extending THK rails, rail alignment

[Cliff_J]

I purchased some HSR20 rails off ebay new-in-box. Each box has a ~47" and a ~19" rail and two slides. One end is precision ground flat and the other has like a thick layer of paint on it. I'm planning on using them for a 4' x 4' gantry.

Laying on a table if I but one rail up against the other I can slide the block from one rail to the other without issue. However, I made a wood mockup to measure the sliding force and I'm finding it nearly impossible to get them perfectly lined up. So:

1) Are these rails designed to be 'linked' or 'extended'??

2) The misalignement is small, seems insignificant but yet persists. Are my concerns realistic that once I get these mounted on some 80/20 aluminum extrusions that I may still have alignement issues? If so, how do I line these up??

Ahhh, why can't economies of scale work in the mechanical world like in portable electronics where small is expensive and big is cheap????

Thanks for any help.
Cliff

[Graham S]

1) no
2) it will likely cause wear. Certainly THK would turn in there grave if they had one.