Linear bearing blocks not sliding between tracks

[Greg Rutter]

I recently bought six small NSK linear bearing blocks and several meters of spare track in 14.5 cm long lengths of Ebay. The bearings are in good condition and slide along the tracks well.

The problem I am having is that I am unable to get the blocks to slide smoothly between any two lengths of track when they are clamped together for testing (they will go with force).

The tracks are in excellent condition and I know that the ends haven't been cut or ground since leaving the factory as there are still numbers stamped into the ends of each length of rail. When placed together there seems to be a tiny natural bevel around all sides of the tracks but this would have been manufactured in. I lined the tests up using spare lengths of track pressed flush along side the two that I was joining to ensure that they were perfectly straight and visually they look perfect apart from the bevel marks.

Should I try to machine the ends off these tracks to get them to line up better? I don't know why I would need to do this but as that is the way they were manufactured.

[ger21]

The balls are probably getting stuck in the bevel. Not all rails are made to be butted together. Rails made for butting together need to be machined or ground perfectly square. When assembled, the seam should be almost invisible. At work we have a router with 2 8ft rails making up a 16' section. You can't tell there is a seam in them from more than a foot away, the seam is that good.

[Greg Rutter]

Thanks for that Gerry,
I will pick out the worst couple of tracks and try machining the ends in the lathe or borrow my friends mill. I still don't get why they would have been bevelled in the first place but as I got such a large quantity of track lengths and so few blocks from the same source on ebay that they must have been using them as long lengths butted together. Anyway I should be able to machine the ends off pretty quickly.

[RICHARD ZASTROW]

Greg, You might also verify the height is exactly the same between adjacent sections. Often matched sets are required to be able to butt them in line.

Dick Z

[ironDigit]

wouldn't the material sorrounding the punched figures on the en of the rails be pushed up interfering with your seem?

I woul never go ad machine no thk rails and especially if new myself.
I assume ,that if you have the means necessary to machine these AS SHOULD you mioght as well made yourself some rails.Saying you can ony make things worse.

I'ld try to check if the numbers are causing any of this and tackle them with the smallest dremeldiamond bit as slowly and as patiently as i can.But don't even breathe on the ground ballways.

Good lukk.

[schbrownie]

Sorry to be the bearer of bad news... as a general standard, profile rails are NOT made be be but jointed. If you want but jointed rails, you have to order them that way and the factory will grind the joints flush and then laser mark the rails so you know how to line them up.

The tolerance are so tight on the rails that there is no way that they could actually make every rail but jointable. Usually a rail would be held to 0.0001" (or so) down the entire length of the rail; however, the variance from one rail to the next could be much greater. You can try to grind the rails to remove the bevel; however, you could still end up with a situation where one rail is not the same dimensionally as the other.

~Jon

[Greg Rutter]

That certainly does sound like grim news. Unfortunately I have over 30 of these tracks which would not be resaleable for long track lengths. I did wonder out loud in an earlier post as to why so many matching tracks would be available without a bearing block on each one if they weren't meant to be butted together. I am now thinking that the bevel may be just a manufacture indication that the rails have not yet been ground to the customer specification although they were purchased from a second hand dealer.

I had been planning to just take these tracks in to a professional machinist and get him to stack them up together on their sides and mill off 1mm from the ends in one hit. Do you think that this would be workable or would it be a waste of money?

[Greg Rutter]

I just spoke to my friend from the model engineering society who has a mill and is an experienced machinist. He said that he has done a far bit of grinding working with the mill and it is very accurate. It will be a while before he can help me out but he said that he would be quite happy to show me how its done. This sound like the only option with these rails so I will give it a go.

[schbrownie]

The bevel is put into the ends of the rails to aid in the installation of the runner blocks (aka wagons, sliders, trucks, carriages, trolley). If you're not careful during installation, you can easily pop out some and/or all of the balls which could ruin the runner block if you can't find the balls.* Lower grades of profile rails are made to have "interchangable rails and runner blocks" so that you can put any runner block on any rail. This works in concept, however, the performance difference (and physical measurements) from one rail/carriage to the next can be severe.

That all being said... if you're mounting these rails to an unmachined surface (i.e. 80/20 or similar), it won't matter. If you're mounting these to a qualified (machined/ground) surface, you will see a difference. I know guys that have had to skin cut the tops of the carriages in order to get them to be within 0.0005" so that when they tied multiple carriages to gether, everything would be flat and level.

In honest opinion, profile rails are great, and if you're only going to make a system out of one rail and one carriage then just about any profile rail will work. If you are going to make the system out of one rail with multiple carriages, you may have to machine the carriages flat and level. If you're going to make the system from multiple rails and multiple carriages, you'll either have to order a matched system from the factory (expect to spend $500-$3000, dending upon size & length) [If remember correctly, last time I had a system quoted, I used a 25mm tall combo, 1400mm long, with 2 wide rails and 2 blocks/rail with high preload and matched together, it was around $1300 and an 8-12 week lead time]... just be careful buying rails from eBay or other auctions/second hand dealers.... you may end up spending more trying to get them to work than if you paid for the system from the factory.

Hope that info helps.

~Jon


* OK... it won't actually ruin it... you can replace the factory balls with second hand balls; however, you will most likely NOT replace them with the exact same size ball, which will reduce the performance of the system.