Problem Head nod? Loose Z gibs?


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Thread: Head nod? Loose Z gibs?

  1. #1

    Default Head nod? Loose Z gibs?

    So I am pretty happy with adjustment /calibration when tramming. Twist in bed I adjusted using a couple layers of tinfoil. That being said. I have a shell mill that runs 6 carbide cutters (too much for my 440.) I faced a piece of A2 tool steel and I'm not thrilled whit what I see. I was taking .75 step overs and I couldn't get over a .002" DOC, it would shoot out red hot chips and bog down over that. I probably won't use this cutter again, but the finish is foretelling of something and that is the point here.
    On my surface plate with a test indicator, it really isn't as bad as it looks, but I am seeing slight scalloping. Picture pretty much sums it up. (maybe .0008" variance)
    Thoughts?Head nod? Loose Z gibs?-img_2964-jpg

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  2. #2
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    Default Re: Head nod? Loose Z gibs?

    Gotta love tin foil for shimming
    Not a Tormach but I had to use foil to tilt my column by 0.004 (0.1mm) to get my face offs flat.

    Not sure how yours is fitted on.
    I'd prob uncouple the Z stepper to see how loose the head is (I find it easier to get the gibs right).
    If it's not that easy to move, it's prob not the head.



  3. #3

    Default Re: Head nod? Loose Z gibs?

    Hmmmm.... I wonder if I uncouple the stepper, would the head just fall? Yes though, I believe to get a better feel on Z gibs, that maybe be necessary. I really don't know the best technique on a CN mill. No doubt I used that shell mill more as a very low abrasive sander than a cutter. MAYBE what I'm seeing is the material more pushed around causing that finish. I really don't know at this point.. The machine doesn't have the power for a large diameter cutter...well maybe a fly cutter, but again, I'm more concerned with what I THINK I'm seeing, but knowing my machine pretty well now (mechanically), it doesn't make sense.



  4. #4

    Default Re: Head nod? Loose Z gibs?

    I know on my 1100 i will see really bad edges if I'm pushing the tool hard. Even with a 1/4 or 3/8 endmil I've ended up with steps that will catch your finger nail with ease. First few times it happened I blamed the machine for being out of alignment but then I decided to try a light finish pass and that cleaned it up and left a nice smooth finish.



  5. #5

    Default Re: Head nod? Loose Z gibs?

    Yeah, I know that carbide shell mill is more than my little 440 can handle. The more I research, the more I see that. Though interesting side note, I was under the belief that carbide equals speed. I ran at 2000 rpm, seems more like it should be below 500rpm! Rubbed the hell outta that chunk of steel! Carbides seem fine but I’ll rotate them and maybe just use that on my Pm-727m I’ll move to a boring head and see if I have better luck. I’m glad to see no one else here seems to think it’s _____ machine issue.
    The piece is 4x5”, really didn’t want to drop down to .500” end mill, then again I was only going .750” step over so...



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    Default Re: Head nod? Loose Z gibs?

    carbide equals speed
    You can (and should) run carbide at fast SFM. The specific SFM depends on the material.
    However, when your spindle or mill isn't powerful/rigid enough, then the speed is hard to maintain.
    If you're getting rubbing, perhaps you're not feeding fast enough? Or not taking a deep enough cut?
    Those, too, of course need sufficient horsepower and rigidity, so again, makes it hard for our little mills to do.

    Personally, I use 3/8" as the upper size, and use a fly cutter when I need a wider swath and smoother finish.



  7. #7

    Default Re: Head nod? Loose Z gibs?

    There probably is multiple issues, can’t do a decent depth of cut, machine bogs too much. Do anything above .0015 and speed slow to much, actually will stall. Not sure what I was thinking with the 2” shell mill with 6 carbide inserts. I guess I like my machine so much I give it way too much credit. I learned! Gotta keep it realistic. Works great on aluminum....not so much on tool steel. : )



  8. #8

    Default Re: Head nod? Loose Z gibs?

    Maybe a silly question but can you run the tool mill with every other insert removed? That should cut your HP requirements in half.



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    Default Re: Head nod? Loose Z gibs?

    I use a 2.5 facemill with just 2 inserts, works fine.I bought one with an even number of inserts just for that reason.

    mike sr


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    Default Re: Head nod? Loose Z gibs?

    Likewise I use a 50mm and 63mm with two inserts and a 75mm with only one SEHT insert (out of 5).



  11. #11

    Default Re: Head nod? Loose Z gibs?

    Hmmmm.. that might be crazy enough to work. Like I said, on aluminum it worked great, A2...not so much. I'll have to give that a shot. I struggled for 45 minutes and managed to pull about .022' off that someb1tch! Before I jump to the boring bar, I'll try 2 inserts and see what happens. I know it wanted to throw a lot of sparks and I kept it just below that. I'll have to post some pic of the "chips" it cut, looked more like I was sanding. They are round inserts and have....I don't know, 8 cutting edges.RPMT (1204 MOE-JS / RPMT1204MOE-JS
    Grade VP15TF) For the lathe I swear by carbide, I really wanted to carry that over to the mill but have to be cognizant of the power/rigidity I'm working with.
    Great idea on the insert removal guys.



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    Default Re: Head nod? Loose Z gibs?

    Quote Originally Posted by soofle616 View Post
    Maybe a silly question but can you run the tool mill with every other insert removed? That should cut your HP requirements in half.
    It may change the HP requirement slightly I dont know?? I think the HP required will be about the same, fewer cutters but a larger load, more cutters, less load per cutter for a given rpm and feedrate.
    I do have to keep the rpm down to 2500 or so because the surface speed is too high and it will smear the surface on aluminum. I try to use it dry as it is really good at slinging oily chips all over!

    mike sr


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    Default Re: Head nod? Loose Z gibs?

    If you remove half the inserts, and then feed it at the same inch-per-tooth, you'll get half the feed speed, and thus half the HP requirements.
    If you've invested a lot in the tool and inserts, that might be something to try!



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    Default Re: Head nod? Loose Z gibs?

    Quote Originally Posted by popspipes View Post
    . I try to use it dry as it is really good at slinging oily chips all over!
    Kind of silly to force tool paths to control where swarf goes, but I try!
    Surface ops right to left, back to front, helps keep most swarf to one side for cleanup.



  15. #15

    Default Re: Head nod? Loose Z gibs?

    So interesting update. I ran it with only 2 inserts...only marginally better...not really enough to make it mentionable. HOWEVER, I ran it on my PM727m and it did well. I am back to wondering if there is some play in the Z gibs. Perhaps the cut is just forcing head up/back and every so often the carbide bites pulling it into the cut from play in head. I expected similar results with my manual mill, but it was nothing like it. I cannot get the DOC the carbide wants, if I do, the motor about stalls. I even wonder if the motor has some sort of issue. At points it would slow so much, I don't know how something didn't pop, then I slow feed and it continued along its merry way of rubbing the hell out of my part. SOMETHING isn't right, but right now I'm not sure where to start to problem solve. Motor (how) Z gibs...I'll have to research the manual.
    Nice blue curly chips from my PM727, black dust from 440.



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    Default Re: Head nod? Loose Z gibs?

    On my side of the hill (woodworking), the rule of thumb was the number of teeth engaged in the cut (actually removing material) dictates the power required. Fewer teeth engaged, less HP required to make the cut. Obviously, if you're cutting at the same feed rate as before, the surface quality my suffer.



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    Default Re: Head nod? Loose Z gibs?

    Quote Originally Posted by Tigster View Post
    So interesting update. I ran it with only 2 inserts...only marginally better...not really enough to make it mentionable. HOWEVER, I ran it on my PM727m and it did well. I am back to wondering if there is some play in the Z gibs. Perhaps the cut is just forcing head up/back and every so often the carbide bites pulling it into the cut from play in head. I expected similar results with my manual mill, but it was nothing like it. I cannot get the DOC the carbide wants, if I do, the motor about stalls. I even wonder if the motor has some sort of issue. At points it would slow so much, I don't know how something didn't pop, then I slow feed and it continued along its merry way of rubbing the hell out of my part. SOMETHING isn't right, but right now I'm not sure where to start to problem solve. Motor (how) Z gibs...I'll have to research the manual.
    Nice blue curly chips from my PM727, black dust from 440.
    If you want piece of mind as to wether the machine itself is off or not.
    Put a dial indicator in the spindle, center the table, spin the needle round the table, and check it.
    If Y+ , Y-, show different... Then something is off.



  18. #18

    Default Re: Head nod? Loose Z gibs?

    Yep, when I disassembled the X and Y a couple months back, checking for twist, I did tram it fully. Now I haven't torn into the Z yet, but if it was "loose" I'm not even sure how to check it.....lost motion test/adjustment? Manual didn't really cover it other than that, but it's something. It just seemed to easy to bog the motor to a near stop. It never truly stalled, but it had to drop to 100 to 200 rpm (from1800) I barely caught it. My PM727 isn't THAT much more capable. Something is a miss...I'll post when I get to the bottom.



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Head nod? Loose Z gibs?

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Head nod? Loose Z gibs?