One Z Rail?

[lgalla]

I saw on the Mechmate forum someone used a huge single rail with a large router spindle on the Z .One huge THK rail and block is cheaper than 2 smaller rails and4 blocks with less mounting problems.Any thoughts on this?
Larry

[ger21]

Last week I put a 9HP router spindle back on our point to point machine. On the back of the spindle is an aluminum plate, about 1/2" thick, 3-1/2 x 8 or 9" long. 2 25mm blocks are mounted to this plate end to end, and run on a single 25mm rail. The blocks are Star and use needle bearings, but I don't think that makes much difference. The spindle weighs about 30-40 lbs. I think the key to this system is that the rail must be attached very securely so it can't rock from side to side. But it does work just fine. Runs about 20 hours a week for about 8-9 years now with no problems. (except the spindle bearings failed, )

[svenakela]

I now a guy who made a router with single rail mounts on both the gantry and the Z-axis. The bigger rails can take extremely high torque values, and his machine is still going strong.
I have a THK27-rail (I think) in the garage waiting to be used for a project, and it can take something like 120-130 Nm on each wagon. That's more than my Ducati sportsbike delivers!

[RICHARD ZASTROW]

If the one large truck has sufficient capacity for the moment load, fine.
Two trucks of the same rail size and half the length have much more than twice as much capacity. ex. IKO LRWH 25 single truck is rated @50.3 kgf.m and (2) IKO LRWH 25 mounted in close contact are rated @ 287 kgf.m It all relates to "how much do you need, comfort zone and $.

[walter]

Originally Posted by RICHARD ZASTROW Two trucks of the same rail size and half the length have much more than twice as much capacity.

There has to be a limit somewhere..

I don't think you can put 8 bearings on a single rail and expect to octuple the capacity. The rail (mounting) will most likely give up....

[lgalla]

Here is a link.
www.mechmate.com/Forum/messages/1168/1205.html

[RICHARD ZASTROW]

Igalla, That entire Z axis is neat.

Walter, If we used extra wide rails and extra long trucks, we could build an accurate overhead hoist.

[walter]

Yeah, the wide rails are cool. I think it's the HRW series, extra wide and nice low profile. I see these on Ebay occasionally...

Here's something interesting on THK linear bearings. The biggest blocks can handle around 800 tons- but only in 4 rail configuration.

Which means you can put 3200 tons on 4 blocks mounted on 4 separate rails. But you can't put 800 tons on a single block mounted on single rail...

That kinda makes sense and I think this info can be scaled back to the small 15mm rails...

[RICHARD ZASTROW]

This has nothing to do with the subject, just an off-hand comment. Allis Chalmers had what might have been the largest machine in the world. They had a radial drill built that had the base suspended upside down from an overhead hoist. The arm was reversed on the column to be facing down in the normal operating position. I was told it was on the lowest tracks of three levels of overhead hoists. That way, the other hoists could pass over the top. The traveling bridge traversed Right- Left (Y) 75 ft. width of shop, Front-Rear 1,440 ft. length of shop. I don't know the height (Z) but I imagine it was limited to the arm and spindle travel. It was gone before I was there.

[lgalla]

To over kill and use 4 blocks and 2 rails or suffer the simplifyed single rail route.Tis' nobler to justify the simple route or over complacte?Too die to sleep
Sorry wrong forum.I thought this was my Shakespher forum.Anyways maybe someone can share thoughts on the problem at hand.
I haveth on hand uno rotar spindle ofth 7Horse powerth weiting 50pounds.I haveth uno THK-HRW-27 and two blocks.Isth this capable of the moment?[loads}
Larry

[ger21]

Like I said, it works on our 9HP spindle. If I ever get around to building a big 2 spindle router, I'll be going this route. One rail per spindle.

[lgalla]

Thanks for the reply Ger,hath given me new paths to follow.In the real E-Bay life humongus THK Rails and blocks go for a song.
Larry