[spalm]

Well I am starting the build of my machine #3. I have always been intrigued with V-bearings, so I bought a couple of sets and plan to give them a go. I will give ply/MDF one more try. I am itching to mill aluminum, so am hoping that this machine will give me the strength to do it.

I kind of started this log before, but it digressed into epoxy and suchnot. This project will probably take a little while as I want to test and change as it goes along. I have been thinking about it for months now, and I have decided on a 24” x 40” with about 4” of Z.

I am going to try to get rid of the support of the gantry under the bed. This means that the gantry will have to be stiff. It will probably take a couple of tries to get it acceptable. It will be stiffer than the drawing suggests. This also means running the X leadscrew on the side. This in turn may lead to dual leadscrews, which will be a new adventure for me.

Comments always welcome,
Steve

[spalm]

I built the Y beam and test fitted it with a piece of scrap for the Z carriage. It is really stiff yet slides with ease. All 4 bearings have eccentrics installed for adjustment.

I used some old pieces for the internal support web, just to add some memories to the evolution of this build.

There are holes drilled though for threaded rod to attach to the gantry walls. I also plan to add dowels after final placement.

Steve

[ViperTX]

So, why do you need dual scews for the x-axis.....go down the center and save yourself some headaches...

[tobytorkn]

steve, where did you get the bearings, and slides? how much? i built my cnc using the rollers for sliding screen doors. it has very little slop, but your rollers look better made. thanks for the help. toby....

[Rance]

Viper, The pivot point of any axis is the lead screw by which that axis is driven, so if you're only gonna have one, then by having it closer to your router bit should give you better accuracy. Interesting diversion Steve, I like it.

[spalm]

Tobytorkin, I bought the bearings from the Zone’s own imserv at
http://www.cadcamcadcam.com but they are really from SuperiorBearing.

They are not the cheapest way to go, but I am really impressed with them. They are built for taking this kind of abuse. There is an eccentric collar that slips into the bearing and then a 1/4” bolt passes through this collar for mounting. As you twist the collar you can change the bearing pressure against the rail. I can not think of an easier adjustment scheme.

The X axis to me is the long axis. I think Viper is referring to the X while Rance is referring to the Y. (?)

Viper, I hear ya. I could just float the bed in the air and send a cross beam under the gantry to get to a center leadscrew mount ala JGRO. Since I am kind of playing here, I guess I want to try to push it and get rid of that box. My plan is to try the short gantry first and see what kind of racking I get, and then make a decision on going under the bed, adding a second leadscrew, or leaving it as is (preferred).

Rance, I hope I can take advantage of the space under the Y beam for it’s leadscrew since the rail and bearing already hang down about 2”. I think this is a good mechanical connection to the router as well.

The Y rails are 3/4” and the X rails are 2” angle iron.

Steve

[ger21]

Well I am starting the build of my machine #3.

Did you finish #2?

[spalm]

(I hope you are not talking baby potty talk to me )

Hmmm…. Finish? It runs and cuts well, just looks kind of crude. Rather than prettying it up, I wanted to try this. I still get to steal a few parts from #2.

Attached pics from #2.

BTW, have you finished yours? :stickpoke

Steve

[spalm]

Started making the X axis. Got the MDF beams cut and holes marked for support for the angle iron. Yea for sawsall, it cut the 2” angle like butter.

Made a test piece out of scrap to prove the hole locations for the bearings. I was really disappointed at first. I am cheating and using skate bearings on the bottom of the angle. When I first ran the assembly back and forth, it wanted to tilt in at the middle and then tilt out at the edges of the rail. I just went back into the shop to take pics to show you the problem, but I seemed to be able to fix it by running it back and forth a bunch of times and by loosening the bearing pressure a bit. Not sure if it will be a future problem or not.

What is angle iron coated with? I constantly get black dust every time I touch it. I guess the bearings are wearing it down. Is it some kind of cheap paint or maybe anodized? Can I paint over it without completely removing it?

Steve

[2muchstuff]

That coating is from the manufacturing process. It is a slag type (black) oxide from the metal being hot rolled or formed. Unless you grind it off it will continue to flake off. If you leave it on you might have to roll those bearings over it a million times or so to wear it down.

[Rance]

Yep, I was referring to the 'Y' axis.

Steve, one thing to keep in mind is that the taller angle you use, the less stable it will be. Have you considered going down to maybe 1" or less? Actually, you still need the 2" side to bolt it to the table so do they make 'L' iron (2"x1")?

[ger21]

BTW, have you finished yours? :stickpoke

Steve

I wasn't sure you had actually finished it.

I can see the light at the end of the tunnel. Another coat of paint on the gantry parts tonight, and I'll start final assembling next week.

[whateg01]

...so do they make 'L' iron (2"x1")?

You can have any color you want as long as it's black.

I don't know about 1x2, but I know I have some 1.5x2x.25 angle at home, so it is likely somebody makes it. It's probably just a matter of how much do you want to pay to find it. Actually, 1x2 seems a bit odd, but then again, you never know what you might find.

Good luck.

Dave

[spalm]

Rance, I have been having the size of rail debate with myself for quite a while. (I hate debating myself, but I do it way too much.) Yes, it seems like a 2” x 1” (or .5”) rail would be the best. 2” for mounting and 1” for rail. I actually had convinced myself that a taller rail would be more stable because the bearings were more spread apart. Now I don’t think so, and I see you agree. I think this will still work, but I really need to control the C shaped gantry from any parallelogram’ing.

On another note, I was talking to some coworkers about how strong angle iron was. Anyway, we googled angle iron bending and got the following pics. I had no idea that you could do such things. Then again, there is a lot that I have no idea about.

Steve

[whateg01]

Anyway, we googled angle iron bending and got the following pics. I had no idea that you could do such things. Then again, there is a lot that I have no idea about.

Steve

Steve,
Angle is malleable just like most other steel. It just takes the right tooling. Angle iron's main weakness (IMHO) is its lack of torsional rigidity. However, if one leg is held fixed, it should be well suited for low-tech applications like this. (THK gods would probably strike me down if I didn't include the low-tech blurb. )

You are correct with the thought that spacing the two bearing surfaces farther apart will decrease the effect that any play has on the system. That is simple physics. Doing so should also reduce the stress on the bearings. You can spread the bearing surfaces simply by filling in the space between the, in this case, angle iron with a slab of MDF or otherwise providing externally the necessary rigidity.

Something else worth mentioning is that while I do not know how widely available 1x2x? is, and I would suspect that you would want at least 3/16" thickness, I do know that 1.5x2x.25 is pretty easy to get, and in that thickness should be plenty rigid when mounted to something else.

Dave

[spalm]

Well, good news and bad news.

Good news: I finished the X beams and mounted the angle iron. I clamped the beams to a table and drove my test gantry over it by hand. Looking real good. Thanks for the help Dave, I sanded the angle iron and the black dust has disappeared. Plan to paint the rails later for show. It slides right nicely. I really like the way the Y travels. All initial testing has shown that this is superior to the wrap-around Y carriage that I came up with for machine #2. There is no front/back tilt and it should be much simpler to construct a carriage for the Z. The adjustments are simpler than the bearing plate thingy. I am sticking with this.

Now for the bad news. Did a lot of testing. The gantry racks terrible. I was concerned with parallelogram’ing or that the gantry could tilt left to right. Not a problem, the combination of the bearings and the Y torsion box seemed to take care of this. The problem I have is the gantry twisting. If I lock the left side, the right side can be moved front to back +/- .25”. I removed the gantry to the bench and repeated this test. It is defiantly caused from the 3/4” ply not having sufficient torsion strength. It is amazing (to me) how much it can twist. I clamped (not as good as gluing) a second sheet of ply for a total of 1.5” and got virtually the same result.

So now what to do. The gantry walls need help. Lengthening them while floating the bed and having a box underneath would help, but I really don’t want to do this. So strengthening them is my first choice. I guess it comes down to three things: torsion box sides, aluminum, or a better choice of wood.

Steve

[whateg01]

Steve,

I'm glad the angle iron will work for you. Regarding the sides of the gantry, you're right that clamping is not as good as gluing. When you clamp, you essentially have two thinner pieces side by side. When glued, you effectively have a single thick piece. A torsion box does the same thing as adding thickness but without the weight of a single piece the same thickness. The quick fix, glue a couple of pieces of plywood together. This should stiffen it up quite a bit, if that is, in fact, where the flexing is at. I don't know whether MDF or particleboard would be stiffer or not. I'm sure it would be heavier.

One thing that might help is a piece of 1/4" aluminum plate bolted/screwed to the side. I think aluminum cutoffs that I buy run about $1.50/#, so that would be a little over $5/sq. ft.

Just my 2.5 cents.

Dave

[paulC]

Would it be possible to add a glue block in each corner of the torsion box?
Adds a lot of strength when used on wooden joints.
Paul

[Rance]

Steve, are the V bearings rated for both axial AND radial loads? You are using both on them from what I can determine.

[ger21]

Steve, would the problem be solved by dual lead screws, or is it moving side to side?
With any luck, I'll be putting assembling my gantry this weekend, and I'll let you know if I get similar results. But I'm using dual screws to keep mine from moving.