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  • lazlo
    replied
    Originally posted by camdigger
    it would seem that the side of the tool's geometry would have more effect on chip flow than the nose as the feed is along the axis and not a plunge feed like a form tool. Most HSS tools I use are ground to a point and the tip has little to do with chip flow.
    A CCMT toolholder has 5° side clearance: if you look down on the insert from the top of the toolholder, the insert is rotated 5° towards the headstock -- it's a single-point cutting tool. So the chip should be flowing over the tip, across the land, and down into the chipbreaker, like the diagram shows.

    Most CCMT inserts don't have that flat land, which I think is what's screwing you up...

    Edit: here's a picture I just drew that shows how a chipbreaker with a flat land can interfere with the insert rake angles. Until you take a DOC deep enough that the chip passes the flat land, you effectively have a flat-topped insert:

    Last edited by lazlo; 07-14-2009, 03:36 PM.

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  • camdigger
    replied
    Hmmm... Not what I would have expected. The illustration clearly shows what I thought was happening at the nose of the insert, but the same thing should be happening along the side of the insert. I visualize a step being cut into the side of the work as the insert does its' job. I'm surprised there isn't some requirement /consideration for the effective back rake along the side of the insert ie, the "riser" of the step being formed as the insert cuts.

    Again, intuitively for me, it would seem that the side of the tool's geometry would have more effect on chip flow than the nose as the feed is along the axis and not a plunge feed like a form tool. Most HSS tools I use are ground to a point and the tip has little to do with chip flow.
    Last edited by camdigger; 07-14-2009, 02:54 PM.

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  • lazlo
    replied
    Originally posted by camdigger
    So... How does the DOC/feed per rev IPM affect the cutting relief angles?
    Just the DOC, the feed rate doesn't matter. I'll draw a picture later this afternoon, but picture the insert with the flat land pressed against the workpiece. If you take a smaller DOC than the width of the land, the insert acts like it's flat across the top. If you take a chip that's wider than the land width, you get the back-rake from the chipbreaker:



    That only happens when the chipbreaker has a flat land. If the Chipbreaker runs up to the edge like most positive inserts have, you don't have the DOC effect.

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  • camdigger
    replied
    Originally posted by lazlo
    If you look at the picture of the CCMT's at the bottom of Glenn's chart, it shows the land width and the minimum DOC to make the insert positive: the first insert, which is a finishing insert, needs a minimum DOC of .1 mm, an optimal DOC of .5 mm. In other words, it's .1 mm to the edge of the chipbreaker.

    The roughing CCMT at the bottom has a big land -- you need to take at least a 1 mm cut to get past the flat land, and a 2 mm DOC is optimal. I'm guessing that might be the insert you have.

    Notice that there's an open box for the third letter -- that's indicating that the land size/geometry is the same whether it's ground or molded. So if you switch from a CCMT (molded) to a CCGT, you're still going to have the same minimum depth of cut. The edge on the CCGT will definitely be a lot crisper though.

    The CCMT's I've have from Sanvik don't have that flat land -- they have a linear transition straight from the edge.
    So... How does the DOC/feed per rev IPM affect the cutting relief angles? Intuitively, I'd say you need the same feed/rev as DOC to have the same effect on the swarf in both directions. Otherwise you have a different effective backrake angle along the axis of the work. Cutting a 1 x 1mm spring seems a tad agressive even in an industrial setting

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  • lazlo
    replied
    If you look at the picture of the CCMT's at the bottom of Glenn's chart, it shows the land width and the minimum DOC to make the insert positive: the first insert, which is a finishing insert, needs a minimum DOC of .1 mm, an optimal DOC of .5 mm. In other words, it's .1 mm to the edge of the chipbreaker.

    The roughing CCMT at the bottom has a big land -- you need to take at least a 1 mm cut to get past the flat land, and a 2 mm DOC is optimal. I'm guessing that might be the insert you have.

    Notice that there's an open box for the third letter -- that's indicating that the land size/geometry is the same whether it's ground or molded. So if you switch from a CCMT (molded) to a CCGT, you're still going to have the same minimum depth of cut. The edge on the CCGT will definitely be a lot crisper though.

    The CCMT's I've have from Sanvik don't have that flat land -- they have a linear transition straight from the edge.
    Last edited by lazlo; 07-14-2009, 11:57 AM.

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  • camdigger
    replied
    Thanks, I'll check with the supply houses in Cowtown while I'm at work here.

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  • Glenn Wegman
    replied
    As far as Korloy....

    They recommend trying a CCGT insert with a HFP chip breaker in a NC3010 grade for mild steel.

    Last edited by Glenn Wegman; 07-14-2009, 08:25 AM.

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  • Glenn Wegman
    replied
    A CCMT that is recommended for finishing is what you should try.

    Another consideration is the geometry difference between the two types you have. The SDXT, mounted in the holder as you have it, gives a 45° lead angle which will be a more free cutting configuration than a CCMT mounted for turning and facing to a shoulder, which would be a negative lead angle so to speak. What you are doing is comparing a 45° lead free cutting finishing (relatively sharp) insert with a higher rake cutting edge that won't cut to a shoulder to a dull edge negative lead insert with 0° top rake that will cut to a shoulder. Basically apples and oranges although, as far as finish goes, a CCMT configured for finishing should give good results, but require a little more power to do so.

    If your concern was fast stock removal, you would want a 45° lead oriented, negative rake, roughing insert and a bunch of HP and spindle speed. Set it for full depth of cut of the insert and grab a garbage can lid for use as a shield whan you engage the feed lever and stand back!

    There are many different insert configurations and orientations for a reason.

    Glenn

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  • camdigger
    replied
    Originally posted by Glenn Wegman
    Is your SDXT insert bare or coated?
    Both inserts are coated. The SDXT inserts are slightly more pure yellow than the CCMT which seem slightly brownish yellow.

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  • Evan
    replied
    The reason I suggest this is because it will have the same effect as tilting the insert to a slightly negative top rake. Try shimming the insert then in the holder ever so slightly to tilt the top toward the work. Keep the speed way up. According to the Sowa specs that insert is recommended to run at 800 to 900 sfm or so for soft and mild steels. If you can't run it at that you should at least try it on a larger diameter workpiece to see if it really performs better at the recommended sfm.

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  • Glenn Wegman
    replied
    Is your SDXT insert bare or coated?

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  • camdigger
    replied
    Originally posted by Evan
    Try the ones you have slightly below centre. You will be surprised.
    I'm reluctant to do that as I'd have to bodge up a different holder (PITA with my limited shop time of late) or skim the bottom of the existing holder (so I'd need shims for the rest of it's life) for the experiment I don't have a lot of optimism for. At best I have one afternoon a week in the shop due to assorted circumstances and obligations, hence my reluctance to mess with an insert I have no confidence in....

    IIRC, when I checked the alignment, the holder presents the insert to the work on center.

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  • Evan
    replied
    Try the ones you have slightly below centre. You will be surprised.

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  • camdigger
    replied
    Originally posted by Glenn Wegman
    Different edge configuration.
    So the obvious question following that statement is what 80 degree insert C??? will have similar free cutting characteristics to the square SDXT inserts that I know how to make work?

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  • Mark McGrath
    replied
    http://www.pgstools.com/servlet/the-...ification/Page

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