Linear bearing problem

[ranchak]

I am working on my Z-axis, I am using IKO linear rail and bearings. My Z-axis is made out of 3/4" x 6" aluminum. The rails are mounted on 3/4" x 1 1/2" bar that is bolted to the 3/4" x 6" plate. I have my rails parallel (within .001). My problem is when I start to tighten down the plate (made out of 1/2" x 4" aluminum) that ties the two trucks together, the trucks start to bind when rolled down the rail. You can tighten a bolt here or there and eliminate some of the binding, but not all of it. I noticed that on the underside of one truck someone (previous owner) etched .010. Does this mean that they had to shim that side to allow for smooth movement? I am about 99% sure that I have my trucks parallel with each other, I used a square to set them up. I didn't think I would need to shim, but at this moment I am out of other ideas. Any suggestions?

[LeeWay]

When I mount mine, I use a little larger hole than needed in the top plate. I use the right size cap screws for the rail holes. If shimming needs doing, do it on top of the truck. Never under the rail. I am sure you know that, just throwing it out there. Technically, rails should be mounted against machined bosses. At least on one side. The master rail.
Depending on how snug your rail bolts are to the holes, you may be able to loosen one rail. Snug the plate onto both trucks, then run the trucks up and down the rails tightening the rail screws a little at a time. That worked for me on the last rails I mounted. They were close to start with though.

[ranchak]

I've never tried to adjust the rails. I went to great troubles to get them parallel. My trucks slide freely when seperated, it's when I start to bolt down the plate that they get snug. I think what I'll try next is bolt down one truck and then use a feeler gauge and see what kind of clearance I have on the other truck. They move freely when one truck is bolted and the other is loose (there is enough pressure to hold the loose truck while it moves). I really don't have any way to surface the main plate. Amazing how you could really use the project that you are building to build the project you are building!!!!

[LeeWay]

You are right about it takes one to make one. Another observation I have made is the smaller the rails are, the less forgiving alignment is. The first ones I used were THK size 12. They are on the Z of my router. They were a bear. After the first try with the aluminum plate on the trucks, I made a template out of lexan and mounted that. The second template was perfect, so I flipped the original plate over, drilled new holes and they turned out perfect as well. Luckily, I didn't need any shims. If the axis will work from gravity alone, that is close enough.

The next rails I mounted worked much better and worked the irst time. They were size 27's and 25's. I did change the design on the mill to accomodate the type of mounting the trucks had though. Apparently I could not build them with the axes in the correct position starting at the bottom up on my new mill. I have to remount them. Not enough forethought on my part. It did give me some practice though.

I have seen some nice aluminum plate and some that was really bad. I have found that using a ROS will at least help to level the plates and knock the burrs off. Bars are even worse than plates and 80/20 stuff is worse than all of them. Once my router was done, I have used it to surface everything for my mill. You may just have to get it close and move on until it is up and running. Then make new parts with the machine running to make it more accurate. You may find that it will work great with shims or with a little larger holes in the trucks plate on one side. I mill aluminum with my router quite often. It works great.

[ranchak]

Lee, you haven't made me feel any better! I am making my router out of aluminum bar and 80/20 products. My axis isn't working from gravity alone, I still don't have the router mounting plate and router attached, but I think it should move on it's own without the added weight. My rails are IKO 20s. What is a ROS? What are you using for grease? I know some grease has "stiction" and can add to the problems instead of helping.

[rowbare]

ROS = Random Orbital Sander. I had to search to find it...

[LeeWay]

Rowbare got it. Just a sander. Orbital type sanders are better than other types for leaving a fairly flat surface. If you are real good with a belt sander, you could use it too, but not really recommended. It can just as easily screw it up worse.
You can also use scrapers. A good card scraper would work. I have a jointer blade mounted in a good paint scraper and that works fairly well on aluminum too. Nothing will get you a surface like milling or grinding would though. Only close, which may be good enough for now, as I mentioned.
The THK 25's that I have are brand new. The rails are as well. They will not fall by their own weight. They are preloaded pretty well. With a little added weight, they do fall by just gravity. If extra weight will make yours fall, it may be good enough, but because there may be a misalignment, you might wear the bearings out quicker. The closer to perfectly parallel and coplaner that you can get, the longer all the parts will last.

What you have now is an egg. Just make breakfast. With a good breakfast in you, you will be able to build a better chicken later.

[ranchak]

Before reading you last post I had just got done reading about scraping. I think this is what I need to do, I can feel the bearings getting tighter as I tighten the aluminum plate. I used a feeler gauge last night and there is about .005 difference on one of the four corners of the bearing truck. I tried inserting a shim and it didn't work (as I had thought). At one end of the rail the truck rolled free and at the other end it was in a bind. I think I will have to get some blueing dye and start scraping/sanding and see what I can come up. Did you say that you have a lathe? Would you be interesting in machining a bearing surface on a ball screw?

[LeeWay]

What I have is a 7 12 Mini Lathe. I did turn my ball screws on it, but had very poor results until I got through the hard outside. Before I do anymore screws or hardened stuff on it, I will have to mount a grinder on it somehow. That is down the road a bit though. Otherwise I would be happy to do it. I just can't promise good results without a grinder. There are plenty of Guys on here with much better lathes than I have. There is also a section of this forum where you can tell guys what you want done, and they would gve you an estimate.

There is also a section on turning and someone there may help you out.
If you consider buying your own lathe, they can be had for around $350 sometimes from HF. They carry the 7 10. What you get is a foundation that requires quite a bit of work to get any useable accuracy from it. Not difficult, but a must and time consuming. Also consider the cutting bits and the possible grinding add on. Consider also whether a lathe would be beneficial to you in the future. I really like mine, but wished it was a bigger machine, however the small footprint is nice in my shop. Through work arounds, I have been able to make it do what I need.

[ranchak]

Hi Lee, I have been busy working on my router over the weekend. I have made some progress, but overall it's going slow. I am also working on some parts that I plan eBaying at the same time, so I guess my time spent has been productive. I knew that this would be a time consuming slow going project when I got started. I'm not sure how many trips I made to Lowe's to get a bolt or spacer that I didn't have. Luckily it's only three miles to the nearest Lowe's. I'll post some pictures once I have something interesting to look at.