[ger21]

If you compare the new proposal with an existing pipe machine... say Joe's for example. Joe has 8 threaded rods used as adjusters running pretty much just to the outside of each corner of each individual tortion box. In his design these were incorporated into the ribs that hold the pipes. In Gerry's alternative we would have to think about how to keep those features since they do help in straightening out any warps that develope in the system over time.

I've never looked that cosely at Joe's design to know what's going on with the threaded rods, but, imo, a well built and well sealed torsion box should not develop any warps over time. It may start to sag, but I'm not sure if you can do anything about that. And I'm not proposing this as a retrofit to a machine like Joe's, but I plan on designing a complete machine

My other question would be, how much stiffness does each of the pipes conrtibute to the system as compared to the flat steel tacks, and how detrimental would it be (if any) to loosing that stiffness. Especially for those of us with fairly sizable tables.

I don't think the pipes contribute much stiffness at all. If they were glued in place they would, but if not, I don't think so. And if you read my first post, the rail would be made of laminated wood strips. Using hardwoods for the laminations would result in a pretty stiff piece of wood. You could also add some carbon fiber in the laminations to increase stiffness, but I don't know how much difference that would make.

On the other hand, several people have reported wear on the pipes and the need to rotate or even change them out. In Gerry's new proposal, changing out the steel flatstock would be a breeze.

Not exactly. I planned on bonding the steel with epoxy to try to maintain parallelism. If left loose, I think dust and chips might find there way underneath and possible create an uneven surface.

[Jason Marsha]

Cool idea Gerry, thanks for sharing.

Jason

[sdantonio]

Hi Gerry,

I aree with your point on a well built tortion box not developing warping, however, you and I have both working in wood for years, not everyone builds to the same standards. I'm not saying anyone is intentionally sloppy. But building in wood is a skill that is developed over years, and a metal worker who has never worked in wood (or rarely does) may not have developed that skill set. My wood skill are good and I'll be the first to admit my metal work skill suck, not because I'm sloppy, but because I haven't developed the feel and intuition for it. I look forward to seeing your complete design.

On point 2 that is good to hear that the pipe may not be that much of a structural member, and I did read the point about the laminated ply making up the main structure of the roller.

As for point 3, and I invite you to try this yourself. Epoxy has very good strength in bonding metals for translational stresses. But it has fairly poor peel strength. take two pieces of aluminum or any other metal (cleaned bonding surfaces of course) and glue then together. Try to pull then apart in a way that one has to slip across the others surface. Tough to do. Now, take a knife and slide it under one edge. Torque the knife to start the peeling process. They will peel apart pretty easily. This is my point about changing out the metal strips. The epoxy will anchor the metal strip very well when the whole mechanism is clamped together by the rollers and you will get no longitutinal slipping of the metal strip. But when the piece needs to be changed out you can peel it off fairly easily by applying a stress that it would never see in the normal course of operation of the machine.

[sdantonio]

take two pieces of aluminum or any other metal (cleaned bonding surfaces of course) and glue then together.

Metal and wood will give the same result with the only difference being virtually all the epoxy will be on the wood side of the resulting peel.

[ger21]

WHen I was building my Z axis, I made some panels by epoxying decorative aluminum sheet to 1/4" plywood in my vacuum press. Extremely rigid, until I drilled a hole and it started to separate at a corner. Once it started, it peeled off easily with my fingers. I was assuming it just didn't bond well to the anodized aluminum.

I plan on putting a screw at each end to keep it from sliding around until the glue cures, and clamping them to a flat surface with a flat caul on the other side to get them as flat as possible.

Also, if the bond is real good, you can heat the steel with a soldering iron until the bond breaks. But I wouldn't think that the steel will need replacing.

I forgot to mention it before. You mentioned hardened steel bars. Very expensive, at least at McMaster Carr. Relative to the standard stuff anyway. I was planning on using 1/8" x 3/4", btw.

[thkoutsidthebox]

Fantastic thread. This idea would be a great alteration to the solsylva machine.

One thing, an idea drawn from the solsylva design and adapted, instead of the metal flat, why not run your rail edges on a router table to create a groove for each piece of metal, and use square tubing recessed in the grooves.

This will give the same effect as the flat bar, but you can then drill and thread the inside edge of the tubing to take bolts. The tubing can be bolted in from the opposite sides with the bolt head's recessed into the wood also. This would also work with solid square bar, or thick enough flat.

Again, great idea. Simple, easy to build, I imagine very ridgid with some alterations, and could be very inexpensive. I like it!

I'd use 4 flat metal surfaces instead of 3. The three shown in the 1st pic, then a 4th on the other edge near the top. This should give plenty of ridgidity.

L8rs.

[Oldmanandhistoy]

Fantastic thread. This idea would be a great alteration to the solsylva machine.

One thing, an idea drawn from the solsylva design and adapted, instead of the metal flat, why not run your rail edges on a router table to create a groove for each piece of metal, and use square tubing recessed in the grooves.

This will give the same effect as the flat bar, but you can then drill and thread the inside edge of the tubing to take bolts. The tubing can be bolted in from the opposite sides with the bolt head's recessed into the wood also. This would also work with solid square bar, or thick enough flat.

Again, great idea. Simple, easy to build, I imagine very ridgid with some alterations, and could be very inexpensive. I like it! .

Do you mean a groove in the side of your machine table and a square tube fitted into that? Using the groove to align the square rail?

I'd use 4 flat metal surfaces instead of 3. The three shown in the 1st pic, then a 4th on the other edge near the top. This should give plenty of ridgidity.

L8rs.

Can you elaborate; can’t quite see what you mean?

John

[ger21]

instead of the metal flat, why not run your rail edges on a router table to create a groove for each piece of metal, and use square tubing recessed in the grooves.

Because it's very hard (read impossible) to get a precise dado (groove) on a router table. You will have variations in depth, no matter how good you are. They may be small variations, but they will be there none the less. With a properly set up jointer, you can get 2 very straight edges. Then run it through a planer and you will have 2 sides that are about as parallel as you can get, with woodworking tools. The mounting holes in the rail should allow for adjustment of any slight bowing that may occur. The rails need to be very precise. If not, you'd be better off with round rails.

Also, you'd rather drill and tap a ton of holes, rather than spread a little epoxy and clamp? No thanks. I'm just going to use a small woodscrew at each end to hold the rails in place until the glue cures, so they don't slide around.

I'm re-drawing it with the eccentric bushing and bigger bearing on the bottom. I'll post a new image soon.

[thkoutsidthebox]

This might make it a bit clearer OMH. Its only a quick freehand sketch so I hope it illustrates the point ok.

The drawing is a bit off, only three (3) 'L' sections are necessary, not four (4) as shown. But this is what I was thinking before drawing it. The 4th one I mentioned previously is shown top right and would allow securing from the 4th (In this case right hand) side. The top left 'L' section would not be necessary if the wooden beam was less thick, or if the bolts joining the left hand two were longer (Just pretend its not there! ) I just don't feel confidant about the epoxy alone holding the flat bars in position over time.

The groove doesn't have to be perfect, the tubing would be levelled by tightening/loosening the bolts along the length of the beam. The bolts can be glued in and adjusted before the glue dries, so once its level the glue can set and it'd be solid. Perhaps a set of bolts every 24 inches or so, depending upon the size of the machine.

Obviously the bolts are staggered, not all in one spot as shown in the pic.

The carriage can be adjusted to allow for however amount of bearings you feel necessary, thus reducing the load on any individual bearing, as with the original idea of the bar, and this way the bearings on the carriage can be individually tightened into the rail from four sides giving a lot of ridgidity. To make it even more secure you could add in another 'L' section in the bottom right so the beam is entirely surrounded. And the bearings are tightened in to prevent all movement in any direction.

Ger, about your point relating to the grooves, you could do this with the tubing section sitting on the beam and not in any grooves at all, this would still allow securing with bolts instead of just epoxy alone.

Related to the tubing not being flat, you could cut 12" sections and place them along end to end for whatever length, reducing the unevenness I think, and also over time they would flatten even more through being pulled to the beam by the bolts.

Just an idea.

Edit: See following post, I think it shows it better.

[sdantonio]

I just don't feel confidant about the epoxy alone holding the flat bars in position over time.

Just an idea.

Gerry mentioned to me in one of his replies that the ends of the flats are being screwed down.

In your diagram you have bearings on all 4 sides of the beam. Correct me if I'm wrong (you will anyway) but I would think that the beam would derive a great deal of it's strength and rigidity from being attached directly to the tortion box as in Gerry's original drawing. Allowing it to be free floating (attached only on the ends) as would be necessary in your scheme would greatly weaken it and possibly open in up for harmonic motion. I'd hate to think of the Tacoma Narrows Bridge disaster, CNC version happening to someone http://upload.wikimedia.org/wikipedi...estruction.ogg

[thkoutsidthebox]

The beam would be attached along its length on the right hand side below the 4th rail. I'll do up a proper 3D diagram and you can give me your thoughts.

[thkoutsidthebox]

Ok heres the 3D pics. The first two are using sets of 4 bearings. The second two show using blocks for more ridgidity on two sides. The 5th & 6th photo just shows the bolt mechanism for attaching the metal tubing.

Here is also two videos of the two alternate design to give you an idea.

Without Blocks:
http://video.google.com/videoplay?do...87917422&hl=en

With Blocks:
http://video.google.com/videoplay?do...42261723167242

[ger21]

Do you really think you can get all those bearings in a perfectly straight line? I'd guess that 2 of the 4 will never touch the rail. And wrapping around to the bottom just makes it too weak, imo. But feel free to build it and see how it works. Just seems much too complicated, and not as strong.

[thkoutsidthebox]

One of the beauties is that you can use more or less bearings as necessary, or like in your first pic, can use more than one bearing on each bolt beside each other. While saying that, you are more than likely correct, and as always I value your comments. This is your thread after all. Not sure what you mean about strength though, there is just as much strength as in your design....

[ger21]

Not sure what you mean about strength though, there is just as much strength as in your design....

Your right, sort of. Those long bolts you drew through me off. I did add a block of wood in between the two pieces of angle, because I felt that the bolts alone might not be stiff enough.

[thkoutsidthebox]

Your right, sort of. Those long bolts you drew through me off. I did add a block of wood in between the two pieces of angle, because I felt that the bolts alone might not be stiff enough.

I see what you mean. When I drew it I simply used a piece of 4x4 for the rail beam because it popped into my head. Because of its size, compared to the 1x1 aluminium angle, the bolts are fairly long, but the beam could be 'squashed' from whatever side you want in order to make the bolts shorter. 4x2, 4x3, 2x2 etc etc

PS: I have now added my second video above.

[ger21]

The one in my original pic is 1-3/4" x 2".

[thkoutsidthebox]

PPS: That attractive guy in the second animation is me!! rofl

I cant seem to find the 'embed' info for the google video's anymore...anyone see it? Thanks.

[fyffe555]

Something you might want to consider is that the weakest part of these interesting designs is the aluminium area around the hole the cantilevered bolts run through. The bearings hung on a bolt supported at one end only will lever against the Al. extrusion and deflect a surprising amount. If its 1/8th thickness extrusion the max load will be surprisingly low. Calcs are somewhat complex but roughly speaking 60lbs at 1" could deflect the Al. enough to move the bearing 1/32".

If the cantilever is necessary I'd think about using steel angle instead of Al. Also try reducing the moment arm by having the cantilevered bolts, or rather the distance between the Al. extrusion and the bearing as short as possible. Use LARGE washers on the Al. extrusion to increase area under load. Try to avoid having the major load(s) on a cantilevered bearing if at all possible.

Post #18 looks pretty good to me, mostly because it looks readily repeatable with regular tools. If you do the 90% rotate on the right hand option you can make the depth of the beam as deep as you'd like, although you'd loose the bottom retainer bearing...

Hmm... need to go see if I can find my saw under all the c@#P in the garage....

[ger21]

I use 1/4" extrusions. The 1/8" you can bend a 12" piece in your hands. 1/4" is a LOT stronger.