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  1. #41
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    I'm not following any of this logic. The tool is following a path that is instantaneously tangent to the intended workpiece interface point, and the vector relationship between the tool centerline and the cutting edges is fixed by diameter and RPM, not by the toolpath. If anything I would think the observations of less chatter when slowing the tool centerline velocity (IPM) down would be better explained by inertia and backlash?

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    The reduced shank tools work because there is no simultaneous contact on the upper flutes.
    Depth you can get away with depends on flute helix angle as this changes the way this works.
    Very simplified and not quite correct, too many cutting edges in contact and you get chatter.
    Bob

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    Quote Originally Posted by Rick Finsta View Post
    This is why my race car has a spool instead of a differential. No math! LOL
    So did mine. They did not do well in corners and even trying to push one on a slight turn to the trailer would result in the tires "winding up" and it would spring back at ya.
    A u-turn under power and the entire body would lift and twist lifting close to foot in a crazy fashion until one tire broke free and slipped.
    Most people don't have a spool and 14 inch wide slicks so they expect the car to turn.
    You can't road race with a spool. Go fast, go straight.
    Bob

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    Quote Originally Posted by davidsfg View Post
    Have used the Maritools reduced shank. It worked.
    +1

    Worked great for me.

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    Default Drill chuck picture

    What is this I am seeing? A long end mill located in a drill chuck, milling a slot in a piece chucked up in a drill chuck located in a v block located in a vise? Looks like a Rube Goldberg invention. Can't be serious.
    Attached Thumbnails Attached Thumbnails drillchuck.jpg  

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    What Am I looking at? How many no nos do I see. 1. End mill way too long. 2. End mill held in a drill chuck? 3. Part located in a drill chuck. 4. Part extended too far from V block.
    This has to be a joke.

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    Have you tried putting lint in the pockets? The only times I get chatter from my pockets is when there’s no lint in them.

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    Cam should automatically reduce feed in the corners based upon the tool diameter. Can you directly edit the G code, or does your machine not use G code notation? Basically you want to multiply your normal feed rate by ((part radius-tool radius)/part radius). This is because the feed rate of the tool is actually the feed rate of the center line of the tool. When milling an inside corner the cutting edge of the tool is traveling faster then the center line of the tool. On an outside corner, the cutting edge is traveling at a slower feed rate than the center line of the tool. This assumes your tool is not hogging material, i.e. a finish cut. Rule of thumb. The closer in size your cutting tools is to the size of an inside radius, the more you need to cut the feed rate. You can not let the tool dwell in the corner however. To reduce chatter, optimize rigidity of the tool (consider carbide tool, minimize of length of tool protruding from collet, maximize the tool diameter.) Also generally lower spindle rpms reduce chatter. And rigidity of clamping is important. There is nothing you can about rigidity of the machine tool assuming the ways and spindle bearings are not compromised.

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    Strictly speaking slowing down affects feed rate, which is apparent progress of the tool through the material, which does depend upon tool path. You can find suggested feed rates for various tool and material combinations in handbooks. Obviously you don't want to feed too fast which puts a strain on the tool and the machine and you don't want to feed to slow basically because it wears out the tool. When it comes to chatter experience also counts.

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    Yes too many edges can get chatter, on the other hand 2 flute tools are not as rigid as 4 flute tools because the core of the tool has a smaller effective diameter.

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    Quote Originally Posted by donwhit View Post
    What is this I am seeing? A long end mill located in a drill chuck, milling a slot in a piece chucked up in a drill chuck located in a v block located in a vise? Looks like a Rube Goldberg invention. Can't be serious.
    It wasn't serious.. That was from years ago, a thread kind of like this one, so I cobbled up the
    most horrendous cluster fuck I could, and labeled it "no chatter"... I did not take a cut, the part was
    already made, I didn't even turn on the spindle.

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  14. #52
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    Quote Originally Posted by litlerob1 View Post
    Now that Cosmo has his issue worked out. This is the second time I have seen this statement on this here forum, could you please explain to me how a Tool is "Feeding" faster at the periphery than at the center (or centre for people who don't know how to spell).

    The Feedrate doesn't change, it is programmed in IPM. I think I understand what you may think is true. But what you are implying is the diameter changes chip load.
    During a linear feed path, you could imagine a single flute of the tool coming around and taking a cut every .005", leaving a scallop mark every .005" on the wall. When that 1/2" diameter tool gets to a sharp corner, the scallop is .392" wide, because the tool gets one swipe at the corner. So how is that not a 7800% increase in effective feed rate? Small wonder the tool reacts to that impulse. So adding a small radius to the toolpath in the corner allows for a few more swipes at material removal, but obviously (to me) if you don't lower the feed rate for that arc, then you're still taking a pretty high chipload with only a turn or two of the tool presenting very few flutes along that substantial arc length. High chipload translates into increased effective feed rate.

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    Quote Originally Posted by HuFlungDung View Post
    During a linear feed path, you could imagine a single flute of the tool coming around and taking a cut every .005", leaving a scallop mark every .005" on the wall. When that 1/2" diameter tool gets to a sharp corner, the scallop is .392" wide, because the tool gets one swipe at the corner. So how is that not a 7800% increase in effective feed rate? Small wonder the tool reacts to that impulse. So adding a small radius to the toolpath in the corner allows for a few more swipes at material removal, but obviously (to me) if you don't lower the feed rate for that arc, then you're still taking a pretty high chipload with only a turn or two of the tool presenting very few flutes along that substantial arc length. High chipload translates into increased effective feed rate.
    I wasn't asking about "effective", I was asking about programmed IPM or actual or literal. But it's a thoroughly squashed topic as far as I'm concerned.

    But what is the guy up above trying to make sense of?

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    Quote Originally Posted by HuFlungDung View Post
    During a linear feed path, you could imagine a single flute of the tool coming around and taking a cut every .005", leaving a scallop mark every .005" on the wall. When that 1/2" diameter tool gets to a sharp corner, the scallop is .392" wide, because the tool gets one swipe at the corner. So how is that not a 7800% increase in effective feed rate? Small wonder the tool reacts to that impulse. So adding a small radius to the toolpath in the corner allows for a few more swipes at material removal, but obviously (to me) if you don't lower the feed rate for that arc, then you're still taking a pretty high chipload with only a turn or two of the tool presenting very few flutes along that substantial arc length. High chipload translates into increased effective feed rate.
    Yes the chip might be that long, but what is the thickness of the chip?

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    Quote Originally Posted by CosmosK View Post
    I've started a job shop in the last few months. I'm not a formally trained machinist, so I'm still learning a lot. Things are going pretty well, but I keep having issues in the corners of deep pockets. I'm getting swirl marks and the machine chatters in the corners.

    Today, it's a particularly tough one, so I'm hoping you all might have some advice. The pocket is about 2.5" deep. Corner rad is .3125. The tool I have to finish it is a 3 flute 1/2" carbide end mill with a 3" LOC. Tool holder is a hydraulic. I rough out all the material and leave .004". (6061 is the material)

    I thought to do multiple depths, so maybe 15mm deep passes. I plug this into HSM advisor and it says 10k rpm and 200 IPM. This seems crazy, so I knock it down to 4k RPM and 40 IPM. The results were awful, see picture.

    Most of the way through, I stop and reprogram taking this time 3mm deep passes. Maybe it helped, but I don't think it's going to get the part to pass.

    Can anyone help me on feed/speed for this? Should I really be going 10k RPM? [edit: machine is a 10kRPM Speedio] My instinct tells me to slow down. Thoughts?

    Attachment 219854

    Attachment 219855
    A sharp end mill is your enemy when feeding into a net corner radius. I have some fine grit rubber abrasive wheels and a trip up and down the end mill flutes will eliminate some of the attitude. As has been mentioned reducing the RPM will help to prevent chatter in a net radius. If you are using a hobby level machine then you most likely aren't going to eliminate the chatter.

    Ron

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    Default Please correct me if I'm wrong.....

    Unless you use a smaller cutter than the corner radius and adjust the feedrate,the length of the .010" depth of cut loading is minimal(small red area in Y),but if you just do an X-Y move to the corner,the cutter when it hits the turn,will have a nearly FULL 90 degrees of contact,plus the small amount the .010 adds applied to it,at the instant the turn is made(Large red area).Perhaps that can explain what you are trying to get across.Being it only looks like the chatter is in the corners,I'd drill .010-.015 under and leave the feed alone on 1 part just to see how it turns out.I might even try one of those 1-flute mills if you can get the right size.If this is not right,let me know what I am misunderstanding.Forgive my artwork,I used MS paint,and it's late for me.
    KGB
    Attached Thumbnails Attached Thumbnails mill-rad..jpg  
    Last edited by Bowtie41; 02-28-2018 at 10:50 PM. Reason: missing sentence

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  20. #57
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    I think the word missing is that the RELATIVE feed rate is different at the outer edges than the center of the cutter. Of course the actual feed rate in IPM of the center of the endmill does not change unless you change it. But look at what the rotation of the tool does to the cutting edge as it enters the material. On one side of the tool (depending on climb or conventional feed), the outer edge moves in the direction of the feed. The other side of the tool has the edge moving in the opposite direction of the feed. The side moving in the feed direction has a higher speed "relative to the material being cut". The opposite side has a slower speed relative to the material being cut. The center of the tool, which has zero rotational speed, has the exact programmed feedrate as its speed relative to the material being cut.

    I'm sure everyone is sick of this topic by now, but I think this explains the phenomenon as best as I can. I'm not quite Einstein.

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    Divorce the two variables and look at them individually - you have IPM and SFM and both are measured relative to the work surface.

    Stop the cutter's rotation and move it past the surface. Is the surface nearer the workpiece traveling faster relative to the workpiece than the cutting edge opposite the workpiece? No, there is no difference in velocity, even as the tool "turns a corner."

    Now, stop X/Y motion and rotate the tool. No matter what speed you rotate it, the edge nearer the work piece is traveling the exact same velocity as the edge furthest from the workpiece, which is fixed by RPM and distance from the axis of rotation (radius).

    So if you have no difference in linear velocity (IPM) and no difference in rotational velocity (SFM) then how can there be a net difference in velocity? I'm having trouble expressing this with the vector sums (IPM is easy, but SFM has me licked) to show the actual math.

    All that said, I don't think anyone here is trying to argue that the tool doesn't see more load moving into a corner, but to say that there has been an actual or effective velocity change seems to be completely wrong to me. What about a tool with a large number of flutes at high SFM and high IPM feed, where the chip can't physically get longer in the corner but there are more cutting surface engaged at any time?

    Either way I'm enjoying having to engage my brain like this.

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    I have an excel sheet that I use regularly for this type of thing.
    Can I attach for others to download and use?
    feed-rate-sheet.jpg

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    Quote Originally Posted by CosmosK View Post
    I've started a job shop in the last few months. I'm not a formally trained machinist, so I'm still learning a lot. Things are going pretty well, but I keep having issues in the corners of deep pockets. I'm getting swirl marks and the machine chatters in the corners.

    Today, it's a particularly tough one, so I'm hoping you all might have some advice. The pocket is about 2.5" deep. Corner rad is .3125. The tool I have to finish it is a 3 flute 1/2" carbide end mill with a 3" LOC. Tool holder is a hydraulic. I rough out all the material and leave .004". (6061 is the material)

    I thought to do multiple depths, so maybe 15mm deep passes. I plug this into HSM advisor and it says 10k rpm and 200 IPM. This seems crazy, so I knock it down to 4k RPM and 40 IPM. The results were awful, see picture.

    Most of the way through, I stop and reprogram taking this time 3mm deep passes. Maybe it helped, but I don't think it's going to get the part to pass.

    Can anyone help me on feed/speed for this? Should I really be going 10k RPM? [edit: machine is a 10kRPM Speedio] My instinct tells me to slow down. Thoughts?

    Attachment 219854

    Attachment 219855

    1sto not take advise from someone using a drill to hold an endmill....holding the part in another drill chuck too.
    2nd: The shank of the roughing endmill will not hurt anything while rubbing against an aluminum part, except possibly push the part in the vise or fixture.
    3rd: RPM is the biggest factor when chatter occurs, and your choice of a .500Ø endmill is fine, DON'T ever use the same radius tool as what is spec'd on the part, always interpolate the radius if possible.
    4th: Don't conventional mill a wall, pocket or anything else unless you have already finished the wall, or pocket. IF you have deflection that you are trying to remove. Lets say a 3" deep pocket that has some taper due to the end mill deflecting. After you have finished the pocket to size, and it is smaller at the bottom, you may run around the pocket to conventionally to get the wall straight.
    Be aware that you could cut a reverse taper into the wall by conventional cutting it, so maybe backing off a .001" or .002" in offset or program might be the safe way to attack it.....unless you got a boat load of parts and don't mind scrapping one?

    That said, you are leaving a small enough amount of stock that with the right feeds and speeds you wont have any issue's. You may want to drop down to maybe 500RPM, and .001"/.002"IPT, coming into the corner, so about 1.5-3.0IPM on the G3 code of the corner.....you could do it before, but it will slow down your cycle time.

    We advise the use a "high torque" retention knob, especially on the 40 taper machines, the 50 taper are stronger but still prone to the same issue.
    High-Torque Retention Knobs | JM Performance Products | American Machinist

    GOOD LUCK!!!!


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