Diagnosing a Milling Machine problem

Discussion on all milling machines vertical & horizontal, including but not limited to Bridgeports, Hardinge, South Bend, Clausing, Van Norman, including imports.

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John Hasler
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Re: Diagnosing a Milling Machine problem

Post by John Hasler » Sun Dec 09, 2018 9:07 pm

KellyJones wrote:
Sun Dec 09, 2018 7:19 pm
I also notice that this cutter in this particular collet seems to be out of round. In other words, when I spin the tool in the collet (not in the machine) I feel alternating tightness and looseness between the two.
That sounds pretty wrong. Check for that effect with that collet and a different cutter and with that cutter and a different collet.

I'd get rid of that nubbin of locating pin. It can only do harm if it is too short to perform its locating function but still sticks out.

I had trouble with tools sometimes sucking out of my MT3 collets until I took to carefully cleaning every tool shank and the inside of every collet every time and also lubricating the outsides of the collets with Neversieze.

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mcostello
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Re: Diagnosing a Milling Machine problem

Post by mcostello » Sun Dec 09, 2018 9:27 pm

Try another end mill if You have it, possibly a smaller size so as not to have to remove the part from the vise.

whateg0
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Re: Diagnosing a Milling Machine problem

Post by whateg0 » Mon Dec 10, 2018 10:01 am

I agree that it is wrong for the EM to feel tight in spots and loose in others as it is spun by hand in the collet. Another thing I didn't see mentioned is the sharpness of the EM. A dull EM will have increased tool pressure, which in my experience is worse when side milling like you are. That will spin the EM. I have a scar on my table from a 3/4" EM pulling out when side milling 1/4" mild steel after the EM became dull. That was in my early days and I thought I could get through "one more pass" and be done with the part before having the EM sharpened.

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Re: Diagnosing a Milling Machie problem

Post by jcfx » Tue Dec 11, 2018 8:24 pm

Richard_W wrote:
Sun Dec 09, 2018 7:05 pm

I don't think that this is the problem. If it did slip on the pin it would only grip tighter, unless the spindle is run in reverse. The pin is only designed to assist in the removal of the collet in the event the threads are tight and not meant to be a drive key. By either damaged threads or trash material in the threads. Most shops don't have the pin installed or haven't replace it when it was sheared off and have no problem.

My thought would be the no name collet being to soft to get a good grip on the end mill shank.

Richard W.
What you said could well be, I looked at my L20 lathe collets and they don't have a anti rotation groove
just a notch on the face of the collet that the collet cap which has a the anti rotation tab fits into.

KeyyJones, if you're feeling an out of roundness in the collet it could be a manufacturing defect or the collet
may have been dropped and ever so slightly bent one of the segments.

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ctwo
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Re: Diagnosing a Milling Machine problem

Post by ctwo » Wed Dec 12, 2018 11:26 am

KellyJones wrote:
Sun Dec 09, 2018 7:19 pm
Too soft? I’m still trying to figure that one out. Maybe. I can see if it was too hard it wouldn’t flex enough... There are witness marks in the collet and on the OD of the cutter, but not vertical. There is evidence the tool has spun a little, but not much. I also notice that this cutter in this particular collet seems to be out of round. In other words, when I spin the tool in the collet (not in the machine) I feel alternating tightness and looseness between the two. This different than all the other collets and cutters. Maybe one is out of round enough that it can’t grip?
That sounds like the cutter has a defect. I would try stoning it, especially around that dent.
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pete
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Re: Diagnosing a Milling Machine problem

Post by pete » Wed Dec 12, 2018 5:09 pm

I did a bit of thinking about this thread. Is this a new to you collet and/or endmill? In other words has this collet worked in the past on another endmill or tool shank without issues? That apparent internal lobbing while the tool shank is spun in the collet is for sure a definite indication something ain't right. If it were me I think I'd rule out the endmill shank first since it's the easiest to test and set it up between centers in the lathe then hand spin it to indicate the shank just to be sure it's correct. Then mike it for size. I strongly suspect it's a collet issue, but checking the endmills shank first narrows the problem. If the collet was ground oversize, tapered or it didn't fully clean up while grinding after the initial boring, reaming and heat treatment any of those issues would reduce the collets grip. No quality control program is ever perfect and even the best manufacturers have the odd mistake get out the door.

I'd also address that internal set screw nub as soon as possible. If it shears in use it can create numerous problems if things go really wrong up to locking the collet inside the spindle taper or scoring the inside of the spindle. They got that set screw in there so it has to come out. I know nothing about your mill, but generally there's an outer spindle cap that's threaded to the outside of the spindle that needs to be taken off first and the spindle lowered a bit to gain access to that set screw. Mark the cap and spindle first so you know how far to tighten it when reinstalling it. A lot of mills have that set screw installed to the correct depth then a second set screw is used to help lock it in that position. With the end of that set screw already being buggered up I'd screw it in until it just falls out instead of trying to back it out the way it went in. Grizzly should have a parts list of that area that will give you a better idea of how to gain access. Some parts diagrams aren't as accurate or detailed as they should be, so I still wouldn't count on it showing one or two set screws as being correct. I also wouldn't rule out them using loctite to retain that set screw either.

KellyJones
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Re: Diagnosing a Milling Machine problem

Post by KellyJones » Wed Dec 12, 2018 10:10 pm

I did check the end mill by setting it on a V-block and rotating it under a test indicator. No discernible out of roundness of the EM. I also checked it for size.

I am a relative newbie to the hobby, although i got my lathe nearly 20 years ago, and the milling machine nearly 15 years ago. Can't say for certain that this EM ever worked with this collet, but I do know this is not the first time i have had this problem. I'm just experienced enough to recognize that i need to track it down this time.

I'm pretty sure the collets were pretty cheap. I started to tear down the milling machine and ran into an issue that i'm not entirely sure how to proceed. I think what is will do is put it back together and order a new collet. It's not that expensive, and if it is the collet, is would save me the risk of tearing down the milling machine beyond my expertise to put it back together.

Thanks for the comments.
Kelly Jones, PE
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mcostello
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Re: Diagnosing a Milling Machine problem

Post by mcostello » Wed Dec 12, 2018 10:13 pm

Could You show a picture of how much the collet sticks out of the spindle?
Maybe the collet is bottoming out and the locating taper is worn out.

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Re: Diagnosing a Milling Machie problem

Post by Harold_V » Thu Dec 13, 2018 2:58 am

KellyJones wrote:
Sun Dec 09, 2018 3:18 pm
Took the setup down and cleaned an measured everything. No debris, tools are the size marked.
Found a small dent in the end mill. Looks like it came that way as it appears to have TiN coating in it. Found no burrs in the collet or spindle. Lubricated the draw bar and the threaded end of the collet. Put it all back together and after the first pass the collet walked about .030”.
Stopping for the day or until I figure this out.
In the third picture, I see something that's sending up a red flag for me.
It may be deceiving, but it appears that the end mill is making contact at the end of the primary relief. If that's the case, cutting pressure would increase considerably, and the resulting finish wouldn't be great. What helps me think that may be the problem is that there's a respectable burr being created, which is often the result of improper relief or a dull tool.

I'd suggest you remove the end mill from the machine and examine it closely, looking for evidence that it is making contact as I suggested. If it is, you likely found the problem. Worth a try.

H
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KellyJones
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Re: Diagnosing a Milling Machine problem

Post by KellyJones » Fri Dec 14, 2018 1:48 pm

Harold
You got me. I'm not sure what you mean be "making contact at the primary relief". (Newbie, remember? :D )

I think you mean that then entrance to the ID of the collet there should be a relief? and the EM is contacting there? OR are you referring to the relief on the flute of the EM? I can see where that would cause the issues you describe.

thanks
Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
George Bernard Shaw
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KellyJones
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Re: Diagnosing a Milling Machine problem

Post by KellyJones » Fri Dec 14, 2018 2:01 pm

After responding to Harold, I started thinking about this. I took some photos of the end mill. There is some evidence of contact behind the cutting surface (the relief?) and some evidence of chipping and cratering of the edge. Didn’t notice before because my eyes are not what they once were.
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Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
George Bernard Shaw
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John Hasler
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Re: Diagnosing a Milling Machine problem

Post by John Hasler » Fri Dec 14, 2018 5:02 pm

Looks like at least one flute is not cutting at all while at least one is worn all the way back to the secondary relief.

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