[rlrhett]

Ahren,

Will the bearings be on eccentric bushings, or how will you assure that they are tight on a piece of 1/4 thick steel?

[ahren]

The moveable bearings ride in a slot. A nylon set screw is used to set the gap between the fixed bearing and the moving bearing. Once the gap is set, you tighten the screw that the moving bearing rides on. In this way, the set screw doesn't have to absorb high loading, as the bearing is held in place by the clamping force of the screw and nut. Also, the plastic set screw can deform slightly as you are tightening, providing a small defense against excessive preload.

[alexccmeister]

Hi guys, one more idea for not too stiff constructions, which is usable for wood routers like my one:
Attachment 39213

Attachment 39214

Attachment 39215

Attachment 39216

Attachment 39217

Attachment 39218

Hi Constantine,

I have been reading this thread and I have to say your design is simple and straightfoward. I am thinking about using this method for linear rail guide for a mill I am planning to build.

I have a question if you or anyone here can help me to answer. I noticed that alot of the guide rail plans here by many experts don't take into account of play in the system. I.E. if you place the bearing into the guide, chances are there will be some play hence creating some sort of backlash. Is this something I should be worried about? Or is it not a concern when creating such a rail system with bearings?

With the rail system you are using, does the outer diameter of the bearing exactly fit the aluminium guide or do you expect some play?

Thanks.

Alex

[alexccmeister]

Hi DeWalt58,

Thanks for your explanation. I am getting some of what you are saying although I believe for me to really understand how the concentric and eccentric bushing will remove play will be for me to buy some and test them out. Will the V bearing rotate also? If so, I wonder how the eccentric bearing will rotate? If you know what I mean.

I have a picture here which I have linked from another thread and its from Gerry (ger21). And it show his design for using skate bearing as a guide rail for his router. Now looking at the picture, how do you ensure there are no play for the top and bottom bearing? There doesn't seem to be any adjusting plate to get the two bearings to move closer so they will sit tightly on the flat metal surface.

I am planning to build my own mill using similar system of rails and would like to know how they actually work before building one. Thanks.



Alex

[ger21]

Alex, I moved your question back into this thread. There is no easy way in the pic you copied to adjust the bearings. Further down in this thread I was going to use the eccentric bushings for the adjustment.

The eccentric and concentric bushings are not bearings, and do not rotate. They are 3/8 diameter, to fit inside the bearings of the V-rollers, and have a 1/4" bore , so the rollers are mounted on 1/4" bolts. The eccentric bushing has the 1/4" hole off center, so as you rotate the bushing the roller can be adjusted tighter or looser. Once you have it the way you want, you tighten the 1/4" bolt to lock it in place.

[DeWalt58]

ok Alex, lets try again here.....see picture below...if the brass is the bushing....and the hole in the brass is not centered, it is known as being Eccentric. Now if a bolt was inserted into hole and the brass was rotated, it will move off center, moving the bearing. So if you have two of these on the left side of the Z-axis, you could adjust the slop out, provided you don't have more slop then you can adjust for. Can you see it now?

Cheers
dewalt58

[alexccmeister]

To Gerry and DeWalt58,

Wow, so simple and straightforward. Now i see it. Before this I was cracking my head trying to figure out how to get the bearing to sit tightly on a rail to remove any play or slop.

And DeWalt58, appreciate the photo showing the use of the skate bearing with the brass bushing as oppose to the V-groove bearing. I was going to use more of the skate bearing in my plan.

Gerry, is the bushing a standard fit and do they only come in 1/4" bore? I was hoping to get some in metric measurement. I can easily get bearing with mm measured bore in Brunei. Not sure if it is easy to get inch bearing here.

Once again thanks for the explanation guys.

Alex

[ger21]

The bushings being discussed are made to fit the V-rollers, and are only available in the one size, afaik?

[DeWalt58]

Alex, I used something similar on my last mill, z-axis, long bolts with bearings on the ends and found they will flex, even bend under stress. I was up to 5/16" bolts with nuts stacked up and they still bent under stress. So I recommend keeping the bearings as close to the angle as possible. And large flat surfaces like to collect wood dust, which builds up under the bearings and adds friction. Not a good idea. Heres one to ponder, two bearings on a bushing, spaced apart, riding an angle, iron of course not alum. I know its not too great for the bearings, puts a side load on em, but could work. Just a thought off the top of my head.

Cheers
dewalt58

[alexccmeister]

Thanks guys for the help.

Will look at the design as suggested by DeWalt58 but I have to say I am more comfortable with Gerry's design as it is easier to do I guess as oppose to the angle rail. Will need to use some sort of way covers to prevent chips from clogging up the rail. Will see. Thanks.

[alexccmeister]

Oh! Another question. I have seen people using linear bearing (open type) for their rail support. Any chance these bearing will have play or slop?

[the__extreme]

Here are some pics from my machine. Well, my machine so far. If you've read this thread through, they're the same designs I talked about before. John (oldmanandhistory) also tried the square tube approach. I haven't been able to really test the square tubes setup on the table, but it seems like it'll work well. The hex rails & bearings work well.

Shawn

[braidmd]

I've finally made enough progress on my router's frame that I was able to rough out one of the gantry's bearing trucks. It still needs a bit of work. But it seems to function quite nicely. It rolls smoothly and has no detectable lateral play. Of course, this was tested by rolling on the rail and twisting the truck by hand... Fortunately, my wife didn't see "testing" it. We'll see how it functions when the gantry is assembled. But so far, so good. :banana:

[ger21]

What's going to keep it from lifting?

[braidmd]

Hi Gerry - The trucks will be paired on upper and lower rails to keep it from the assembly from lifting. I plan to use this design for the X and Y rails. I have an IKO rail that I'll be using for the Z axis, which is not reflected in the design pic shown. I still need to work on the mounting scheme for the Z, which will likely happen once I get the gantry roughed out and assembled. Ah, but that's another thread...

Regarding this truck design, the bearing axles have tensioning bolts that apply inward pressure against the rail. The axles ride in slots, which were crudely formed by drilling holes and using a dremel w/cutoff wheels (it took several to finish one truck) to connect them. They aren't pretty. But they work. I had posted earlier in this thread... post #270, I think... which has some more detail and pics. I hope to make some progress in the days ahead... maybe something worth posting?!?

[dertsap]

what i used for mine was square tubing welded to angle with v-groove bearings , it s quite simple , effective and solid

angle iron and skate bearings could easily be substituted for the v bearings


http://www.cnczone.com/forums/attach...6&d=1174507965
http://www.cnczone.com/forums/attach...5&d=1174507965
http://www.cnczone.com/forums/attach...4&d=1174507965
http://www.cnczone.com/forums/attach...3&d=1173990542

[braidmd]

Dertsap - That's pretty cool! The square tubing looks like it would pivot on the angle iron... Seems to defy gravity. But I'm sure some good welds are holding it securely. Amazing...

[beone]

OK guys,
I don't want to start any flame wars but I have to comment.
It has been many years since statics and dynamics in engineering school but I still remember it. If you draw the vector diagrams for a skate wheel bearing trolley you will see that they combine to a vector directly out of the trolly. thus, there is NO, I repeat NO axial load on the bearings. all load is radial to the bearing from the centerline of the tube thru the center of the bearing. This assumes of course proper design and construction of the trolley. Think of it this way, if you removed the bearings and replaced them with a dowell of the proper length between the tube and the bolt which holds the bearing, it would support any weight up to failure but the dowells would not slip out as there is no side force.
Thus, axial loads on the bearings is not an issue, simply whether the bearing is within its radial load capability.
Like Joe2006, I have been running my machine pretty hard for 1 1/2 years with no sign of any bearing problems and I use standard 1 inch conduit for my tubes. I think you guys are trying to solve a problem that dosn't exist.

[alexccmeister]

OK guys,
I don't want to start any flame wars but I have to comment.
It has been many years since statics and dynamics in engineering school but I still remember it. If you draw the vector diagrams for a skate wheel bearing trolley you will see that they combine to a vector directly out of the trolly. thus, there is NO, I repeat NO axial load on the bearings. all load is radial to the bearing from the centerline of the tube thru the center of the bearing. This assumes of course proper design and construction of the trolley. Think of it this way, if you removed the bearings and replaced them with a dowell of the proper length between the tube and the bolt which holds the bearing, it would support any weight up to failure but the dowells would not slip out as there is no side force.
Thus, axial loads on the bearings is not an issue, simply whether the bearing is within its radial load capability.
Like Joe2006, I have been running my machine pretty hard for 1 1/2 years with no sign of any bearing problems and I use standard 1 inch conduit for my tubes. I think you guys are trying to solve a problem that dosn't exist.

Great info. Thanks.

[the__extreme]

Hi Dave,

The statics and dynamics are very fresh in my mind, I'll be finished my mech eng & management degree in April. You're forgetting to include friction in your analysis. True, in a contact between a cylinder (bearing) and a perpendicular cylinder (tube) the force vector will be purely radial with respect to both cylinders. However, once you start to push two 90 degree opposed bearings, like the typical aluminum angle-skate bearing-tube setup, against the tube to maintain good contact, two things happen. First, the radial load increases as more force is applied, and this is as you correctly say, purely radial. Secondly, there is friction between the bearings and the tube. Granted this isn't much, but it's still there and it does cause some axial loading.

Fortunately, the nice thing about deep groove radial ball bearings, is that they can support some axial load. Even better, is that this potential for axial support increases with the radial load, up to a point of course. For the most part, that's why most people never have any serious trouble with their bearings.

Where you may see problems is when using deep groove bearings to support a lead screw, because in that case, the bearing is (almost entirely) axially loaded, and they're really not designed for that kind of use. On the bright side, the operating speeds don't get too high, and reducing the life expectancy by 100 or 1000 times, given the 'potential' cost of replacing some cheap ball bearings, is a pretty reasonable trade-off, at least in my mind.

Where most of these designs really benefit is moving from a perpendicular cylinder-on-cylinder contact, to a cylinder-on-plane contact, which reduces the contact pressure, reduces deformation of the tube and bearings, and won't fatigue the materials as quickly.

In any event, even if axial load isn't a huge issue, it's a great thread to develop ideas that all of us building CNC machines can benefit from. I also think its great when someone challenges the logic and objectives or presents a different perspective. It keeps ideas fresh and keeps people thinking, and not following blindly.

Cheers,
Shawn