G0704 Issues, First Setup

[DRock]

Hey everyone,

I am in the process of converting my G0704 with bdtools mounts and linearmotions2008 ballscrews and nuts. I was running the Z-Axis today with just the slide and no head yet in an attempt to verify a good range of motion. It was running good but started to bind when it reached near the top of its travel, I included a video...can anyone identify this sound?

I ended up popping off a coupling because the slide was bound up and the stepper was still driving the screw and it ended up loosening the chinese jamnut and the acetal disk popped out once the lead screw dropped.

I then loosened the Z-Axis mount from the column so that I could see where it "naturally" wanted to be when it was at the top of its travel and it wanted to tilt the mount forward which leads me to believe that the Z-Axis ballnut mount that bolts to the carriage is too tall and that I need to machine it down some.

I am including a picture of this problem and a video to hopefully identify the noise.

Does anyone have any experience with this issue and know how to fix it?

Thanks a bunch!

"http://www.youtube.com/watch?v=V2-37VnsPwg&feature=plcp"]Z-Axis Binding - YouTube

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[hoss2006]

That's the sound of a stepper missing steps because it can't move the axis any more.
Are you sure the ballnut mount isn't at it's highest point in the slot?
Looks pretty close to max stock travel.
Loosen the 2 screws securing the ballnut mount to the slide and see if it'll go higher.
Sure looks like your top plate is askew.
That could be skewing the ballscrew and mount.
Loosen the screws and readjust it.
Snug the 2 bolts with the z slide at the top to lessen the binding.
Doesn't the kit maker provide instructions?
Hoss

[DRock]

I was in the process of readjusting the assembly when I came across this problem, I was bringing the slide up to the top and that is when it was binding.

I just took these other two videos, it seems my screw is not centered correctly and I am not 100% sure if it was like this before the binding happened or if the binding caused this. The jamnut is preloaded decent against both bearings and the ballscrew does not slide around in there, the whole thing is solid, so how can it be running crooked?

http://www.youtube.com/watch?v=6WqEzxnc3hQ&feature=plcp]IMG 0594 - YouTube

http://www.youtube.com/watch?v=7Hs7AEhvm8A&feature=plcp]IMG 0596 - YouTube

Thanks again.

[hoss2006]

Yep, that's a problem.
Either the ballscrew end got bent or wasn't machined right.
If you take the screw out and roll it across a flat table you'll see where it's bent.
You may be able to bend it back somewhat close and live with a little wobble or have it replaced.
Chai may work out something if they mismachined it.
At slow speeds you should be ok with a little wobble but the faster you go the vibration will affect the machine.
Hoss

[DRock]

I would have to put my money on wasn't machined right, then maybe bent during shipping, I am going to take it back out I guess and see if the threaded portion is bent or if it is just the machined end...if it is the machined end I can have a local machinist touch it up for cheap hopefully.

Does anyone know the best way to assembly the Z-Axis in the mean time?

I feed the screw through the mount and then install the jamnut so that it becomes a single assembly. Then I put the ballnut mount in the column and then the assembly comes in through the ballnut mount and I screw it in place inside of the column while the ballscrew assembly is being held up by rope.

I have not found a way to get the ballscrew and ballnut mount into the column as a single assembly, is the method I have been using the fastest/easiest way or am I just not seeing something right in front of my eyes?

Thanks again.

[SuperFlyLoser]

Mine was also bent like that. I ended using a setup similar to this video to straighten it.
http://www.youtube.com/watch?v=dzIsR4Mg158]Rollco - Ball Screw machining - YouTube
I used my 4" V-Blocks and a pickle fork as the set up. On my indicator I used the largest point I could find. I think I was able to order it from MSC.

BTW mine came from Linearmotionbearings.

SFL

[DRock]

Chai sent me a link to a Roton page explaining all about straightness:

Screw Shaft Straightness

He said that I should attempt to straighten the screw out according to that page and I will use the video for reference...I will report back with the results.

Also, can anyone help me with the Z-Axis assembly and let me know if there is a faster way?

Right now I have to screw the ballnut mount onto the ballnut while they are both inside of the column and if I am going to be doing this a couple times I want to find the best way to do it.

Thanks a bunch!

[Fastest1]

Take the column off, lay it down and insert the screw thru the front slot and up thru the mount? There was no real easy way but if the column is laying down is does make it easier.

[DRock]

So I straightened the screws, turns out that wasn't my problem but I made them a little better. The screw spins straight when I chuck it up in the cordless drill, but when I install it in the Z-Axis mount it wobbles a bunch. I believe that the chamfer on the end of the screw is causing it to not seat flush against the bearing and that is where the wobble is coming from.

Has anyone run into this issue before? I am thinking that I can just get a small washer and use that between the screw and bearing so that when I tighten the jam nut it doesn't want to walk at all.

[Fastest1]

Chai's packaging does leave a bit to be desired. What do you mean about the chamfer of the screw? It should have a flat shoulder against the bearing.

[DRock]

It seems that my screws might have a slight chamfer which allows the screw to shift in the bearing and cause them to wobble. I do not know if this is the issue or not, but it is the first thing I am going to investigate.

The screw spins nice and straight on v-blocks but when I install it and tighten the jam nuts the screw wobbles all over the place which makes me think that it isn't sitting in the bearings correctly. Upon visual inspection I can't really see any other clear issues...going to mess around some more tomorrow.

[Fastest1]

If you have a lathe, you could recut the shoulder and eliminate any chamfer. Check those locknuts he provides too. I am suspicious of their quality and used standard nuts cut down to make lock nuts. I also used a small spacer to put the locknuts in a more accessible position even though I removed the tubes on the stepper mounts to tighten them. The couplers with the acetal disc will allow for quite a bit of misalignment. I am curious as to how much the end moves at the stepper mount when the ballscrew is mounted to the Z carriage.

[DRock]

I was messing around with this thing again and I put a washer in between the bearing and ball screw hoping that it might solve my issue if it wasn't seating flat on the AC bearing but the problem was still there.

So I took the mount off the screw and put it under the dial indicator, the thrust bearing was only out about .0005-.001 around the perimeter which I think is acceptable. However, the AC bearing was out .002-.0025 along the perimeter of the inner race and I think this may be the source of my problems. I am attaching a couple pictures to show my test process.

Does anyone know if that seems like the issue or am I chasing ghosts?

Thanks.

[Winnfield]

Are the AC bearings in your mount arranged so that they are back to back? There should be no space between the bearings.

[DRock]

I have one AC bearing, maybe about .75" of material then the thrust bearing.

[Winnfield]

Can you bore it out and put another AC bearing in there?

[DRock]

I could...I have to be certain that is the issue before I go that far though.

I am thinking maybe there is some chip or something under the AC bearing...I don't know.

It's frustrating to say the least.

[Winnfield]

You'd feel the bump in the bearing if there were something in it. The bore that the bearing is in being completely parallel with the other bearing is the issue, which is why AC bearings are designed to be mounted against one-another. They will allow for the misalignment of the shaft, insofar as they will support a load while misaligned. That is part of your problem - it is allowing the shaft to tilt with the inconsistencies of the bearing on the other side. If it is a needle-type bearing or a poorly ground ball thrust bearing, for example, or if the face it is sitting on is not perfectly perpendicular to the bore the bearing is in.

Did you try rolling the screw to see if the end of the screw (machined portion) is bent? Maybe chuck it in your lathe close to the end and see.

[Winnfield]

The problem is either your screw or the bearing block. You need to eliminate one of them as the issue before trying to address it.

[DRock]

I don't have a good way of checking to see if the screw is bent, I can throw it in the lathe at work but that will have to wait until Wednesday. I just got back in from the garage and I popped the AC bearing out and cleaned under it then pressed it back in and it varied only .0005"-.001" so I though I was OK but when I installed the screw and spun it with the drill the mount still wobbled in my hand.

At this point I think it is the screw...it doesn't seem to be the mounts because they are from bdtools on eBay and people seem to use his mounts all the time with great success. I think that maybe the QA slipped when they were checking over my screw and I believe the machined portion has a defect somewhere.

I am going to try to grab the ball nut flange in a vise and then spin it with the drill to see if the end wants to walk around...maybe that will tell me.

Thanks a lot for the help!