I have a Venture VMC (Fanuc Oi-MC control) that is leaving a bad finish when running in CNC mode. When running the machine at 10K Rpms in a program the machine leaves a bad edge mill finish. It is worse in Y than in X. The bigger the tool the worse the problem looks. If I slow down the spindle to 7K the finish gets better. If i go into manual mode and spin the spindle 10K and feed at 40 ipm the finish is much better than in a program. Here is some background on my machine. Venture was sold thru Emco Group in America for about two years and they quit selling and supporting them. I purchased the machine new 7 years ago. The machine cut beautiful at any speed. The only problem with the machine was it rounded corners off when running a program at 40 ipm. The tech that installed the machine adjusted some parameters and the problem went away. The machine cut great for 3 years and all of a sudden the problem came up overnight. The machine is made by Finetech model SMV-1060-H3L. The machine is a linear guide machine so I looked at the trucks, screws, nuts and the bearings for the pretensioned screw and all check out great. No noise or loss of motion. I then thought it might be my spindle. I have ran the machine around 4000 hours since the problem came up and the spindle went out so I thought great I can solve my surface finish problem with the spindle replacement. No, with the new spindle installed and a Conitech silent sync belt system now in place the surface finish is no better or worse than when it first showed up. I now am starting to think that the control is the problem. I have no idea what to do to get this machine fixed. Anyone have any advise?
The best way I can describe the finish is if you were to climb at a extreme feed rate on a loose old mill. example: 4000 rpms at 200 ipm. That is what it looks like. I usually run 10K at 40ipm for finish passes and that is where I am experiencing a bad finish. If I slow down the feed and keep the RPMs high the finish almost doesn't change. If I slow down to 20 ipm it still looks horrible. I do agree that it does not sound like the control but I have exhausted all of the mechanical components of the machine. The fact that it has not got worse or better over 4000 hours of operation is also baffling to me.
I do NOT have balanced tools. I have experienced the problem with rigid, ER and hydraulic (Big Kaiser) tool holders. I purchased the hydraulic holders thinking it was a balancing issue. When I measure the tool in the holders right up against the tool holder I next to nothing on my tenth indicator. When my spindle was rebuilt the builder (PDS) said that the tool taper was in excellent condition. When the spindle was rebuilt they also checked and replaced any items needed in the clamping assembly. I really want to say this is the spindle but it has been rebuilt and the finish is the same before and after the rebuild. I even changed the type of belt that drives the spindle.
Please describe the 'bad finish'.
Does it look like a thread? What is the pitch? Does the pitch change with feed and/or speed? What's the depth of the roughness? Can you post pictures of the finish?
The finish feels like a 125 turning finish. If I slow down the spindle from 10K to 7K and leave the feed at 40 ipm it gets better. If I leave the spindle at 10K and slow the feed the finish does not improve. I will check the feet on Tuesday. I have a job running thru the weekend and I just can't stop the job until it is done. I will update on the feet as soon as I check them.
i am still sustaining my point is the spindle that gets vibration over 6000 rpm.
it seems hilarious but sometimes i do a simple test with an aplication on android called Vibormeter that is showing you vibration amplitude if you stick it to the spindle head.
it is a simple test that can show you if you run the spindle from 5000 to 10000 with 1000 step if the vibrations gets bigger values even the machine is not moving on axes.
as you said with the same feedrate and the spindle with 5000 is gets better it seems has nothing to do with the movement of the axes.
as i saw your picture you milled a circle,how about a square, to see the diference between the X and Y surface,maybe there is a problem in one of the axes ballscrew or end bearings and you can see it when you do a milling square.
I finally got some time to check some things out on the machine. I checked the tram and level. I did have some feet just barely touching the ground. I got it all back even, for sure something I needed to do but, It did not make any difference in the edge mill finish. I also got a vibration analysis app for my phone and I got some data from it. This is the RMS vibration values. To be honest, I am not sure what this data means except the Y value seems to have a somewhat consistent rise. I pressed the top for the phone up the the spindle so Y should represent spindle vibration in the Y axis if the machine. I did this check on one of my other machines and the values are also below. By looking at the data I would think the Fadal would cut worse but it cuts great so I guess I am still looking for the problem.
If someone can give some good advise on how to check the ball screws and linear guides I would appreciate it. I have check for visual indications for problems. Listened for noise with a stethoscope and looked for backlash but I am by no means an expert in ball screws and linear guides.
I have done some other test and I think I could have found the problem!!! I put a magnabase on the outside of the spindle housing. I then put a tenth indicator on the spindle ( the moving part not the tool ) with a tool clamped. If i push back on the tool ( pushing by hand hard ) and get a reading after releasing pressure then pull and get a reading after releasing pressure I get .0002 difference. I get a total of .0003 difference while applying pressure. I am no expert but that sounds bad to me. I would assume no movement would be measured. I can find no movement in my other mill spindles. On a previous post I measured the run out of the tool, I did not look for movement ( slack ) in the spindle. Any thoughts? This is on a spindle that was rebuilt only 300 hours ago by a spindle rebuilder not by me or some guy saying he can rebuild it correctly.
i told you,if you can give me a mechanical drawing of the spindle i can make a document with step by step procedure how to change bearings ,i have done over 100 spindles by now and none of it failed and i did spindles from 60mm shaft diameter to 300mm sfaft ,all kinds of bearings configuration,even with spindle going on gearbox.
I take it by your response that NO movement of the spindle nose should be measurable by pushing and pulling on the tool holder. This is measuring the spindle shaft not the tool holder. That is what I am thinking. I have attached pics of where I was measuring from. I did not rotate the spindle during this measurement.
do you know what type of bearing you have on?
is first bearing an NN type with rollers?
you checked the radial movement,can you put the clock under the nose and try to push up to see if you have axial movement too?
I do not know the part numbers for the bearings but I do know some about the bearings. The lower bearings are angular contact bearings that are rated at 18,000 RPMs. The bearings are sealed bearings as well. The spindle does have a chiller on it as well. As for your question about axial movement, the rebuilder asked for that same information this morning. With the tool removed, when i clamp and unclamp the tool I get a total of .004" for movement.
that move should not be there so my final decision is that the angular bearings are not tighten corectly or the whole set of bearings are not close in the housing and that is why vibration is present.
Thanks for the responding. After seeing your response I have got in touch with the people that rebuilt the spindle and they are now taking the problem seriously. I have sent them all the pictures and even a video of me moving the spindle in the radial movement. I am feeling confident that they will fix the problem.
Now that we have established that my spindle is loose. Keeping in mind that the spindle is belt driven. Would the machine leave a different finish when edge milling in X and Y axis due to the belt pulling on the loose spindle? That sounds possible to me. I will be sending the spindle back on Monday to the rebuilder. They are covering cost so I can't complain.
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Fanuc mill control making bad finish
The finish feels like a 125 turning finish. If I slow down the spindle from 10K to 7K and leave the feed at 40 ipm it gets better. If I leave the spindle at 10K and slow the feed the finish does not improve. I will check the feet on Tuesday. I have a job running thru the weekend and I just can't stop the job until it is done. I will update on the feet as soon as I check them.
