[jharvey407]

Hey guys,

I am upgrading my CNC machine. It is an aluminum extrusion router with a cutting area of 36"x52". I am using a 2.2kW spindle. I cut mostly wood and some aluminum.

The machine currently has V-rails and bearings from Pacific Bearing. I am designing an upgrade to widen the working area and change from v-rails to square profile rails.

I would like to use Misumi linear rails. I will be ordering the extrusions from them and thought it would be convenient to order the rails at the same time.

I have posted the specs from their catalog below. There are two sets of specs, the first is their medium load - dust resistant rails. The second is the heavy load - dust resistant rails.

Will someone please look at these specs and let me know if the rails will be adequate.

The rails will be 1480mm long and spaced 120mm apart on center.

The actual part numbers are:
Medium Load SV2RD28-1480-TMS-WC
Heavy Load SX2RD28-1480-TMS-WC

Here is a link to the page on their website: Linear Guides - Medium Load - Dust Resistant?MISUMI?Product Specifications

If you need any additional information, let me know.

Thanks for the help,
James

[jharvey407]

No one? I was really hoping that one of the engineers would step in and help me understand this.

I guess at this point I'll try to find the specs on some of the popular rails and do a side by side comparison.

If anyone has anything to contribute, feel free.

James

[dmalicky]

The H=28 medium rails (20mm wide) are more than strong enough, even if you machine steel regularly. Their dynamic load rating is 7.2 kN, or 1600 lb. "Dynamic load rating" refers to how much load the blocks can safely carry while moving. (Technically, it's the load that 90% of the blocks can carry without failure for some long distance, typically 50 km for profile rail.)

For a lower Y rail, assuming the cutter tip is 180mm (7") below that rail, the Y rails are spaced 120mm (4.7") apart, and there are 2 bearing blocks per rail, it would take a longitudinal cutter force of 1300 lb to put 1600 lb on each lower bearing block. (See the xls calculator here, using AB=4.7 and BC=7: http://www.cnczone.com/forums/diy_cn...ml#post1408004).

If you only had 1 bearing block per rail, the high torques on each block might eventually wear them out. But 2 blocks per rail is important for stiffness, so there will be no issue for load capacity.

The smaller H=24 (15mm wide) rails would be fine, too, if the screw sizes were acceptable (usually they're quite small for 15s).

[jharvey407]

You sir, are awesome.

That is exactly the type of explanation I was looking for.

Thanks for the help.

James

The H=28 medium rails (20mm wide) are more than strong enough, even if you machine steel regularly. Their dynamic load rating is 7.2 kN, or 1600 lb. "Dynamic load rating" refers to how much load the blocks can safely carry while moving. (Technically, it's the load that 90% of the blocks can carry without failure for some long distance, typically 50 km for profile rail.)

For a lower Y rail, assuming the cutter tip is 180mm (7") below that rail, the Y rails are spaced 120mm (4.7") apart, and there are 2 bearing blocks per rail, it would take a longitudinal cutter force of 1300 lb to put 1600 lb on each lower bearing block. (See the xls calculator here, using AB=4.7 and BC=7: http://www.cnczone.com/forums/diy_cn...ml#post1408004).

If you only had 1 bearing block per rail, the high torques on each block might eventually wear them out. But 2 blocks per rail is important for stiffness, so there will be no issue for load capacity.

The smaller H=24 (15mm wide) rails would be fine, too, if the screw sizes were acceptable (usually they're quite small for 15s).

[dmalicky]

Glad it's helpful!

[jharvey407]

David I sen you a PM.