How to put a knife edge on a piece of 7075 aluminum? - Page 3
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  1. #41
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    Quote Originally Posted by trevj View Post
    Not getting you. Were you thinking of cutting with the stock up on edge? Don't. Screw the stock down to the angled section between the two side rails. That way, if you wanted to, you could bevel the fin stock across a width far wider than the length of the router bit.

    The jig that I proposed above is to be used with a regular square ended router bit or end mill in a router, with the table of the router on top of the two side rails.

    A table saw or some care with a jig saw or even a hand saw and protractor, and you can make the bottom block at any angle that you wish. As I see it, a fella would be able to make the jig angle adjustable by adding a couple blocks of wood across the ends and pivoting the bottom block that the stock is screwed to.


    Set it to half the angle if you want a centered edge, or at the full angle if you want it at the edge. Adjust your depth of cut until you reach the depth you need it to be.

    I have cut a few hundreds of feet of various sheet aluminum aircraft parts out with a cheap Dewalt router. It works pretty well, though you REALLY want good eye protection and a zipped up coverall on.

    Clear? Or not?

    If not, I'll really (really!) crudely mock up what I mean, and take a picture of it. Tomorrow, though.

    Cheers
    Trev
    Trev I see what you are saying now with the router on top of the jig with the bit pointed down. No need to take a picture I see what you are saying...I think that would work well just need to keep the router moving in the right direction around the curve of the fin. I only need to do one side too (unlike a knife where both sides are beveled).

    I am going to try to make a bending jig with wood, didn't think the wood would be tough enough to bend the metal

  2. #42
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    Quote Originally Posted by aaronhl View Post
    Trev I see what you are saying now with the router on top of the jig with the bit pointed down. No need to take a picture I see what you are saying...I think that would work well just need to keep the router moving in the right direction around the curve of the fin. I only need to do one side too (unlike a knife where both sides are beveled).

    I am going to try to make a bending jig with wood, didn't think the wood would be tough enough to bend the metal
    Ayup. You got it now.

    Maple from the pallets in the hallway at work, was the go-to for making quick and dirty forming dies and hammer forming patterns for the aircraft parts I used to make for a living. Try it, it works very well.

    Most of the stuff we did was repairs or replacing parts that were not available, but were likely never needed again either, so there was no benefit to having any more permanent tooling made up, which would have to be stored, cataloged, found again when (if) needed, etc. So we made what we needed, and either turfed it into the bin when done, or if it was a big enough piece of wood, chucked it in a box to be cut from when we needed a smaller piece.

    If you do your bend across the end grain of the wood, it'll last quite a long time.

    Best way to see is to try it.

    Cheers
    Trev

  3. #43
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    Default Knife edge on 7075

    Quote Originally Posted by aaronhl View Post
    I have a piece of 7075 .100" thick aluminum approx 5" x 3", one end is curved and along the curve I need to have a bevel cut like a knife. I have tried to grind it down with my handheld grinder and smoothing it with a file. It does not look very good...looking for a better way to put this kind of edge on it...any ideas?

    My tools are mostly for woodworking but not limited. I don't have a mill or something to cut the edge..here is a picture of the curve I am talking about and also if you could give me some ideas on how to bend the piece to a smooth curve after I add the edge it would be helpful too

    Attachment 164244
    I routinely put knife edges on 7075 material. I use a multi step process. First, I rough the angle with very coarse sanding belt, like 60 grit. (Yes, I use aluminum oxide belts). It may take several times at the belt because the blank will get very warm and you will have to let it cool in between. The aluminum will start to gall and fill up the abrasive if you let things get too hot, and it will suddenly become very "heavy". (I.e., you will have a sudden urge to put it down.) Once I have the shape of the edge roughed, I use finer and finer sanding belts to start finishing the profile and bringing the edge of the material to sharpness. You will see the edge start to curl over if it gets too thin. Sand off the curl and start bringing the edge up to the sharpness. It will be difficult to get s smooth, sharp edge, there will probably be some small irregularities. I usually will take the finest belt I have (say 220) and very carefully blunt the sharp edge to achieve an even thickness at the edge of perhaps .010". Next, I switch to a "scotchbrite" type (non-woven abrasive) belt in a fine grit. They come in several coarseness ratings, usually broawn is very coarse, maroon is medium and blue is fine. Working with an extremely light touch and sanding in the direction so that the belt is moving away from the edge, I softly kiss the edge while moving the part sideways to the belt, repeating on one or both sides (depending on the type of edge I am creating) until the edge is just about perfect. A final touch that I use is a very fine fingernail filing sanding stick (available at drugstores in the nailcare aisle) to hone the edge. You can just about shave with that edge.
    I don't know if this techniique will be of use, but, I bend all sorts of metal plates over a variety of mandrel shapes by holding the edge of the part in a 6" machine vise while passing it under the arbor of my horizontal mill. I use an arbor with freely rotating bushings and I don't have the spindle running. The closer to the vise you get, the sharper the bend. I have bent 1/4" steel. 2" wide to 90 degrees, and 6" wide 3/16 aluminum to various radii, using bar stock or tubing as a mandrel. It probably would not work on material much thicker than 1/4" without damaging the arbor. It is crude, but it makes nice smooth curves.

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    I do not know if it has been mentioned here in this thread or not. But get some "bee's wax" and use that when you are sanding ally. Same goes for cutting ally with a 1mm cutting disc, cut some wax first then cut the ally. Makes a huge difference when you use bees wax. The wax that we get comes in a slab about 10"x10" and about 1" thick. When we ran out of wax we bought another lot that came in a cardboard tube. It was marked as a cutting wax, but it was not as good as the plain bee's wax. Bzzzz Bzzzzz

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    Had back luck guys when I was cutting the aluminum. I bought a Craftsman router about 4 years ago. Been using it quite a bit but was working fine until I tried to cut the aluminum. I was cutting aluminum with it on the router table (3" dia chamfer bit)...after a few passes the router slowed down and shut off all of a sudden. When I flip the switch all the lights work but the motor doesn't spin (no noise either)

    I thought maybe the motor was burned out because it's several years old, so I bought the same router tonight at Sears to try it again.

    Several seconds after cutting the aluminum the router pulsated and shut off. I didn't even have it on for a full minute before it shut off. Same as before when I flip the switch all the lights work but the motor doesn't spin.

    Bad luck or what???

    This is the router edited link: Sears.com
    Last edited by aaronhl; 03-16-2016 at 08:49 PM.

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    Quote Originally Posted by aaronhl View Post
    Had back luck guys when I was cutting the aluminum. I bought a Craftsman router about 4 years ago. Been using it quite a bit but was working fine until I tried to cut the aluminum. I was cutting aluminum with it on the router table (3" dia chamfer bit)...after a few passes the router slowed down and shut off all of a sudden. When I flip the switch all the lights work but the motor doesn't spin (no noise either)

    I thought maybe the motor was burned out because it's several years old, so I bought the same router tonight at Sears to try it again.

    Several seconds after cutting the aluminum the router pulsated and shut off. I didn't even have it on for a full minute before it shut off. Same as before when I flip the switch all the lights work but the motor doesn't spin.

    Bad luck or what???

    This is the router Yikes! - Sears
    Now you have a better appreciation of why the site owner forbids discussion of Sears tools. And your Sears link does not work.

    Larry

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    Quote Originally Posted by L Vanice View Post
    Now you have a better appreciation of why the site owner forbids discussion of Sears tools. And your Sears link does not work.

    Larry
    Haha well I have had good luck with Sears tool, no doubt they are lower quality but for the price they work and maybe not as heavy duty as the more expensive brands.

    The link doesnt work because the page expired or something, here is another link to it actually bought it in the store for $130 Sears.com

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    Exactly.
    Ok, for $5 you can get a 4" wheel for your right angle grinder, and the job will be roughed out in 5 minutes.
    Failing that, generous amounts of beeswax.. grab a chunk of wax and grind it until you get as much as the wheel will hold.
    Then, for the finish, get the flap-sandpaper-disc, and load it with wax as well.
    I could'a done two of them blades by now. It really works, works fast, works cheap.


    Quote Originally Posted by Apples View Post
    I do not know if it has been mentioned here in this thread or not. But get some "bee's wax" and use that when you are sanding ally. Same goes for cutting ally with a 1mm cutting disc, cut some wax first then cut the ally. Makes a huge difference when you use bees wax. The wax that we get comes in a slab about 10"x10" and about 1" thick. When we ran out of wax we bought another lot that came in a cardboard tube. It was marked as a cutting wax, but it was not as good as the plain bee's wax. Bzzzz Bzzzzz

  10. #49
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    Quote Originally Posted by fredhh47 View Post
    I routinely put knife edges on 7075 material. I use a multi step process. First, I rough the angle with very coarse sanding belt, like 60 grit. (Yes, I use aluminum oxide belts). It may take several times at the belt because the blank will get very warm and you will have to let it cool in between. The aluminum will start to gall and fill up the abrasive if you let things get too hot, and it will suddenly become very "heavy". (I.e., you will have a sudden urge to put it down.) Once I have the shape of the edge roughed, I use finer and finer sanding belts to start finishing the profile and bringing the edge of the material to sharpness. You will see the edge start to curl over if it gets too thin. Sand off the curl and start bringing the edge up to the sharpness. It will be difficult to get s smooth, sharp edge, there will probably be some small irregularities. I usually will take the finest belt I have (say 220) and very carefully blunt the sharp edge to achieve an even thickness at the edge of perhaps .010". Next, I switch to a "scotchbrite" type (non-woven abrasive) belt in a fine grit. They come in several coarseness ratings, usually broawn is very coarse, maroon is medium and blue is fine. Working with an extremely light touch and sanding in the direction so that the belt is moving away from the edge, I softly kiss the edge while moving the part sideways to the belt, repeating on one or both sides (depending on the type of edge I am creating) until the edge is just about perfect. A final touch that I use is a very fine fingernail filing sanding stick (available at drugstores in the nailcare aisle) to hone the edge. You can just about shave with that edge.
    I don't know if this techniique will be of use, but, I bend all sorts of metal plates over a variety of mandrel shapes by holding the edge of the part in a 6" machine vise while passing it under the arbor of my horizontal mill. I use an arbor with freely rotating bushings and I don't have the spindle running. The closer to the vise you get, the sharper the bend. I have bent 1/4" steel. 2" wide to 90 degrees, and 6" wide 3/16 aluminum to various radii, using bar stock or tubing as a mandrel. It probably would not work on material much thicker than 1/4" without damaging the arbor. It is crude, but it makes nice smooth curves.
    I seem to be replying to my own post, but I wanted to add, my process is not a one-off. By my calculations, I have made over 600 turn fins for a major customer over the past two years. Some as small as 1.5" x 3", with a very gentle radius, and some as large as 5" x 8" with a larger radius. Most of the smaller ones were made out of 6061-t6, but the G-forces on boats like 100+ mph outriggers were just bending the larger fins until we switched to 7075-T351. In 2015, I bought over 200 square feet of 7075 sheet, .090 thick. I have had discussions with many people about the "grain" issue, and IMHO, it doesn't matter, unless you are building a real-life fighter jet. I have bent all sorts of pieces of 7075 into curves, totally disregarding the "grain", and the only time I had any cracking was when I attempted to bend it to a sharp 90 degrees. Grain, schmain. As a rule of thumb, you need to over-bend about 30% to achieve the desired curve. That means using a 30% smaller mandrel than the desired curve. As a final step on some of the fins, I use the "non-woven abrasive belt" in the finest grade (blue, usually) to remove all tool marks and grain, in the "trailing edge-to-front-edge" direction only. The other way around will catch on the belt. Bad things result. Then I use a rag polishing wheel and appropriate abrasive compounds to produce a mirror finish on both sides. It takes time and sometimes the polishing will reveal scratch marks that I have to go back to the n-w-a belt to remove. But the finished product has a mirror shine like polished chrome.
    Last edited by fredhh47; 03-23-2016 at 01:29 PM. Reason: errors

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    Quote Originally Posted by L Vanice View Post
    Now you have a better appreciation of why the site owner forbids discussion of Sears tools. And your Sears link does not work.

    Larry
    Sounds like maybe you got fine aluminum dust in the router and shorted it out. Too bad. But I think the process was as dangerous as it was destructive. The frictional forces of a large cutter could have easily turned that piece of aluminum into a killer missle. I would stick to the belt sander for safety.


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