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  1. #81
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    Quote Originally Posted by implmex View Post
    Good morning TeachMePlease:
    That was a brilliant post (post #75).
    I really appreciate the time you took to answer my questions in such detail, especially since you took the trouble to explain your reasoning too.
    As you can probably tell, I have only the most rudimentary understanding about how I might go about doing a part like this in a Swiss, so it's great to get a step by step lesson from someone who does it for a living.

    I do have another couple of questions though.
    You refer to the sub as if it is a less capable spindle with regard to broaching the hex than the main is, or perhaps I'm misunderstanding you. The sub is just as capable, but I'd feel better pushing a broach into the full diameter bar (which is supported by the guide bushing) than pushing a broach into the part being held only on that tiny thread. You're correct that you could also use a stepped/form collet to grab onto the head of the screw instead, but overall, broaching into the full bar would be the most stable scenario. I'll get into that a bit more in a second.

    Do you favour running the hex in the main because it's a better spindle for it, or is it because the part is flimsy by the point the thread is turned and can't tolerate the push from a wobble broach? Mainly the flimsy part. Also, on something this small, I wouldn't use a rotary broach, I'd use a skive/single point broach that pecks out one corner of the hex at a time, using the C axis to index. Something like Horn USA part number N105.SW20.20.01.B1. This has the advantage of much lower cutting force, and being adjustable for size, and is not TOO much slower than a rotary broach. It also generally doesn't require going back in with a drill to clear chips after broaching.

    I thought you'd advocate having a pocket in the sub collet so you could clamp on the head...holding it by the 0.025" you have available and then facing, drilling and broaching the head. Yeah, I suppose if I went into high production on them, and was processing them that way, I could do that. I still prefer my original method. Also, nothing but gut feeling here, but the method I initially proposed would balance the sub/main working times better. Broaching on the sub spindle would be slower, in which case the main spindle would likely end up sitting and waiting for the sub to finish broaching.
    You could easily put both chamfers on the head while the part is still in the main so you'd have lots to hang onto. (I suppose it depends on how you define "lots")
    Do you think you'd have enough to avoid popping the part out of the sub when the broach retracts? Absolutely with a skive broach. For a rotary broach? Probably doable if you kept your sub collet as tight as possible without marring your part... It'd be a fine balance, and you'd have to broach real slowly.
    Are you afraid of ripping the threaded shaft right off the head as the broach gets near the bottom of its push? (assuming there's no way to create end support for the threaded shaft in the sub)Not with a skive broach. Usually DOC is only .001"-.002", and when you hit the bottom of the hole, you retract in X and Z simultaneously. With a sharp broach, there is very little pressure on the part. With a rotary broach, possibly. You can get stepped collets that would have an axial support for the end of the screw. (Really, you can get a collet in any shape a WEDM and/or Sinker can cut, if you'll pay for it) But that just adds complexity (What happens when the guy making the collet makes the step .005" shorter than it should be? You have to adjust your pickoff position, or the collet will crash into the part.)
    Also I assume you'd turn these out of 303 SS if you had a choice or would you pick a stronger alloy to minimize the chance of ripping parts in half when broaching them? If I had my choice, I'd make them out of 17-4 H900. I'd make everything out of 17-4 H900, if given my druthers. Metallurgy is not my strong suit, I know the basics of the most common stainless steels, alloy steels, aluminum, and Delrin/Acetal... But a chemist or engineer, I am not.

    Thanks TeachMePlease...I really appreciate it. Well, after all the stuff I've learned from your posts, it's only fair I return the favor when I can.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining



    Replies above, in bold.

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    TeachMePlease that's fascinating!
    Now I want a Swiss to play with.

    Problem is I could never justify it and unrestrained tool lust is just not reasonable for me anymore (no space, too old, declining desire)
    Thank you so much for laying it out this way...I learned a lot today!

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    what is a skive broach? (i know you can skive gear theeth.)

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    Quote Originally Posted by TeachMePlease View Post
    Nah, he's legit. A little googling tells a lot. Not trying to doxx the guy or anything. But there's enough details out there to know he's no alter ego. Just a big ego. I was surprised to learn he's 61. He posts more like a cocky 25 year old.
    You talking about Otto Ralat? The shaper/vice jaw guy?

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    Quote Originally Posted by implmex View Post
    TeachMePlease that's fascinating!
    Now I want a Swiss to play with.

    Problem is I could never justify it and unrestrained tool lust is just not reasonable for me anymore (no space, too old, declining desire)
    Thank you so much for laying it out this way...I learned a lot today!

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

    This is one a cool demo video of a Swiss doing a not super complex part, but I think it's neat that it's 3 parts machined in one process, and pressed together during the cycle. Citizen K16 - Whistle Demo - YouTube

    Always happy to share the little that I know when it's applicable here.


    Quote Originally Posted by dian
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    what is a skive broach? (i know you can skive gear theeth.)
    If you google the part number I gave, for some reason you get the German version of the Horn website, but this oughta show clearly what I mean: eShop - Paul Horn GmbH The broach has the 60° corner of the hex, you start at C0, peck from the minor diameter of the hex to desired diameter in X, index 60° and do it again.

    Quote Originally Posted by Homeshopblob
    You talking about Otto Ralat? The shaper/vice jaw guy?
    No comment.

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    Quote Originally Posted by TeachMePlease View Post
    Nah, he's legit. A little googling tells a lot. Not trying to doxx the guy or anything. But there's enough details out there to know he's no alter ego. Just a big ego. I was surprised to learn he's 61. He posts more like a cocky 25 year old.
    This is the sort of thing I bet he wrote in his text books when he was back in school....
    Attached Thumbnails Attached Thumbnails capture.jpg  

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    I thought I wrote that in the third grade, and how the hell did you get ahold of it?

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    Marcus, I apologize for being such a nuisance about this part. I had one last thought, though.

    Have you considered the reduction in area that is caused by the hexed-out portion?


    It is reduced to 0.02387 square inches at the area of attachment. If it is dynamically loaded, it could have a shortened life. Of course, this is just a guess.

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    Hi David:
    I always appreciate anyone taking time and effort to brainstorm a problem with me, so please don't apologize for your valuable contributions to this brain trust we call PM.

    In response to your commentary specifically; this is a very low load application; essentially, I am just trying to hold a collar onto a stub shaft, and the forces involved are very low.
    If I could get a small enough snap ring it would serve just as well, except it would probably take up too much height, and would be a cast iron bitch to install with my old eyes.

    The strength of a standard 1.6mm setscrew is more than adequate, so as you can imagine, it's not a super demanding application.

    So yeah, you make an excellent point about the strength of a hex broached in the end of the screw, and if the hex were to penetrate into the vicinity of a thread relief on the other end of the head, it would be paper thin and probably fail just from tightening the screw against the shoulder.

    How this spins out if the customer ever goes into production with this design is going to be an interesting conversation, and I'm sure many brains will be racked to find a workable solution.
    Clearly, at ten minutes per screw, this current solution is not going to be the way forward.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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