Yo machinists - Carbide cutter brazing and such ??

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I know it's been mentioned a few times recently, but I lost track of the posts, and wasn't very interested then... But now... Anyway, could I braze (silver solder) these to a boring bar?Attachment 50365Let me start over... I know I can braze them, I'm mostly wondering about the angle.What's the theory when hole boring? Is it preferred that only a very small part of the cutter contact the work piece, or that most of the cutting edge be nearly parallel to the desired final cut? The job is to bore-to-size holes which have been flame cut in heavy plate.I know that before the bluing wears off my finger, I could read all this:Attachment 50366And still break a few tools and mess up a few holes, but this time I was hoping to do it the easy WeldingWeb way, and hear from someone who's been there. Thanks in advanceLast edited by denrep; 10-19-2010 at 11:45 PM.
Reply:I silver braze custom cutters together often. Under powered machines like the least ammount of the insert in cut, that goes for cutting parts not clamped well. Oh and positive rake small radius. I usually go 90 to cut.High power, well clamped can stand more insert in cut. Neg rake last longer and much stronger for interupted cut (flame cut) larger radius. I usually go 20-30 degrees of cut.Peter
Reply:You could braze them to a bar, but if you were me you'd just buy a boring bar and use the inserts like they were designed to be used. It's not blasphemy or anything, but replaceable inserts are so handy to use.Those inserts can be rotated when the tip gets dull so you have at least two corners (on the one in the lower left corner, which is a milling cutter insert anyway) 4 on the diamond-shaped ones, 6 for the triangle inserts and 8 for the square ones. A brazed-on insert can be ground sharp again (and technically an insert can be reground too), but it only takes about 60 seconds to rotate an insert to one of the sharp corners.It was a few years back, but I bought a fairly large one (1-1/2" diameter shank and 14" long) for $35 without trying. I'm sure you can still get a decent import bar from a local machine tool supplier or on-line for about 30 bucks or so.Personally, I would recommend getting one to fit a CNMG insert (diamond shape). The standard, most common size is CNMG43x (x= the nose radius - 1=sharper corner but less durable, 3= larger radius but more surface contact so sometimes chatters). Probably the most common insert in existence is CNMG432, and it's hard to go wrong with those to start with. You get more corners for the triangle (TNMG) but the CNMG is so common you can get them very cheap from any supplier on the planet and they just work really well. The triangles are OK, but speaking from experience (20-year machinist) you just can't go wrong with the CNMG tooling. Also, the same insert fits several different types of tool holders, so you can use the same insert for OD turning as well as bores.OK, to attempt to answer the original question though...The bottom of the diamond inserts will drag inside a bore unless you have negative rake, which means you have to tilt the insert down, like it's kind of dragging through the cut rather than cutting like a knife. That doesn't seem intuitive, but the heat generated actually improves the finish (shinier). Then you need clearance on both the face of the insert and also behind the cut. The precise angle isn't really all that important, but just situate the insert so it doesn't drag on the bore behind the tip as it feeds in, and also so it doesn't hit the face behind the tip at the end of the bore. This second clearance area isn't important if you're boring all the way through, but if it's a blind pocket it will matter. Hopefully this makes some kind of sense - it's a bit hard to explain in the printed word.The other answer is "yes" you only want a point of contact rather than being parallel to the final cut. the relief will keep the chips from being pinched between your just-cut surface and the tool and galling up. More relief = better chance of a good finish. Of course all these angles are taken care of for you if you just buy an insertable boring bar, but it may be helpful to know. Typically the face clearance angle is 5 degrees. They make them in other configurations, but that works for most everything and is what most shops buy. One thing you could do for free is take a look at an insertable bar at a supplier just to see what kind of angles the bar has so you can kind of copy what you see with brazing. Or maybe look some up online and save gas.Here ya go:http://www1.mscdirect.com/images/sol...ctionGuide.pdfMore detail here. I'd go for "L" on page 2http://www1.mscdirect.com/images/sol...arIdSystem.pdfParent page with tons of other tooling info links:http://www1.mscdirect.com/content/so...lProducts.htmlBy the way, none of the inserts you pictured are CNMG (bummer), so you'll have to buy a couple inserts with the bar if you want to move up to insertable stuff. The square inserts don't lend themselves well to boring and those may be good candidates for brazing and grinding them to a useful shape. The diamond or triangle could be brazed and used with no grinding.Last edited by tyrone shewlaces; 05-04-2010 at 12:51 AM.
Reply:Denrep, if I had to guess it would be that you got either a bunch of used ones from a production shop, or got a number of new or partly used ones but of many different designs which it doesn't make sense to buy bars/holders for, Right? I have made some cutters by milling small pockets in regular round bars or rectangular sections, and brazing, but that is usually for an odd job where strange geometry is needed. Castweld's and Tyrone's advise is about as good as I could give. Remember you also need the correct height for the cutting edge. Also, stiffer tool steel keeps its rigidity better than mild steel, under pressure.Special shimstock with a copper center surrounded by silver solder is sold for this purpose, but also is easy to duplicate, if cracking of the carbide is ever a problem. Somewhere, I have some copper foil which is only a few thousandths thick; I think it originally came from a hobby shop.
Reply:I would recommend using HSS if the holes are flame cut, at least on the first cut.  HSS will take a lot more impact, a lot more tool pressure, much slower bar speeds, require less rigidity and you can sharpen it over and over again.  I have taken single cuts with HSS on very roughly welded bores that are .250" per side, (.500" total), with a .030" feed rate per revolution on a 10" diameter bore many times with no problems, that would NEVER happen using carbide.  I make all of my own cutting tools with HSS and for roughing like a 15 degree negative lead angle, 10 degree end relief, 5 side relief, 5 degree heel, and a large top rake. Slow the bar down and it will cut like a dream.6 Miller Big Blue 600 Air Paks2 Miller 400D6 Lincoln LN-25's4 Miller Xtreme 12VS2 Miller Dimension 812 4 Climax BW-3000Z bore welders Hypertherm 65 and 85Bug-O Track BugPair of Welpers
Reply:Men, thanks for the advice and counsel.I broke down and sprung for the new bar. Attachment 50418Couldn't buy USA from stock. I'll feel bad cutting it off to shorten it, but oh well.Tyrone shewlaces - I'd have went with your specs if I could have bought from stock. One of these days I'll try braze job and post it up.This is what cooks:Attachment 50419Even though flame cut, the holes are smooth and concentric so I'm not expecting cutter trouble.Thanks again all, for the helpLast edited by denrep; 10-19-2010 at 11:45 PM.