View Full Version : THK Rail question

08-23-2004, 11:53 PM
I am mounting THK SRS15M (2H058) rails for the x axis of
my current project. I will be mounting a small gantry on the
4 blocks, my y axis is only 14 1/2" wide (RSR12),
with a 3 7/8 travel z axis. My spindle will be a
Porter Cable trim router.

My question is I have read in several threads that mounting
the rails sideways are better for keeping dust and dirt off the
track, however (as in the case of Cold Fusion's machine) he
was suggested that he should mount them on directly under
his gantry for better load support. Which is the better
placement for support??

Is my machine so small that the load wont make a difference??

Thanks, I know someone has been here before!!!

08-24-2004, 09:41 AM
Is my machine so small that the load wont make a difference??

THK's can carry tremendous loads (even the small ones), so no, it really shouldn't make any difference on a small homebuilt machine. Unless you're gantry is 500+ lbs. :)

08-24-2004, 05:44 PM
The SRS series can carry loads equally well in all directions.
This is not true with some other types that carry the load best from the top side.

08-24-2004, 09:29 PM
Thanks guys, just another quick question --
does anyone know the difference between
the srs rails and the rsr rails??

08-25-2004, 12:41 AM
I also have some SR15's for a larger machine I will be building
next year, I belive that they can only take loads from the
top, is this correct??

Cold Fusion
08-25-2004, 01:45 AM
Just a quick note here,

The dust and swarf get everywhere when I cut so mounting them on the sides wouldn't have helped a whole lot.

08-25-2004, 05:19 PM
Chas: Yes. Well they won't fall off their track if turned upside down, but the load carrying capacity is much lower. Be aware this also affects their ability to cope with a tilting moment. So using only one block per rail to carry a gantry is not desirable. When you try to tilt it, one end will have a lifting force.

08-25-2004, 10:14 PM
If I did it over again, I would mount them on the sides of the frame rail instead of on the top. Chips tend to want to collect in the bolt holes when they are mounted on top. Plus, I get nervous loading material into the machine for sake of hitting one of the rails. And, mounting on the sides would also conserve a little space.

08-26-2004, 01:32 AM
Both machines will have 2 blocks each side of the gantry,
smaller machine will have srs's supporting the gantry, which
are rated for top and side loads.
larger machine will have sr15's supporting the gantry, i have
read somewhere on the forum that sr15's should not be
mounted on the side of the frame, they are not rated
for side loads, can anyone confirm, or has anyone used
sr15's on the side???

08-26-2004, 08:16 AM

Yes SR15 is for forces from above.

The best allround linear rails is HRW27 they can take all kind of forces and can also be used with one guide block.

08-26-2004, 06:13 PM

I would have to agree on this. I went for HSR-R type bearings. I found these easyer to come by on Ebay and these allso take loads from all directions. Mine are HSR25R1SS type and i think they are sturdy enough :p

By the way, i checked the THK website and searched for some manuals. I believe i filled in a form on their website.They were more than happy to help me and now i have a small collection of fine manuals about all their styles and types of bearings. Of course, HRW was in there too. It's a low-profile bearing for wide rails. HSR is higher and offers more depth for mounting bolts. The rails for these is narrower too. I hope to have zero to none flexing with mine :banana:

If there are any requests to look for some types in my manuals i'd be more than happy to help out.


08-27-2004, 01:24 AM
I too just joined the THK website and will be downloading the manuals on the

Has anyone on the forum used the SR15's on their machines??
Results?? Pictures??