Keyway broach 5" - 6" long help
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    Default Keyway broach 5" - 6" long help

    I have broached keyways up to 3" long in various types of steel with no issue.

    I have a two - one-time pieces that need to be broached. Customer wants 6" long pieces. He can go down to 4" if needed.

    #1. ID 2.250" with 1/2" keyway OD 4" Length desired - 6"
    #2. ID 3.1875" with 3/4" keyway OD 4.5" Length desired - 6"

    Material: 1045 Round

    Press: 20ton hydraulic press

    Will there be any issues with a standard Dumont type broach at 6"? My concerns are the length of cut and pressure needed for the broach to effectively push through without excessive build up.

    My thoughts are two separate bushings or one bushing with two slots milled at different depths to reduce the depth of cut. Keep the cuts minimal due to length.

    I appreciate any comments or suggestions on how to go about this efficiently.

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    Quote Originally Posted by drom68 View Post
    I have broached keyways up to 3" long in various types of steel with no issue.

    I have a two - one-time pieces that need to be broached. Customer wants 6" long pieces. He can go down to 4" if needed.

    #1. ID 2.250" with 1/2" keyway OD 4" Length desired - 6"
    #2. ID 3.1875" with 3/4" keyway OD 4.5" Length desired - 6"

    Material: 1045 Round

    Press: 20ton hydraulic press

    Will there be any issues with a standard Dumont type broach at 6"? My concerns are the length of cut and pressure needed for the broach to effectively push through without excessive build up.

    My thoughts are two separate bushings or one bushing with two slots milled at different depths to reduce the depth of cut. Keep the cuts minimal due to length.

    I appreciate any comments or suggestions on how to go about this efficiently.
    Doesn't your bushing use shims ?

    Make the bushing keyway deeper so that you take a smaller initial cut, shim and take additional passes as needed.

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    Quote Originally Posted by digger doug View Post
    Doesn't your bushing use shims ?

    Make the bushing keyway deeper so that you take a smaller initial cut, shim and take additional passes as needed.
    It does use shims and I plan on using them.

    My main concern is broaching at 6" long. Maybe there is no issue...

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    Quote Originally Posted by drom68 View Post
    My main concern is broaching at 6" long. Maybe there is no issue...
    It will only cut as much metal as there are teeth. You'll probably have to make an externder thingy tho, otherwise you won't be able to push it all the way through.

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    Is there a reason the keyway needs to be that long? Some of our parts have a similar 6" or so long bore with keyway, but we relive the middle so it's only bored to size and keyed on the ends. In my experience, it's much easier to line up two key ways on opposite ends of a roll (make a bushing that goes the full length of the part and alternate which side you cut from) then to manually broach the whole length of the bore. Most keyway cuts only have a few teeth cutting at once, but that long they would all engage.

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    I have done a few longer broached keyways and there is a second problem. All the metal you cut has to roll up and be stored in the gullet of the broach teeth. Using smaller shims will reduce the amount the first tooth takes, but the remainder all take the cut built into the broach.

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    Send it out to wire EDM

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    Jeeze, guys, it's not a big deal. Works fine. Broaches are designed to have enough space in the gullet for the chip. He just needs a spacer thing to push it farther down the hole than normal.

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    Quote Originally Posted by M.B. Naegle View Post
    Is there a reason the keyway needs to be that long? Some of our parts have a similar 6" or so long bore with keyway, but we relive the middle so it's only bored to size and keyed on the ends.

    Most keyway cuts only have a few teeth cutting at once, but that long they would all engage.
    The full length will need to be done. It is an adjustment bushing with set screws on the opposite side. All the teeth cutting at once and building up chips is what I want to address before I make the part.


    Quote Originally Posted by wheels17 View Post
    All the metal you cut has to roll up and be stored in the gullet of the broach teeth. Using smaller shims will reduce the amount the first tooth takes, but the remainder all take the cut built into the broach.
    That was/is my concern. At 6" I can see the gullets being filled.

    EG: I will have an extender to push through the entire length.

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    Quote Originally Posted by drom68 View Post
    At 6" I can see the gullets being filled.
    Those teeth are usually pretty hefty, you could grind a little more space on the back side without weakening them very much, if you are really worried.

    Or you could drill a hole where the keyway will go to take out a bunch of material. Make a plug, drill half in the plug and half in the part. For two parts, that's pretty simple then no worries about chip volume..

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    Quote Originally Posted by Booze Daily View Post
    Send it out to wire EDM
    Just did a keyway in A36 5.12 tall, 22mm keyway. 20 ton press and I snapped the broach. Sent it out to wire edm, way easier, less dangerous.

    Here is Abom doing some impressive broaching, but his press is a lot higher quality than mine.

    Boring & Broaching a Kop Flex Shaft Coupling Part 3 - YouTube

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    I have done similar in the past, and ended up broaching from the other end to get rid of taper in the depth.
    If I were doing that job, the keyways would go to one of my buddies with a keyseater.
    They could have it cut by the time I messed with it.

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    You will pack the gullets with chips on a really deep bore, the chip load is determined by the tooth to tooth step amount ground into the broach. Grinding the gullets deeper will help, as will pre drilling to remove as much material as possible, until you get to the od wall of the pre- drilled hole. Thinner shims will not help to avoid packing the top most teeth on the broach- only the starting teeth. A keyseater or wire EDM might be the way to go here, just about any keyseater will handle a 6" long keyway.

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    Push broaching anything over 3/8" width is not practical. Especially at longer length with so many teeth in contact. I believe the Dumont site still has great guidelines for force requirements. Even on a 3/8 key we will push 1/4 and 5/16 first. Anything larger we EDM or cut with a P&W slotter.

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    Quote Originally Posted by Dan from Oakland View Post
    the chip load is determined by the tooth to tooth step amount ground into the broach.
    That's easy enough to change, ten minutes' work in a surface grinder ... but kind of an expensive broach to butcher. Would still work afterwards but take a few more pushes. I've pushed broaches way deeper than they are supposed to go without a problem but ... maybe shouldn't recommend that

    Lots of ways to do it but seems like there's only a couple parts to do, and he doesn't want to spend outside money (can't blame for that, if outside costs are too much then you don't make anything and you can't just jack the price up to the roof.)

    Pre-drilling is probably safest and easiest.

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    I'm on the side of a second bushing with a deeper slot for the first couple passes to prevent chip build up in the broach. It doesn't need to be said but make the bushings slightly longer than the part to be broached. Key seater would be the way to go but not everyone has one. Stopped by a shop I worked a while back. We had a Baker Bros. key seater. Probably from the year 1920 maybe 1930. This thing was a beast, 2 1/2" capacity. Not hard to figure out if you applied yourself. Even for it's age it didn't have a lot of run time on it. In the 16 years I was there I don't think we put more than 100 hours on it. New guy took over and scrapped it. It didn't have flashing lights or a DRO it's worst fault, it wasn't a (Everybody bow) CNC.

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    Quote Originally Posted by Dan from Oakland View Post
    You will pack the gullets with chips on a really deep bore, the chip load is determined by the tooth to tooth step amount ground into the broach. Grinding the gullets deeper will help, as will pre drilling to remove as much material as possible, until you get to the od wall of the pre- drilled hole. Thinner shims will not help to avoid packing the top most teeth on the broach- only the starting teeth. A keyseater or wire EDM might be the way to go here, just about any keyseater will handle a 6" long keyway.
    I agree with this post. A keyway broach is designed to take so much cut on each sucessive tooth and even if you use a fairly small shim it will still fill up the last few gullets and you can't back them out without breaking them at that point. I had a pretty large keyway that I needed cut and a guy near me had a keyseater and did the job in no time. With a 20 ton hydraulic press you are going to be pumping that thing for hours on end.

    Find someone with a keyseater and save yourself a lot of grief.

    edit: If you can find someone with a vertical shaper aka slotter you can do that keyway easy peasy too. I've cut up to 1" wide keyways four to six inches deep and not had any problem aside from the pucker factor the first few times I cut them. I was pretty sad when our shop sold the slotter but it only got used every few years. They probably farmed the work out to whoever bought the slotter.

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    Send them to me. I have a vertical Slotter. I can cut up to 12" Keyways with no problem.

    Sent from my rotary dial flip fone

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    I didn't see anybody mention this explicitly, but Dumont and the other broach makers document both minimum and maximum length of cut. Minimum so you have enough teeth in the cut to be stable, and maximum for the gullet-filling issue already discussed.

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    Minimum so you have enough teeth in the cut to be stable,
    I've gotten around that by clamping two or more together so the broach "Thinks" the length is longer.

    The slotter advice is the best I think. I ran a Morrison Key seater long ago that used a single cutter, which didn't care about chip packing of course.


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