Wednesday, April 18, 2007

 

Nozzle Updates

Well, last night I went to the shop, and I was completely disorganized. I think I was just a bit frazzled from nuking my MacBook. However, I did find some interesting things out:

1. JBWeld holds up damn well under heat. I ran the 30awg insulated nichrome / jbweld barrel for an hour with straight 12v power and it held up fine. The coil was 14ohms, so it didnt get super hot, but it was definitely enough to melt the HDPE I had with me.

2. JBWeld is super easy to machine. I easily drilled 0.5mm holes in each of the JBWeld nozzle attempts. The only question remains is whether they can stand up to the forces of being an extruder nozzle. My gut feeling tells me no... but hopefully I'm wrong.

3. The mechanical pencil nozzles were super easy to grind down, giving a very nice tip. I had to make them nice with the top of a pushpin, but that was really easy. The end result is a very nice looking nozzle. I haven't tested it yet, but I have high hopes for this.

Now, those were the good things I learned. Here are the bad things:

1. keep a nut on threaded rod before you cut it (especially if you use bolt cutters + dremel to smooth the cut) its impossible to get a nut back on once you do that. if you keep the nut on, then you can force it off, and hopefully restore the threads.

2. i need a cross slide vice for my drill press. otherwise it is impossible to drill a 1/8" hole down a 1/4" bolt. twice i ended up coming out either side. either that or move to a higher size. i'm particular to 3/8", but i bet 5/16" would work too. i chose 1/4 because that is the size that the pencil tips screw on to, but if it is nigh impossible to drill correctly, then it could still be possible to jbweld it to a larger nut, then attach that nut to a drilled length of threaded rod. the pencil tip fit best in the 3/8" nut, so I'll probably try with that.

Comments:
***The only question remains is whether they can stand up to the forces of being an extruder nozzle. My gut feeling tells me no... but hopefully I'm wrong.***

Zach. Do what I did. Slap your extruder barrel in a vise, fire it up and gently push a length of HDPE filament through it with a pair of pliers.

I emphasize "gently". It doesn't take a lot of force on a 3 mm filament to create substantial pressures in your extruder barrel. You just have to member that the force you press down with on that filament is concentrated on that 3 mm diameter cross-section. That's 7.05 mm^2. A few pounds of force does the trick and if it doesn't you need to check to make sure that your extruder orifice isn't jammed.

That's how I did my initial experiments with HDPE, HPP and ABS
 
thanks for the suggestion. i would have definitely tried it... however because of the failure to leave a nut on the threaded rod, i had no heater barrels that would accept the nuts. i just ran out of time. i'll be making some barrels tonight, hopefully.
 
Yeah, a quarter inch bolt is cutting it a little fine. That's only 6.356 mm wide and less than that if you count the threads.

Of course, you can always braise one up out of 5/32 inch hard copper tubing. That's not standard, though, lol!
 
jab aside, there is some merit to the copper tubing style that you did. i even looked into getting the parts for it.

unfortunately, i cant find copper sheeting anywhere (at least not at the hardware store...) however, 3/8" bolts and nuts are VERY common, as are metal cutting 1/8" drill bits.

there is one thing about your design that i *really* like, and that is the flat bottom. this gives you two important things: perfect (small) thickness, and its easy to drill.

i came up with a 'best of breed' concept that i will be testing out sometime soon. hopefully this weekend. let me just say... it will allow us to make interchangeable nozzles for pennies! =)
 
The copper sheet is easy to come by. You ask for either copper shim or ask to be directed to the metal display rack where they have small standard sized sheets of copper and brass used for engraving the sort of discreet signs that you see on the door of doctors' offices in ritzy urban areas. You can also get it at a shop that engraves the little plaques for bowling and other sports trophies.

If you have an Ace franchise hardware store anywhere near you you'll find the 0.005 copper sheet in the same rack you find the 5/32 inch hard copper tubing in.

Lastly, I'm not sure if that flat bottom on the extruder barrel is such a wonderful idea now that I've worked with it for a while.
 
interesting. i guess i'll have to look harder next time i make a trip down to the hardware store.

the biggest hangup i'm looking at now is how to thermally isolate the barrel from the extruder. currently, i'm using a wood dowel. for obvious reasons, its not a good long term solution. i'd like to try out the setup you have, with a metal sheet attached to the bottom of the extruder. does that cause any sort of melting / heat transfer to the plastic? my guess is no since you havent reported any problems.

it seems like that would be the easiest way... drill 7/16" or 1/2" hole in the sheet, put the bolt through that (with some jbweld to keep it in place.. might also offer some minor xtra thermal insulation) and then bolt that onto the bottom of the extruder.

if this setup works, it would combine the thermal barrier / nozzle tip from your extruder, the interchangeable nozzles from the mk2, and the ease of hardware store parts. plus, the total cost for raw materials would be <$1.00

the only tools required would be a hacksaw, and a drill (press). i'm not sure if that is an upgrade or a downgrade from brazing, but it does offer the advantage of a removable nozzle.
 
Yeah, those bolt barrels like you and Vik make carry heat pretty evenly right up to the thermal barrier, especially since they're insulated.

Whew, let's see. You're going to be using HDPE or the like, so your temperatures are going to be about double what you use with CAPA. Are you threading that extruder barrel into the dowel?

According to the manual HDPE melts at about 126 degrees C. I'm extruding it at about 150-170 degrees. That's about a 325-350 F oven. I'd suggest that you do an experiment and run a piece of your dowel in your oven and see what happens after a few hours. I noticed that poplar tends to get a very thin surface char after being exposed to that kind of heat for several hours. I don't know what kind of wood you have in mind, so I can't generalise.

Take a look on my website in the documentation and find a pic of the assembled barrel. The barrel is 55-60 mm long. The heating coil is 7 inches long and is wrapped around the bottom 25 mm of that.

What that means is that there is a long way between the metal plate that attaches to the thermal barrier and the heated part of the barrel.

I did a lot of measurements of the temperature of that attachment plate when I first built the Mk 1 AEM in that I was worried that I might get the PTFE block too hot. In those days I was running the extruder barrel at 2 amps and getting a tip temperature of about 210 degrees. Most times when I was doing that that plate next to the PTFE block was running about 80-90 degrees. Once after running it for several hours I measured that it got up to 105.

I haven't reported any problems with the PTFE thermal barrier largely because I haven't had any. The way I designed it precludes it from getting anywhere near its melting point.

When I get things running properly I'm going to try to replace it with a HPP block that I've reprapped. I should be able to get by with that, but you never know till you try.

Reading your description of what you want to do again I that you haven't read just exactly what I've done closely enough. The mounting plates on the barrel are brass, not copper.

There's a copper flange that I braised onto the 5/32 copper tube so that the brass mounting plate couldn't slide off. I had to do it this way because I was using a cheap propane torch and couldn't do a proper job of braising the copper tube directly to the brass mounting plate.

http://3dreplicators.com/New%20Front%20Page/Documentation/Extruder/Mk%201%20Extruder%20Barrel.htm

If I'd had a MAPP or acetylene torch I'd have been able to do the whole shooting match out of brass tube and made it much less complicated. As it was, I was trying to stick to tools like a propane torch which are already likely to be in dad's workshop.

I see you like Vik's removable nozzle. It's a nice concept, but my allergy to getting too much mass in the extruder barrel precluded me from going that way.
 
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