Jack's unistrut build

[Jack000]

hi guys

so I'm starting a new build, this time a 4x4 with all steel and aluminum construction. It will be based on the idea of using unistrut as rails (it seems to fit the butcher boy bearings on ebay perfectly).



I've pretty much designed the whole thing out in cad, let me know if you see any design issues! I will probably start buying materials this week.

[FandZ]

I can't tell you how many times I've walked by the unistruts at lows and said hrmmm I wonder if... I've also checked out the slotted ones too.



Checking out your designs, I'm thinking if you have your rails butted up against each other, It'll be much stronger. It would be like have a steel extruded H beam. Very sturdy. I'm attaching a picture of what I mean. You could drill them every 6 or so inches and bolt them together making them even stronger. Or you could keep it the way it is and drill it every 6 inches and get a some long bolts and nuts and and secure them to each other that way. I played with useing two tubes with bearings running only on the top and bottom and found it was easy to bend them inwards which could lead to racking or would it be chattering.

The way you have your table top supports going underneath the angled tabs, could the unistruts be moved above the front and back cross beams and the tabs used underneath? Maybe you could just get rid of the little tabs all together and just drill some holes and bolt them together. Just seems like there is a lot of stability and strength to be gained from mounting them differently.



Also, how do you plan to adjust your bearings? If you've found a good supply of concentric bushings, please share.

Looking forward to your progress on this build.It's funny we both are building another cnc machine at the same time again. I'm going smaller though .

[FandZ]

Oh yea, on your X and Y rails. you basically have 4 rails on each side, why not use 8 rollers instead of 4? You could mirror your gantry sides and bolt them together easily enough and it wouldn't add much to the cost.

[Jack000]

actually I wouldn't have to bolt them together, unistrut can supply them welded back to back (the engineering catalog at http://www.unistrutbc.com/literature.html has a list of all unistrut parts).

The reason that they are separated is for adjustment - that is, I will move the rails up and down to get a tight fit, instead of the bearings. I tried looking for u-groove bearings with eccentric bushings, but didn't find anything affordable (less than $10 a bearing). They really add up when you need 32 of them!

my total budget is only about $1700

$600 for strut, fasteners
$500 for electronics (probably cncrouterparts kit)
$200 screws, nuts
$200 milled aluminum parts
$200 for bearings

I did think about using both rails, but it will probably double my aluminum and bearing costs..

I've actually already bought the unistrut strut parts, so no going back now

[FandZ]

Ya know, It crossed my mind briefly that you may adjust the rails but I was hoping for a deal on those bushings...lol

I'm thinking you are going to need to support it like the picture I'm attaching. Then again, the stuff you have may be stronger than what I've seen before. Outside of my work, I've seen some unistruts that was ran in unsupported 5 foot lengths at the base of a guard rail. I tried bending it and I could get it to flex by hand towards the center. Hopefully yours will be thicker and stronger. Either way it won't be a big deal to stiffen it up if it's needed.




You stepping up to the G540? Gecko was running a deal a month back or so for g540 for 200 or 220. Probably over now but it may be worth a try. I really like the pre wired steppers on cnc router mounts but Crevice reamer posted something the other day that makes me wonder if your comfortable with soldering if it's the best option. Quick check on my drawing before ordering parts

[ger21]

I have to agree. Unistrut can be quite flexible, I think you'll need to stiffen it up.

Of bigger concern to me would be the rollers wearing out rather quickly riding on the unistrut. Are they aluminum? You need them to be very tight against the unistrut. From my experience with bearings rolling on steel pipe, the bearings form flat spots on the steel in a very short period of time. I'm guessing you'll see excessive wear in a matter of days??

Edit:

For a few more dollars, I'd recommend bolting steel angle to the unistrut and using V-Rollers riding on the edge of the angle. That's what the older shopbots did. Even better, browse around the Mechmate forum and see how to grind a precise angle on them to fit the V Rollers with a handheld grinder and a jig.

Vrollers for cheap are available at http://www.cadcamcadcam.com/v-groovewheel2.aspx
At $12 each, it shouldn't add more than $150 dollars to the cost, and I think you'd see a big improvement.

[Jack000]

thanks for the suggestions! I am planning on re-enforcing the beams the way Fandz suggested. I did think about the angle and v bearing method, but didn't want the extra complexity (and drilling!). I may very well have to go that route though, if my current design doesn't work out.

From my calculations the deflection will be highest at the x axis beams, but it will be a bit less than 0.01 inches which is fine for what I'm doing with it.

[Jack000]

small update, the frame is semi-assembled. I'm finding it very difficult to get the whole thing square, may need to disassemble and readjust later if the gantry binds. How do I make sure the beams are exactly 90 degrees to eachother? Would a carpenter's square be accurate enough?

also, I really need to get that garage door installed! Not fun working in below freezing temperatures

[sds357]

How sturdy is your frame so far? How much pressure does it take to deflect your horizontal struts?

[FandZ]

small update, the frame is semi-assembled. I'm finding it very difficult to get the whole thing square, may need to disassemble and readjust later if the gantry binds. How do I make sure the beams are exactly 90 degrees to eachother? Would a carpenter's square be accurate enough?

also, I really need to get that garage door installed! Not fun working in below freezing temperatures

I think you need to pull out the tape measure and start measuring.

Left front to right front, back left to back right, then in an X from corner to corner. How's the tolerances on the lengths of the leggs? You could also measure the beams to the top of the leggs.

[Jack000]

the rails bend a little when I put my weight on it, but I haven't put on all the supports yet. I don't imagine it will be too much of a problem.

I did square it as best as I could with the tape measure, but it's a little inaccurate given that the edges of the beams are rounded, it's hard to find a good sharp reference point to keep things consistent.

Maybe it's alright for now, I could always loosen it up and re-adjust if it comes to that.

[FandZ]

I cnc'd a tool to help me align my rails on my current build. It's more accurate than I'll ever get with ruler and tape measure. Perhaps that's the direction you should think about.