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1Instructables72,887Views17CommentsOregonJoined November 11th, 2015
I have an MS in Mechanical Engineering from Oregon State University. But I got a job as a software developer so I feel the need to make my degree seem more useful by doing mechanical projects in my free time.

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  • Pa Lemur commented on Pa Lemur's instructable 3D Printer Part Recycling Grinder4 months ago
    3D Printer Part Recycling Grinder

    I don't have pdf's right now. But I'll convert and upload them when I get home so you can print them. Shouldn't libre office be able to read a dxf?

    Nope. But I guarantee it would not be successful at cutting through an iphone screen. The process that makes the glass on Iphones makes it very hard and fairly tough. It might crack and explode, but it will probably just deform the steel in the grinder. Its only 1018 mild steel, and even hardened steels would have a had time with phone glass. If it were just the screen without the glass it might work. But again I wouldn't recommend it.

    I added pdf's of the templates I used to make the grinder. All the hole centers are marked already. When you print them double check you have the size set to 100%. If you don't it may adjust to something like 98% to fit the 8.5x11" paper.

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  • Pa Lemur commented on Pa Lemur's instructable 3D Printer Part Recycling Grinder10 months ago
    3D Printer Part Recycling Grinder

    That's unfortunate, a lot of people have been suggesting using a food processer. This grinder works great for HDPE I just got around to testing it.

    I tried to find some square center bearings that were large and mounted in a flange, but came up short. It would have also added a lot of work when making the holes in the blades. So I stuck with a circular shaft and dealt with a key and making a hex drive.

    I made a top level comment about this just now. But I'll answer to make sure you see this. HDPE is an ultra low surface energy polymer. It only has about 50% more surface energy than PTFE (teflon). So its not sticky at all, including with itself. The only way that HDPE bonds to itself is when it is completely melted, it has not cold-welding ability. So it does not work as an FDM plastic. It also doesn't really have a glass transition temperature, or its really close to the melting temperature. Which means you can hold it above Tg to improve interlayer adhesion because it is incredibly close to the melting point and you might melt the part. I worked around another research group that focused on printing HDPE, and they had very limited success. The prints would usually fail after...

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    I made a top level comment about this just now. But I'll answer to make sure you see this. HDPE is an ultra low surface energy polymer. It only has about 50% more surface energy than PTFE (teflon). So its not sticky at all, including with itself. The only way that HDPE bonds to itself is when it is completely melted, it has not cold-welding ability. So it does not work as an FDM plastic. It also doesn't really have a glass transition temperature, or its really close to the melting temperature. Which means you can hold it above Tg to improve interlayer adhesion because it is incredibly close to the melting point and you might melt the part. I worked around another research group that focused on printing HDPE, and they had very limited success. The prints would usually fail after 3-4 layers from either falling off the print bed, or just not sticking the previous layers. They never had a successful print in the years they worked on it.I think modifying the surface energy by adding another polymer would help. But I'm not familiar with what polymer blend well or what can be done to increase surface energy. Doing this would kind of defeat the purpose of having a readily available recyclable material though.*Surface energy is how much extra energy the outer face of a material has. High surface energy means it really wants to make the face get smaller or go away, so its 'stickier'.

    Finally got my car and garage put back together so I could do a followup on this. Lets start with the things I changed/added to it after this Instructable:1. I added another stationary blade to each side. This spaced all of the moving blades of the outer plates and reduced binding. 2. I lapped the plates using some valve grinding compound. Which was a little aggressive, but still improved clearance. 3. Made a base that can be attached my workbench with space for a catch basket. This is shown in one of images I attached.How it performed:1. It was able to cut EVA and HDPE easily. 2. PLA was also fairly easy, but sometimes a drill was not enough and I had to use a ratchet. I didn't get a chance to test ABS, but it would be very similar to PLA. The major difference between the two...

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    Finally got my car and garage put back together so I could do a followup on this. Lets start with the things I changed/added to it after this Instructable:1. I added another stationary blade to each side. This spaced all of the moving blades of the outer plates and reduced binding. 2. I lapped the plates using some valve grinding compound. Which was a little aggressive, but still improved clearance. 3. Made a base that can be attached my workbench with space for a catch basket. This is shown in one of images I attached.How it performed:1. It was able to cut EVA and HDPE easily. 2. PLA was also fairly easy, but sometimes a drill was not enough and I had to use a ratchet. I didn't get a chance to test ABS, but it would be very similar to PLA. The major difference between the two is impact strength and thermal properties. 3. I was able to cut PETE, but it is incredibly difficult. I think the cutting surfaces weren't tight enough so it would slip into gaps and bind. Testing this plastic broke one of the blade spacers in half, by binding against it and bending it out the bottom. Now for things I would do differently:1. Use precision ground plates, or grind them flat yourself. Cold rolled steel is nowhere near flat and caused a lot of clearance issues. Which were mostly sorted out by lapping, but not completely.2. Gear by 2-3:1 using a chain drive. It would be much easier to use if the torque was multiplied a little.3. Find a cheapy 1/4-1/3HP electric motor to run it continuously. I only have a battery powered drill which get irritating when I can kill it in ~20 minutes. Side notes for those interested:1. HDPE is not a printable plastic using FDM. Many have tried and many have lied about success. HDPE is very low surface energy plastic, so it hates bonding even to itself. The only time it adheres to itself is when it is all melted, it has no cold-welding ability. So it is theoretically possible to print if the part is kept a few degrees below melting, which causes the interlayer portion to melt when the next layer is laid. I've worked around a research group that focused on FDM of HDPE, and they haven't solved it in a few years of trying (but they are trying to run it through a makerbot instead of a good non-proprietary research printer).2. The two materials in the attached photo labelled R1 and R2 are the materials I developed for my Masters thesis. They are intended to be made into filament, printed, solvent debound, thermal debound, and sintered. I had mild success at producing metal components and still work on it sometimes outside of work. These materials are what I intended this grinder to be used for. They are much weaker than virgin polymers because of the 55vol% powder content reducing the effective cross-sectional area. So the grinder cuts them up easily, instead of me sitting with a pair of wire cutters like I did for the other 100 samples I tested (ggrrrrr). 3. I am going to make an attempt at making a small batch polymer melt blender for samples of about 40mL. I'll probably put up an Instructable for it also, but it will be a while.

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  • Pa Lemur commented on Pa Lemur's instructable 3D Printer Part Recycling Grinder10 months ago
    3D Printer Part Recycling Grinder

    Thanks! I have to admit, this project did convince me to buy a belt sander. Filing is quite terrible when you need to remove any significant amount of material.

    I'll respond to all your comments here to keep it simple. I think I understand what you mean about the blade shape. It is probably possible to make the blades out of a small piece of rectangular stock with a relief cut into the outer edge. I chose to make large circular blades for a few reasons:1. I wanted a small cutting face to reduce required cutting force. The biggest feature that can be captured by the blades is a 0.5" cube.2. By having the cutting gap only open just before the blade cuts material doesn't fall through the grinder as easily and there is a higher chance of smaller pieces being cut (this is just a guess).3. The extra material gave me space to have bigger keys and avoid failure.4. The most important reason to have the larger blades is to keep them in contact ...

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    I'll respond to all your comments here to keep it simple. I think I understand what you mean about the blade shape. It is probably possible to make the blades out of a small piece of rectangular stock with a relief cut into the outer edge. I chose to make large circular blades for a few reasons:1. I wanted a small cutting face to reduce required cutting force. The biggest feature that can be captured by the blades is a 0.5" cube.2. By having the cutting gap only open just before the blade cuts material doesn't fall through the grinder as easily and there is a higher chance of smaller pieces being cut (this is just a guess).3. The extra material gave me space to have bigger keys and avoid failure.4. The most important reason to have the larger blades is to keep them in contact with the stationary blades for their whole rotation. The whole thing is held tightly together and the constant blade-blade contact keeps everything aligned. Without this the rotating blades would easily fall out of alignment and cause it not too work. The overlap might be achievable with a different blade shape, but I stuck with what I have seen in other grinders.The mesh screen has been suggested a few times. I chose the blade thickness to be the size i needed the pieces cut into. Larger pieces can get through by lining up with the blades, so I was planning on feeding the material through a few times to reach the needed consistency. I might test the screen later if I find this method annoying or ineffective.Having the grinder cut on the upstroke might work (in combo with the screen). The downside to this would be if 2 blades engage simultaneously. If its 2 thick pieces, you'll need over ~100ft*lbs to cut through it. This is where another part of the design comes from. I only wanted 1 blade to be cutting at a time. Which is why they are all 90° to each other. It can still be difficult to cut through large solid pieces with only 1 blade, so I would suggest not doing multiple blades that can engage simultaneously. Unless you are going to add reduction to the drive. I hope this gave some insight into some of the design decisions I made. If you have anymore ideas/questions feel free to ask!

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  • Pa Lemur commented on Pa Lemur's instructable 3D Printer Part Recycling Grinder11 months ago
    3D Printer Part Recycling Grinder

    I would caution against using ceramic as a cutting material. To cut like this grinder you need a material that has good compressive and tensile properties. Ceramics suck in tension. Also the faces would need to aligned perfectly for ceramics because of the materials low flexibility and elongation at break. So they wouldn't bend enough and the cutting faces would easily fracture.If you want to make something food safe and/or washable I would recommend a hardenable stainless steel. It will be harder to work with, but will produce a very functional grinder.

    HDPE is a very soft plastic, so it would easily shred it. It was trash day today so I don't have any HDPE that I can use to test it. In a few days I'll throw some HDPE into it to verify.

    Thanks, I added dxf's to the design step.

    That's part of the plan. I wanted to make it independent of the mounting solution so I can modify it without having to also modify the mounts. Quick-grips work for now, but your right they aren't enough to keep if from moving during use.

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  • Pa Lemur commented on Pa Lemur's instructable 3D Printer Part Recycling Grinder11 months ago
    3D Printer Part Recycling Grinder

    I added a video and a picture of the ground up PETE to the conclusion section. While cutting it up I came across some problems that the grinder has. I added a future work section that discusses the problems and what I think will fix it. I made this thing as a proof of concept and it has shown some shortfalls that may make it a bad option for shredding things like water bottles. I'll keep working on improving it and I'll keep you updated.

    Added the prices. The total comes out to about $52 for materials. It could be much cheaper if you searched a little bit for a the steel. I drive the thing with either a drill on low speed, or a ratchet. I use the ratchet when the drill gets stuck.

    I should easily cut through PET which has similar strength to PLA. I'll put some in it after I get off work and link you a video.

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