Slightly out of square rails

[GeneMpls]

I am setting up a new to me early PRS 4x4 SB. I am taking my time trying
to get it right the first time- I learned enough on my Buddy 32 to have a
pretty good idea of what is important to me and what is not. When I cross check the rails I get .5 inches out- but they are straight and parallel.
The alum part that the rails and gears are attached to are not exactly
lined up with the 1.5x6 extrusions they bolt on top of and the gears
appear to be attached with VHB tape and almost certainly are not the
same side to side. So... does it really matter if the rails have a slight
parallelogram shape? Is the idea to make the rack gears exactly square
or what am I really trying to accomplish here. I have lots of other upgrades
that I am working on- Chicom spindle/vfd, y axis e-chain, modifying
the bed, storage under the machine and a pivoting laptop mount so I
have another couple weekends before I will be functional. Thanks Gene

[Brady Watson]

No it doesn't really matter if it is "parallelogrammed". However, this will limit your travel by 2X whatever the deviation from perfect square is...so I would try a little harder to get it within 1/16" of square on such a small table.

Measure the length of each X rail, it should be around 72" long. If there is a deviation in length, this should be taken into consideration. Check that the crossmembers are square to the table sides. If they are not, they can attribute to the parallelogram effect and while the gantry will run fine on parallel rails, EVERYTHING you do to the rest of the table will be messed up...like when you go to deck it, the table will be way off. Since there are only 4 crossmembers total on that little tool, this should not be too hard.

Also, check floor to leg and leg to table side square. If the legs splay out too much in either direction it can cause difficulty...and of course, make sure you are dead level.

-B

[bob_reda]

I agree with Brady. You are at this point and it would worth the time to get it right the first time, before you add other things to it. Just like in woodworking, if its a quarter inch off in the beginning it will be 2 inches off when finished and take a lot longer to deal with.

Bob

[GeneMpls]

Thanks Brady- that is what I thought and I will probably square it- I
just like to understand what is going on. The travel seems to be about
49x 52 as it is. Thanks Gene

[curtiss]

I made a simple hardwood T square for setting up /with a digital caliper taped to the far end.

A groove in the top of the T for one rail.... the "depth guage" worked as a "feeler guage" to get the rails exactly parallel.