Using old THK SR15?

[mmomike]

I am working on a cnc router design. A friend has offered some older SR15 linear guides. A company, he worked for several years ago, was throwing them away. The grease is gummed up around some of the trucks. There are a total of 19 trucks. I would only need 12. There was plenty of rails for my needs.

I moved the trucks with my hands and most of them seem to slide well. Two of them moved unevenly. There was some internal vibration as they moved (the ball bearings?).

I want to build a 34" x 48" x 6" moving gantry cnc router table. I plan on 3x3 inch steel tube frame and gantry and a variety of aluminum parts.

Motors about 425-495 nema 23
Geko drivers
Dual X-axis motors
Ballscrew for Y and Z
Either ballscrews or R&P for X-axis

My question is can I use the SR15s or should I forget them and buy the cncrouterparts guides and the steel plates required for them?

Can the SR15 be cleaned up?

Budget is an issue. I had not planned on buying the guides and I am maxed out on my budget as it is.

[JustPlaneSweet]

Use the SR15s. They are excellent guides.

Stan

[mmomike]

Are the SR15s big enough? I see most people using SR20s.

Also if there are ball bearing problems, can I repair them?

[ger21]

Are the SR15s big enough? I see most people using SR20s.

Also if there are ball bearing problems, can I repair them?

You can't really repair them, but most likely they just need to be thoroughly cleaned.

I'd be willing to bet that everyone you see using 20mm rails could be using 15mm rails without any problems at all. Unless parts of your machine will weigh 1000 lbs or more.

[louieatienza]

Skate bearings on cold rolled steel, versus precision linear bearings on ground and hardened linear rails... I think the choice is obvious. The biggest challenge is having a precision surface to mount the rails on, getting them straight, and aligning them precisely to each other.

[mmomike]

For a couple of weeks I have been reading all the great advice given to us new comers. It's been incredibly educational.

You guys have come through again. Thanks!

I will be posting my design in a couple of weeks. I can't wait to see your feed back.

[jsheerin]

You could probably reball the trucks if you had to similarly to how people reball ball screws, but if you've got 19 trucks available and only need 12, it sounds like you have some spares...

[Drools]

You might want to read the load rating on the SR(uncaged) and SSR(caged) line of THK rails as their orientation is specific. If I remember correctly SR and SSR rails are rated for horizontal loads while the SHS and HSR and some others can handle loads in any direction. Just saying I would check up before mounting them.

[mmomike]

You make a good point so I looked it up to make sure.

The SR-W 15 (what I have) will take 9.51 kN basic dynamic-load rating down on the block (called Radial direction). This is noted as 'C'.

0.62 * C in the Reverse-radial direction.
0.56 * C in the Lateral direction

9.51 kN comes out to 2138 pounds.

That's 1325 pounds in the reverse radial direction and 1197 pounds in the lateral direction.

Also I will have four trucks for each axis so my machine should handle 4 times any of the forces listed above for each axis. Wow these things are incredible.

[Drools]

They do make nice rails. I have been trying to find refrib kits and replacement seals for my THK bearing blocks but no luck so far.

[jsheerin]

Fyi, you don't want to actually run them at the load limits. There are life calculations in the THK catalog that use those load ratings. The lower the applied load relative to the rated load, the longer the bearings will last, so it's a good thing to over size them.

[mmomike]

They do make nice rails. I have been trying to find refrib kits and replacement seals for my THK bearing blocks but no luck so far.

I hope the seals are good on the ones I will be using. How can I tell if they are bad?

Fyi, you don't want to actually run them at the load limits. There are life calculations in the THK catalog that use those load ratings. The lower the applied load relative to the rated load, the longer the bearings will last, so it's a good thing to over size them.

Interesting. Good to know.

I have really gotten the cnc bug over the past couple of weeks. Building a machine is very addicting. I find myself thinking about the two machines I will build after this one.