Bridgeport 1000 vmc retrofit with y axis surface finish issues

Some radial movement in the ball screw is OK. The axial movement is what you are most interested in. Based on your measurements it looks like the ball screw/nut is not too bad. In a perfect world, the axial play in the ball screw would be 0 under any normal operating condition. The ball nut should be preloaded for 0 axial play.

The real measurement needs to be taken with the machine assembled and look at the table movement with the ball screws locked. Not locked with the servos, but rather mechanically locked with a clamp of some kind to prevent any rotation. Then it's just a matter of tracking down where any movement is coming from. Could be the ball nut, or thrust bearings.

[QUOTE=Jim Dawson;2405036]Some radial movement in the ball screw is OK. The axial movement is what you are most interested in. Based on your measurements it looks like the ball screw/nut is not too bad. In a perfect world, the axial play in the ball screw would be 0 under any normal operating condition. The ball nut should be preloaded for 0 axial play.


The real measurement needs to be taken with the machine assembled and look at the table movement with the ball screws locked. Not locked with the servos, but rather mechanically locked with a clamp of some kind to prevent any rotation. Then it's just a matter of tracking down where any movement is coming from. Could be the ball nut, or thrust bearings.[/QUOTE]


I'm in the process of taking the saddle off now and cleaning all the oil lines and the liners. Ive got the saddle off and there was some junk in the oil grooves that were machined into the liner. The ballscrew and nut are tight. There is no noticeable play when I move it by hand. I will check with an indicator later on today. Im beginning to think that this whole issue may be slip stick since I definitely have some oiling issues going on both the table and saddle.

Well after 2 long days working on the cnc cleaning all the oil passages and oilers did not fix the problem. I DEFINITELY had an oiling issue. Several of the lines under the table were blocked and a few of the oilers were not pumping oil. Now with everything cleaned this machine drips oil everywhere. Ive verified that the oil is getting everywhere is should be once everything was put back together by removing all the oil galley plugs in the table and saddle. When everything was taken apart putting the indicator on the ball nut or end of the ball screw really didn't show any deflection. If I just slightly put any force down on the ball screw I could easily have .0005 of play on the ball nut just from the flexing of the ball screw.

I ran the machine for about 2 mins after I got everything put back together and ran the same test cuts and the surface finish was still not the best on the y axis. I was kinda frustrated so I stopped for the day. I sure thought that was the issue.

So setting the gibs. Should I have about .0005" play back and forth on the table and saddle? I put a 2x4 in the vice and used it for leverage to set it. Is that what I need to do? I need to go back and retune the x axis servo too. Its tuned to tight because it whines just a little. I messed with the tuning before I took everything apart and haven't changed it back. Now that the oiling is working right I will see what kind of axial play I can get from the ball nut and end bearings. How much force do I need to put on the saddle and table to check for axial play? I've been using a 2ft pry bar. Could my y axis servo be to small and not holding the position during the y axis cut?

[QUOTE=Raceman17;2405274]Well after 2 long days working on the cnc cleaning all the oil passages and oilers did not fix the problem. I DEFINITELY had an oiling issue. Several of the lines under the table were blocked and a few of the oilers were not pumping oil. Now with everything cleaned this machine drips oil everywhere. Ive verified that the oil is getting everywhere is should be once everything was put back together by removing all the oil galley plugs in the table and saddle. When everything was taken apart putting the indicator on the ball nut or end of the ball screw really didn't show any deflection. If I just slightly put any force down on the ball screw I could easily have .0005 of play on the ball nut just from the flexing of the ball screw.

I ran the machine for about 2 mins after I got everything put back together and ran the same test cuts and the surface finish was still not the best on the y axis. I was kinda frustrated so I stopped for the day. I sure thought that was the issue.

So setting the gibs. Should I have about .0005" play back and forth on the table and saddle? I put a 2x4 in the vice and used it for leverage to set it. Is that what I need to do? I need to go back and retune the x axis servo too. Its tuned to tight because it whines just a little. I messed with the tuning before I took everything apart and haven't changed it back. Now that the oiling is working right I will see what kind of axial play I can get from the ball nut and end bearings. How much force do I need to put on the saddle and table to check for axial play? I've been using a 2ft pry bar. Could my y axis servo be to small and not holding the position during the y axis cut?[/QUOTE]

Your servos are plenty big enough and have much more to offer than where you have them set up, the main Gain and the other parameters need to be changed as well, start at 60 for the main gain and work from that as being the main starting point

2.x4 is the best way to check the gib setting .0005 is correct pry bars are not something you need to use to check backlash, it is easy to do under power moving the axis back and forward

Now that you have the oil flow working what damage has been done from no oil on the ways and how many years did it run with no oil, this is common on machines like this factories just run them to death with little to no maintenance

I dont think the machine was run hard like that. It just came from a local machine shop. It sat at two different machine shops not being used because they could not figure the electronics out. Im gonna guess it easily sat for 5 plus years. Ive ran it probably for 20 hrs on a limited out supply. My gain settings are more around 30. I will go and tune then around 60 and see what happens. Both speed and main gains are around 30 with integration at 5.

So I went back and just did a stand backlash test using the controller to move the table with an indicator up against the table and the mag base sitting on the ways.. x looked to be at around .0017 or so and y was at .0045 or so. After the backlash test I went and tried to see where the backlash on y was coming from. I cannot get any movement on anything. I put the indicator mag base on the ball screw and the indicator on the table to check the nut. No movement when gently prying/forcing the table to move againt the nut. Maybe I need to crawl back behind the table and push the other way. Same thing for the ball screw itself. I locked the ball screw from moving and put the mag base on the base frame and the indicator on the end of the ball screw. I gently pried the saddle at the base of the machine and no movement. This was also in one direction only.

A couple weeks ago I took out the front y axis axial bearing to look at it. This is what I found. Is this normal?
[url]https://youtu.be/XZKydSaMKvE[/url]

[QUOTE=Raceman17;2405428]So I went back and just did a stand backlash test using the controller to move the table with an indicator up against the table and the mag base sitting on the ways.. x looked to be at around .0017 or so and y was at .0045 or so. After the backlash test I went and tried to see where the backlash on y was coming from. I cannot get any movement on anything. I put the indicator mag base on the ball screw and the indicator on the table to check the nut. No movement when gently prying/forcing the table to move againt the nut. Maybe I need to crawl back behind the table and push the other way. Same thing for the ball screw itself. I locked the ball screw from moving and put the mag base on the base frame and the indicator on the end of the ball screw. I gently pried the saddle at the base of the machine and no movement. This was also in one direction only.

A couple weeks ago I took out the front y axis axial bearing to look at it. This is what I found. Is this normal?
[url]https://youtu.be/XZKydSaMKvE[/url][/QUOTE]

Yes that is completely normal they are an AC Bearings, it must have some wear though, if it has .0045 of play with checking the Ballscrew movement

Mactec54...
I went and messed with the gain settings this afternoon. In general on both x and y the main and speed gains were both right around 30ish. Integration was at 5. Changing the speed and main gain higher than 33 both axis servos start to whine loudly. So I went and started with the main gain at 50-60ish and speed and integration gain were put back at 1. The servos would move without much noise. I went a redid the test cut and still the surface finish on y is choppy.. x axis is beautiful. What is the correct procedure for the servos to get them tuned? Is there a general starting point for tuning? What setting should I change first etc. Etc? I appreciate all the help from all who has contributed.

[QUOTE=Raceman17;2405466]Mactec54...
I went and messed with the gain settings this afternoon. In general on both x and y the main and speed gains were both right around 30ish. Integration was at 5. Changing the speed and main gain higher than 33 both axis servos start to whine loudly. So I went and started with the main gain at 50-60ish and speed and integration gain were put back at 1. The servos would move without much noise. I went a redid the test cut and still the surface finish on y is choppy.. x axis is beautiful. What is the correct procedure for the servos to get them tuned? Is there a general starting point for tuning? What setting should I change first etc. Etc? I appreciate all the help from all who has contributed.[/QUOTE]

It just depends on the load the servo motor has as I said before they won't change the surface finish, the servo can be set where you had them if the have enough holding

The Dmm servos have adapted control so they will adjust to suit as the load increases but the initial setup the motors want to be able to hold the axis without any movement when the other axis is moving under load ( cutting )

Ok. Thanks. I took out the front axial bearing on the y axis ball screw and putnut in a vise between two sockets to press the bearings together. I put an indicator on the bearing and check for axial movement. I had some. Maybe .0015" or so. I swapped that bearing with the end bearing on the x axis to see if I could get the surface finish to change axis. The x axis was affected slightly. Then I went back and ran the test program but with a finish cut of .01 at 10ipm and the finish of the parts is ok. Not great but ok. So I bit the bullet and bought a set of axial bearings. Im gonna change out the bearings on the y axis and see what happens. Its sad when the cost of TWO bearings were more than 2/3 of what I paid for this machine!

I just shimmed mine to tighten them up a bit.

I'm not sure my bearings can be shimmed. They are setup to be tightened from both directions with preload on them from two spanner wrenches

Its been a few... so an update. I put next axial bearings in the y axis ball screws. No change what so ever. A waste of 350$ but anyways. So I was talking to the previous owner about the machine. He bought it but never did anything with it. It sat at his shop. He suggested I check the z axis play in the head and to check if the gibs in the z axis are tight. I put the base of the indicator on the table and the gauge tip on the spindle. I can grab the top of the head and pivot it up around .001" I can put the head down. 0005" or so. So I'm thinking that the head is moving in the y axis back and forth as it cuts in the y axis and giving me the crappy finish on the axis. From where the two gib adjustment screws were on the top of the head I moved them down about .2" from where they were to tighten up the gibs. Moving them down didn't tighten them up much. I checked the taper and they are about .015" per inch of gib. I put a .004" shim behind the gib to try to see if that would help. Now the gibs are tighter but I still have aboit .001" total movement up and down. The gibs are tight and now the servo faults out on the z axis when it moves up. I haven't tested yet with a cut. Any suggestions on something I'm missing? I'm considering taking the z axis off the machine and checking the machines gib strip things (i can't think of the name they are called but they are the bluish green strips attached to the gibs and box way mating surface) i was also gonna see if the oil lines on the machine side are cleaned. I was able to clean the gib oil line and it was not oilijg correctly so I'd guess that the oil lines cast into the machine head are stopped up too. Am I checking the z axis gib movement correctly? I'm checking movement right at the spindle nose.

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