MPCNC Version 2 -opinions-

20 and 25 mm can be found quite easily. The “inches” fractions are very difficult to find in Italy and, I think, I the major part of the EU. Except of the uk, maybe…

I think overall your most common stock/rail/rod/conduit size worldwide is going to be 1" or 25.4mm. Second is going to be 25mm. You could easily account for this by using some sort of eccentric spacer with the bearing holes. This would also be good for adjusting pre-load/tension on the rails. I mean you can buy eccentric spacers, get them made in bulk for cheap from china, make them yourself…drill a piece of round stock off center or and even print them. If you aren’t sure what I am talking about, it’s basically a nut where the hole is off center, that way when you tight it it moves the bearing/wheel closer or further since it’s off center.

Eccentric Spacer

3D Printed Eccentric Spacer

DIY Eccentric Spacer Idea

The problem is conduit is measured by its ID, so the OD varies that’s how we end up with 23.5mmOD. Unless we find something priced within reason with similar rigidity/mass measured as tube (OD) instead of pipe (ID). Or I pay for a large quantities of hex extrusion (deluxe version, but would need to ship rail) I think its best to stick with what we have. I do want to give 25mm Carbon fiber or fiberglass tubes a try, super common and cheaper than stainless, but I doubt it can handle the point loads without delaminating quickly.

Updates on the current parts, then maybe a deluxe version down the road seems to be the best coarse for now.

Eccentric is actually very expensive and they all vary in size and shape, it would be hard to spec a universally available one. I though about a printed insert to change one of the three bearings position but the problems happen on the combo axis with the Z. It can be done but I think we would be sacrificing rigidity to make it happen, If I just suck it up and make my models more friendly to edit I should be able to maintain 3 builds for the best rigidity. Then to handle the tool holder fragmentation issue, people only making holders for there sized conduit. We can just switch to a universal mount, which I have been worried about because another point of attachment reduces rigidity. The users here have already came up with a nice one so I will leave that alone until the design changes significantly.

1" inch
+1 here

I am near to the end of the build of my MPCNC.
I have finished the basic frame, legs and gantry.
But I still have to print one rigid joiner and that will complete the middle assembly.
Then I will measure & print the Z motor support and tool holders.

I decided, early on, to go for stainless steel tubes despite the additional expense.
(I couldn’t find the original galvanised steel conduit in the UK where I live and because I reckoned stainless would last longer and be resistant to rust).
But I chose 1 inch diam tubes, and only discovered, after delivery, that Ryan’s design would not accommodate that diameter!
So, having committed myself, I realised I would have to modify the design to cater for 1 inch tubes.
The main change (apart from inserting triads of bearings circling a one-inch diam tube section) was to split most of the monolithic parts, like middle_ends, into two parts.
The idea was to insert/remove shims as required to adjust the ‘grip’ of the bearings on the tubes.
My redesign removed a small amount of plastic from each mating face so as to allow for closing down the size if needed.
Also, I planned to make the single bearing bolt hole into a slight slot, so I could shim that bearing in/out.
So, I could move the two Y bearings closer or further away form the tube by flat shims between the new joints in my split middle_ends, and slide the single bearing in/out by putting curved shims around its bolt.

Did it work?
Yes. When first assembled it was a loose fit. I just shimmed until the fit was correct for each part of the assembly.
It took most of a day but was straightforward.

Thanks very much, Ryan, for a really original design and thanks for being so generous by making it open-source.
I am really enjoying the build and the technical hurdles I introduced and am looking forward to adding the electronics very soon.
Thanks for the cable kit and the drag knife; it all arrived safely. (postage was a killer though!)

I have attached a photo of my middle_assembly with dark lines in places to try to show the joins I have mentioned.

John

Dang, that’s a lot of work, nice job!

Have you checked to make sure your z axis is 90 degrees from the bed in all directions? That center section is a beast to get right.

Thanks Ryan.

I admit I hadn’t thought about vertical alignment!
I will check that out when I have completed the last part (rigid joiner) of the mid assy and assembled it.

Have just bought a dial indicator which can show dimension differences down to 0.01mm. That should reveal the truth about alignment!

If necessary, I plan to ream out the appropriate bolt holes in the rigid supports and shim until the twin tubes are vertical in both planes.

I should find out in the next couple of days.

The fundamental issue:
Metric or Imperial
then we need to add tolerance

The original design (V1?) already mixed it up with the bolds and nuts, M8 and 5_16, M3 / M4 vs 6_32. Being from Europe in a big city i can source the Metric parts easily (just round the corner in some hardware stores) Imperial becomes a bit more expensive, and time consuming option (i need to order them).

Same as for the Conducts/Tubes/Pipes
Coper, Aluminium or Steel, Metric or Imperial, i can order impirial, but if i go to the local hardware store… i’m stuck with 22mm (dirt cheap) and if i get 25mm it might be close to 25.4 depends on the store/the batch and tolerance.

Example : i printed the International version of the Roller, to find out that the rollers (bearings) and the 25 mm Aluminium pipes don’t fit properly, there is around <1mm space.

So for V2 i would say that there is a need for some tolerances in the (great) design.

Regards
Flos

ps: i’m still in printing phase…

I was afraid of that. To build in some adjust-ability to the z axis I will probably have to add hardware to the z axis.

Still in the planning phases again. I will update the current design first. The next one will probably involve new rail material.

While waiting for the next part to finish… i designed a kind of eccentric spacers (mentioned also by Atomist)
Not having a working CNC yet (still printing and building) the part seems to work to adjust the single bearing side of the roller
No clue if it would hold and can work with the forces of a CNC machine, i can’t try yet :slight_smile:
It converts from M8 to M5 to bold the bearing, but you can tune it so the bearing nicely gets to the tube

(update:) tried to upload the .scad files… didn’t work…

// fix the MPCNC issue regarding the roller and the Pipe/Tube
// print 2 of those and the other part
difference() {
union() {
translate([0,0,3.75])cylinder(h=3.5,r=3.9, center=true, $fn=360);
translate([0,0,1]) cylinder(h=2,r=6, center=true, $fn=360);
}
cylinder(h=20,r=2.6, center=true, $fn=360);
}

The M8 replacement
// MPCNC 608ZZ Bearing adjuster
// bearings specs : M8 , 7MM high
/// M8 to M5
difference() {
union() {
translate([0,0,10.5]) cylinder(h=21,r=4.0, center=true, $fn=360);
translate([1.5,0,2.5]) cylinder(h=5,r=6.3, center=true, $fn=6);
}
translate([1.39,0,0])cylinder(h=50,r=2.6, center=true, $fn=360);
}

That way works fine, until you get to the center assembly, that throws off the z axis. That means all 4 would have to be adjusted very well to get a 90 (normal) z axis. Then that changes the tool holder dimensions, the motor mount dimensions, and the z nut lock dimensions. Meaning everyone’s machine would require custom z axis parts.

Interesting… as if i don’t use the ‘fix’ there is a bit of space (the single bearing on the roller not touching the tube) which means, that one way or another it will never properly fit… until i find 25.4’s (as i presume the issue is, 25mm vs 25.4mm) ?
let me print the international version first… and struggle :slight_smile:

Not sure what you are asking there.

There is not a 25.4 version yet. 25mm should work.

let me first finish the printing :), and try to make some pictures of what i mean

Just finishing my build, and it all went together almost perfectly – with the exception of the corner blocks (and roller locks), which were very tight. I’m using 25mm tube (chrome-plated wardrobe/closet rail), and while it fits perfectly into the roller assemblies, the corner blocks were a very tight fit. I did file down the holes a bit, but still ended up banging in the tubes into the corner blocks with a hammer.

It’s all snug, but the bottom of the blocks now sit at an angle. I only noticed this after gluing on the feet of course – which now aren’t vertical.

I guess I can fix my corner blocks without taking everything apart with a bit of a blast from a heat gun – but to deal with cases like mine (where the rail seems to be the right size, but the printed holes a re a bit tight, it might be a good idea to either make it clear in the instructions that it is worth spending more time filing… or provide a parametric shim (e.g. in openscad) that can be glued onto the bottom of the corner blocks.

Sounds like you could use something like the taller corner block I’m designing.

I’ve only made a 23.5 version for now but I guess anyone could jump into tinkercad and bring over the 25mm version.

Impressive stuff – although that looks like a lot of PLA… are they hollow?

There’s a 25mm hole going up the inside for support and for to reduce the amount of material. 4 Posts will most likely need one fresh roll of filament to be on the safe side, and about 30 hours per leg. which is why I havent actually made any yet

Couldn’t you do something like this, slot one or both sides of the bearing bolts and have a set screw on the outside to adjust/lock them in place? Why would something akin to this not work for different size rails? We are talking a couple mm different between what’s available in the US and other places around the world. Is this a bad way to accomplish this?

proto4_7.jpg

adjustablecarriage.png

I’m looking over the other pieces to the MPCNC, I don’t see any reason why there couldn’t be a slotted version with lock screws. I’m mainly just interested in the possibility of there being a single design that can accommodate a variety of rails/pipes/stock.