Yet another welding/machining/misalignment problem on Saturn 2. Sigh.

[micknm]

We have a Saturn 2, CNCRP P&P with NEMA 34 drives, Mach3. Just over a year in service. For the most part, we've been happy with it.

Until the past month or so it's been a hobbyist machine. An hour or two a week, rarely running for more than 30 minutes at a time. We recently did an extended 3D file (4 hours) and about halfway through, the Y axis A side R&P drive squawked and lost position, plunging through the material and ruining the project. We retoolpathed (Aspire) the file and ran it again with no problems. In the last two weeks or so we've been running a sign job, 20 pcs, 19" x 31" in signfoam. Zero stress on the machine. It's like cutting air. There's a woodgrain pattern that runs for maybe 30 minutes, followed by some letters. Rinse, repeat. It's done the same thing 5 - 6 times, losing position and ruining the piece.

We've cleaned, greased, Checked and double checked the file.

This afternoon I put a straightedge on the Y axis racks. Y left out about .021", dipping toward the frame over about 18". Y - A side out .034" over 36". It's binding in the same spot, but only when the machine is warm. With the motors disengaged, pushing the gantry back and forth, there's a very noticeable rumble and resistance on the A side, but generally not smooth at all. The Y - A side large belt sprocket that the pinion is attached to wobbles noticeably with the belt going from one side to the other at that spot. I suspect that the rack misalignment is twisting the pinion causing the belt to move from side to side. Again, racks and pinions have been cleaned and lubed.

Saturday we'll try shimming the rack to straighten it out. i'm thinking maybe thermal expansion due to extended run times is just enough to cause the issues.

The rail and rack mounting surfaces should be machined after welding and normalization. Period. It doesn't cost that much to have it done by someone with the right equipment. Most of the recent complaint posts I've seen here have been about similar issues.

Tomorrow I'll go up to school and finish the job on the freakin' ShopBots until we can resolve this issue.

Similar Threads:

• Build Thread- Saturn 2 4x4 w/ Nema34 closed-loop - In Canada
• Fanuc 18m pot problem
• Problem with Step2linear
• Wireless network problem

[difalkner]

Sure hate to hear that, Mick. It's good you've found the problem area, though. Are you going to get with Nate on this? Just curious, really... not that there's anything he can do at this point other than compensate you for loss of material and time.

Will you be posting photos of the repairs? It could be helpful for others.

David

[wmgeorge]

I hope your talking about the linear rails on top, not the gear rack like you said. Squawking sounds like you have been running a bearing dry or worse. You have been greasing the bearings, not just after they made noise?

[micknm]

No, it's the rack. You can watch the drive wheel twist as it passes a particular location on the Y axis. Bearing noise wouldn't occur at the same point every time.

[wmgeorge]

No, it's the rack. You can watch the drive wheel twist as it passes a particular location on the Y axis. Bearing noise wouldn't occur at the same point every time.

That's a new one. Rack screws are tight and nothing in the gears are you sure the bearing in the gear is not bad? Since the gear is spring loaded I do not see how it can bind.

[micknm]

That's a new one. Rack screws are tight and nothing in the gears are you sure the bearing in the gear is not bad? Since the gear is spring loaded I do not see how it can bind.

Picture yourself looking straight down on the rack on the right side of the machine. The front of the machine is to your left. Holding a Starrett straightedge on the face (the bolt hole side) of the rack itself, there's a crown about 18 inches from the left (front) end. With the straightedge firmly against the rack to your right, there's a .034" gap at the left end. That means the teeth of the rack are not perpendicular to the Y axis. When the pinion passes that spot it causes the pinion to twist in order to stay engaged in the rack. The drive pinion binds up and starts skipping in the rack - rat-a-tat-tat! It's consistently in the same 4 - 6" section. The rack and pinion are clean and well greased, as are the bearings. Well shim the racks this weekend, but for now we'll have to use the ShopBots to finish this job.

Had the frame been machined with datums for the rack (and rail) mounts this would not happen.

[wmgeorge]

There is a modification for the gear rack and I do not know the details but David had one of the early models like you did. I was not aware the Saturn 2 welded frame and gantry model was available a year ago? I ordered mine in June 2018 and it arrived in July. Mine has a 3/4 .(750) thick rack.

[micknm]

There is a modification for the gear rack and I do not know the details but David had one of the early models like you did. I was not aware the Saturn 2 welded frame and gantry model was available a year ago? I ordered mine in June 2018 and it arrived in July. Mine has a 3/4 .(750) thick rack.

Ours was ordered Oct of 2017, just prior to Nate switching to ¾” rack. We have the version with the spacer between the rack and frame. Not sure it would make any difference.

[wmgeorge]

Ours was ordered Oct of 2017, just prior to Nate switching to ¾” rack. We have the version with the spacer between the rack and frame. Not sure it would make any difference.

So your saying the 3 inch square tubing has a dip or rise in just one area or the rack is bent out? I have been on here a lot and never heard that issue before, maybe GME can comment. He had a Lot of issues with his machine and more than likely busy building his new one.

Have you checked that gear bearing and made sure its not bad? Some of those were made with bronze bushings and not ball bearings. But I think the Pro ones like I have were all ball bearing.

[micknm]

Yes, that is (one of) the issue(s)*. It's the tubing. The rack is securely bolted to the frame and is flexible enough to conform to the tubing, in our case, with FLA provided shim spacers to give the pinion clearance. My career was in industrial CNC machines - 25+ years in the field working with several different manufacturers. My mistake was in assuming that FLA would have followed the norms of the industry and machined a datum anywhere a rack or rail was mounted. The tolerances and repeatability he claims on his site would be "hard" to achieve without doing so in my opinion. Otherwise you're relying on the accuracy of the tubing, of the welds, the paint, etc. My fault for making that assumption.

After assembling the drives to the frame of our machine we had issues - wobble, belts not tracking right, etc. At the time there was a thread here by a user with similar issues and Nate offered to credit the user for the price of the R&P drives so he could replace them with CNCRP drives. We opted to do the same and the issues went away until we started using the machine more heavily.

* Tomorrow we'll measure the parallelism of the Y axis rails and racks. While the racks need shimming, it may not be the only or even the primary issue.

[GME]

I threw in the towel before I measured the racks. However, the frame wasn't square, so the the racks couldn't have been. That there were peaks and/or dips alone the length of the frame rail sides comes as no surprise to me. I'm betting you will find that the linear rails are not straight and/or out-of-parallel.

What surprises me is the discovery of the defects versus when you purchased the machine. Many of us have been operating under the assumption that Saturn 2s were built well in the earlier days of production, but quality slipped (read "slipped" to be "fell apart") in more recent days. Your experience suggests otherwise.

I have noted that some other owners have commented that their machines run fine, so they are satisfied. I believe most are hobbyists, but some use them in a small business. I cannot help but wonder whether most of these folks' machines are really okay, or whether they have defects as well. I wonder, because I haven't seen comments from others saying they took measurements, and what they found. I suspect that most, like you, assumed that the machines were built right, and as long as there wasn't something that was "stand out bad" happening, they pronounced everything good and kept moving on. For others, it could be that they just don't want to know. Had it not been for shims between the gantry and interface plates to tip me off, I wouldn't have been tipped off to look further. I thought my gantry seemed to take too much effort to move, but I didn't have a good point of reference. My predecessor machine was a FLA kit, and although I had a 3"X6" profile for my gantry, it was way lighter than the welded steel on the Saturn 2, and it was running on skate bearings, not profile linear rails. Often, we just don't know what we don't know. Anyway, once I started measuring, one thing led to another.

I look forward to learning what your further expedition into measuring discloses.

Gary

[micknm]

Thanks, Gary. I'll keep you posted, as I've been following your efforts, as well. What's surprising to me is that this machine is so close to being the one to beat for twice the price, but for just a few minor production issues.

Edit: I'm also surprised and perplexed as to why the problem hasn't popped up before. That's what made me suspect thermal expansion - longer run times = more heat. Aluminum and steel expand and contract at different rates.

[wmgeorge]

So are the dips and peaks in the 3 inch tubing or only where it was welded to the uprights?

Gary, how goes the build?

[micknm]

So are the dips and peaks in the 3 inch tubing or only where it was welded to the uprights?

Gary, how goes the build?

I'm heading that way to work on it this morning. I'll let you know. Not sure it makes a difference - a dip is a dip.

[Ntl]

Thanks, Gary. I'll keep you posted, as I've been following your efforts, as well. What's surprising to me is that this machine is so close to being the one to beat for twice the price, but for just a few minor production issues.

Edit: I'm also surprised and perplexed as to why the problem hasn't popped up before. That's what made me suspect thermal expansion - longer run times = more heat. Aluminum and steel expand and contract at different rates.

I'm not surprised considering the issues I've had with the build quality, I think a lot of the guys who have the machine don't use it enough to have problems. Now you have me worried about the rack and pinion on my machine since it's very noisy. I may have to add a piece of flat bar that is machined like the majority of steel routers have. It will also help with giving the rack and pinion better engagement, since even with the 3/4 inch gear rack it still isn't engaging enough. I just won't weld it on since it's already painted. Look at how shop Saber mounts their rack and liniar rails. It's because mill stock steel tube has a dip in the middle. What I would do is run some 3" flat bar get it level and parallel and mount the gear rack to it. Or just say F it and replace the rack and pinion with ballscrews. The ball screws would be the easiest since you only have to get it flat and level in 4 small areas, you will just lose some rapid speed.

I'm just going to run mine the way it is though until there is a problem.

Dan

[GME]

S
Gary, how goes the build?

Bill,

I haven't started it yet. I had some tooling and optical scales/DRO on order. All have arrived, and I'm in the process of working out installation of the scales. After that, I should start moving things along. I will start a new thread to document the build. Thanks for asking.

Gary

[wmgeorge]

Bill,

I haven't started it yet. I had some tooling and optical scales/DRO on order. All have arrived, and I'm in the process of working out installation of the scales. After that, I should start moving things along. I will start a new thread to document the build. Thanks for asking.

Gary

Hi Gary, Yes I have installed two sets of DRO on two separate machine and its a challenge. Good luck.

[wmgeorge]

So Micknm What did you find?

[micknm]

We haven't finished, yet, but here's what we've done so far:

1. We started by dropping the motors on the Y axis, then fixed a Starrett straightedge to the outside face of the rack using 1" x 2" rare earth magnets to hold it in place. Using a flashlight below, we measured the gaps with feeler gauges along the length of the straightedge and then shimmed the rack. We did it on both sides, but the slave side was considerably worse than the Y side. The worst spot was out .039".
2. With the motors still dropped there was still considerable binding in two places along the Y axis - just behind the point where we had trouble the pinions and about 20" behind that, near the back limit of travel. We popped the caps off the rails, loosened the gantry mounting bolts above and below and all the bolts on the slave side rail since the straightedge indicated a slight bowing in the rail. We used a spreader bar squared against the Y side rail to get the rails as parallel as possible, tightening the first bolt and moving two bolts down, tightening, etc., before retightening all of them. We then did the same thing on the other side. HUGE improvement in the gantry motion. We still have some bearing noise on the slave side and will replace those bearing cars soon.

3. Since we already had the machine apart we decided to order a replacement motor drive cable that had been giving us random trouble as well as the pinion on the slave side which showed more wear than a machine with maybe 200 hours on it should. That should be here Wed. or Thursday. Once installed we'll recheck resolutions and I'll update the forum on our results.

[Ntl]

Did you take pictures of what you did? Just curious to see in case any issues pop up on my machine now that it's getting used.