What tooling should I use in this boring bar?
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  1. #1
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    Default What tooling should I use in this boring bar?

    In my collection of stuff is this (probably home-made) boring bar. It's about 50mm (2") in diameter and about 200mm long, and I'd like to use it for making some clean 60mm holes in cast iron. It has an SK40 taper so is much stiffer than anything I can mount in a Wohlhaupter boring head.



    My question is, what tooling can/should I use in this? Is there a suitable standard insert holder I can buy at reasonable price? And why are there two sets of holes? (Note: in spite of the apparent joint line or split line, it seems to be one piece, not screw-apart.)

    The holes are 10mm diameter on the smooth part, and the one that is threaded on the end is M12. I don't do this sort of boring on a regular basis so am OK with having something that I adjust by tapping or by trial and error.






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    Fishy setup....no idea what tooling one would use on that bar in its current form....

    Perhaps you could turn the shank of a brazed square shank tool like an "AL6" style down to 10mm cylinder
    To fit in the round cross hole and clamp it in position with one of the cross holes....Best if the cross hole was drilled and tapped for a fine thread set screw.
    You can then use the screw to move the tool out for size adjustment. Can set such a setup with an indicator with the boring bar in the spindle.....Make a trial cut and measure, then indicate the tool tip and adjust the tool
    out using the screw to correct the size.

    If it was me, i would cut the end off and machine the end to accept a DeVlieg "Micro More" style insert.Or cut a slot across the end and use a small shank turning tool like an "SCLCL" fitted with a high positive
    insert like a"CCGX 2 (1.5)1-AL

    Or, use a square socket across the bar that accepts the square tool for holding inserts...Making a socket is easy. I bore the appropriate cross hole and press in a square ID sleeve (Sturdy Broach) they can be had with
    threads on the ID at one end for an adjusting screw.....

    Some examples:
    The one on the left is the DeVlieg microbore setup. Has a micrometer collar that is threaded to the insert, Held in position via the through bolt...See these inserts on E-bay form time to time.

    The other too bars are both shop built...Center using a "Speedie Broach sleeve" to make the square hole for the tool.
    Slot cut to set tool insert on centerline in the right example....
    Tool and holder are as indicated above...Both Sandvik.



    Close up of tool and holder.....And yes these get used often and work well....


    Example of the AL6 brazed tool...think for the !10mm holes you would need to go larger to get the base circle at 10mm...Likely a AL8 ....Easy to turn if you have a square collet...can be gripped short so
    you can get a long shank turned....



    An example of turned shank brazed tools...make these for my Berco line boring machine...(8mm shank)



    Cheers Ross

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    I would guess that they used 10mm round HSS blanks and hand ground their cutters. To guess further the front one was the rougher that they had to reginde more often so they put a pusher screw to adjust it out after grinding.

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    Good call on the HSS blanks. Totally blanked on that one...Guessing if you want to keep it on the cheap, you could sharpen up a used 10mm end mill (2 flute) to be a usable cutter
    Made me think...My Berco cylinder boring machine uses 10 mm tooling...Available in brazed tip or with replaceable inserts.
    These guys are the US parts source for Berco...gotta be a Euro source for same...

    Supplies & Deals
    Cheers Ross

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    Broken center drills work well in boring bars like that one.

    L7

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    I think There have been two hss cutters at same time, roughing done with the one in front and Finishing with second.

    Also might be used as a roughing boring bar just to enlarge the hole enough with one tool before Finishing.

    I would use some 10mm hss blanks and grind some flats to them, for bolts and sharpening.

    Also could use a chopped 10mm boring bar with insert tooling.

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    Hi to all,

    I've made a couple of similar bars, much smaller though.

    Using HSS blanks or broken carbide endmills has always worked perfectly for me. Single lip cutter grinder can easily sharpen both satisfactorily.

    BR,
    Thanos

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    To those of you who are grinding your own cutters, I would be grateful if you could please post a few closeups of the cutting edges. I have ground a handful of bits but I normally use insert tooling.

    My preference would be an insert holder, but I am not sure if I have enough space to squeeze one in for a 60mm diameter hole (the bar itself is over 50mm).

    Ross, I like your idea of boring a larger hole at the end, and adding a square ID "Sturdy Broach" sleeve which was holding a tool holder. This might also provide clearance for insert tooling and make it simple to push it with an adjuster screw.

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    Quote Originally Posted by ballen View Post
    To those of you who are grinding your own cutters, I would be grateful if you could please post a few closeups of the cutting edges. I have ground a handful of bits but I normally use insert tooling.
    Bars like that were pretty common for old timey production tooling. Think bore (small depth) and then counter bore or face with one tool. Most often seen on transfer lines stuck in machine tool columns or big wisconsin milling/boring spindles. When Cat dumped the crib in the ‘90’s some of them looked like porcupines with 4-6-8 tools in them...

    The 10mm is close to TRC(30°), TRE(45°) or TRG(90°) -6 (3/8”dia) size, so google TRC-6 carbide boring tool or TRC-6 brazed toolbit etc for info.

    I mostly used TS(square shank) tools like alfaGTA does & they make for a very solid setup with everything locked up. I’ll attach a page so you can get the nomenclature right. I’ll add something from an old post showing what a 0° back rake looks like when centered in a boring bar (it’s what the work sees, it is what it is)… These tools look like they won’t cut right out of the box but they do!

    Most of my recipes have no back rake & +5° side rake, lead angle from 5-15°, end cutting edge angle (ECEA) 3-5°, then the end relief around 4-6° (less is better) and side relief 3°ish. I expect to break chips (with NO chatter) when I bore & the above works well with steels from 200-380 brinell hardness.

    Good luck,
    Matt
    Attached Thumbnails Attached Thumbnails precision_boring_tools.jpg   ttypetoolback-side.jpg   ttypetooltop.jpg   boresleevesa1.jpg  

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  16. #10
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    Hi Bruce,

    Your 50mm boring bar was made for a special purpose, something like putting a
    finish form on the edge of a bore (champfer, radius, etc.), in one operation.

    If it was meant to to be a rougher and finisher, the holes would be closer together, to
    make it more of a general purpose tool.

    I would ask what is the specific job you are trying to do that you need that
    stiff a boring bar? Stiff is always good, but why go out of your way if you don't
    require that stiffness to do the job.

    Are you making a small start hole,in which to bore out to the finish size, so
    you want to really hog out the extra material?

    If you have lots of extra material to hog out there are many other ways to
    do it without using a big boring bar.

    Is this a through hole? How thick is the material?

    How many holes of this kind do you need to make - is it a one-off or
    1,000 holes?

    Here is one quick way to rough-out a hole as a prep to the final finish boring:
    YouTube

    Best Regards,

    Paul Hoffman
    Last edited by toolnuts; 01-23-2020 at 02:09 PM.


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