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  1. #1
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    Default Real Time Speeds and feeds

    I've now been using my updated Boss Series 1 Bridgeport mill for over 2 years. I've had time to play with all possible speeds and feeds over that time, in everything from 3003 aluminum to 17-4PH Stainless. By now you would think I could set the machine and let it roll until it is done...but I am not even close.

    I find the published speeds and feeds are not obtainable. I would assume they are for full flood coolant, which I decided was just too complicated on the Bridgeport to support...even though it came to me with it. I tried mist coolant, but got tired of it rusting all my parts and tools. I am using only forced air cooling.

    What happens, I have found, is if the speed and/or feed is even a slight bit too fast, then the tool gets thermal runaway...getting cherry red, gumming the work and breaking flutes if not the entire end mill. I often think I have the correct speed running and all looks good...only to have thermal runaway 10 minutes later for no obvious reason.

    Long winded explanation...my question is, has anyone come up with a "real world" rule of thumb for speeds and feeds when running air only?

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    Can we start with "published" where?
    I too love dry cutting.
    Full width slot so way different than simple milling.
    Gumming up the works is chip weld to tool surface. Turns out that there is range of speeds where this occurs in carbide tooling.
    Go slower works, go faster works,
    Opps maybe this a HSS cutting tool.
    Bob

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    If spray mist is rusting things, that means you are mixing the stuff with too much water or maybe the water (guessing you are using "city" water)has some sort of contamination.

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    Using mist systems I've had best luck with high volumes of high velocity air and no noticable liquid in the stream
    Parts come off the machine cold but not feeling wet.

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    Published speeds and feeds by a tool manufacturer are for the very best conditions, so hard to match in a real shop. Textbook it is good to start at 50% and work up.

    but I would say I can surface grind faster than most books would dare claim. Using open wheels and hog down feeding to near than a dress skim and tickle finish.

    I have ground some jobs that the part would turn cherry. yes, I know these can fill a part with stresses so only for certain work...Like duplicating a machine part where stress doesn't matter... or racing the mill guy for most parts.

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    Thanks for the replies.

    Still not quite sure what to do. If 50% from recommended is the target...would that mean dial both feed and speed down 50% each? Or, leave the speed and dial back the feed...or, conversely, dial back the speed and leave the feed? I would think there would be a rule of thumb.

    I have begun to realize there is a huge difference in heat generation between tool brands. A cheap tool will heat up when barely cutting, and if the feed is slowed, simply generates heat faster. A good tool cuts much faster before generating heat.

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    Quote Originally Posted by CJD View Post
    I would assume they are for full flood coolant, which I decided was just too complicated on the Bridgeport to support...even though it came to me with it. I tried mist coolant, but got tired of it rusting all my parts and tools. I am using only forced air cooling.

    What happens, I have found, is if the speed and/or feed is even a slight bit too fast, then the tool gets thermal runaway...getting cherry red, gumming the work and breaking flutes if not the entire end mill. I often think I have the correct speed running and all looks good...only to have thermal runaway 10 minutes later for no obvious reason.

    Long winded explanation...my question is, has anyone come up with a "real world" rule of thumb for speeds and feeds when running air only?
    I have used Kool Mist with one of their mist nozzles which requires compressed air. The solution mixed with water does provide rust prevention.
    Whatever is in that stuff works good. I don't use it anymore but I could. Don't like the mess. If I could sew up a few aprons to drape on the
    machine then maybe.

    I also have a question out in BP/Hardinge section about speed/feed. The book usually gives me a rpm number that is a lot more than I use
    when running everything by sound and feel.

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    How long is a string?

    Soooo different depending on tool and workpiece. I use feed & speed wizard app for my phone, and found it works pretty good. Would highly recommend it, even though you will need to adjust a bit for your application.

    But, regarding glowy mess. I had that problem when running SS 316 or 304. Played it safe after the N:th endmill and went to max 45m/min and using HSM toolpath with quite high feed and lower (8-10%) radial depth of cut. With stainless, dont rub it as that will workharden the material real quick. I used those numbers and run a whole batch of parts dry with one EM after ruining about 13 of them. Was my first time running SS and have learned a lot since then.

    Get a feed and speed calculator to get starting points. After that you will learn by sound and chip appearence how it should be. Thereafter you will start to put those f&s numbers into context and thereafter it will all start to make sense. Atleast thats the way it worked for me.

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    Thanks, I'll give the apps a try. I am also using the HSM software...I find it interesting you have dialed back the radial depth of cut. HSM is normally pretty aggressive radially. I'll give it a try dialing it down to 8%.

    I know what you guys mean by sound and feel. The trouble is sometimes I dial the speed way back, so there is more depth per flute, and all seems great. Then, later that causes problems and I find that winding the speed back up does better. Same material, just different areas. Maybe I am over compensating each direction. Then again, I notice that heat builds when cutting near the edges of a part, and dissipates better when cutting near the center.

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    Talked to my old man about the issue. He loaned me a 1930's era machinist's book. Just a skim so far, but I think it's going to answer my questions about dry, wet and mist cooling. Those guys were real machinists! They built the war machine with tool steel mills non of the modern gimmicks.

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    Quote Originally Posted by CJD View Post
    ......
    I know what you guys mean by sound and feel. The trouble is sometimes I dial the speed way back, so there is more depth per flute, and all seems great. Then, later that causes problems and I find that winding the speed back up does better. Same material, just different areas. Maybe I am over compensating each direction. Then again, I notice that heat builds when cutting near the edges of a part, and dissipates better when cutting near the center.
    How hard can it be?
    And why sometimes does it work better if you go faster, that seems so wrong.
    Bob

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    I figured out half my problem is cheap chinese end mills. I ordered some decent OSG mills and the problem with run-away meltdowns seems to have gone away. I'm working on getting rid of all my unmarked, no-name end mills.


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