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  1. #1
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    Default Broaching puzzle

    I attempted my first ever broaching today. Material was cast.
    Broach was DuMont 7/8" bushing C series. I used plenty of cutting oil. Dake arbor press. I even watched a video on YouTube. This was a two cut, I use the included shim.

    The broach was brand new and I thought maybe it was bent. Dead flatBroaching puzzle

    The piece goes on a raised panel router.

    Please notice the extreme differences on either end of this sprocket.

    I can't make crap up like this Broaching puzzleBroaching puzzleBroaching puzzleBroaching puzzle

    Happy New Year !!!

    Tom


    Sent from my SM-G960U1 using Tapatalk

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    Quote Originally Posted by TFPace View Post
    I attempted my first ever broaching today. Material was cast.
    Broach was DuMont 7/8" bushing C series. I used plenty of cutting oil. Dake arbor press. I even watched a video on YouTube. This was a two cut, I use the included shim.

    The broach was brand new and I thought maybe it was bent. Dead flatBroaching puzzle

    The piece goes on a raised panel router.

    Please notice the extreme differences on either end of this sprocket.

    I can't make crap up like this Broaching puzzleBroaching puzzleBroaching puzzleBroaching puzzle

    Happy New Year !!!

    Tom
    It happened to me and probably every apprentice I gave the job if he wasn't warned. This is why you always turn the part sideways so you can observe if the broach is angling off vertical and back off the pressure to make sure. The face angle of the tooth makes them want to dig in.

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    Thats why you put a set screw over the keyway.

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    Quote Originally Posted by MrWhoopee View Post
    It happened to me and probably every apprentice I gave the job if he wasn't warned. This is why you always turn the part sideways so you can observe if the broach is angling off vertical and back off the pressure to make sure. The face angle of the tooth makes them want to dig in.
    Been there,done that. I didn't work for Mr. Whoopee, but like he said almost every apprentice has done it if not forewarned. Fortunately my (first) mistake was on a part that was easy to remake. It wasn't my only mistake, but like I said in a previous post "it isn't a mistake if you can fix it before the boss sees it".

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    You don't just push it through. Start in, back the press off and let the broach straighten up. Repeat. Don't try too much at once.

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    Sometimes when the broach starts to dig in you have to turn the part over and start the broach from the opposite side.

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    Thank you guys.

    When I flipped it over I was really disappointed. The front side is correct it's the rear that's awful.

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    We routinely turn the part and bushing around so that the broach is facing toward the rear, toward the frame of the arbor press. Seems the ram wants to flex toward the front from the pressure of the pinion and the lower frame flexes downward helping the broach to tilt into the cut. Even on my Greenerd #6 press turning things around makes it go a lot better.

    Edit - Placing the broach at the rear of the ram also puts the force more in line with the rack teeth which reduces deflection.
    Last edited by Mud; 01-03-2020 at 09:17 AM.

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    I have sometimes purposely angled the broach a little the other way (opposite direction from digging in) at first, and let the bushing bring it straight. But yes, push a little, back off, see how it's going/let the broach straighten out, then proceed.

    Regards.

    Mike

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    Well, here I am, that broaching apprentice. I never would have suspected.

    A great big thanks for the heads up.

    Now, if I can just remember that until my first broach job.

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    I respectfully submit that you all are wrong in this case. The part probably was supported on either side, maybe with parallels, perhaps even some distance on either side of the broach causing the part to tip forward under pressure. I've had this problem until I put the support directly in front of the broach insuring clearance for same.

    Bob....not the cat.

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    In cases such as these I've occasionally made up a "dummy" sacrificial part to put under the thin one. That way the broach isn't cutting over such a narrow distance. The parallels probably contributed to the problem, as Bob noted, but this would probably have happened anyway with this broaching setup because the part is so thin - there needs to be a little more support and more teeth in contact at once if you want it to be trouble-free and easy. The tooth hook angle is what does it on these thin buggers.

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    Bob,

    Dake arbor press. Pretty straight forward. I lubed and relieved pressure multiple times.

    Thanks for your input.

    T

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    ekretz is onto something..... How thick is the part? The pic does not show, and I did not see a reference.

    You MUST have at least two teeth in contact at all times, which pretty much means the part needs to be three teeth thick, or you need a backup piece. But even that depth does not guarantee no issues, it is just a minimum. If the part is several more teeth thick, you probably will not have any issues.

    I asked about a similar thing years ago, and that was the takeaway.

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    Quote Originally Posted by JST View Post
    ekretz is onto something..... How thick is the part? The pic does not show, and I did not see a reference.

    You MUST have at least two teeth in contact at all times, which pretty much means the part needs to be three teeth thick, or you need a backup piece. But even that depth does not guarantee no issues, it is just a minimum. If the part is several more teeth thick, you probably will not have any issues.

    I asked about a similar thing years ago, and that was the takeaway.
    1.875"

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    Another trick I've occasionally found useful is to place a small piece of drill rod or other straight pin sideways on top of the broach (parallel with top of keyway) and as close as possible to the cutting edge side of the broach while broaching. This helps prevent any off-kilter pressure getting applied in case of slight misalignment.

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    This thread has made me laugh. Unfortunately, I made the same mistake when I broached my first keyway. I never had anyone to show me how it should be done, but I figured it out in short order.

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    Quote Originally Posted by steve-l View Post
    This thread has made me laugh. Unfortunately, I made the same mistake when I broached my first keyway. I never had anyone to show me how it should be done, but I figured it out in short order.
    Sir,
    Please elucidate and enlighten us.

    Bob....not the cat et al.

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    I am pretty sure he's just looking back and laughing at the memory of when he had the exact same thing happen. Same as me.

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    Quote Originally Posted by eKretz View Post
    I am pretty sure he's just looking back and laughing at the memory of when he had the exact same thing happen. Same as me.
    Yeah...I get that.

    Bob....not the cat.


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