[tkms002]

I would like to know what the relative rigidity is of the following linear rail/bearing types and their pros and cons.
Thanks
CNCRP skate bearing
V-bearings on steel angle ala Joes
V-bearings on hardened v rails
delrin wheels riding on 8020 ala openbuilds
Round (SBR) rails
profile rails (THK and HIWIN).
Others?

Thanks

[ger21]

1 - profile rails (THK and HIWIN).

The rest are a bit of a guess, and the machine construction can play a role in their stiffness.

2a - Round (SBR) rails
2b - V-bearings on hardened v rails
3 - CNCRP skate bearing
4 - V-bearings on steel angle ala Joes
5 - delrin wheels riding on 8020 ala openbuilds

[tkms002]

1 - profile rails (THK and HIWIN).

The rest are a bit of a guess, and the machine construction can play a role in their stiffness.

2a - Round (SBR) rails
2b - V-bearings on hardened v rails
3 - CNCRP skate bearing
4 - V-bearings on steel angle ala Joes
5 - delrin wheels riding on 8020 ala openbuilds

Thanks for the fast response Ger. You must live on this site.

With regards to the X axis where MOST of the force on the rail is in the down direction(weight of the gantry) are round rails more viable if I want to save some money over option 1?

[wizard]

Thanks for the fast response Ger. You must live on this site.

With regards to the X axis where MOST of the force on the rail is in the down direction(weight of the gantry) are round rails more viable if I want to save some money over option 1?

With round rails you have to commit to spacing the bearings further apart due to the inherent looseness of round rail bearings. That means your rails need to be longer to end up with the same working area. Now given that in many cases people using profile rails will have them too close together. So it really is a matter of what you can get away for your design and what you are making. Round rail bearings generally have more clearance compared profile bearings thus need to be spaced farther apart. Also the round rail solutions are generally not as stiff as profile rails under load.

One way to visualize this is too consider a pyramid with its base on the ground. Stable right, it resists tipping. Now imagin an upside down pyramid. Not so stable right? Many diy designs (gantry supports) are closer to an upside down pyramid than is ideal, this puts excess load on the bearings, and even profile bearings suffer though far less than round rail bearings. For round rail I’d look at triangles tha have long edge at 45 degree angle with respect to the base. With a high mounted gantry this can result in a very wide base.

The other problem with round bearings is that they can rotate some around the linear rail. So your gantry supports need to be able to resist this small freedom of movement.

[routalot]

We don't really have enough information to give answer other than in the most general terms since we don't know what kind of work the machine is intended for.The ranking given by ger21 is excellent and accurate.Clearly if you are intending to build a router for full size sheet materials the loads will be greater than for a laser operating over an area the size of a letter and this will affect what you may be able to make use of.

[ger21]

With regards to the X axis where MOST of the force on the rail is in the down direction

During use, most of the forces on the gantry are in the horizontal direction, which translate into both up and down forces on the bearings.

[tkms002]

During use, most of the forces on the gantry are in the horizontal direction, which translate into both up and down forces on the bearings.

Are you saying that because of a twisting force on the gantry? I can imagine of the router bit was stuck(worst case) and the Y or X motors were pushing it would cause a twisting moment on the X bearings. Is that what you are referring to?

[tkms002]

With round rails you have to commit to spacing the bearings further apart due to the inherent looseness of round rail bearings. That means your rails need to be longer to end up with the same working area. Now given that in many cases people using profile rails will have them too close together. So it really is a matter of what you can get away for your design and what you are making. Round rail bearings generally have more clearance compared profile bearings thus need to be spaced farther apart. Also the round rail solutions are generally not as stiff as profile rails under load.

One way to visualize this is too consider a pyramid with its base on the ground. Stable right, it resists tipping. Now imagin an upside down pyramid. Not so stable right? Many diy designs (gantry supports) are closer to an upside down pyramid than is ideal, this puts excess load on the bearings, and even profile bearings suffer though far less than round rail bearings. For round rail I’d look at triangles tha have long edge at 45 degree angle with respect to the base. With a high mounted gantry this can result in a very wide base.

The other problem with round bearings is that they can rotate some around the linear rail. So your gantry supports need to be able to resist this small freedom of movement.

My gantry plan is to have a short riser (maybe 3 inches or less) on the gantry and have a work surface that is below the X axis bearings maybe 3-6 inches.
Like this

[ger21]

Are you saying that because of a twisting force on the gantry? I can imagine of the router bit was stuck(worst case) and the Y or X motors were pushing it would cause a twisting moment on the X bearings. Is that what you are referring to?

Just the forces from accelerating the gantry and cutting will impart a lifting force on one of the bearings.

With regards to the X axis where MOST of the force on the rail is in the down direction(weight of the gantry) are round rails more viable if I want to save some money over option 1?

Personally, I don't think round rails should be used at all (for any machines), so I can't say they'd be more viable.

[tkms002]

Just the forces from accelerating the gantry and cutting will impart a lifting force on one of the bearings.

Got it
Thanks

Personally, I don't think round rails should be used at all (for any machines), so I can't say they'd be more viable.

Lots of people are using them but I appreciate your opinion.

[ger21]

It always comes down to whether you want a good machine, or a cheap machine.

[tkms002]

It always comes down to whether you want a good machine, or a cheap machine.

Ya I got you there.
Any comments on the picture I posted above?
I think having a lowered work surface rather and a raised gantry should be stronger, right?

[skrubol]

Ya I got you there.
Any comments on the picture I posted above?
I think having a lowered work surface rather and a raised gantry should be stronger, right?

Raising the rails and having short gantry risers has its advantages (saves moving mass,) but you still need to build the frame that the rail sits on strong or you'll just have flex there instead.
A downside is it makes it a little tougher to get material into and out of the router.

[tkms002]

Raising the rails and having short gantry risers has its advantages (saves moving mass,) but you still need to build the frame that the rail sits on strong or you'll just have flex there instead.
A downside is it makes it a little tougher to get material into and out of the router.

Thank you

[tkms002]

It always comes down to whether you want a good machine, or a cheap machine.

OK you convinced me but that leaves 2 more questions.
1. can square rails be butt joined so I dont have to ship 9 ft of rail?
2. You point out automation overstock for these, where do they source their rails and parts? I have tried contacting them but the link fails.
3. Have you ever tried the chinese options?
Thanks

[ger21]

1) Ideally, they should be ground so that the seam is perfect. But I think that CNCRP supplies unground joints for their machines.
2) China. low-cost BLH linear guideways equivalent to Hiwin HG series of you
3) No. I purchased their surplus Hiwin's before they ran out.

[tkms002]

1) Ideally, they should be ground so that the seam is perfect. But I think that CNCRP supplies unground joints for their machines.
2) China. low-cost BLH linear guideways equivalent to Hiwin HG series of you
3) No. I purchased their surplus Hiwin's before they ran out.

1. I will contact CNCRP to see how they do it and what issues they have.
2. If these are Chinese is there a reason to buy them for $5-$600 when I can get "the same thing" from LINEARMOTIONBEARINGS for $300?
3, Lucky for you, bad for me.

Thanks again

[ger21]

2) Having someone here in the states that stands behind their products is worth something. If you have problems, it's worth a lot.

3) I still spent $1500. They were more expensive than the Chinese versions they sell now.

[tkms002]

ya, I hear ya.

Thanks again

[nlancaster]

And if you want Hiwins, automation4less.com has from what I can see pretty good prices on them.