The Chimera Project - Laser + 3D Printing

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The Chimera Project - Laser + 3D Printing

Postby bdring » Sat Aug 14, 2010 4:04 pm

Chimera: An Animal descended from two genetically different animals.

After seeing all the quality 3D printed parts at Maker Faire I really wanted to build my own printer. While I was trying to justify the $600-$900 it would probably cost, I realized that my laser could probably be converted to a dual purpose machine. It already had all the motion control needed. That would save a lot of time and money. Also all the others building my laser could benefit.

z_rail1.JPG

z_carriage.JPG


Currently the Z Axis is not ideal for a printer because it is not constrained from XY motion while moving. It wiggles a bit when moving. I decided to add another v wheel track for the Z. I have also heard that some people are having a little wiggling when engraving at high speed. This should help.

z_rail_extr.JPG


I am using the widest Misumi 25mm extrusion available 80mm. I think that should work. I do not know if I need this on both ends, but I have material on order for two. I decided to try the smaller v-rail this time. I don’t know why I went with the next size up for the laser. I think I had some already. I got the material and it should work fine. This rail could save about $50 on a build.

rail_dims.JPG

sm_vrail.JPG
Bart
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Z Carriage

Postby bdring » Sun Aug 15, 2010 2:36 pm

I cut the parts for one z carriage. There a few things I might change, but it should work for testing. The extrusion parts are on order and should be here mid next week. I want to get some Weld-On 3 Acrylic Cement to permanently fuse these parts together. I am not sure if I want to use 3 or 4 v groove wheels, so I allowed for both options and made it symmetrical.
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z_car1.JPG

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z_car2.jpg

I also started modeling the MakerBot Plastruder. Their design purposely elevates the extruder head. I actually need to get it lower because the Z surface is lower on my design. I am going to order a unit from them soon.
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plastruder_model1.JPG
Bart
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Re: The Chimera Project - Laser + 3D Printing

Postby rEd86 » Mon Aug 16, 2010 3:49 pm

Bart,

Before getting too far with this extruder design, you should look at what they've done here:

http://www.ultimaker.com/

By removing the extruder motor from the moving head, you eliminate a lot of vibration, which effected the precision of the print. I think it's a much better design and is something we should consider. It also makes it easier to change "heads" since most of the extruder hardware can be permanently mounted in the case area on the left by the other electronics. The extruder itself would be a "quick connect" item that just snaps on the gantry. When not used it would just be coiled and stored in the enclosure on the left. (at least that's how I imagined it working)

Thoughts?

--Ed
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Re: The Chimera Project - Laser + 3D Printing

Postby bdring » Mon Aug 16, 2010 5:43 pm

I was actually considering that. I am having trouble finding a quick (and easy) release system for the print head.

Right now the belt is not in an ideal spot for adding another carriage as needed. The best I have come up with is a quick way to loosen the belt while the other carriage is put on.

It sounds like the extruder system is the weak link in these systems. What typically goes wrong? Is it the feeder slipping? Does the melted material ever start squirting up backwards?

Has any one ever tried two, geared together feed rollers instead of a feed roller and an idler?
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geared_roller.JPG
geared_roller2.JPG
Bart
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Re: The Chimera Project - Laser + 3D Printing

Postby rEd86 » Mon Aug 16, 2010 7:03 pm

I wasn't thinking about removing the entire laser carriage but just having a spot to mount the extruder when necessary. If the carriage is a little longer and has another hole just like where the mirror/lens is mounted, with a couple of threaded screws to lock the extruder on is all that's needed. (the same hole can be used to mount a flex-shaft for a small dremel like router) I see the cabinet being closed when using the laser cutter but open when extruding (so there's room above for the ABS feed line) and using other heads.

Yes, the extruder is definitely the weakest link. This can be due to several reasons:

1) The heating element is usually hand-wrapped nichrome to keep it at the right temperature, monitored with a thermistor. Over time these elements can start to come apart and effect how exact the temperature of the nozzle is.
2) With the Makerbot, a standard motor is used to feed the ABS. You can't vary the feed rate depending on the tightness of the curve, which you really need. The RepRap Mendel uses a stepper motor to improve upon this.
3) Many variations of the extruder have been developed over time, since the PTFE thermal barrier on a Makerbot wears down over time and does not handle pressure and heat well, gaps form where plastic oozes out. You need a hot tip area to melt the plastic but a cooler barrel further up to dissipate the heat from the rest of the head.
4) The original extruder designs also didn't allow for easy changing of plastics. (whether color or types) Newer designs allow for quick release mechanisms to improve this.

The other issue when printing larger items with ABS is the fact that the plastic will warp if it cools down too quickly. (the edges will start to curl up) Many use a heated platform to reduce/eliminate the warping. Others have tried a heated chamber to allow for slower cooling.

I haven't had much of a problem with having a geared wheel with an idler wheel, but we have also rebuilt/upgraded our extruder head a couple of times so maybe that's why. We are looking for a quick-connect option, although I don't know what one of the other guys at our hacker space is considering.

Later!

--Ed
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Bowden Cable Concept

Postby bdring » Wed Aug 18, 2010 3:05 am

I decided to run with the suggestion rEd86 proposed. This moves the motor away from the moving head and feeds the material Bowden Cable style. This significantly reduces the size of moving head. I show it next to the laser lens carriage, but it could simply quick mount to the carriage.

I decided to go with mostly stock MaketBot parts to start with. I am sure many people can suggest improvements, but I need to get something going so I can get up to speed on how these things work.

I ordered the parts from Makerbot and have some tubing coming from McMaster. i will try both HDPE and PTFE. I want to get a feel for the flexibility and the friction.
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bowden_head1.JPG

bowden_head2.JPG
Bart
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Re: The Chimera Project - Laser + 3D Printing

Postby bdring » Wed Aug 18, 2010 5:59 pm

I got the tubing from McMaster already. McMaster is amazing. I ordered it at about 1:30pm yesterday and it was delivered the same day! i am about 15 miles from the warehouse.

I thought a great way to attach this would be to thread the tubing into each end. It did an experiment on both the HDPE and PTFE, which are both 1/8" ID 1/4" O.D. I think it turned out great. That is a 1/4-20 thread.
The trick is holding onto the slippery tubing. I used a 1/4" lathe collet. I put a 1/8" brass rod inside first to keep it straight and keep it from collapsing. The thread hold strong (about 40lb pull) on a standard thickness nut. The thread is very slippery so it will easily loosen. I think I might use a long coupling nut to get more thread engagement.

This is the PTFE tubing. It has a tighter ID and is more slippery, so that will be my first test.
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threaded_tubing1.JPG
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Re: The Chimera Project - Laser + 3D Printing

Postby rEd86 » Wed Aug 18, 2010 6:11 pm

Great job! Another source that has done a lot with extruder head design is:

http://www.makergear.com/

They are in the Midwest (Cleveland Ohio I think) and have been a pleasure to work with. Rick has really improved on the MakerBot process and has a new compact head pictured here:

http://www.makergear.com/blogs/frontpag ... sneak-peek

I think they would be a great solution for our final version. I see a u-slot that this would slide into and lock in place... I can reach out to Rick to see what his thoughts are and if he would be interested in getting involved. We've ordered a lot of products from him for our MakerBot at the HIVE13 space.

--Ed
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Re: The Chimera Project - Laser + 3D Printing

Postby bdring » Wed Aug 18, 2010 9:06 pm

slide into and lock in place
...yes i was thinking along the same lines. This uses some thumb screws to lock it in place.
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bowden_head3.JPG
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Re: The Chimera Project - Laser + 3D Printing

Postby bdring » Fri Aug 20, 2010 3:39 am

I cut the parts and test loosely assembled the extruder. This uses a stock MakerBot nozzle, barrel and insulator. The rest is custom. I threaded the lower metal plate. I thought this might reduce stress on the insulator. The tubing threads into a 1/4-20 coupling nut.
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head1.JPG

head2.JPG
Bart
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