[samsagaz]

Hi guys, is possible to calculate if can use just one linear Bearings or need to use two?

I have 2 models SBR16UU and SBR16LUU

SBR16UU is 45mm length and SBR16LUU is 90mm

i show 3 drawings, top base are MDF 220x170x18mm size

need to choice between these configurations

Option 1 - Use Two Small Bearings



Option 2 - Use just one Small Bearing (45mm)



Option 3 - Use one long Bearing (90mm)


Thanks

[louieatienza]

The farther they're spread out, the better at resisting twisting forces. so I'd say the first, by a mile

[Falcon69]

Or, better yet, get rid of those and go profile rails and bearing blocks.

[samsagaz]

Or, better yet, get rid of those and go profile rails and bearing blocks.

Can you show me a pic of these?
Thanks

[Walky]

You can't use only one block per round rail, you need at least two.
Profile rails are way better but they can cost about 3X more.

[samsagaz]

You can't use only one block per round rail, you need at least two.
Profile rails are way better but they can cost about 3X more.

Ok, will use two then!

[Falcon69]

These here, on this site, are profile rails.
overstock & surplus automation products: Motion Control, Linear Bearings/Rail

[samsagaz]

I see it, are a little expensive im trying to not spend too much money, now i have other question, if my gantry are 2000mm x 200mm wich of this conf will be better?

SCUUL - More Expensive, 95mm each support and 95mm bearing inside.



SCLUU - Default, 45mm each support and 45mm bearing inside.


SCVUU - Cheapest, 25mm each support and 45mm bearing inside. The same as Default one but with small support.


think that the cheapest is the best option. because the bearing are the same as Middle image, but little support, just 2 holes instead 4.

Reading the specs the cheapest and default ones have the same Load Ratings.

Specs Here... http://www.goodluckbuy.com/16mm-sc16...hing-4pcs.html



Question 2 - About the distance of the rails, is better to get separated or near? Right now are like 180mm away. i can put it at 120-140mm


(Sorry for my english)

[Walky]

The SCXXLUU (long blocks) have two bearings each (it's pretty much equivalent to two SCXXUU) so you only need one on each rail. Of course, this means you can't spread the bearings apart.

All the SC blocks are all closed (for unsupported rails) and are NOT adjustable. They are also not always exactly the same between each other. This means that different shaft and bearing tolerances can give different results. I recently got some SCXXLUU blocks which had too much play in one of my 16mm rails pair (completely unusable for CNC) and a perfect fit on another pair of rails of the "same" diameter. The difference in their diameter? about 0.036mm. I've also gotten stuff with a good fit and have actualy build a quite precise machine with this kind of blocks and rails, but there's a lot of luck factor involved.

As an extreme measure, you can replace the LMXXUU internal bearings on them with LMXXUUAJ, then drill a couple of holes, tap them and insert adjustmenmt screws to press the bearings against the rail. I suggest 2 holes for each internal bearing, so the SCXXVUU are not a good candidate for this modification.

Using 2000mm unsupported rails is completely unreal, as for them not to flex you'd need a very, very high diameter rail, which means bigger blocks, and it would most likely be more expensive than just using supported rails.

The actual effect of the rail separation really depends on the complete design of your machine. It would be good to have a look at a preliminary design of your complete machine.

Now I wonder, you're talking about a gantry (which usually refers to the horizontal bridge for a CNC router), but you say your machine is for a wire cutter?.

I though you already had bought the linear components? What do you have at hand to work with right now?

[samsagaz]

The SCXXLUU (long blocks) have two bearings each (it's pretty much equivalent to two SCXXUU) so you only need one on each rail. Of course, this means you can't spread the bearings apart.

All the SC blocks are all closed (for unsupported rails) and are NOT adjustable. They are also not always exactly the same between each other. This means that different shaft and bearing tolerances can give different results. I recently got some SCXXLUU blocks which had too much play in one of my 16mm rails pair (completely unusable for CNC) and a perfect fit on another pair of rails of the "same" diameter. The difference in their diameter? about 0.036mm. I've also gotten stuff with a good fit and have actualy build a quite precise machine with this kind of blocks and rails, but there's a lot of luck factor involved.

As an extreme measure, you can replace the LMXXUU internal bearings on them with LMXXUUAJ, then drill a couple of holes, tap them and insert adjustmenmt screws to press the bearings against the rail. I suggest 2 holes for each internal bearing, so the SCXXVUU are not a good candidate for this modification.

Using 2000mm unsupported rails is completely unreal, as for them not to flex you'd need a very, very high diameter rail, which means bigger blocks, and it would most likely be more expensive than just using supported rails.

The actual effect of the rail separation really depends on the complete design of your machine. It would be good to have a look at a preliminary design of your complete machine.

Now I wonder, you're talking about a gantry (which usually refers to the horizontal bridge for a CNC router), but you say your machine is for a wire cutter?.

I though you already had bought the linear components? What do you have at hand to work with right now?

Hi Walky, as you know my english sux


The SCXXLUU (long blocks) have two bearings each (it's pretty much equivalent to two SCXXUU) so you only need one on each rail. Of course, this means you can't spread the bearings apart.

Well, i prefer to use the SCXXUU then, to give me the option to spread the support

All the SC blocks are all closed (for unsupported rails) and are NOT adjustable. They are also not always exactly the same between each other. This means that different shaft and bearing tolerances can give different results. I recently got some SCXXLUU blocks which had too much play in one of my 16mm rails pair (completely unusable for CNC) and a perfect fit on another pair of rails of the "same" diameter. The difference in their diameter? about 0.036mm. I've also gotten stuff with a good fit and have actualy build a quite precise machine with this kind of blocks and rails, but there's a lot of luck factor involved.

Yes i know about that, i will use the open ones for the longest axis and the closed ones for the Y axis, so can get the Y Axis a little light. i have some rails and cnc parts at home, but will purchase others, because this proyect are a little big, and all the rails that have are less than 500mm.

As an extreme measure, you can replace the LMXXUU internal bearings on them with LMXXUUAJ, then drill a couple of holes, tap them and insert adjustmenmt screws to press the bearings against the rail. I suggest 2 holes for each internal bearing, so the SCXXVUU are not a good candidate for this modification.

I see, was thinking abt purchase SCXXVUU because will be easy to attach to the Base/plate where will attached the wire. really dont know what to do then.

Using 2000mm unsupported rails is completely unreal, as for them not to flex you'd need a very, very high diameter rail, which means bigger blocks, and it would most likely be more expensive than just using supported rails.

I dont need 2000mm rails, i will use 1220mm rail, in X Axis with support, and in the Y Axis without support. Y Axis will be 720mm rails or 1220mm rail, dont know yet, dont know if make the machine to cut 1000x1000x2000 foam or 500x1000x2000

The actual effect of the rail separation really depends on the complete design of your machine. It would be good to have a look at a preliminary design of your complete machine.

Will finish the drawing in a few minutes

Now I wonder, you're talking about a gantry (which usually refers to the horizontal bridge for a CNC router), but you say your machine is for a wire cutter?.

Yeah, i read the word gantry in the forum, and i use it, but i was talking about the Y Axis Base where i will attach the wire and will be attached to the Nut of the ballscrew.

I though you already had bought the linear components? What do you have at hand to work with right now?

I have some components, but will place an order this week, as i told a few lines before, i dont have the enough length, and is ok to change the rails and support. for example i will use BK12/BF12 for X axis and FK12/FF12 for Y one, have some BK at home, but will purchase more

HOpe that understand what im trying to say will post some pictures of the final drawing asap

[Walky]

For 16mm rails, even 1220mm is still very long, in fact it would jump all over the place if it were a CNC router under cutting forces. On the other hand, this is a wire cutter so the forces are much lower, but I'd still be a little worried about vibration at such length, especially when cutting at the top of the Y axis where forces and inertia would be magnified (for example when changing direction, which would be more noticeable with higher accelerations). Regarding that, a good separation between the X (ground) bearings would help a lot to stiffen things up. About 30 cms between them won't hurt.

Weight shouldn't be such a big concern, in fact it adds rigidity, and a hot wire cutter cuts very slowly anyway (and stepper motors have more torque at low speeds).

What motors/drivers will you use?

Your english is not bad at all, it's quite easy to understand

[samsagaz]

For 16mm rails, even 1220mm is still very long, in fact it would jump all over the place if it were a CNC router under cutting forces. On the other hand, this is a wire cutter so the forces are much lower, but I'd still be a little worried about vibration at such length, especially when cutting at the top of the Y axis where forces and inertia would be magnified (for example when changing direction, which would be more noticeable with higher accelerations). Regarding that, a good separation between the X (ground) bearings would help a lot to stiffen things up. About 30 cms between them won't hurt.

Weight shouldn't be such a big concern, in fact it adds rigidity, and a hot wire cutter cuts very slowly anyway (and stepper motors have more torque at low speeds).

What motors/drivers will you use?

Your english is not bad at all, it's quite easy to understand

Want to use G540 + 4 x KL23H2100-35-4B

You know if is possible to use SBR16 horizontal? (let me show you a pic) so you understand what im asking...

[samsagaz]

maybe can distribute the force weight better using this kind of configuration instead use the X axis in the floor.

But think that the SBR16 will not work very well in that configuration :/

[Walky]

Of course you can, they will work OK, no problem at all. Most CNC router gantries that use SBR rails are like that, at 90º.

I like that design, it would allow you to join both sides (left and right) of the machine structure both at the top and the bottom, and it would also not create so much cantilever on the Y uprights.

[samsagaz]

[Walky]

That's looking good!. Spreading the X carriages will reduce racking even more, but even as it is it should be fine.

You can also spread the rails more, even to the extremes.

[samsagaz]

Was thinkgin abt use 40x40x3.2mm tube for the frame. Impossible to get 8020 or similar in argentina. and cost will be low using 40x40x3.2mm, the cost of each tube are 40USD, will need 1 for each side. so for 100USD can made the frame (without join the both sides), maybe will join both side later.

An can save some bucks usint 40x40x2mm or 40x40x1.6mm

[samsagaz]

That's looking good!. Spreading the X carriages will reduce racking even more, but even as it is it should be fine.

You can also spread the rails more.

You say that move the sbr16 close to the edge of Y base, right?

I m using like 250mm space between ballscrew and rails.

[Walky]

The side to side joint could be adjustable (so you can use different material sizes depending on the kind of work). It would also be OK to just fix each side independently to the floor, perhaps with a couple of diagonal tubes each so the top doesn't move too much.

Look at the time! I'd better go to sleep haha, see you tomorrow!

[Walky]

You say that move the sbr16 close to the edge of Y base, right?

I m using like 250mm space between ballscrew and rails.

Yes, one SBR rail at the bottom, and the other at the top.

The space between the ballscrew and rails is not really important as long as it's centered between them.

Spreading both the rails and the bearing blocks will reduce racking (which is the small play you'll feel if you push one side of the vertical Y assembly in one direction and the other side in the opposite, with the ballscrew position as the pivot.

Good night!