Will this work?

[SatanKlawz]

I asked a more technical question about this setup in another thread and now I am looking for more feedback about it. Basically I am kicking around the idea of mounting 2 linear bearings on the back of my z axis since the mounting pattern will fit perfectly. Originally I was going to make a plate that the z axis mounted to and that plate would of mounted to 4 linear bearings. I know that 4 would be more than sufficient I am just wondering if 2 will work.... I attached a pic of what I am considering and also of the specs of the linear bearing. I am using 381oz-in steppes to move this axis (the Y axis). Does anyone know if these HIWIN blocks can be mounted in this orientation and if it affects its load bearing capabilities to do so?

[YZF]

The blocks can certainly be mounted in this configuration but this setup will be less stiff and be able to take less force/torque in the My (see the block diagram) direction. What force is your stepper going to be applying on the tool when you take into account the ballscrew?
Think about pushing the bottom of your tool in parallel with your Y axis with your nut/ballscrew fixed, this creates a force/torque on the bearings. Having four blocks spaced apart will make a *big* difference (it's the distance between the corners that is important) and that's a fairly standard configuration. You could also do three! If you're not expecting heavy cutting forces you should be able to get away with two depending on the force and the distance to the tool.

By the way, is the surface you're mounting the blocks on flat? It needs to be.

Originally Posted by SatanKlawz I asked a more technical question about this setup in another thread and now I am looking for more feedback about it. Basically I am kicking around the idea of mounting 2 linear bearings on the back of my z axis since the mounting pattern will fit perfectly. Originally I was going to make a plate that the z axis mounted to and that plate would of mounted to 4 linear bearings. I know that 4 would be more than sufficient I am just wondering if 2 will work.... I attached a pic of what I am considering and also of the specs of the linear bearing. I am using 381oz-in steppes to move this axis (the Y axis). Does anyone know if these HIWIN blocks can be mounted in this orientation and if it affects its load bearing capabilities to do so?

[SatanKlawz]

If I were to lower the Z axis to where the tip of the cutter was on the table it would be in the very close neighborhood of 4.75" from the center of the lower rail to the end of the cutter. I did read that these HIWIN blocks can be mounted in this configuration just fine. I also read this but do not know where to start to figure the math....

# Use a 4-5 times safety factor for static and moment loading (10 times if you actually will be doing work i.e. gluing, routing, etc. while the load is moving). # If you use two blocks on one rail you can double the direct load carrying capability and the Mr moment capability of a single block. You can also use a factor of 5 times the Mp and My moment loading capability of a single block. # The Basic Dynamic Load Rating heading is a figure that says "90% of all identical guideway/bearing combinations will have a life of 50 km (31 miles) of travel at this load."

I am using 1/2-10, 5 start acme screw that has 1/2" of movement per rev. If that matters at all.

[YZF]

The rating of the bearing in My is 35.9kgf m or ~350Nm .

So if you have an arm of 1m you can apply 350N. Since your arm is 4.75" you can apply 1m/4.75" x 350N = 2900N per bearing block and approximately twice that for two closely situated bearing blocks.

My quick back of the envelope (hopefuly correct :-) ) calculation shows that maximum force your motor can put on the tool is 1270N. I don't think the actual cutting is going to be significantly larger.

So you should be fine...

Originally Posted by SatanKlawz If I were to lower the Z axis to where the tip of the cutter was on the table it would be in the very close neighborhood of 4.75" from the center of the lower rail to the end of the cutter. I did read that these HIWIN blocks can be mounted in this configuration just fine. I also read this but do not know where to start to figure the math.... I am using 1/2-10, 5 start acme screw that has 1/2" of movement per rev. If that matters at all.

[SatanKlawz]

Ok, thanks for the info. I do not plan on doing anything heavy duty with this machine. Just wood and acrylic mainly. I may still do the 4 blocks just for peace of mind it is just going to be a bunch more work and the extra cost of the blocks and material to make it work with 4 blocks. It was just a freak coincidence that I noticed that the Z axis has the same mounting pattern as the bearing blocks that I bought. The blocks in the pic are for another axis so I have to buy more either way. Its just either going to be 2 or 4.

Also is what you figured in line with what was suggested above with a 10x safety factor?

Did I do my own conversion correctly that if you say each block can take 2900N in the My direction with an arm of 4.75". That calculates to near 652 lbs. of force right? And that would be near double with 2 blocks? I do not think I will be putting near that amount of pressure on the cutter.

[YZF]

Your conversion is right. So allowing for a safety factor of 10 you shouldn't put more than 580N on the tool which should be more than enough for your application. The blocks you're using are decent size and these things are designed to take large loads. There's also a question of the service life you're looking for. The other difference in using 4 blocks is that you'll see higher stiffness, i.e. in the presence of force there will be less deflection, but I don't think that is an issue for your application, we're talking very small deflections.

Originally Posted by SatanKlawz Ok, thanks for the info. I do not plan on doing anything heavy duty with this machine. Just wood and acrylic mainly. I may still do the 4 blocks just for peace of mind it is just going to be a bunch more work and the extra cost of the blocks and material to make it work with 4 blocks. It was just a freak coincidence that I noticed that the Z axis has the same mounting pattern as the bearing blocks that I bought. The blocks in the pic are for another axis so I have to buy more either way. Its just either going to be 2 or 4. Also is what you figured in line with what was suggested above with a 10x safety factor? Did I do my own conversion correctly that if you say each block can take 2900N in the My direction with an arm of 4.75". That calculates to near 652 lbs. of force right? And that would be near double with 2 blocks? I do not think I will be putting near that amount of pressure on the cutter.

[SatanKlawz]

Thanks for the info you guys are some smart cookies. I will go with the 2 for now. If I do detect issues I can always add 2 more with a little work. The math says that I can still put around 130lbs of force on the cutter with a 10x safety factor.