Preparing to crash a Series I mill on purpose
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    Default Preparing to crash a Series I mill on purpose

    Hi,

    I'm pretty clueless when it comes to machining, and what experience I have is from machines that will not bog down. I've set up a small machine shop for maintenance and some RnD, but I don't use the machines enough to get a real feel for them.

    Thing is, I want to push the Bridge though it's paces to learn how it speaks when something is wrong, but as it stands every noise it makes sounds strange and critical to me. I can't afford to break it, but I can't keep on taking 0.01 DOC forever either. I consider the machine a lightweigh, but it probably can do more than I think it can.

    A bar of mild steel, 3/8 four flute and hog away with settings until something gives? But will it be the end mill, the collet or the machine?

    Any suggestions on a schedule to to push the machine reasonably safely? What to look and listen for? I can afford to snap a few end mills.

    Jon

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    As long as your locks are tight enough that the mill doesn't jump because of backlash what you speak of will not overpower anything. Even a 1/2" mill will not break a sweat. All assuming your collet is tight enough to keep the tool from pulling out some under heavy cuts. Extend the quill the least amount possible for the most stiffness.

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    A 3/8 endmill isn't tough enough to hurt anything in a Bridgeport, the EM will break first. Get a couple 3/4 or 1" endmills and go at it. Use HSS endmills and set the RPM for 50fpm and take wider and deeper and faster cuts until the machine protests. Once you have a feel for that, try a roughing endmill just to get a feel for how much easier it cuts.

    I once bent a 1-1/2: R8 shank endmill holder .015" TIR with a 1-3/4" endmill in it while notching a piece of tubing, by forgetting where I was and suddenly spinning the handwheel the wrong way, in a Wells Index 747. All it did was fold up the tubing and knock it out of the vise, nudge the head out of alignment and raise my heartrate. Machine still works perfectly 40 years later,

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    3/8? Dammit. I meant 3/4. I'm metric. Yes, 3/8 is a matchstick even for this one.

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    Quote Originally Posted by Mud View Post
    A 3/8 endmill isn't tough enough to hurt anything in a Bridgeport, the EM will break first. Get a couple 3/4 or 1" endmills and go at it. Use HSS endmills and set the RPM for 50fpm and take wider and deeper and faster cuts until the machine protests. Once you have a feel for that, try a roughing endmill just to get a feel for how much easier it cuts.
    This. Thanks.

    I was messing with it just now (2am) and it jumped on me (pulled the X-axis, other three axes were locked) using a 5/8 roughing end mill on a climb cut with a 1/4" DOC and 1/16th WOC. I'm not sure it should have. Had it at 750 rpm and 10"/min. A bit over 100 fpm in total.

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    Forgive my newbie questions. :lol:
    So, is the 50 fpm a good baseline for cutter head speed when using HSS? What about carbide? Is your 100 fpm just cutter head speed, or a combination of that and the linear travel?

    Jonan, are you going to leave the RPM and feed rate the same, and increase depth and width of cut until failure?

    Or, some other method?

    Please post your results.


    Thanks

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    I just did a calculation of the 5/8" bit - at 750 rpm, that is 122 fpm at the cutter head. Correct"

    So, that does NOT factor in the travel speed. How do you factor in the travel speed? Just directly add it in? At 10"/min, it is negligible, I suppose.

    And your 1/4" DOC is the vertical amount of material in the Z axis, and the 1/16" WOC, is the amount in the Y?

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    50 fpm is a good speed for HSS milling turning or drilling soft mild steel like 1020 or A36. Go slower (35 fpm) for tapping and form tools like countersinks. Slow it down for harder materials like SS or 4140. Try 300 for aluminum (6061-T6)
    Don't try to climb mill on a bridgeport, leave that for heavier mills with anti-backlash leadscrews or CNCs with ballscrews and servos. The exception to this is when you are within .005 or so of your finished surface, you can speed your FPM up by 25 to 50% and take a light climb cut to get a good finish(if the material responds to that). In this case the drag of the ways and weight of the table is enough that the .005 climb cut won't overcome the friction and drag the work into the cutter. Making lots of mistakes will show you when you can apply this technique so start making them.

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    Just a couple more clarifications on the great suggestions that you've received above.
    First, they assume you're using a new/very sharp endmill. A good thing to try is indeed to compare noise, vibration and resistance between a new endmill (sharp enough that, if you aren't careful how you handle it, will cut your skin) and a dull one.
    Second, be extra careful on how you secure your part: one common thing mills do when you crash them is to try ripping the part off the vise and throwing it at you (and, if it has enough mass, it will cut you open..
    You would be amazed how much even significantly more rigid machines than a Bridgeport flex during a crash.
    Especially at the beginning, set up the piece with extra blocking mostly in the directions where it could be taking off if grabbed by the cutter.

    Paolo

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    Quote Originally Posted by acrosteve View Post
    I just did a calculation of the 5/8" bit - at 750 rpm, that is 122 fpm at the cutter head. Correct"

    So, that does NOT factor in the travel speed. How do you factor in the travel speed? Just directly add it in? At 10"/min, it is negligible, I suppose.

    And your 1/4" DOC is the vertical amount of material in the Z axis, and the 1/16" WOC, is the amount in the Y?

    Please post your results.
    I calculated the travel speed from the chip load (pretty arbitrarily) at 0.003 in/tooth. Yes, yes, and yes (eventually).

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    Super helpful info everyone. I have bucket loads of variously dull endmills from the foreclosure I got most of this stuff. Didn't find a single unused four flute. I'll go get a few new ones from my indurstrial supplier next week and begin my stress(ful) testing.

    So, lets say I get a good quality stubby 5/8 HSS roughing mill and go at it with a chunk of mild steel at 50fpm, everything locked down proper and just upping the hog. What should I expect to be on the limit for the machine feed, depth, width wise? This is all dry. I can run flood cutting, but it's messy.

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    Quote Originally Posted by Jonan View Post

    This is all dry. I can run flood cutting, but it's messy.
    Machining is messy. Use the coolant. Your HSS end mills will thank you.

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