Gear noise from interrupted cuts on FP2NC
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    Default Gear noise from interrupted cuts on FP2NC

    I sometimes get a lot of noise from the vertical head or the gear train when I am using a face mill with a small number of teeth (3) and the cut is interrupted. It sounds like gear slap to me, and I can’t help but think it is not a good thing. Is there anywhere in the gear train where there is an adjustment for gear lash?

    There is no sound from the gears when the cutting is mostly continuous, enough that two teeth are always engaged.

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    There’s no way to adjust the backlash short of putting in new gears. All of the shaft center distances are fixed except the bevel gears in the head, but messing with that adjustment won’t fix your noise problem, and stands a good chance of messing up that gear mesh.

    I doubt you are harming anything with the slap. You could mitigate the problem by using a smaller cutter relative to the width of cut. Rather than, say, running a face mill centered on a narrow strip feature, climb cut with the teeth barely reaching out past the edge of the part. If facing something wide, take cuts at least 75% as wide as the cutter. In other words bury as many teeth as possible in the cut. Run the spindle as fast as the cutter and material will allow, while feeding fast. That will give the cutter less time to oscillate and slap.


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    The cut I was making was an iron casting with 2” webs. 3” face mill with 3 cutters. .050” cut and a feed of around 20-40. Not sure what the feed units are, the Deckel manuals aren’t clear whether or not feed settings remain metric when in inch mode. The iron was quite tough; the chips were continuous not powder, so cast steel might be a better description. I did try faster feeds, 80-125, but the clatter got louder.

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    On their manual machines they have a device that puts some adjustable drag on the spindle
    Perhaps you could imitate that

    Peter

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    Quote Originally Posted by Peter from Holland View Post
    On their manual machines they have a device that puts some adjustable drag on the spindle
    Perhaps you could imitate that.
    Just to elaborate on what Peter wrote...

    My 1964 FP2 manual mill has a knurled steel ring at the top of the vertical head, exactly for this purpose. The ring is threaded, and when you tighten it in the downwards direction, it pushes on three steel pins, which in turn push a circular bronze "brake shoe" downwards into contact with a steel track on the top of the bevel gear. (The teeth of the bevel gear are on the bottom). I have used this from time to time when making interrupted cuts with a large face mill, and it does reduce the chatter/vibration quite a bit.

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    Could also too much spindle speed. I once milled improvised straight edge from tough rectangular cast iron (maybe even ductile iron) bar on my FP4NC, speed something in 500-600rpm range, DIY carbide flycutter, something 80-100mm diameter. That thing made very evil noises.

    Sharpened the endmill, reduced speed to 200rpm and everything was running smoothly. I think it was because the cutting edge was burning up and because of hardening of cast iron, as the dull cutting edge was rubbing.

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    To see if drag on the spindle would help to reduse chatter you can nip the top of the spindle between 2 pieces of wood
    A groove in each piece of wood will keep it positioned
    Peter

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    Feed units are in/min in Inch mode and mm/min in Metric mode. Dial graduations are mm/min. Make sure the feed override is at 100%, of course. What RPM were you using?

    It pays to work out the RPM and feed rate math systematically. I would start with 0.003" per tooth at 200 ft/min (cutting speed,, not feed rate) if it's a carbide cutter. If you really had 40 in/min feed rate, that sounds rather fast, but depends on the RPM. What was the feed per tooth under those circumstances.

    A 3-tooth 3" cutter sounds "iffy." What is it? I think mine has 8 teeth, and I have a 2.5" one with 6 teeth.

    Quote Originally Posted by rimcanyon View Post
    The cut I was making was an iron casting with 2” webs. 3” face mill with 3 cutters. .050” cut and a feed of around 20-40. Not sure what the feed units are, the Deckel manuals aren’t clear whether or not feed settings remain metric when in inch mode. The iron was quite tough; the chips were continuous not powder, so cast steel might be a better description. I did try faster feeds, 80-125, but the clatter got louder.

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    Quote Originally Posted by rklopp View Post
    Feed units are in/min in Inch mode and mm/min in Metric mode. Dial graduations are mm/min. Make sure the feed override is at 100%, of course. What RPM were you using?

    It pays to work out the RPM and feed rate math systematically. I would start with 0.003" per tooth at 200 ft/min (cutting speed,, not feed rate) if it's a carbide cutter. If you really had 40 in/min feed rate, that sounds rather fast, but depends on the RPM. What was the feed per tooth under those circumstances.

    A 3-tooth 3" cutter sounds "iffy." What is it? I think mine has 8 teeth, and I have a 2.5" one with 6 teeth.
    I was using mode 7, so the feed dial was in play. It was set to 80 and I varied the % dial between 20 and 80 (or more if the cut was light). So in mode 7, feed is in mm/min? RPM was 200. The face mill was a Valenite Econo-Mizer, MCN90-306 5R3-125F. Photo below.

    img_1028.jpg

    I have a couple more face mills, photos below. The large one (Stellram) I have never used, it weighs at least 10 lbs. and I have worried about whether that would cause spindle problems. The 4" Kennametal says 4100RPM max, but I have only ever used it at 200 RPM. It needs to be disassembled, cleaned and the cutter seats examined, because one tooth does all the cutting.

    img_1030.jpg

    img_1031.jpg

    img_1032.jpg

    img_1035.jpg

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    Adding a flywheel to the spindle used to be a trick used on horizontals to stop gear clash on interrupted cuts, I'd think a 10 lb cutter would have some of the same effect, certainly wouldn't cause more load than the cutting does. I run a 10" face mill on mine that weighs 43 lbs with the holder with no problems, but it is a little larger machine. More inserts, positive rake inserts, and/or a lead angle on the tool would all go far in reducing the protest from the machine. Those negative CNMG inserts just look like old school hammering. That stellram tool is a step or two in the right direction.

    For an example, I have a 6 insert 2" iscar face mill with 6 square positive inserts that is my favorite to run in Bridgeport size machine, a cutter with 3 TPG inserts that I bought 30 years ago in the same machine makes life miserable.

    For an experiment, try the Stellram tool running it with only 3 inserts and see how it behaves, I do that frequently for jobs that don't need maximum feed rates for economy.

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    The Varnamo universal mill I just picked up came with a flywheel about 15lbs that bolts to the top of the right angle vertical head for dealing with this type of thing.
    Attached Thumbnails Attached Thumbnails flywheel2.jpg   flywheel.jpg  

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    Mud is on it...more positive, less radius....Run it hard enough to keep the inserts working....90* side angle is not helping either....
    Don't think the heavier face mill poses any issues as to spindle bearings....If the balance is good it should be fine....

    Flywheels and friction devices were made to accommodate slower cutting speeds using high speed tooling...Coated carbide is different, speeds high enough that the frequency
    of the inserts entering the cut is high enough that the "pounding "is held to an acceptable level....More teeth will help providing the setup is rigid....fewer teeth used when part is springy or thin....
    Less chatter for those setups...otherwise more teeth work better.
    Cheers Ross

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    OK, thanks Mud and the others who made suggestions. I will give the Stellram a try. Maybe its time to invest in some new tooling and get rid of the old face mills.

    When using a face mill on a surface that is smaller than the face mill, should the cut be centered on the face mill or on the side?

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    I like offset as far as practical. When centered the teeth are smacking into the side of the part almost at right angles. More grazing tooth entry works better.


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    Quote Originally Posted by rklopp View Post
    More grazing tooth entry works better.
    I have a question about this which was surely answered in "Machining 101", but I never took that class. I know that there are people here who have not just taken that class, but actually taught it, so I was wondering if one of them could set me straight.

    My question is not about the gear train of the machine, but instead the effects of an interrupted cut on carbide cutters.

    Think about two different ways of doing a cut, where the tool is wider than the cut. In the first way, the cutting edges have a grazing entry and an abrupt exit. In the second way, the cutting edges have an abrupt entry and a grazing exit.

    In the first way, when the tooth enters the material, the chip is thin, so there is no shock on the tooth upon entry. The force or pressure build as the tooth moves through the material. Finally, when the tooth exits, the chip is thickest and so there is a sudden jump (downwards) in pressure on the tooth, as it exits.

    In the second way, when the tooth enters the material, the chip is thick, so there is sudden shock as the force or pressure leap up. The force or pressure then decrease as the tooth moves through the material, because the chip is getting thinner. Finally, when the tooth exits, the chip is thinnest and the pressure on the tooth, just before it exits, is almost zero. So when the tooth does exit, there is no sudden downwards jump in pressure on the tooth.

    In the first way, the shock on the tooth happens in tension, a large compressive force is suddenly released. In the second way, the shock on the tooth happens in compression, a large compressive force is suddenly applied. Now I always thought that carbide was a material like concrete: strong in compression, but weak in tension. If that's true, wouldn't the second approach preserve the cutting edges better than the first?

    Cheers,
    Bruce

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    Think about how a typical carbide end mill handles a climb profile cut along the edge of a part, when the width of cut is less than 25% of the cutter diameter. The carbide survives just fine. I like to set up my facing cuts the same way. The teeth come in at full thickness, but not at 90 degrees to the part surface. They exit gently. However, on a narrow part cutting full-width, I don't think it matters too much whether you offset left or right, just include an offset. The worst situation is having the teeth smack the side surface of the part at close to 90 degrees and max chip thickness, which is what happens if the face mill is centered on a narrow part. Some CAM programs feature face-mill lead-ins that "roll" the mill around the starting corner and into the cut, giving the gentlest entry possible.

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    Quote Originally Posted by ballen View Post
    I have a question about this which was surely answered in "Machining 101", but I never took that class. I know that there are people here who have not just taken that class, but actually taught it, so I was wondering if one of them could set me straight.

    Cheers,
    Bruce
    Bruce:
    Invest in this book....very good on application of cutting tools, has nice illustrations .....Very concise.

    https://www.amazon.com/Metalcutting-.../dp/B000RY5DNI

    Cheers Ross

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    Hi Ross, Thank you, but I could not find that in Europe. I did find this, a 391 page "Training handbook - metal cutting technology" from Sandvik Coromat. Is it an updated version? I'm not sure, since 391 pages might not qualify as "concise". Cheers, Bruce

    https://tibp.blob.core.windows.net/c...DC-2920-40.pdf

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    Bruce:
    Believe that text is the result of a program that Sanvik had to "certify" machinists......
    Think at one time they had an online course and that was the text.

    The book i reference is a bit different if i can judge by looking at the link you posted....The handbook seems a bit more basic...
    Can't say about the number of pages....the Tech Guide is broken up into sections and each section has its own page numbers....so to know one would have to add up all the final numbers of all the sections...
    and frankly i am too lazy ...I can tell you that it calipers at 1.090" thick without the hard covers, pages are roughly .003" thick...so maybe 360+ pages...
    Tech Guide seems to have more specific product info in it (sales tool). Not an issue for me as i like and use use their tooling .

    That handbook you linked looks to be a good start. Some info there on face milling and approach techniques.
    Cheers Ross

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    Hi all,
    I try to face mill with the horizontal spindle. It eliminates the vertical spindle gears.
    45 degree lead in on your cutter is better than square.shoulder.
    Dave

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