Slide bearings on Aluminium Extrusion (no smooth bars)

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rayhicks
Interesting Radian - I wonder if it's "special" or just carbon fibre tape they've measured the resistance of and sell as heating tape? (there's a lot of plain carbon tape on ebay, but it tends to be fatter - there's other stuff on the general web on composite/fibreglass sites that's cheaper and may be worth a punt - I'll get some and try it!). Looks like the resistance is around 8-20 ohms per metre (for tape ranging 15mm-25mm), so I'll have to try to remember Kirchoff's (?) laws and work out how to spread a network over an A4 area that'll work. Looks like people sew copper wire into the tape to connect it.
Ray

It is easy to work out if you first find the resistance of a square of the material. The great thing is that it doesn't matter what size the square is, the ohms-per-square will be the same for any size square (for a given material), because you are effectively adding just as many resistors in parallel as you are adding in series when you increase the size of the square so they cancel out. To find the resistance of any given rectangle you just multiply the ohms-per-square by the ratio of ( side A )/( side B ) where the connections are made to the whole length of the "B" sides.

You can also halve the resistance by laying down two sheets on top of each other (doubling the thickness).

From your figures, if 15mm tape has a resistance of 20 ohms per meter, that's 20 X 15/1000 ohms per square = 0.3 ohms per square
If 25mm tape has a resistance of 8 ohms per meter that's 8 X 25/1000 ohms per square = 0.2 ohms per square, so assuming the figures are approximate they probably indicate that a value of 0.25 ohms per square would be in the ballpark for that material.

Dave
(#106)

Edited 2 time(s). Last edit at 03/07/2014 07:50PM by dmould.

Interesting Dave - I'm used to thinking in terms of ohms per linear metre for a fixed cross-sectional area (from using resistance wire) - I guess what you are saying is that the converse applies, and you can think in terms of ohms per square metre for a given length (or both for that matter)

Cheers

Ray

Edited 1 time(s). Last edit at 03/07/2014 07:47PM by rayhicks.

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rayhicks
Interesting Dave - I'm used to thinking in terms of ohms per linear metre for a fixed cross-sectional area (from using resistance wire) - I guess what you are saying is that the converse applies, and you can think in terms of ohms per square metre for a given length (or both for that matter)

Cheers

Ray

As a youngster I used to do the layouts (using tape and rubylith on a drawing board) for what were called "hybrid" modules (now pretty much out of fashion, but cutting-edge stuff in the early 80's). Silver conductive paste and graphite resistance paste was screen-printed onto a small ceramic substrate (tile), with upside-down I.C. chips, capacitors and some other components put on later either with conductive glue or microfine wires were ultrasonically friction welded to a right-way-up IC chip under a microscope. The graphite paste came in a fairly small range of values that were marked in ohms per square, and you designed in the required resistance using a chosen paste and rectangle of the appropriate aspect ratio. The overall size also had to take the power dissipation into account of course. After screen printing and before mounting the other components the ceramic tile was put into a machine where test probes measured each high tolerance resistor and laser-trimmed them to the exact value by cutting a line part-way through it - so you always designed the layout to give a slightly low resistance to critical resistors.

Dave
(#106)

Even more interesting
Around that time I was messing around trying to make pcb's with letraset (and that expensive crepe tape that RS sold back then - well, Electromail, RS wouldn't sell to me) as a hobbyist. I was reminded of that when I was trying to do a "repstrap" heated bed using the 30micron copper tape on glass this afternoon.

Ray

Mulling over potential names for the hybrid I'm producing, I'm torn between IGORmerod (nodding at the Frankenstein movies, since I'm putting into it mostly what I can dig up), or McLintock, since I'm transposing elements from one machine into another framework, and Barbara McLintock was the discoverer of genetic transposition (and won a nobel prize for it) and these evolving machines are meant to be named after geneticists, right?

I've got to admit to having a genetics degree and never having heard of Eleanor Ormerod:/

Edited 2 time(s). Last edit at 03/07/2014 11:05PM by rayhicks.

Yo Ray

Just call it Frankenrod, then you are truly free to migrate in any direction you want, don't you just hate fences?

"Erik the Orme Red", no more, going white, Ha!

Indeed Erik But then again, I'm hoping to get rid of the smooth rods, so maybe Ormerslide?

Ormerslide? - I think that one is taken, it's a dance innit?

Erik

? Frankenslide!

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Mykey
? Frankenslide!

You nailed it!

Edit: no that won't do it, no Franken without the Orme

Erik

Edited 1 time(s). Last edit at 03/08/2014 06:53AM by ormerod168.

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ormerod168

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Mykey
? Frankenslide!

You nailed it!

Edit: no that won't do it, no Franken without the Orme

Erik

Damn, I thought I'd had a genius moment!

Erm, Ormenslide, Igormenslide........

Igormenslide's the front runner! -especially if I end up using some Igus rail

Ray

Ray, you use plastic cement?
Do you have a thread on this? A quick search and I couldn't find one, but I am most intrigued...

Awesorme?

---

Ormerod #007 (shaken but not stirred!)

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badman.teddy.edward
Ray, you use plastic cement?
Do you have a thread on this? A quick search and I couldn't find one, but I am most intrigued...

It's popped up in a few places, but maybe not recently - it's Marley KS10 solvent cement for PVC and ABS pipework (from B&Q behind the counter, plumbase etc) It's pretty thick and hard to spread very evenly - Dave Mould realised you can thin it with acetone, and it's much easier to apply ( did mine at around ten to one and it goes on so thin you can hardly see it, but it still works very well). It comes off on the bottom of the print, but you just brush mor einto the gap on the bed - it holds PLA and ABS very weel without being too strong (I tried PVA once but broke the print trying to remove it). It has the advantage that it "self cleans" the bed - but every now and then you need to remove the build up - a stanley blade paint scraper works well for that.

Ray

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Treth
Awesorme?

maybe too subtle treth - took me a while to see the "r" in there!


Ray

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rayhicks
(...)
It has the advantage that it "self cleans" the bed - but every now and then you need to remove the build up - a stanley blade paint scraper works well for that.
Ray

Try simply holding the glass at an angle under a running hot tap. I find the running water gets under the film of solvent cement and most of it lifts and washes away by itself - and the bits that are left come off with a brief rub with a scrubbing brush or scouring pad. Don't let too many bits go down the plughole, because I have a feeling they'd block the drain fairly easily.

Dave
(#106)

I used plastic cement for a while and I can confirm that it works well; but now I'm back to printing direct on glass. The secret to printing direct on glass seems to be:

1. Use the right piece of glass, some pieces seem to work better than others (and one side of the glass may work better than the other side). The original glass supplied with the kit works well for me. The glass needs to be free from scratches.

2. Clean the glass with hot soapy water, NOT acetone or isopropanol. This is only necessary every several prints, if you avoid fingermarking the glass.

3. Just before printing, wipe the glass with a clean tissue dampened with vinegar.

4. Use a sufficiently high bed temperature. I normally use 70C for printing direct on glass, but once I left it at 60C by mistake and the print still stuck OK. The print comes off easily once the glass has cooled to room temperature.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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dc42
I used plastic cement for a while and I can confirm that it works well; but now I'm back to printing direct on glass. The secret to printing direct on glass seems to be:

1. Use the right piece of glass, some pieces seem to work better than others (and one side of the glass may work better than the other side). The original glass supplied with the kit works well for me. The glass needs to be free from scratches.

2. Clean the glass with hot soapy water, NOT acetone or isopropanol. This is only necessary every several prints, if you avoid fingermarking the glass.

3. Just before printing, wipe the glass with a clean tissue dampened with vinegar.

4. Use a sufficiently high bed temperature. I normally use 70C for printing direct on glass, but once I left it at 60C by mistake and the print still stuck OK. The print comes off easily once the glass has cooled to room temperature.

I like the idea, but when I tried it with ABS it was completely hopeless - the plastic did not make the slightest attempt to stick to the glass. It was so obviously completely non-stick that I did not try it again on the other side of the glass or with a vinegar wipe (I cleaned with dishwashing liquid & water, rinsed off, dried it then wiped down with acetone). Painting on a diluted very thin solvent cement solution is the same effort as wiping with vinegar and works a treat, so I am sticking with that for ABS. The bottom of the print ends up covered with the residue which I used to have to trim off around the edges by hand - but I found that if I wipe around the bottom of the print with an acetone-soaked cloth, it dissolves off the thin residue quickly and effortlessly.

Dave
(#106)

Edited 1 time(s). Last edit at 03/10/2014 10:25AM by dmould.

I should have made it clear that my direct-on-glass instructions were for PLA. I've not heard of ABS being printed successfully direct on glass.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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dc42
I should have made it clear that my direct-on-glass instructions were for PLA. I've not heard of ABS being printed successfully direct on glass.

Yes, it's a shame - when Kim first reported using vinegar I tried with ABS, and like dmould ended up with something behaving like raclette on a teflon griddle It's why I stick with the cement, it works great for both plastics.

Dave, I seldom remove my glass, occasionally I get fed up with the scraping (the flakes of used cement are very sticky with static, and make a bit of a mess when dry), and I take the plate of and give it a good clean under the hot tap, and you're right it is easier (just further away)

Cheers

Ray