Comments on RepRap: Blog: Aluminum Barrel Success!

ABS has some insoluble polybutediene (the B in the...

2007-04-30T21:35:06.355+01:00

ABS has some insoluble polybutediene (the B in the acronym) that should make it translucent even when melted. This means microscopic gobs of rubber that blunt a passing crack tip, making the material shatter-resistant. I have seen transparent ABS in the case of a TI calculator, but I think they probably had some kind of a copolymer in the butyl rubber to match its index of refraction to the PS/acrylic matrix.

By the way, it's these little gobs (micelles, technically...) of rubber that differentiate ABS and "high-impact" plastic from the ordinary polystyrene used in model kits and picnicware. The "A" is acrylonitrile, added for strength.

actually i had no problem with breaking drill bits...

2007-04-29T18:37:46.116+01:00

actually i had no problem with breaking drill bits and aluminum... it was a dream.

also, the acorn nuts were machined in such a way that the thickness of the aluminum where i was drilling was very small (~1mm i would guess. could be even less.)

although its good to get that information into various places =)

Sorry if I'm teaching people things that they know...

2007-04-29T12:33:47.576+01:00

Sorry if I'm teaching people things that they know, but Zach had a bit of trouble breaking drill bits, especially the fine ones. When drilling deep, or fine, use a woodpecker cycle; that is drill a short way, then raise the drill bit to clear the swarf and brush it off if need be, then drill a little more and so on. It's slower, but it stops the swarf fouling the bit and causing it to snap.

This is a particular problem with aluminium, as its so soft, which you'd think would make it easy to machine, but paradoxically doesn't.

larry,nice find! if its the proper size, then all...

2007-04-29T01:17:41.429+01:00

larry,

nice find! if its the proper size, then all you'd have to do is drill straight through the rod, then tap both ends, and you're good to go. (is that what you call making threads?)

Zach, special ordering the bolts may not be needed...

2007-04-28T23:29:17.081+01:00

Zach, special ordering the bolts may not be needed, most big box hardware stores sell 3' lengths of aluminum bar stock that is not too difficult to machine into shape . I made a few prototype heads a couple of days ago that I haven't yet had a chance to test.

The ever popular Harbor Freight had very good deal...

2007-04-28T22:48:52.379+01:00

The ever popular Harbor Freight had very good deals on tungsten carbide bit sets last time I was in the store. It looks like there are currently two sets listed online 20 and 50.

Are you wrapping insulation round the heated barre...

2007-04-28T21:16:39.008+01:00

Are you wrapping insulation round the heated barrel? That can up the temp quite a bit.

the thread is standard american 3/8". the aluminu...

2007-04-28T20:24:06.229+01:00

the thread is standard american 3/8". the aluminum bolts and such will need to be ordered from a specialty place. although i plan on making up barrels and nozzles for anyone that ones them. using an equivalent metric size would work fine too.

i'm trying the ABS as we speak. hopefully i can get it to work. i'm running at 1.3 amps. i'll make a 2 amp barrel this week to do further tests. i just dont think its getting hot enough. i also want to try a slightly different approach to wire wrapping / heater barrel fabrication.

as for the drill bits... i got them from http://drillcity.stores.yahoo.net/index.html this place really rocks.

I have a Loew-Cornell Cutting mat (part 70212) tha...

2007-04-28T20:22:12.810+01:00

I have a Loew-Cornell Cutting mat (part 70212) that is black with a white grid. I use it to protect my table from cuts, and take pics

Oh yeah, where did you get your wire gauge drill b...

2007-04-28T19:19:01.918+01:00

Oh yeah, where did you get your wire gauge drill bits?

ABS, at least the white pigmented ABS that I've us...

2007-04-28T19:18:27.021+01:00

ABS, at least the white pigmented ABS that I've used, doesn't go transparent. I don't know what virgin ABS would do. What I found is that it requires not so much a very hot extruder barrel, though that helps, as a lot more pressure from the polymer pump.

That's why I'm redesigning the Mk 2 so that it can deliver more pressure. The only problem that I can see is that HDPE puts me right at the top level of torque that the GM3 can deliver before the clutch kicks in already with HDPE. We have have to find a higher torque gearmotor for an ABS extruder.

You may want to go to 2 amps for ABS. You can do HDPE on 1 but it's a bother. Just half the length of your nichrome and you've got it.

That's brilliant Zach! What thread is it, and wha...

2007-04-28T18:52:49.796+01:00

That's brilliant Zach! What thread is it, and what diameter? Then I can add it to the extruder page when I update it shortly.