Hi VRC friends
Could you please share what tools you find most useful for grinding/filing after cutting steel shaft and aluminum bars?
Thanks
CJ
My own flesh.
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Generally a grinder (bench, or rotary mounted to a dremel), and a file are what I use to grind and file metal.
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Dremel is great tool for both cutting and grinding, small, multipurpose, and portable. As for the type of bit for the grinder, I would suggest using metal ones, the grinding stones for me at least tend to have metal/plastic stick to it and it becomes useless
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Our organization uses a combination belt and disc sander.
My org uses dinky little 3" nail files…
Oh, the misery
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You guys file them down? We usually spend the first hour of a competition sharpening ours after inspection. But in all sincerity, dremels are worth the investment. There are a few online stores that let you buy bulk bits that are cheap and high quality. A couple of good files can also be helpful… And that gives me an idea. Proceeds to install a file in place of a sawzall saw
For hand tools, we keep several files around. For power, this little HF grinder is cheap and functional: https://www.harborfreight.com/1-in-x-30-in-belt-sander-61728.html
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So hand files are fine, but nobody takes the time to teach / learn.
Size matters. You want at least an 8" long file for most VEX stuff. Yea, I have three 12" mag strips with files from 2" to 10" with teeth from super fine to coarse, from flat through triangle to round/half round. Get the right set of tools for the task.
Do your files have handles? Get handles. Put the handles on.
Gonna anger some people here, but get a roll of the electrical tape. Tape a 3" section at the tip, two layers of tape thick. You want something your novice builders can grip without the “Ouchie” You want the layers thin so they can guide the file, Not having a big bulb at the tip makes it easier to learn skills so when the tape isn’t there it’s fine.
- Put the metal part in a vice. I’m going to guess it was just in one when you cut it. Position it so you can file the sharp edges. Yea, I sometimes shoop/shoop two handed, but vice makes a big deal.
- Eye protection - making small chips of metal here.
- File with two hands. Hand on the front guides, hand on the back pushes.
- Note that I said push, metal mill files cut on the forward stroke. If you watch a machinist, they push/cut/clean on the forward stroke and then a lift on the back stroke. The lift is only a 1/16" but it’s not dragging the file. Your front stroke removes the metal, the back stroke if you don’t lift creates a snag. So push stroke remove, lift, push stroke remove, lift and in seconds you are done.
But the key is to have a sharp blade that cuts cleanly. Take your time, cut clean and then the file work is just seconds.
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We use two belt sanders like this for most things.
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Someone has tested this and found that back dragging outperformed lifting with a negligible difference of file damage between back dragging and lifting:
My suggestion is to use the full file length forward and full file length backwards similarly of using a saw, and barely press the file against the metal. Let the blades on the file do the cutting with the entire length of the file back and forth motion, almost as if you are using a knife on steak.
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It depends on the type of file. Note that the one in the video has straight teeth. Some also have two way teeth. These types of files are effecient both forwards and backwards. Slanted tooth files are only effective one direction. I have no idea what the technical terms for these files are, but I think you get the idea.
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Similar to cutting blades, I believe the type of teeth are to be used for specific materials. I think the type of file you are talking about is for wood, as usually blades with small tiny teeth are for metal.
I believe that even for just metal filing there are multiple types of files. But you’re right in the fact that generally metal files have small, sharp, slanted teeth.
Edit: Presumably Foster knows better. We’ll see when he chips in again soon 
OK, lots to capture in the discussion.
- Pferd files are top of the line at about $85 a set. Most teams are using Harbor Freight files at $9.
- Big difference in the tooth spacing and geometry between wood and metal files. Wood files have larger teeth and more depth. There are also different pattern that are used to go from coarse (big parallel grooves) to fine (tiny cross hatch). So when buying files think of you material (soft steel) and how clean the cuts are. And @keys is correct within metal there are lots of cutting variations (not to mention the size / shape) in files.
- If you look at the chart in the video (16:20) you can see for the medium file that cut lift gives .526 of cut, if you do both you get .735, but drag only produces .164. So in the forward cut gives you most of the results, the drag adds a little.
- His tests runs for 90 minutes for each test. The machine, being a machine does the same force for 2500 strokes. If a roboteer is doing 2500 strokes with equal force on both strokes, they are going to be very, very tired. Power in the forward stroke, lift back, saves roboteer energy.
But the big takeaways from the video are.
- Files have a very limited life depending on the material. Going from coarse, medium, to fine gives you the best finish. But even the best files wear out. So you may only get a season’s worth out of a file. Now would be a good time to check yours to check out the condition.
- Use of a file card (a brush to clean the teeth) every time you use the file helps. The test shows that just 100 strokes can fill the teeth up with metal. So cleaning is a good thing.
- Some people have way too much time. The amount of jig building, testing, results compile, etc was amazing. It’s like my favorite, Project Farm testing. Just dozens of hours to prove things out.
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We use this dremel 4000 (With a disc on the end)
