Friday, September 28, 2007

 

Equations of Extrusion

When I first tested my extruder I found that the filament diameter varied with extrusion speed. The filament expands after it passes through the nozzle aperture and this is known as die swell. I seem to have variable die swell whereas others have reported constant die swell. I have done some fairly detailed experimental work to get to the bottom of it and I think I have a simple explanation and a mathematical model to exploit it.

Further details here:

Incidentally, I read that die swell in polypropylene can be eliminated by the addition of carbon nanotubes: http://www.azom.com/details.asp?ArticleID=2601

Labels: , ,


Wednesday, September 19, 2007

 

Request for a look

Hello RepRappers!

I am a prospective fabber in Taos, New Mexico, USA. While I plan to build my own Rep-Rap I am currently aiming to join forces with other fabbers and prospective fabbers in my area. I have been in discussions with local educators and technologists and have been able to generate some interest on their parts to participate in a program to make some of the technical capability available in an educational setting. Most are not aware of the state of the art in 3D printing or other additive fabrication technologies.

I'd like to locate any fabbers in the northern New Mexico area who may wish to participate or, possibly, just to show me and a few others how a RepRap works and what may be possible. Nothing like seeing is believing and all.

If interested please post a reply or send email to normc at eclecticelectricks dot com if you're inclined.

Thanks!

Norm of Taos

Labels:


 

Gears are going to be possible

Just got through with my first 7-toothed gear perimeter. The print layer has bad settings for height and flow rate, but it's pretty obvious that the work I put in on improving the positioning system, never mind making a new extruder barrel is paying off. The teeth on the gear all look the same regardless of their location on the gear perimeter. I made them really big so that I could be sure and not fool


A lot of the problems are coming from the routine that I use to generate the perimeter. It does the teeth twice at the same level for each layer. I've got to fix that.

(Read the full story)

Tuesday, September 18, 2007

 

Run in

I got the extruder barrel finished this morning and ran it in for a few hours. After the last coats of paint were done I rebuilt the extruder barrel/PTFE block/filament guide assembly.

When I rebuilt the barrel correctly on the second try I used the recycled PTFE block flange from the old barrel. That was warped, of course, and when I tried to reassemble the pressure system that holds the guide, block and barrel together, nothing wanted to fit right.


I solved this by putting the whole assembly in the vise and giving it a squeeze. While I was at it I tightened the nuts and bolts. That was handy.

(Read the full story)

Monday, September 17, 2007

 

Finishing the extruder barrel

I finished up the painting of the extruder barrel about dark yesterday and let the six coats cure most of today. Late this afternoon I designed a 2 amp heating coil of #32 glass fibre and Teflon insulated Nichrome 80 wire. It is rated at 0.32 ohms/foot. Using Ohm's law...

R = V/I = 11.5v (measured off of the power transistor)/2 amps = 5.75 ohms


LENGTH (inches) = (5.75 ohms/10.32 ohms/ft)(12 inches/ft) = 6.686 inches

(Read the full story)

 

I2C + GM3 = problems

A while ago there was a discussion about using the I²C protocol for linking RepRap boards. My RepStrap machine uses I²C but when I started using it to control the GM3 gear motor of the extruder I ran into problems with electrical noise. Although I managed to solve them, my recommendation is that I²C is not a suitable protocol for off board communication, and the GM3 needs suppression. A triangle of three 1nF ceramic capacitors, one connected across the terminals and one from each terminal to the can works well and a couple of ferrite beads plus a fourth capacitor works even better.

More details in my blog:
hydraraptor.blogspot.com/2007/09/bus-stops
hydraraptor.blogspot.com/2007/09/dc-to-daylight

Labels: , ,


 

Was it Vikodin or was it just being 60?

This morning just after midnight I woke up and had a "left the faucet running" moment, viz, had I put the support plate on my new extruder barrel before I braised the copper PTFE flange onto it. I decided that I really didn't want to know right then and if I got up and looked at it I'd be tempted to try to fix it. I'm not that wonderful at midnight work sessions.

This morning, I got up and sure enough I'd left the brass support plate off.



I used the recycled copper PTFE plate this time to cut down on the amount of sawing I'd have to do. Having had a trial run at it last night I avoided some of the mistakes I'd made then and got the whole thing done, with the 0.5 mm hole drilled too, in about 5 minutes. I wasn't hurrying, either.



Here it is.

http://www.3DReplicators.com

Sunday, September 16, 2007

 

Building a "new" heated extruder barrel for the Mk 1

I woke up on Saturday at 0100 with a gonzo case of food poisoning thanks to my letting a few New Zealand mussels get past their best before date when I was making an Udon for supper on Friday night. After a day, a couple of litres of IV fluid, some Vikadin and muscle relaxants I was ready to do on Sunday morning what I had intended to start on Saturday.

Given my "warmed over death" state of health I decided to stick with with making another copper heated extruder barrel rather than attempting to make one out of brass with a MAPP torch.

I used measurements off the old one and reused the bottom mounting plate. Since you will be clipping and grinding everything that isn't right on the bottom of the extruder barrel you need take no great care with measurements.


Recovering the plate was a simple matter of simply cutting the old extruder barrel and sliding the mounting plate off with a pair of pliers and my vise. After that I had to cut a .005 inch blank for the extruder orifice.

(Read the full story)

Thursday, September 13, 2007

 

Refurbishing the Mk 1 Extruder (again)

I haven't run the Mk 1 in over a month and before that I'd run it pretty much 24x7 for several months. When I started testing the new xy_move routine I noticed that it was having a bit of trouble keeping a steady extrusion rate and seemed to require a much higher operating temperature than before.

It sounded like time to schedule a maintenance workup. Usually, rising demand for power in the Mk 1 indicates that the nichrome heating coil has begun to separate from the barrel. Oddly, though, this time the coil was tightly bound to the barrel.

(Read the full story)

Wednesday, September 12, 2007

 

First perimeters traced

I got the new xy_move routine working with the rest of the Control Panel and firmware ensemble this morning. There were a few false starts until I tracked down some code in the z_move routine that turns off the interrupts that was left over from an earlier version of the firmware.

Aside from that I hadn't run the z-axis in some time and it was a little sticky from a slight, humidity driven expansion of the wooden slide assembly. Once I ran it a half-dozen times, however, I had no further problems.

From the looks of it I can keep 95% slewing errors well below +/- 0.1 mm for line segment lengths and closer to +/- 0.1 mm for 0.1 mm line segments.

Now, I've got to hook up the code that controls the Mk 1 extruder and I should be good to go.

Tommelise

 

Tommelise blog back...

This time they got it running within 24 hours. :-D

Tuesday, September 11, 2007

 

The Tommelise Blog has crashed ... again

My ISP crashed the Tommelise blog again. They tell me that it will take 24-48 hours to remedy. Of course, the last time the blog crashed they spent about two weeks trying to blame the crash on me and then when they finally took responsibility took several more weeks to actually get the problem fixed.

They don't get a month to fix it this time. ISPs these days are tuppence the bucket, well tamped down.

If they don't sort it out in a 48 hours I'll start posting on blogspot again and get a new ISP.

Monday, September 10, 2007

 

All eight done

My grown "kids", both on holiday, slept in this morning leaving me to my own devices so I got the four paths for the condition (Y2-Y1) > (X2-x1) done and working.

Now I am going to see if I can print the outline of a proper involute profile gear properly.

Sunday, September 09, 2007

 

Four down, four to go

I've had my youngest daughter here for the past week or so on holiday, so I haven't been devoting as much time to Tommelise 1.0 firmware development as I might. All the same, I have been able to make some progress. Here are a few highlights.

(Read the full story)

Monday, September 03, 2007

 

Fruit of My Labor (Day Weekend)

Today was the American holiday, Labor Day, and that means I had a 3-day weekend. Instead of doing the traditional thing and drinking beer all weekend, or going on vacation, I decided to use my free time to work on RepRap. Don't worry, I did leave the house, and also enjoyed some nice afternoons in the park.

The majority of my work was focused on this awesome instructable that has caught the eye of the forum members. It is a nice, simple design, and immediately caught my eye because it was obviously something that is simple enough for someone with basic woodworking skills could construct. It also lends itself very well to lasercutting, which makes it even more accessible to people who dont possess such skills. Finally, it appears to be a successful design, as he used it to actually mill plastic, foam, and PCB's. I emailed the creator, Tom McGuire, and he seemed very interested in collaborating with RepRap, or at least letting us use his design.

Upon hearing that good news, I sat down to draw out the machine in QCad. My CAD skills were a bit rusty. Other than Kicad, the last time I used any CAD programs was the 3 years I took in high school. I really enjoyed it then, and all the stuff I learned started coming back to me. I didn't have any measurements to go on, so I was going off what I could gather from the pictures, and my previous knowledge from trying various other approaches to building a cartesian machine. It was tough, and there were a few false starts, but I think it turned out all right.

All of the files are in the RepRap Subversion, and I've even gone as far to create a page on the RepRap wiki that has a TODO, basic information, and the skeleton of a HOWTO page. As I progress, I plan on documenting that area more and more.

Please check out the designs, view the video, and give me any feedback you come up with. Once I do some final tweaks to the design, I'm going to do a test-run with sticker templates and cardboard. If that looks fine, then I'm going to go ahead and do a one-off lasercut order. If that turns out well, and I end up with a working machine, then I'll definitely be looking into doing a bulk order. Thats probably a month or two off, but with your help, I think we can get this design to the point where it can serve as a good solution to the chicken/egg problem that we've been dealing with for a while.

Read more on the main wiki page for the design.

 

Printing very short line segments on Tommelise

For the past several weeks I have been doing a major rebuild of the Tommelise 1.0 firmware. Heretofore, I was able to achieve fairly good accuracy (~1 mm) for printing as long as the line segments that I was trying to print exceeded about 5-10 mm in length. That enabled me to print, for example, a polymer pump as long as I didn't attempt to print the bolt holes through it.

I had designed Tommelise 2.0 before it struck me that it was pointless designing an improved model of Tommelise without achieving better positioning accuracy for the sorts of very short line segments one needs to delineate such things as bolt holes.

(Read the full story)

This page is powered by Blogger. Isn't yours?

Subscribe to
Posts [Atom]