No, they are all about equal and none are easy to stop. One of my primary tests is whether they all resist being stopped by hand.can you push the bearing block and hold a bearing with you fingers, tight enough to stop it rolling?
That's about the distance I have between the two ground bars.although mine will only be about 600mm wide at most.
You probably have some false alignment, so they are fighting each other. If I back off the pressure a tad, mine flows quite nicely.That's not far off from how mine behave, except I don't think mine are nearly as tight as yours.
Does that last one show you want you wanted, that was new, I just uploaded it earlier.I just wanted to have a look underneath.
I have a freeCAD model but you'll need the "assembly3" build of FreeCAD, it is an assembly of axis, bearing, washers and the block.
Last edited by reg.miller; 03-19-2019 at 06:18 PM.
Please send the model. I'll figure out some way to check it out. I'll do the alignment as soon as I get a few hours to spare. In the meantime, I'll be working on a revamped design of mine in sketchup. I forgot to ask whether your bearing blocks (x-axis) completely surround the rails. It doesn't seem so from the photos and the video, but I just wanted to confirm. If it doesn't, wouldn't you have had a chance of fully supporting the "open" length of the rail and completely eliminating deflection?
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Never mind. After taking a closer look at the photos, I found the answer. Your design is efficient in that you could fully support your I beams from the inside. I on the other hand, don't have that privilege since all my rails will be completely surrounded by the bearings blocks.
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No, I did originally intent to hold just from one side but flex is the vertical plate allowed the bearings to separate slightly under load, leading to a lack of overall rigidity. This was not acceptable for what I am aiming to do, so I 'closed the box' and added a link between the bottom bearing and the bearing blocks at the top. That made a world of difference. You can see that in one of the videos I already posted, where the gantry is under motor control. In that case I have a 4mm steel , V-shaped support on the RHS and thicker ali plate on the LHS. Now I have steel V on both sides. ( The lower bearings were different at the time too. Now both sides are running U-groove as previous described ).
http://solaire-chauffe-eau.info/cnc/DualX.mp4
BTW I have also changed the bendy dog-leg vertical members. I really liked the look of them but again not rigid. I now have another sturdy ali extrusion there.
In fact you can just see the steel V in the other video but the table tends to obscure it. It's obviously much more compact than your tubes but I do also completely enclose the I-beam girder.
http://solaire-chauffe-eau.info/cnc/slide.mp4
Sent from my computer, using my tapafingers.
Hi,
here is the download page for the most recent Assembly3 version of FreeCAD. If you use Linux, the AppImage is the simplest way to test it. It's a bundle of the program and all dependent libraries which you can just run in place. No need to install anything to the machine.
https://github.com/realthunder/FreeC...mbly3/releases
Here is the model of my bearing block. When you run FreeCAD, look on the the Tools menu for View Turntable and you can see the object turn around. That should give you a clear what it looks like.
http://piments.com/cnc/block45-2.fcstd
Here is the assembly with the bearings, spacers and axes mounted into the block. ( I have now replaced the axes shown here with metric screws and I tap a thread in the block )
http://piments.com/cnc/guide-block-assy2.fcstd
I know your in SA but its a modern country I assume unless your out in the bush. For your linear rails why not use some small I beams say 1 inch 25 mm top and bottom by 3 inch or 75mm high? Cut to length, lay side by side on a flat surface and use your angle grinder or something better to true up the same. Then you could use your skate bearings on top and under the top rail. The last small I beams I found at a salvage yard.
1000x750 Workbee CNC - Mach4 - PMDX USB - Windows 10 Pro
Profile says Uganda. I don't think either country would appreciate being mixed with the other one.I know your in SA but its a modern country
I-beams are usually quite accurate to start with. If you attack them with an angle grinder you will have a right mess.
I used 80mm I-beams ( a little too small it turns out, not quite as rigid as I had intended but certainly better than steel tube ). Here is how I take the oddities out and get them parallel. Careful work with a file then thick mirror glass and abrasive paper.
I was referring to taking the mill scale off with an angle or flap disk grinder, I have a pretty complete home Fab shop, my retirement project was building a 3 Point backhoe for my John Deere tractor and it worked when I got done. I suggest looking at some commercial machines for some ideas that work. The I beams I used were strong enough for a small trailer. Your country is listed as SA in your location right below your Join Date.
1000x750 Workbee CNC - Mach4 - PMDX USB - Windows 10 Pro
Reg,
Not when I just checked it. Your profile location says Durban SA. Nothing about Uganda, Unless I've got my geography wrong, Durban is in So. Africa. Not sure why it would change spontaneously, but I suppose stranger things have happened. You may want to update your profile.
Regards,
Gary
Last edited by GME; 03-26-2019 at 11:52 PM.
Thanks Gary. I thought WMGeorge was commenting to imbaine13. It is his project this thread is about and it is he who is having trouble sorting out the guide rails. In fact he was commenting about his project suggesting he uses an I-beam, since I have already posted that I used I-beams from the start and suggested that solution to imbaine13.
You are correct though, that is probably where the confusion came from. WMGeorge probably did not read more that a couple of comments before posting and was not clear about whose project this was about.
I was replying to the last post which was Yours.... a reply to Me. You made a comment about my suggestion to use a angle grinder with a wheel or flap disk to clean up the I beams I suggested. Your location is listed as SA? It seems as if this is all about trial and error not design. Hence my suggestion to who ever to look at some successful builds, usually commercially made. I grew up on a farm and I was welding and repairing machines at a very young age. I design and build working projects all the time.
BTW If I was using an I beam, it would have either a 1/4 inch (6mm) or 3/8 inch (10mm) web not the one you pictured. I get my steel from a salvage yard near me.
1000x750 Workbee CNC - Mach4 - PMDX USB - Windows 10 Pro
Why were you suggesting I use I beams? We were not discussing my project ( which already uses I-beams ) we were discussing imbaine's problems where he is not using I-beams.
You were suggesting an angle grinder. The flap wheel walk back came after my comment that a grinder would make a mess.
Since this thread is getting into petty disingenuous arguments rather than discussing mechanics, unsubscribing. Better things to do.
A angle grinder can be fitted with many types of disks, any one can be used to clean off the mill scale. My discussion was about using a little common sense for example using real I beams instead of curtain rods. You pictured I beams in your post that appeared to be way to lightweight.
1000x750 Workbee CNC - Mach4 - PMDX USB - Windows 10 Pro
Hello Miller,
I see what you mean from the videos and also agree that "closing the box" makes a huge difference, which is why I did it right from the start. I also had a closer look at your I-beams (which look beefy), and if you're saying they deflected by 4cm under a 50kg load, then I'm a little worried about mine, mostly because my set up isn't anywhere close to the level of rigidity you've got in yours! My strategy was to use what I have on-hand (spent a lot on the steel so far and have to find a way of using it somehow). In my set up, I came up with the idea to add some 2" flat bar on either side of the 6040 steel (by 6040, I mean 60mm x 40mm x 1.2mm steel tubing) for extra rigidity. The flat bar can take some serious loads along the length if oriented with the 2" side as the height. I figured I'd add the flat bar on either side of the 6040 and see how things turn out. Hopefully, that'll be able to increase the moment of inertia of the X-axis rails.
According to this https://www.engineering.com/calculators/beams.htm site, I should get a 5mm deflection from the flat bar alone with a 30kg gantry, which is about as much as I expect it (the gantry) to weigh. I'm confident that the 6040 steel tubing and the two round pipes on either side, in addition to the flat bar, should reduce deflection to my requirements, but in case it doesn't, I'll have to find another solution. This machine is long overdue and at the moment, I just want to start building and solve whatever problems I face as I move along.
Quick question, how do you tighten up your bearings so they grip the SBR rods tightly? I can't figure it out from the photos and videos.
Thanks.
Thanks for the links, I use windows and as I type this, I'm installing freeCAD so I can have a closer look at your designs. I'm sure I'll get answers to a few questions I'm having, maybe even ideas for improvements I could make to my machine as it stands.
Thanks again.
http://solaire-chauffe-eau.info/cnc/DualX.mp4
Were your I-beams still deflecting at this stage of the build?
Hello George,
You and GME are having me confused with reg.miller. He's the one using the I-beams, with an almost complete machine. I on the other hand haven't started my build. I was having trouble getting my linear bearings to work satisfactorily, but I think I have managed to overcome that challenge. In the latest design, I headed out and bought some 20mm diameter (3/4"), 1.2mm wall thickness round steel pipe from the hardware store. It seems it'll hold a little better than the curtain rod. I might be wrong, but I believe the smaller diameter 3/4" pipe will better resist pressure from the bearings as they roll. Also got some aluminum U channel into which the 3/4" pipes sit comfortably.
Regarding the mill scale grinding, there is no way you can grind the I-beams using a handheld angle grinder and expect to get a straight surface. It is really difficult to maintain uniform pressure on the beam as you grind, and you will inevitably end up with a curved surface. reg.miller's idea makes a great deal of sense, glass is very flat and when combined with sand paper, would provide a relatively flat straight finish, kind of like how a hand planer works on wood. The bottom has to be flat, and should cover up a significant length of the surface being worked on. If you were planing a piece of wood for example, in order to get a desirable flat surface, the length of the planer you use IMO, should be at least 1/3 of the length of the wood work-piece being planed (this may vary depending on the texture of the surface, but holds true for most practice purposes). That way, the planer sort of "averages" the surface until it's uniform. Same goes here, but it still wouldn't be perfect.
Chears,
Isaac.
Final (hopefully) rail.