Joining two THK SHS15 rails

[PEU]

I purchased last week a lot of 8 THK SHS15C1SS rails (12.5" long each) with 1 block each and I was wondering if joining two rails to make a longer one is feasible.



This is picture of the desired configuration, the design will be a moving X table, fixed Y bridge, movable Z.

Drawing in its early stage using THK & 8020 provided solidworks models

Thanks


Pablo

[HacknHew]

It'll work as long as you take care to match up the ends of each mating rail, and also stagger the joints between each rail assembly so that each bearing block doesn't pass over a joint all at the same time.

[Calico]

how do you match the end of each mating rail ?
I mean is there any guide/mark etc for matching ?
any phtos/samples ?

rud

[PEU]

Originally Posted by HacknHew It'll work as long as you take care to match up the ends of each mating rail, and also stagger the joints between each rail assembly so that each bearing block doesn't pass over a joint all at the same time.

The rail end is a clean perpendicular cut, there is no assembly, I ask because I want to be sure that no distortion will appear when the carriage goes over it.

Thanks


Pablo

[rc-cellar]

Save yourself a big headache...
Arrange the blocks so they don't cross the gap (longer table?)

[PEU]

well, thats the idea of the posted picture But the temptation of making a longer unit is big...!

if someone have more insight or done this before, please post, all opinions are welcome!!!

Thanks


Pablo

[Halfnutz]

Im in the process of joining two THK SR15's about 25" long. I sanded the ends flush on a disc sander with a fence and guide, so they are very square to each other and they seem to roll over the joint fine. Before I sanded them flush they grabbed some. One thing I would consider is if you make your cuts at the right place you will have a consecutive bolt pattern and can change out with one piece rails later. If you dont consider this then you will have to drill more holes if you try to change it out some day. THK talks about butt-joining thier rails on thier website, so I geusse it is OK to do. Also note that the extrusion you are mounting to does not have a high enough degree of flatness to satisfy THK's reccomended installation spec's. I dont know how big a deal this is, but Ive heard it discussed before. Im going to do the same thing, Im just checking the extrusions out with a straight edge first, I think they will be OK. Good luck!

[PEU]

Well, I purchased ballscrews with 330mm length, so the extra lenght is almost gone, but anyway joining two rails allows me to use the full lenght of the rail instead of the lenght minus the blocks.

Do you have the link where THK speaks of the rigidity of the rail bases?

Here is the new drawing with the ballscrew added:



Travel for this axis will the maximum allowed by the ballscrew, the bridge will be 317.5mm only

Regarding the rigidity of the extrusion, Im using 8020.net drawings, but since these can't be found here (Buenos Aires/Argentina) Later I will adapt it with the ones I can find.

Work in progress as you see

Thanks


Pablo

[mk2lehe]

Is this what you asked for concerning rigidity?
http://www.thk.se/pdf/235-9ESHS.pdf

[PEU]

I find nothing regarding rigidity, but is very good read on the SHS system. Thanks!!!


Pablo