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  1. #1
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    Default Boring bar selection questions

    I need to purchase a boring bar to bore 10" lengths of 5" schedule 80 pipe (welded seam) to 5.000" inside diameter.

    My lathe is a Series 61 Monarch toolroom lathe, 10 hp motor....plenty of power.

    The part(s) are for a mudjacking pump pumping tube. I'm currently making 8 of them, but this is an ongoing project every few years, so not heavy use. I'd like to buy a boring bar that can be used for other projects, but has a length of 14" so I can do the job without having to re-indicate the tube in a 4 jaw and turn it around. Lighter passes are fine, as I'm removing about .125", and not in a hurry. Tool stickout will be 10", and I'm looking at 1.25" bars. Toolpost is Aloris CA.

    I've seen a few bars advertised with 5° negative rake and CNMG insert. Is this fine, or do I want something else for this?

    The finish doesn't need to be polished, but the a rubber seal is compressed inside this to create a pressure seal for pumping mortar mix, and I want the finish to be decent, as to not chew up the compressed rubber seals.

    Other question is, can I use a #2 toolholder, or do I need to purchase a CA-41?

    Your help is appreciated.

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    Can’t help with the boring bar but any chance of switching to DOM tubing? At a place I used to work, we were making a similar part (4”ID x 13”). For years they made the tubes out of pipe and had to be line bored. We switched to DOM and honed them on the radial drill. It was 10x faster and the customer loved the look of the cross hatched marks of the hone.

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    I'd put a much bigger bar in that 2''+ even if I had to make one with it's own block in place of the Aloris toolpost - which would be a better idea (basically mill a slot across the end of a bad and clamp a tool bit / insert holder in with a few allen screws - plenty on the web and cheap too)

    At 10'' stick out and 1.250 bar you are making a rod for your own back

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    Get (2) turning toolholders (cheap ones will work fine, probably 1/2" shank)

    Cut shanks shorter, make up a bar from some scrap (can be even box tube), mill slot in end.

    Drill & tap for set screws.

    (2) toolholders opposed to each other, one shot feed in and done.

    Or...find some of these cartridges, they have adjustability built in. (check e-bay)
    http://www.toolfab.com/assets/downlo...cartridges.pdf

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    Another vote for big bar. 2” or 3” would keep the lenght/diameter ratio suitable for plain old boring steel bar.
    Probably need to make mounting block for the bar too. But 2.5” shaft and large chunk of steel for mounting block are dirt cheap compared to 1.25” vibration dampened Sandvik bar.

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    OK, bigger is better.

    I'm buying this, as I don't have time to make it. Economically smarter for MY situation.

    Is the 5° negative rake with a CNMG insert the right tool/angle setup, or should I be looking for something else?

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    With a CA tool post, you can get a 2" Boring bar holder from Dorian. You could even buy a bar from them, too if you like.

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    Another question:

    I'm looking at used indexable insert boring bars. Lots of options on the auction site. I'm not looking for cheap chinese tooling.

    What are the decent brands that will service what I need. I need middle of the road quality tooling that will be put to use occasionally, and do the job, with readily available inserts. I appreciate any input.

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    Quote Originally Posted by hawkfan9 View Post
    OK, bigger is better.

    I'm buying this, as I don't have time to make it. Economically smarter for MY situation.

    Is the 5° negative rake with a CNMG insert the right tool/angle setup, or should I be looking for something else?
    How many cut's will it take you with "buying " a conventional boring bar ?

    "once thru & done" with the balanced boring bar has no appeal with the quantities your dealing with ?

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    You may get less deflection and resulting taper using positive inserts because the cutting forces will be lower. A 1.25” carbide bar will do it, but it’ll cost ya an arm and a leg.

    Unless you bore a lot of big holes, I would think about a 3/4 or 1” steel bar stuck in a larger piece of shaft or even square stock for the big hole boring. You will only have to make this larger “tool holder holder” once and have lots of capability from the combination. Its almost no trouble to make.

    Kennametal makes HSS bars like the SCLP for CPMT inserts. KC 730 grade is good all around. Neither is expensive. You will probably use it often.

    You might think about packing the pipe in a v block on the carriage and use a bar supported at head and tail. You could really knock them out if you have the length of bed to handle it.

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    Quote Originally Posted by henrya View Post

    Unless you bore a lot of big holes, I would think about a 3/4 or 1” steel bar stuck in a larger piece of shaft or even square stock for the big hole boring. You will only have to make this larger “tool holder holder” once and have lots of capability from the combination. Its almost no trouble to make.
    Any chance you have a picture of what you're talking about, or refer me to a picture?

    Edit: Something like this?

    3" Body Fly-Cutter Style Boring Bar: 2" Shank 19-3/4" OAL holds 5/8" Tool Steels | eBay

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    Quote Originally Posted by hawkfan9 View Post
    Any chance you have a picture of what you're talking about, or refer me to a picture?

    Edit: Something like this?

    3" Body Fly-Cutter Style Boring Bar: 2" Shank 19-3/4" OAL holds 5/8" Tool Steels | eBay
    Something like that. Also pay attention what Digger Doug was writing..

    Mill the slots along the side of the bar and you can use your existing smaller boring bars or mill the slot in the end and you can use "normal" lathe tool.
    Even a 1/2" shank insert holder/boring bar would be enough big if you mount it to the end of large bar but 3" bar leaves plenty of room even for 1" tooling.

    Probably takes you less time to make one yourself than hunt for suitable one used... especially if you have to make the mounting block/clamp setup in anyways.


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    I also make bars to suit the job. It does not take that long. Quick & dirty works well enough. Most of my jobs are small, so 1" or smaller bars are fine. I usually need a larger bar for repair work, so crude is good enough. I occasionally borrow tooling from a local shop for the once-every-two-year-job where a tooling investment does not make sense.

    Bill

    img_8194.jpg

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    I run a 1” Kennametal boring bar with the cnmg inserts and the same negative rake. It will chatter a bit when it gets hung out too far beyond 6 or 8 inches. Otherwise its been a good tool. Definitely go bigger if you can and make sure your toolpost is super rigid

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    Quote Originally Posted by Bill in PA View Post
    I also make bars to suit the job. It does not take that long. Quick & dirty works well enough.
    Really quick and dirty but perfectly usable for OP's task would be 3" bar with insert holder welded to the side or end.
    Less than 15 minutes total and you are already making chips.

    On any lesser lathe I'd mount the +10" hangout bar directly to cross slide without top/toolslide. Monarch 61 topslide is pretty beefy so it might do the trick.

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    Quote Originally Posted by MattiJ View Post
    On any lesser lathe I'd mount the +10" hangout bar directly to cross slide without top/toolslide. Monarch 61 topslide is pretty beefy so it might do the trick.
    I still think it's a good policy, along with tightening up the cross slide gib.

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    Thanks for all the input. I appreciate the knowledge.

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    Quote Originally Posted by MattiJ View Post
    Really quick and dirty but perfectly usable for OP's task would be 3" bar with insert holder welded to the side or end.
    Less than 15 minutes total and you are already making chips.

    On any lesser lathe I'd mount the +10" hangout bar directly to cross slide without top/toolslide. Monarch 61 topslide is pretty beefy so it might do the trick.
    Go with this. ^^^^^ Use a DCMT insert, CNMG's seem to chatter easier.

    Myself, if I value my time, would simply buy DOM or honed tube.

    Ed.

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    Quote Originally Posted by atex57 View Post
    Go with this. ^^^^^ Use a DCMT insert, CNMG's seem to chatter easier.

    Myself, if I value my time, would simply buy DOM or honed tube.

    Ed.
    Ed,

    As stated above, DOM is not an option. I tried DOM before, and the .250 wall thickness, after their honing process, is not an ideal thickness, due to the application. .3125 wall thickness, after boring schedule 80, is better for my application, and not available in DOM without a large, special order. It would be the ideal solution if it was available in the quantity I need.

    I value my time, too.

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    I am leaning towards building my own bar with 3" square stock. I can mill a slot, and mount a 3/4" or 1" toolholder with set screws. Good idea, or should I mount a toolholder perpindicular to the end of the bar?

    For securing this to my cross slide, do you think a T-nut and one threaded rod/washer/nut through the boring bar is sufficient, or do I need two of each and clamp over the top. Sorry for the remedial questions, but this is my first boring bar build, and I prefer the advice from the experienced.

    Thanks.


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