CNC/Manual Shear question
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    Default CNC/Manual Shear question

    Hey guys, looking for some input on the best process to use from someone that has some sheet metal experience.

    I make some parts that use stainless cages bent into rectangles that are sandwiched between 2 aluminum plates. The material is 20ga perforated stainless (3/16" holes, 1.4" center to center) Currently I get 4x4 sheets cut into 1.1" wide strips and then trim to length myself. The issue with the laser is the burr/dross, it's small but the product is an air filter for an engine so I end up having to sand and wire wheel the burrs off.

    I have reached out to a number of shops in the area (San Diego) and no one seems to want to shear it, they all say we would laser it and that shearing wont be as accurate. What sort of tolerances can be held with cnc shearing something like this? I want the cuts square to the sheet/perforations and the strips need to be a consistent width.

    Here are some photos of the parts and the burrs I am getting from the laser.

    img_4521.jpg
    img_4518.jpg
    img_4519.jpg

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    Why not inquire with the perforated steel supplier ?
    The couple that I use, all advertise in "2nd operations" including shearing, bending, etc.

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    That's a pretty shitty laser cut that they are giving you.
    I make a similar item with smaller holes from 20 g. Stainless using my 4' Pexto foot shear.
    Once I have the back guage set it can hold tolerance to 5 thou. or less and no burr to mess with.
    Last edited by J.Ramsey; 01-02-2021 at 10:10 PM.

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    Quote Originally Posted by woz View Post
    I have reached out to a number of shops in the area (San Diego) and no one seems to want to shear it, they all say we would laser it and that shearing wont be as accurate. What sort of tolerances can be held with cnc shearing something like this? I want the cuts square to the sheet/perforations and the strips need to be a consistent width.
    Are you confirming that these shops have a decent shear? In many cases, job shops are getting rid of their shear when they get a laser, because these days jobs that a shear really shine on are getting fewer and farther between (sheet parts are almost always having some sort of hole, cutout, notch, etc), but yours is one of those that is perfect for a shear.

    When you have a las- uh, hammer, everything looks like a nail.

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    Quote Originally Posted by J.Ramsey View Post
    That's a pretty shitty laser cut that they are giving you.
    I make a similar item with smaller holes from 20 g. Stainless using my 4' Pexto foot shear.
    Once I have the back guage set it can hold tolerance to 5 thou. or less and no burr to mess with.
    That piece in the photo is one of the worst ones, I have very little experience with laser cutting so not sure whats normal. The shop told me perforated is usually a bit rougher than solid sheet. I have tossed around the idea of buying a shear but it would just be for this task and I only go through 1 4'x4' sheet every two months or so.



    Quote Originally Posted by digger doug View Post
    Why not inquire with the perforated steel supplier ?
    The couple that I use, all advertise in "2nd operations" including shearing, bending, etc.
    Mind sharing the suppliers you have used?

    The local supplier I buy the material from said they can only hold 1/8" tolerance with shearing, I also reached out to McNichols but they said they couldn't do pieces that small and recommended another shop they work with to do the cutting, BUT their material cost was higher than than the local supplier I work with and once shipping was factored in it didn't seem worth it.

    Quote Originally Posted by Fish On View Post
    Are you confirming that these shops have a decent shear? In many cases, job shops are getting rid of their shear when they get a laser, because these days jobs that a shear really shine on are getting fewer and farther between (sheet parts are almost always having some sort of hole, cutout, notch, etc), but yours is one of those that is perfect for a shear.

    When you have a las- uh, hammer, everything looks like a nail.
    Yeah that totally makes sense, I have not specifically inquired, to be honest most places I reach out to never even call or email back.

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    shear, or waterjet? If your stock is all the same width (1.1") then have your hole pattern leave solid edge. A shop with a turret punch would be who I would check with. Also, as above, check perforated suppliers- they cut to length. Go big with fancy pattern and have Zahner do it...

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    20 gauge stainless should come straight off of the laser with nothing more than a sharp edge. Even a CO2 laser can do it no problem. You just have to have an operator who cares.

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    Quote Originally Posted by Strostkovy View Post
    20 gauge stainless should come straight off of the laser with nothing more than a sharp edge. Even a CO2 laser can do it no problem. You just have to have an operator who cares.
    Just to confirm, even perforated? Only asking because the guy at the shop I have been using told me perforated wont come out as clean.

    If that is the case I will see if I can find another shop

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    Quote Originally Posted by woz View Post
    Just to confirm, even perforated? Only asking because the guy at the shop I have been using told me perforated wont come out as clean.

    If that is the case I will see if I can find another shop
    It depends a bit on the diameter of the nozzle (whether the nozzle dives over each hole a bit) which can make the beginning look bad but I would be surprised if that can't be worked around. If not, I believe (at least for our laser) larger diameter nozzles are available for perforated. My experience with cutting perforated was at my last job, both steel and stainless, and the cut didn't look any different. However, the perforations were only 3/32, so the nozzle height was easy to maintain with no special setup. But the interrupted cuts were still there, and not a bother.

    If you are in good contact with the shop you could request that they adjust their settings (and possibly even lower feedrate) to get a better cut quality (which you will pay for), but many shops just don't want to mess with things that much.

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    Quote Originally Posted by woz View Post
    Just to confirm, even perforated? Only asking because the guy at the shop I have been using told me perforated wont come out as clean.
    Still shouldn't matter, because that's a shear job, through and through. You should be able to get better quality than you're getting, for less money than you're paying for laser.

    I'd exhaust my options trying to find a shop with a shear before trying to improve laser quality on that.

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    Quote Originally Posted by Fish On View Post
    Still shouldn't matter, because that's a shear job, through and through. You should be able to get better quality than you're getting, for less money than you're paying for laser.

    I'd exhaust my options trying to find a shop with a shear before trying to improve laser quality on that.
    I would fully agree, any precision sheet shop can easily shear it accurately at a much lower cost than laser. What part of CA are you in?

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    I haven't had perforated sheet laser cut but I can't believe 20Ga wouldn't be much better than what you have in the hands of a good shop. Solid stainless is always perfect and not even sharp where I get it done. Waterjetting 20Ga will leave a bit of burr you have to take off with a scotch wheel but that's quick. Thicker perforations would give you the classic waterjet interrupted cut where the trailing jet suddenly skips forward when it hits a hole. Regardless, this is definitely a shear job and which I'm pretty sure even our local Metal Supermarket would do adequately. We get them to do our waterjet tank slats and while they only guarantee around a 1/16th in accuracy, the precision across the set of slats is very respectable.

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    Forget CNC. You need a manual shear with a backgage. If you were here, it would take longer to carry the material to the shear than it would to cut the entire sheet. You would have to work hard to find any variation in the width of the strips. Its got good blades so any burr would be minimal/non-existent.

    I think your problem with finding a shear is most shears still in use are for heavier material. For 20 gage you will need one with good blades set tight.

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