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  1. #41
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    This is a spindle bushing from 2" od 1018 I made for the project. I used a shars carbide indexable tool for the outside and inside. With fine finish cuts I still needed emery to get it smooth and allowed for that, resulting in just a few thousandths clearance, so it came out ok.

    I will also attach a pic of the carbide tool I used. I broke both of them right at the tip when a chip built up, came back around (it seemed) and knocked the tip off with a little bang. But now I know should have been going in at an angle and using oil. Interestingly the first few passes seemed "ok" and it all got worse as the cuts got deeeper and of course I was going slow which apparently is another sin in some situations. This piece is 3ft long so I have a lot of tries availavle and in fact I can even turn failed threads down flad and thread whatever is left a time or two for practice.

    As to the tooling, I'll need to obtain some HSS blanks and go after those resources you guys posted up above and try and figure the geometry out as well as how to achieve that on the bench grinder. Been looking for NOS or other HSS blanks on ebay and fb mktplace etc, be nice to find a box someone is unloading. My QC toolpost system will accomodate 1/2" but whats the ideal size and whats the smallest size for this threading?

    20200318_200457 - Copy by Chris P, on Flickr

    20200308_223902 by Chris P, on Flickr

    20200308_174734 by Chris P, on Flickr

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    Do your math.

    Look up the preferred speeds and feeds for the insert that you are using. At very least, look in a few catalogs and figure out how to read the recommended speeds and feeds charts for similar inserts. Try to get somewhere near that. It'll probably scare the hell out of you how fast the cutting takes place. Get over it.
    Cut off a piece of stock so you don't have a bar start shaking at the ass end of the lathe and walking the whole bench across the floor. leave a little room behind the work, if the hole in the chuck is smaller than the hole in the work.
    Like as not, the top speed of your lathe will not get beyond the recommended top speed of the insert.

    Use power feed. Get used to that.

    Set the feed rate to about half the radius at the tip of the insert. Crank up the lathe, engage the power feed, and take a pass of 10 thou or so. Might need to go deeper than that to avoid dragging the underside cutting edge of that insert on the inside of the bore. It's a negative rake tool, it should be tilted down enough to clear, provided the boring bar is the correct one for the insert.

    Brazed bits, among other things, are either cheap crap, or they are a beginning to a useful cutting tool, but you need a decent set of wheels on a decent grinder, to get the results from them.
    They are very much the reason folks like Baldor make a "Carbide Grinder"

    Edit: Really crude speed calc. 60-100 surface feet per minute for HSS on mild steel. Four times that for carbide, in broad generalities. So, instead of diameter times Pi, use diameter times 4, an easy number to do on a scratch pad. So. Diameter of hole (I'll use 1 1/2 hole), times four (Pi), times 400 (surface feet per minute, carbide, on mild steel, as a generality) 1.5x4x400=2400 rpm. Does your lathe go that fast? It's a starting point. Read your lathe charts to plot out how to get the feed per revolution you need.

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    The first photo of a flat top / no positive top rake tool bit will not shave off steel but try to push it off causing high pressure and chatter. much like a knife blade straight off/right angle to a piece of wood.. slanting that knife would allow it to take a cut and penetrate the wood... that is what a top rake angle does to steel.. the edge can penetrate and shave the steel so it flows smoothly along the bit's top surface.. not try to push it off.

    The flat-top bit won't cut/thread mild steel very well even at 29/30* or changing the speed and feed

    Pushing off as would do a flat top tool bit would be better suited for iron turning because iron prefers to break off with pressure... not flow along the tool bit face..Flat top and even a negative top rake can withstand high heat and pressure but likes a very stout lathe.

    Tool geometry is very important to good machining.
    YouTube

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    Quote Originally Posted by FlyinChip View Post
    I use bits like this. If they chip I just sharpen them again with a grinder and diamond plate.

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    You will continue to have chatter, problems, higher scrap rate, higher costs and higher stress on your lathe ...The are great in the correct use ...but not for cutting mild steel.
    They good for harder steel and cast iron with using a very heavy duty machine.

    Having a surface grinder you could add a positive top rake and then they would do much better.
    Last edited by michiganbuck; 03-21-2020 at 10:29 AM.

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    Positive rake is up slope? Also, what kind of wheel would my grinder need to work that carbide point.

    I am going with HSS but since I have these bits why not experiment a little too.

    This is the tool description, what does E6-C6 mean?
    1/2 Carbide Tipped Threading Lathe Tool Bit 60 Degree E8-C6 USA Morse 73719, G13

    Now back to watching that tooling video... lots of time now for this, unfortunately...

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    QT: Positive rake is up slope?...no it is positive rake.

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    Quote Originally Posted by michiganbuck View Post
    QT: Positive rake is up slope?...no it is positive rake.
    c-6 puts it at the harder end of carbide hardness scale. Low Cs are tougher like more used for irons and the lioke.
    I'll be the contrarian, and say that you can get good results from a flat topped threading tool. You WILL want a cutting oil or fluid. And you will have almost no end to your misery as you sort out the combination of feeds, speeds, and depth of cut, that will work on YOUR lathe.

    But you won't get those results from that brazed tool, as it is. It has no relief under the cutting edge and the tool will drag slightly on the side of the cut below the edge from the helix angle of the thread not being accommodated.

    "Carbide Grinder" Look up what one of those is.

    Carbide tools are great. Once you understand enough, and have the confidence enough in what you are doing, to make them work correctly.
    Otherwise they are expensive, frustrating, and waste a lot of time money and parts.

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    I'll find out about carbide grinder as a side task. I just read your reply and visualized the helix, yes, duh now I can see that a straight down side of the tool would drag since the thread angles in top left to bottom right.

    as to carbide in general, for routine turning such as that bushing which is also 1018, I used those inexpensive shars indexable insert carbide cutters with good results. but that's now looking to me like a whole different and simpler machining task than threading.

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    Quote Originally Posted by FlyinChip View Post
    I'll find out about carbide grinder as a side task. I just read your reply and visualized the helix, yes, duh now I can see that a straight down side of the tool would drag since the thread angles in top left to bottom right.

    as to carbide in general, for routine turning such as that bushing which is also 1018, I used those inexpensive shars indexable insert carbide cutters with good results. but that's now looking to me like a whole different and simpler machining task than threading.
    Not to put too fine a point upon it, but the finishes you are getting with your bushings kinda suck, and you should be able to accomplish WAY better.

    Seriously. Try the high speed that I suggested earlier on the outside of a piece of your 1018.

    If this were in the shop where I was teaching basic lathe operations to beginning tradesmen and women, you would have started out with 12L14 or some 7075-T6, so at least you would get to see what the difference is between starting with crap, and starting with material that will do it's best to actually give good results.

    You also would have been shown the differences between what cutting and feeding at way too slow a rate, and cranking it up to what it should be, look like, so you could skip all this fucking around and sandpapering parts that should have been nicely finished from the outset.

    There really IS a good reason that almost the very first thing you learn about machine tools (beside to not bleed on them when you get cut!) is how to figure out speeds and feeds.

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    OK well I just did a test cut at a much higher speed than usual, 1500 rpm which is about as much as I could get. 330SFM by my calculations. .020doc .0046 fr Finish is "fairly" smooth but could use an emery touch up. Did I learn anything here?

    (thumping is from the glued serp drive belt)


    YouTube

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    If 1500 RPM is as good as you have on tap, watch this video.

    Really not hard to grind good working tools of HSS.

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    Quote Originally Posted by trevj View Post
    Do your math.



    Edit: Really crude speed calc. 60-100 surface feet per minute for HSS on mild steel. Four times that for carbide, in broad generalities. So, instead of diameter times Pi, use diameter times 4, an easy number to do on a scratch pad. So. Diameter of hole (I'll use 1 1/2 hole), times four (Pi), times 400 (surface feet per minute, carbide, on mild steel, as a generality) 1.5x4x400=2400 rpm. Does your lathe go that fast? It's a starting point. Read your lathe charts to plot out how to get the feed per revolution you need.
    1.5" x 4 gives half a foot circumference (very roughly), 2400 RPM comes out as 1200 FPM! Come down to 800 RPM and it's close to 400 FPM, I'd be more likely to run (unknown quality) carbide at 300 FPM in the gummy steels so 600 RPM (and wind the speed up as approaching centre, ain't VFDs handy). Similarly, for e.g HSS and 60 FPM divide the FPM by the circumference *in feet* so for 1&1/2" use 60 divided by a half, 120 RPM is close,

    Dave H. (the other one)

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    Michael,

    I do see some errors in your post and will attempt to correct them. This 29.5 degree thing is often confusing to many and I have developed a way of doing it that will work on any lathe with any way of numbering the angular scale for setting the compound. I am going to try and address each error in turn and mark them in the quoted text. Here goes:

    "This makes the tool cut on the (left) side of the 60 degree tip, and the (right) side has a small bit of clearance."
    This is only half correct. Yes, the tool is cutting PRIMARILY on the left side of the tip but there is no clearance on the right side. If you use a 30.5 degree setting or larger, then there would be clearance. But you do not want any clearance because that would produce a right hand flank of the thread that is stepped. First I will show a threading tool bit being fed straight into the object being threaded and illustrate it's cutting equally on both left and right cutting edges.



    Now, with the 29.5 degree setting the right hand side of the tool tip does still cut, but by only a very slight amount as compared to the left edge. So both flanks of the thread are cut with each pass and this keeps both flanks straight. This drawing illustrates this:



    If you look at the arrow at the lower right of the drawing, you can see that it is at a small, 1/2° angle to the line that I have extended from the right hand cutting edge of the tool. And that 1/2° is in the direction that takes it INTO the right hand flank of the cut. So that right cutting edge is actually cutting a very thin chip. This is perhaps easier to see in the exploded view at the lower left. I have pointed out the movement of the tool's tip from the previous cut to this one.

    You also said, " In the first case, setting the compound to 29.5 degrees means that the motion of the compound will be along a line almost perpendicular to the (lefthand) face of the tool."
    This angle is not almost perpendicular to the lefthand edge/face of the tool. The movement is in that direction, but is about 30.5° off of perpendicular. That's all the corrections that I have.

    Finally, I offer my method of setting the compound. This will work on any lathe, regardless of how the angular scale for the compound is numbered because it just ignores those numbers completely. Here it is in a drawing:



    As you can see, my starting point is the position at 90° from the lathe axis (this is MY ZERO position) and I just move the compound 29.5° from there. This will work on any lathe and can be used for external or internal threads. It can also be used if you wish to cut primarly with the right hand cutting edge of the tool instead of the left one: you just swing the compound in the opposite direction (toward the headstock). For me, it eliminates all confusion and, from my first single point thread, I have never set the compound wrong. Other errors, yes. Compound angle, NO.

    As for eliminating that galling, my thoughts are:

    1. Dead sharp tool. POLISH the faces and the top rake surface.
    2. A good cutting fluid and use a generous amount. I like TapMagic, but there are others. I like oil based ones for threading.
    3. Solid set up.
    4. The alloy can make a difference, but I have threaded 1018 with no problems.
    5. The speed can make a difference, but I have threaded 1018 with a hand crank (DEAD SLOW) with no problems.
    6. Did I say, dead sharp tool and good cutting fluid? I should have.



    Quote Originally Posted by ferretlegger View Post
    In case it is not clear, what people are referring to with the angle of the compound at, say, 29.5 degrees, is advancing the COMPOUND to cut the thread. NOT the cross slide. Thus the tool is entering the cut at an angle, not perpendicular. This makes the tool cut on the (left) side of the 60 degree tip, and the (right) side has a small bit of clearance. When you push the tool in at 90 degrees, you are cutting both sides of the tool, and it is a lot harder to get a smooth cut. It is also very important to set the tool up so that the centerline of the 60 degree tip is PERPENDICULAR to the axis of the part. This is regardless of whether or not you are cutting with the cross slide (90 degrees) or the compound (at 29.5 degrees). The tool MUST be perpendicular to the axis of the part. If you are advancing the tool with the compound, the depth of cut is reduced by the cosine of the angle (0.001" on the compound is 0.00087" in the radial direction for a 29.5 degree offset of the compound from perpendicular to the part axis). So you need to do a little thinking about what that means in your situation.

    Another confusing bit is what is meant by 29.5 degrees. Compounds are marked so that the degree marks are either from a normal (90 degrees) reference line relative to the axis of the part, OR on some lathes, measured from the axis of the part. In the first case, setting the compound to 29.5 degrees means that the motion of the compound will be along a line almost perpendicular to the (lefthand) face of the tool. in the other case, you need to set the compound to 90-29.5=60.5 degrees in order to feed the tool so that the (left) edge is cutting about the same across the (left) edge. I am getting old, and sometimes mix things like this up, so if I have it backwards, I hope someone will correct me.

    Cutting threads in other materials a LOT until you are very comfortable with all the required operations is very good advice. 12L14, brass, aluminum, etc. are all a lot easier to cut than 1018. I use carbide pretty exclusively on most materials on a Hardinge HLV lathe with good success. Which brings up another point. What is your stickout, and general rigidity? You mentioned a long part in 304 stainless. WATCH OUT!! I would recommend using a live center to support the work, especially if the part is skinny, sticks out more than say 2xDiameter (lots of personal preferences here- really depends on rigidity and accuracy of spindle). A non-rigid setup can allow nasty chattering, which also ruins the thread.

    In any case, hang in there, and DO NOT be in a hurry to work on the 304 stainless. 304 can be HORRIBLE to thread if your process is not really dialed in. You absolutely must use a good tapping fluid. Tapmagic, Anchor Lube are well known winners. I use Cool Tool also, and do ok. Seriously though, don't assume that because you can cut threads in 1018 you are ready for stainless. Eventually you will crush it, but it really is an unforgiving material in terms of tool geometry, sharpness, speed, DOC, tapping fluid, and so on. If you only need to do this once, and then you will retire to a nice Island in the Caribbean, you could consider roughing the thread most of the way, and then finishing by hand with a really sharp, new die with lots of lube to get the thread on spec and with a good finish.

    Listen to the advice people are giving you! It is priceless.

    All the best,
    Michael

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    Quote Originally Posted by FlyinChip View Post
    OK well I just did a test cut at a much higher speed than usual, 1500 rpm which is about as much as I could get. 330SFM by my calculations. .020doc .0046 fr Finish is "fairly" smooth but could use an emery touch up. Did I learn anything here?

    (thumping is from the glued serp drive belt)


    YouTube
    Your calculations are right, sensible speed for carbide on small(ish) work. Is the surface you're now getting "torn" looking or more "grooved" (like a really fine thread)? If grooved, the tool nose radius may be too small and either you want a bigger radius on the tip or you need to slow the feed rate until it's less than the nose radius.

    No argument with the suggestions to set the topslide to 29 and a bit degrees, make progressively finer cuts it's always worked for me.

    Be aware that most commercial carbide inserts are aimed at big, rigid, powerful machines and substantial depth of cut (gets production rates up!), creeping up to final size with shaving cuts may not get past the edge radius so they cut pretty poorly - a good reason for *sharp* HSS tooling or application-specific ground-edge carbide inserts.

    Dave H. (the other one)

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    Great posts Trevj (#52)and Epalll (#54)

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    RE from hope: [Be aware that most commercial carbide inserts are aimed at big, rigid, powerful machines and substantial depth of cut (gets production rates up!), creeping up to final size with shaving cuts may not get past the edge radius so they cut pretty poorly - a good reason for *sharp* HSS tooling or application-specific ground-edge carbide inserts.]

    and many TC inserts are not as sharp as a well ground HSS bit.


    Still for a production job. at the right speed, on a heavy enough machine the right TC inserts are good to best.

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    Quote Originally Posted by michiganbuck View Post
    Chip breaker carbide inserts can be/act positive on both right and left edge so may be used straight in, but flat inserts not.
    I still thread only at 29-30 and compound in-feed.

    *The shoulder cut at going near the head looks very poor so likely your bit is not sharp or does nor have any top positive rake angle....or there is not enough clearance under the cutting edge.

    Good to file test parts to know they are HSS compatible...1018 is soft in its normal state..

    McMaster-Carr
    unless you use these:0-114.jpg

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    Many lantern tool holders hold the bit at a back rake angle. these can thread with back rake only so not needing any side cutting edge(side) rake angle. they flow the chip straight away from the part..still 29-30* is beat, and compound in-feed.

    With these you consider the under clearance as the bit sets in the holder..not as it bumps the grinder for sharpening.

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    Quote Originally Posted by Hopefuldave View Post
    1.5" x 4 gives half a foot circumference (very roughly), 2400 RPM comes out as 1200 FPM! Come down to 800 RPM and it's close to 400 FPM, I'd be more likely to run (unknown quality) carbide at 300 FPM in the gummy steels so 600 RPM (and wind the speed up as approaching centre, ain't VFDs handy). Similarly, for e.g HSS and 60 FPM divide the FPM by the circumference *in feet* so for 1&1/2" use 60 divided by a half, 120 RPM is close,

    Dave H. (the other one)
    Well bugger my friggen memory! I feel dumb! LOL! OK, am dumb. But I can learn. Maybe this'll learn me to check my facts!

    Dug out the very book I recommended. Technology of Machine Tools by Krar.

    Looked up the speeds formulae.

    The recommended simlified formula, for inch dimensions:

    Cutting speed in SFM X 4 , Divided by the Diameter in inches.

    So that would, for carbide, be 400 (SFPM), X 4 (pi-ish) divided by 1.5, which by my calculator says 1066 RPM. Do that with 100 SFPM for HSS and you get 267 RPM.

    Those using 100/400 SFPM.

    Cheers
    Trev


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