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  • Fasturn
    replied
    An old trick is to turn the boring bar up- side down and turn on the far side. Now your dials read the same as turning the OD. Sometimes you get less chatter too. You wont strain your neck trying to look down the bore.

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  • mattthemuppet
    replied
    I think you're probably just hitting the limitations of your machine unfortunately. I did a lot of work on an Atlas 618 (similar size/ weight as your SC4) and even in alu I had birds nesting and needed to do several spring passes boring alu with a CCGT insert. Still made good parts, just took longer than I would have liked. Fast forward to my South Bend wide 9 and I tried out a TCGT boring bar. I think I was taking 50 thou or more per pass, 8 or 900rpm and chips were spraying everywhere. It was amazing. Doesn't help you much I know, but you may have to just get used to what you have until you can get something beefier.

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  • Richard P Wilson
    replied
    Originally posted by Doozer View Post

    I don't think a mini-lathe has a back gear, but maybe I am wrong.

    -D
    No, apparently its a Sieg SC4, with a variable speed DC motor, lowest spindle speed 150rpm, so it won't have much 'grunt' left at that speed, unlike my old beastie which has maximum torque at its lowest speed of 25rpm.

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  • Cenedd
    replied
    Originally posted by Doozer View Post

    I don't think a mini-lathe has a back gear, but maybe I am wrong.

    -D
    You're not. No back gears at all but it is at least a brush less DC motor so it doesn't lose all torque at the low end. Also no gearbox and the carriage dial graduations don't match up with actual travel. Ya pays yer money and all that. Still, with my space constraints it wasn't a bad fit - old iron might have been better (minefield if you've no clue what you're doing though) but probably twice the size or more.
    For the purposes of fair comparison, this probably shouldn't be called a mini lathe. Not saying that it's a proper "big boy" lathe but it's one (maybe even two) up in size from what they're selling as "mini".

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  • Doozer
    replied
    Originally posted by Richard P Wilson View Post

    I don't know about 20 thou being a lot for a small lathe. I've got a 100 year old 8" lathe, plain bearings, and it will happily do 50 thou DOC in cast iron at 200rpm, using a tipped tool. Good finish too.
    I don't think a mini-lathe has a back gear, but maybe I am wrong.

    -D

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  • Richard P Wilson
    replied
    Originally posted by Doozer View Post
    So I read you have a mini lathe, running 1700, doing ID boring, in a 24mm bore, in some kind of an aluminum.
    Some wisdom mentioned before, the final pass is what counts to bring it to final size.
    This .5mm (.020") depth of cut is a lot for such a whimpy lathe.
    No wonder you have trouble.
    Take smaller cuts, slow it the heck down, get some positive geometry with a chip breaker to curl the chip,
    and take some spring final passes. I don't see predictive stock removal happening here.

    -Doozer
    I don't know about 20 thou being a lot for a small lathe. I've got a 100 year old 8" lathe, plain bearings, and it will happily do 50 thou DOC in cast iron at 200rpm, using a tipped tool. Good finish too.

    Leave a comment:


  • Doozer
    replied
    So I read you have a mini lathe, running 1700, doing ID boring, in a 24mm bore, in some kind of an aluminum.
    Some wisdom mentioned before, the final pass is what counts to bring it to final size.
    This .5mm (.020") depth of cut is a lot for such a whimpy lathe.
    No wonder you have trouble.
    Take smaller cuts, slow it the heck down, get some positive geometry with a chip breaker to curl the chip,
    and take some spring final passes. I don't see predictive stock removal happening here.

    -Doozer

    Leave a comment:


  • Cenedd
    replied
    Originally posted by MattiJ View Post
    I dont like CCGT for boring bars that much, very small clearance between the bar and bore resulting in chips wedging between. DCGT or TCGT works better if bore size allows.
    This sounds very much like the problem I was having. Any preference between the two? TCGT presumably has the benefit of three cutting points but if that's at the expense of exactly what I'm trying to get more of, it's a poor trade. DCGT is smaller (due to angles) which could be a good thing if it doesn't make it more fragile?

    Originally posted by MattiJ View Post
    60mm depth with 12mm bar is also pushing your luck. Its doable but you are fighting with chatter at some point for sure.
    It definitely was on the tiny bar....but I knew that. I didn't notice problems with the 12mm bar that I could attribute to flex. It was definitely more what you might call "crunchy" towards the blind end, but I'm pretty sure that was chip recutting.

    deltap I was thinking the same as a workaround. I feel there may be a set of 2MT drills in the near future

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  • deltap
    replied
    Boring is a slow process compared to drilling. Drill to 22 or 23 mm and then you just have a few finish passes. Even a small lathe should handle drills up to 25 mm.

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  • MattiJ
    replied
    I dont like CCGT for boring bars that much, very small clearance between the bar and bore resulting in chips wedging between. DCGT or TCGT works better if bore size allows.

    60mm depth with 12mm bar is also pushing your luck. Its doable but you are fighting with chatter at some point for sure.

    for ”singing” parts it makes huge difference when you fill or wrap the part with some deadening material.
    rubber bands, rubber hose, shop rags, thick layer of tape, solder wire.. almost anything improves the situation and often makes huge difference.

    Leave a comment:


  • Cenedd
    replied
    Bented I might have to try pinching your taped tube trick and see if it works with just air. I fear it may need a nozzle of some kind though - especially with the amounts my small compressor can keep up with. Worth a play though.

    Leave a comment:


  • Cenedd
    replied
    Thanks guys.
    Sounds like I need to be doing some testing on something that isn't a part that matters and when I've not got a fairly limited time window to play with
    Interestingly/frustratingly I think I have seen evidence that both tom_d and Toolguy are right.....much as BCRider said. I tend to part with an aluminium profile MGMN200 even with steel. It just seems to work better than the blunter steel profile inserts for that. I tend to do that about 300rpm which is far too slow on paper...but works very nicely. I get a pretty good finish at much lower speeds but there does seem to be a drop-off when it gets too slow and I did get an excellent finish with an alu profile WNMG insert (which might have been BCRider's suggestion originally - thanks for that, works very nicely) at nearly 2000 rpm and it was breaking a chip at really tiny DoCs too shaving off about a thou.

    I was trying to work out why I've not had trouble previously....and I think I have, but managed it very differently. Before I was taking smaller DoC at lower rpm (about 700) and using the fact that the chip didn't break at all to just pull it out in one long string. Clearly it worked but it was slow and I was pushing for faster progress this time. Clearly a higher DoC breaking small chips and evacuating with flood coolant would be faster - if I could do both of those.

    So I can have a play with the angle of the bar and see if going much faster (even HSS calcs are coming out at 2,400 rpm) helps at all. The fact the bar is in the bore should limit the danger should things go awry.
    Has anyone got any suggestions of bar diameter to bore diameter sizes? I've previously drilled to 13mm (largest drill) and then I could just about get a 12mm bar down it....but it doesn't leave much/any clearance for chip evacuation. Tiny bar (6mm if I remember) clearly has too much flex at that sort of extension but was useful to get the bore larger before switching. I have some bars in between but haven't used them previously as I was trying to get up to the biggest bar as soon as possible....and I'm thinking now that I'm not trying to pull one long chip, it might be wiser to be using a bar somewhere in the middle - at least at first.

    Leave a comment:


  • BCRider
    replied
    ...Putting carbide against aluminum requires speed. .....
    Not really. Oh sure, if we're after fast production then sure. But the recent experimenting I've been doing with aluminium specific carbide inserts has me using my lathe at well below those supposedly optimum high SFPM rates and the finish is still coming out just lovely. The supposed need for high SFPM with carbide on a variety of metals has also been pretty well torn down by others in previous threads too.

    So it's more a case of using carbide permits the OPTION of a higher speed..... mind you.... If higher RPM was used then perhaps a lighter chatter free DOC could have been used and simply make more light passes in the same amount of time? So actual cubic inches per minute of metal removal might have stayed the same as a low speed with heavy DOC?

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  • Toolguy
    replied
    Usually if you're getting chatter/ringing, slowing down the spindle will help. You don't need speed to cut aluminum (or anything else) with carbide. It would cut just fine at 200 RPM. I would try it in the 200 - 400 RPM range. It takes a little longer, but not much. Desired finish has to do with cutter tip radius and feed rate, probably want to be in the .004 to .006 IPR feedrate, and depth of cut.

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  • tom_d
    replied
    Originally posted by Cenedd View Post



    Any pointers that I'm going about it all wrong would be quite welcome actually Also testimony that it's supposed to suck that much would make me feel better if that's actually the case!
    Some thoughts: You are not going about it all wrong. All that needs to be done is to fine tune the procedures. Considering the small lathe you're using some of the options are limited. Putting carbide against aluminum requires speed. Hard to do on that small machine. Max. speeds are best obtained with flood coolant. Again, machine limited. Run the machine at the fastest speeds you are comfortable with that give desired finishes. Ball park figures for aluminum are 200fpm with HSS tool and 600fpm with carbide. Ball park, not carved in stone. Not unusual to need to stop and clear chips when roughing a small bore. WD40 works as lube/coolant. It's not much more than glorified kerosene so use that instead if kero is cheaper, better availability in your area. Water soluble oil in a squirt bottle is good too, if you can.

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