Slotting brass, springing apart .040 any suggestions?
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  1. #1
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    Default Slotting brass, springing apart .040 any suggestions?

    Hey all, so i am machining some 1/4" bar stock of C36000 (360 half hard) Brass and when i cut the slot (only one end is open) the part naturally is springing open. I assumed it would but not as badly as it has. Closed end measures 1.730 open end after cutting is measuring 1.76-1.77. I tried placing the open end in a vice and closing it on joe blox but i have a large run and that is not repeatable enough for me to leave it to the floor guys to replicate. Does any one have any suggestions? my thoughts are as follows:

    Would annealing help?

    Would grain direction make a difference to this? (slot runs with the grain)

    I could buy over sized material then cut a small slot, open vise, machine outside and slot to size..etc (i was trying to avoid turning this into 4-5 ops)

    tolerance on slot is +/-.001

    any ideas would be great
    thank you
    pics of op1 and op2 in that order below

    img_0207.jpgimg_0206.jpg

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    If you anneal it, then you can't get it half hard again without cold working it. Anneal (heat red and water quench) might help, but maybe will not fix the problem absolutely. Whatever the part bolts to, should be part of the solution to forcing the sides parallel, even using dowels.

    Stresses from machining may still have a peening effect and could cause the annealed part to distort a little, if you remove the outer skin after cutting a stress relieving slot to begin with.

    Brass can be a PITA.

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    You might need to rough the part, including slotting undersize to let it spring, and then finish machine.

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    How many is a run ?
    The question is are all three of the out side edges bowed or is it just the end?
    if so straigthen the parts by peening the closed end on the bottom side in line with slot as far from slot as possible that will close the c section .
    If long sides bowed then you will have tough time holding +/_ .001
    you might think about water jet roughing fixturing and finishing

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    Just had a notion and googled it. Turns out ultrasonic non-thermal stress relieving is a thing:

    ultrasonic stress relief - Google Search

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    Quote Originally Posted by mhajicek View Post
    Just had a notion and googled it. Turns out ultrasonic non-thermal stress relieving is a thing:

    ultrasonic stress relief - Google Search
    There was an article in MMS greater than a decade ago about that.. The product they were pushing in that article I believe was called "The Black Magic" or something stupid like that. It stuck with me and I remembered it because it seemed like a pretty neat concept.


    Other off the top of my head ideas.. Its a work hardened material? Can you get sawn plate?? ANY time
    I have to do a job that might spring.. Always go for the sawn plate.. ALWAYS..

    If that isn't possible.. Can you turn the part 90 degrees in the material, and see what happens ?? Even
    just a sample part that is similar, just to see what happens.

    Maybe half inch wider material, and chew off the edges and hopefully lose the majority of the stresses.

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    Just wondering

    What is there that makes the parts all spring in the same manner (direction)

    or do they?

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    Opposing surfaces are put in compression by drawing or cold rolling. The compression is the same on both sides, so when looking at the stock, you cannot tell anything is amiss, because the forces are balanced. When you cut down the length of the centerline, then you have unlinked the compressive forces that were counter each other, and thus you get the bending. The trick is that even when the material bends, it introduces a tension force on the side opposite to the compressed side. So you never get a complete relaxation of the compressive force, because a tension force will arise on the slotted side to counter the stress created by the compression side.

    Heat treatment is really the only way to relax the material, but then you have to put up with the material properties you get when annealing.

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    IMHO, just looking at the part, it's an unreasonable tolerance. Customer needs to understand what's reasonable and come up with a better way if they really need that slot so close.

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    Rough it.
    Release it.
    Let it spring.
    Finish it.

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    "And yet it moves."
    Galileo Galilei

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    I understand this is the General sub-forum. But how are you Machining the slot? If your using a Tool that generates a lot of force and heat, it's going to be hard to hold .002". Sometimes on shit like that, I use the tieeniest, tinyiest Endmill I can without losing my ass on time. Like Dew said Rough it out, let it acclimate, Finish with a tiny Endmill.

    R

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    This is why castings are often used for 'C' shaped pieces like machine frames. The shape hasn't been forced into place like it is when bar stock is rolled out.

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    Quote Originally Posted by litlerob1 View Post
    I understand this is the General sub-forum. But how are you Machining the slot? If your using a Tool that generates a lot of force and heat, it's going to be hard to hold .002". Sometimes on shit like that, I use the tieeniest, tinyiest Endmill I can without losing my ass on time. Like Dew said Rough it out, let it acclimate, Finish with a tiny Endmill.

    R
    Sorry all for not responding, i was not getting notifications from the thread. Thank you all for the great ideas and i cant wait to read about the ultrasonic stress relief. I am going to try this method of rough, let it spring then finish the outside and slot. I figured this was the simplest thing to try first. I am going to give it a shot today and ill let you know how i make out.

    Also i rough down the centerline of the slot with a 3/16 3FL and then finish the walls with a 1/16, and then the corners of the slot with a 3/64 to acheive a smaller corner radius.

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    Quote Originally Posted by Conrad Hoffman View Post
    IMHO, just looking at the part, it's an unreasonable tolerance. Customer needs to understand what's reasonable and come up with a better way if they really need that slot so close.
    Unfortunately there is no other choice, the machine this goes on has to have that tolerance because of the "disk" that rides between it. In the past on a similar part we tried opening it up a hair and the scraping action this must preform fails. The similar parts have more meat behind the slot and i have been able to hold them no problem to +/-.001 (the front of the part sometimes opens to .002 but the disk doesn't touch there)

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    Quote Originally Posted by Bobw View Post
    There was an article in MMS greater than a decade ago about that.. The product they were pushing in that article I believe was called "The Black Magic" or something stupid like that. It stuck with me and I remembered it because it seemed like a pretty neat concept.


    Other off the top of my head ideas.. Its a work hardened material? Can you get sawn plate?? ANY time
    I have to do a job that might spring.. Always go for the sawn plate.. ALWAYS..

    If that isn't possible.. Can you turn the part 90 degrees in the material, and see what happens ?? Even
    just a sample part that is similar, just to see what happens.

    Maybe half inch wider material, and chew off the edges and hopefully lose the majority of the stresses.
    im planning on trying a part turned 90 degrees today also, that is how i do the similar parts but i though due to the length on this one holding it longways in the y axis would have worked better. I left for vacation last Friday and haven't had a chance to try anything yet. It bothered me all weekend though.

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    The deal with cutting this part to allow it to spring and then machining it all over is that you loose all your reference surfaces over and over because it may just keep moving and moving. I'd look at annealing at least one sample blank and machining it.

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    Is calling the customer asking for some relief on the tolerance an option?

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    So based on your description of the function of the part, I'm thinking a disc rides through it, and it scrapes something off both surfaces of the disk, hence the tolerance....


    Is this to replace an OEM part, or is this a custom built machine?

    If the latter, could the machine/part be reengineered to use an aluminum or delrin/HDPE/Nylon/UHMW/PEEK scraper that could be positioned with dowel pins? That way the part could spring however much it wanted, and when installed in place with pins would be forced (easily) back to the necessary slot width.


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