[newpatch]

Hi All,

Is one better than the other?

Accuracy, price, load, etc.

Trying to decide which one I should plan for in my design.

newpatch

[ger21]

What are you referring to when you say "linear carriage"?

[newpatch]

Sorry, should have been specific....

These:

CNCRouterParts

The bearings from CNC Router Parts..

vs these:

linear bearing rail 2 SBR16-350mm support rails+4 SBR16UU blocks (with bearing) | eBay

newpatch

[br1]

I got some 20mm from Glacern tools, work pretty good, I use a little White Lithium Grease. No problems yet. 1 year old.

[Phife]

The 20mm Rails from Glacern are great, and the price is excellent. I cant speak for the CNCRP carriages but I think the round rails are going to be a better solution.

Do bother with 16mm Round rails, they are really too small for a cnc router. You'll be surprised at how small the 20mm rails already are, I know I was.

[HorridHenry]

Do bother with 16mm Round rails

I think he means "Don't Bother".

25mm or over is ok,the bigger the better and what you can afford?

[crane550]

Yes, I would also go with the 20mm rails. They are not much more expensive then the 16's, so that is a no brainier in MHO.

Over all, I think the 20mm rails are a more professional solution then the CRP option, but the CRP makes building really easy.

If you really wantto get nice, check out the HSR or SHS 20's from THK. You can find them used for decent prices, and can't go wrong there.

[newpatch]

I was going with the 20mm for my project...the 16mm link was just for a visual.

I would also go for the square rails but I'm thinking they are out of my budget. I've seen linear motion round rails on ebay for a good price, a set of 3, one for each axis. Some of the members here have purchased them and are happy...

Things might change, but so far they are in my design which is a 2ft x 3ft cutting area machine....

newpatch

[HorridHenry]

To be honest there is no substantial difference between 16mm and 20mm really when you look at the diameter in your hand.

You need at least 25mm to shy away from 16mm,an extra 4mm is nothing.

[crane550]

To be honest there is no substantial difference between 16mm and 20mm really when you look at the diameter in your hand.

You need at least 25mm to shy away from 16mm,an extra 4mm is nothing.

I would respectfully disagree. Area of a 16mm radius circle is 804mm^2. Move up to a 20mm rail it now becomes Pi(20)^2 which is over 1200 mm^2, roughly 50% more mass. Considering that bending strength is correlated with mass^2, the difference is exponential.

I would agree that moving to a 25mm rail is much stronger yet (the same math applies), but there is a huge difference between a 16 and 20mm rail.

The weak point, however, is not the rails, its the bearings. I am not sure if the 20mm bearings are 50% again stronger then the 16's, you will have to look at the ratings.

[HorridHenry]

Sorry but equations don't fit into my vocabulrary when comparing size of round rail that are so close in size to each other,I like to see with my own eyes the difference.

Get a caliper and find two disc,1 of 16mm and 1 of 20mm its hardly worth changing from 16mm to 20mm because the difference is minimal.

[ger21]

And the difference from 20mm to 25mm is just as minimal.

If you look at the static load ratings for a single open carriage at VXB, you get:

16mm = 1180N
20mm = 1370N
25mm = 1570N

Using the 20mm shafts, you get 87% of the capacity of the 20mm shafts, for about half the price.

[crane550]

Sorry but equations don't fit into my vocabulrary when comparing size of round rail that are so close in size to each other,I like to see with my own eyes the difference.

Get a caliper and find two disc,1 of 16mm and 1 of 20mm its hardly worth changing from 16mm to 20mm because the difference is minimal.

You cannot argue with the math. What it looks like to you has no bearing on reality. The squared area is 50% larger, no matter what it looks like.

a 16mm shaft with average values for steel rates at 402.12 dynamic torque load. A 20mm shaft is rated at 785.4Nm. Thats nearly double. Still, a 25mm shaft is rated at 1533.98. Nearly double again.

The math does lie. Not that it matters, as Ger21 pointed out and I mentioned earlier, the weak point is in the bearings, not the diameter of the shaft.

[HorridHenry]

And the difference from 20mm to 25mm is just as minimal.

Behave yerself man, 16mm against 25mm is a difference.

[louieatienza]

Does this mean I can swap out my 20mm rails for the pair of 16s I had my eyes on? :banana:

[DonFrambach]

To go back to the OP's question.

For what it's worth, I built a small fixed gantry router using CNCRouterParts linear carriages for the "z" axis and the fixed gantry axis. I used 20mm supported round rails from Glacern for the moving table axis. Both systems worked very well (and one did not seem superior to the other). I selected the supported round rails for my moving table axis because I was concerned that the CNCRouterParts linear carriages might foul with dust when used as part of a moving table in a fixed gantry system. A huge number of people have sucessfully used the CNCRouterParts linear carriages for all axes of routers that do not have a fixed gantry. Many people have used supported round rails for all axes of there routers too. I would suggest that you use whatever fits best into your design.

[newpatch]

Thanks guys...

I didn't want to start a debate, but thanks for everyones input.

Being a newbie, I want to research as much as I can before starting my build. I would rather know things before hand and build my machine right the first time.

newpatch

[louieatienza]

Thanks guys...

I didn't want to start a debate, but thanks for everyones input.

Being a newbie, I want to research as much as I can before starting my build. I would rather know things before hand and build my machine right the first time.

newpatch

You can use the most ridgid linear rails you can. The limiting factor will be your budget and access to materials and machining. The rails are only as good as the frame you bolt them on to.

[LazyMan]

I have used 20mm Supported rails for two machines. On my second machine, the tolerance on my bearings blocks was pretty lousy. A few blocks had a .01" height difference in height. They are not impressively rigid either. I do not know how they compare to CNCRP rails, but there is absolutely NO comparison to the rigidity of profile linear rails. I used the 20mm supported rails on a dual X driven 2x4 ft machine and they work okay but not nearly as rigid as I hoped. Without the dual drive it really takes surprisingly little force to skew the gantry by hand. During setup I also had a problem where the X steppers were not properly synced and the bearings were easily damaged. If you look at the bearings for supported rails, you will see that the ball and rail contact points are not even symmetrical providing very little rigidity in certain orientations. I was a big fan of round rails, until I used some profile rails. If you are building a solid machine, the additional cost of profile rails is worth it.

[newpatch]

LazyMan,

Are these the profile rails your talking about?



If they are, I just scored these yesterday for $85.....I have a thread about it,

http://www.cnczone.com/forums/diy-cn...owards_my.html

newpatch