanded down about 1mm on the outside edge of the main plate, sloped up to no change at the outside (opposite) edge of the top plate. I did this on five surfaces- the three top surfaces of the top plate/main plate subassembly and the top surfaces of the two receptacles for the captive m5 nuts which hold the drive screw subassembly onto the top plate/main plate subassembly (where obviously I filed the top plate side more and the main plate side less, so the angle is the same as the top surfaces). I tried to do this by shimming with washers, but without applying shims in all five of those places I wasn't able to affect the angle of the drive screw reliably.

After making that change, the M8 nut between the two bearings on the drive screw (installed in step 1 of the Extruder Assembly pdf) started coming unscrewed when the extruder was running, causing the gear which connects to the dc motor to lose contact with the dc motor gear. Basically the drive screw started moving up instead of the filament moving down. The nut must be in contact with something when it's at an angle but I wasn't able to find where that was. I replaced the single full size M8 nut with two half-size M8 nuts locked against each other, and they haven't moved since.

I also removed the inner pressure clamp plate (part 37) which is installed at step 10 in the Extruder Assembly pdf. This allows the pressure bearing to press more firmly against the filament in the channel. I tightened the springs on the pressure clamp down pretty close, and the bearing now floats much more clearly when filament goes through it. It also seems to put much more pressure on the filament.

After making those three mods, I haven't had a single feed problem! Before that, I'd seen exactly what you report- leaking, wedging, scratching up of the filament until it's not wide enough to be grabbed.

Hope this helps,
Adam

ps. after all that, now I have some problem where after I've been building something through the host software for anywhere from 30 seconds to a minute, the arduino stops sending any commands. The stepper motors stop moving (but are still locked) but the extruder motor and heater keep running, so I get a big blob of goo where the extruder head is when it gets to this point. Frustrating, but I am at least getting the entire bottom layer and part of the second layer of the minimug done before it gives up. This has let me fine tune the extruder parameters in the host software so the HDPE is going down the right way, etc. Haven't been able to figure out the seeming arduino problem or hear of others having this problem. I went up to three power supplies and went to better heat sinks and cooling fan on the DC motor drivers to see if either of those had anything to do with the problem, no help.

[updated with info re: angle on captive nut filing]

Edited 2 time(s). Last edit at 10/01/2008 12:55PM by ahahn.

Did you try sharpening the thread on the drive bolt, i found this was needed for HDPE to work reliably.

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Ian
[www.bitsfrombytes.com]

Ah, sorry- I did that as well. That was my first attempt since I saw that mentioned in the forums here. It worked ok the first time I used it after sharpening, but then went back to the state where it would get stuck for an instant, which would cause the threads to score the filament just enough to make it start slipping in general.

We have a first minimug! Sharpening the screw was probably the key change but the adjustment of the pressure on the roller is still very sensitive to get a balance between slipping and stalling the motor.

The leak problem returned and I have, I hope, fixed it by improving the clamping of the PTFE tube into the extruder. I have fitting a ring round the washer on the back of the heater barrel so the nuts holding the spacers round the PTFE tube are supported on both sides (equivalent to bigger rear washer with holes in it) so the assembly can be tightened without the spacers splaying out. Also the PTFE tube was bulging at the hot end and getting shorter. I drilled out a big nut and pressed it over the hot end of PTFE tube to hold it in shape.

Congratulations,

Do you have a photo?

jonwise Wrote:
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> We have a first minimug!
>

PICS! PICS! PICS! BLOG 'EM!

Here is a link to my blog: [cmedia.glos.ac.uk]

Jon

jonwise Wrote:
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> Here is a link to my blog:
> [cmedia.glos.ac.uk]
>
Oh come on! Blog it on the Reprap builders' blog. You've got bragging rights.

I noticed the outside surface of the mini-mug is pebbly. Little blobs all over the surface. Is this a 'catch' in the turning of the extruder screw? Maybe a pause between line segments? What software/toolchain/firmware are you using?

I envy you your notable success! Hopefully I'll be joining you in a month or two...

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I'm building it with Baling Wire

> pebbly surface

The movement in X and Y is not smooth and I think the pauses are the source of the uneven surface. It may be because I get communication errors every few seconds. One of my jobs is to hunt these down. The overhang of the extruder from the x axis gantry amplifies any jerks in the y direction. The vertical line down the side of the minmug is due to the pause between layers when material is still oozing from the nozzle. Maybe some reverse drive to the extruder is needed. I am using reprap-host-src-20080523 under Vista-Home on a modest laptop. The firmware is reprap-arduino-firmware-1.3 on a Freeduino.

> ... the arduino stops sending any commands ...

I now have the problem described above. Has anyone ideas on the source of the problem? Should we move this topic to Electronics?

I wasn't able to track this down. I tried with a different arduino and had the same problem. I switched to the gcode firmware and now using skeinforge to generate the code and send.py to send to the arduino all is working fine.
I printed a minimug! Pics / details later, but I also have the pebbly surface problem.

> ... Sharpening the screw was probably the key change ....

After more intermittent extrusion, I removed the drive bolt again and cut the thread deeper, to at least 1.5mm, using a small hacksaw. This seems to have solved the problem as I have run on several days since then without needing to adjust the pressure roller.

Ian: I would like propose three things for your extruder kit:

1. Ship some small quantity of Cerastil with the extruder kit. (the cerastil is the best available option, but comes in 1kg package. Would like to have 100g for 10-15 GBP for example). It would ease the building of a true reprapped version of the extruder.

2. Could I have a gold version of extruder kit? Where the gears are made from steel/aluminium and not acrylic. If Im spending 48GBP for the extruder, it does not make much difference spending eg. 55 GBP for metal gears in plus.

3. 2 GM3 motors instead of one.

Edited 1 time(s). Last edit at 10/25/2008 04:26AM by khiraly.

I'll investigate the Cerastil, but i thought Adrain had adopted fire cement as the preffered solution at present due to it's ease of availbility and I think its preformance seams OK.

The problem with metal gears would be getting them with the correct size hole/ fitting for the GM3 motor I would expect them to cost much more than

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Ian
[www.bitsfrombytes.com]