New to the group - joined to ask / get experiences with the following

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(Shane Painter) #1

New to the group - joined to ask / get experiences with the following question: Can the OX be effectively scaled to a 4’x8’ routing CNC? If so, what additional design/components (if any) need to be incorporated?

Can the belts (dual belts?) handle it? Or are lead/ball screws required? Where to find affordable ball screws this size? Not finding many conclusive answers elsewhere.

Thanks in advance!
-Shane

(Darryl Blandford) #2

Not to cut anything to a decent standard. The Ox Y rails are not braced, so you would have an 8ft span that will flex quite a bit. I have a 1500x1500 and that flexes, but as I now only cut ply and mdf I can live with it.

(Mark Leino) #3

Lead screws in that size would be costly- I have seen a few set ups with rack and pinion. That would be you best option. For my 5 x 10 plasma I bolted t profile steel to the sides of the rails, but it still sags. I need to add a few braces to “level” the rails.

(Mark Leino) #4

Belts at that length have too much stretch and will not be as accurate as you would like

(Shane Painter) #5

Thanks for the feedback. Follow up question re: flex and quality … my use case is really just 3/4 ply and pvc (don’t care about speed of the cut, really) … and would be happy if accurate to a quarter inch. Does this change your responses?

Darryl - @1500x1500 how much slop is in your ‘can live with it’ cut?

Thanks again everyone - much appreciated!

(Darryl Blandford) #6

Mine has at in the region of 1-2mm or so over the 1500mm span. As I mainly use it for pet products and lettering etc, a bit of sanding works OK for me. But if your wanting to do wooden inlays etc then you need the accuracy.

Then again it’s well used machine so it may have more ‘give’ in it than a new one. Although I check belt and wheels monthly to make sure nothings overly loose.

(Darryl Blandford) #7

I think the router/spindle could also be a factor, as I’m using a cheap katsu 700w laminate trimmer as a spindle. I know that has a little play in the spindle as when it’s been on a few hours and gets warm it’s starts a vibrate a little.

(Darrell n) #8

The Openbuilds extrusions are not stiff enough for a machine of that size, particularly the Ox design which has no lateral support for the y rails. Also, to my knowledge, you cannot get rails longer than 1500mm. Belts would have extreme flex at that length as well. Same for ball screws, the longest I have seen is 1500mm.

Look at CNCRouterparts.com, they sell kits at reasonable prices. Their Plug’n’Play electronics package is superb.

If you only need 1/4" accuracy use a jigsaw and a pencil…

MG

(Nathan Lucier) #9

@Darryl_Blandford Wow, yours is that much out? My 1500x1500 w/ 1.5Kw spindle is well under 0.5mm across the whole table in either direction, and as far as any inlay work I’ve done, never had a gap on 2’x2’ pieces. I also probably don’t run mine at full feed rate that I should, but haven’t had any issues on ply, mdf, cherry, aluminum…all either cutting through or only surface. I do a full table testing circle every once in a while to make sure that I’m still kosher, and haven’t had a problem excepting the one time that my motor pulley set screws fell out and ended up under the belts. Replaced all with socket cap screws (much easier to torque) and they have not loosened at all.

(Darryl Blandford) #10

@Nathan_Lucier One of the first things I did on mine was replace the grub screws with socket cap heads and double belt the X & Y axis.

I can cut aluminium at the edges where it’s most rigid, but in the middle the bit just skips and jumps. You can see the Z axis flexing as it changes direction, and when the bit lowers into the material. I was trying to cut alu at 0.2mm per pass, with a 2 flute end mill, at 1200mm/m and 300mm/m plunge).

As for MDF and Ply, I cut at 3mm per pass, 2400mm/m with a 600mm/m plunge using a 6mm straight cut end mill and get a very clean cut.

I’m also not running anywhere near the maximum it will go.

Next month I will be moving the ox into my home workshop as I’m giving up my work unit. I have to disassemble it get it home and into the workshop, so I’m going to use it as an excuse do a full rework and rebuild. Currently considering replacing the X&Y rails with C-Beam, taller and thicker Y axis plates and ditch the X,Y belts for lead screws, and finally get a decent spindle.

If I do go down this route I’ll document and photograph it so can share the experience.

(Darrell n) #11

IMHO, the Ox design has a hard enough time just existing at 800x1000mm. It has no business getting ANY bigger. It is a poor design, which has WAY too much flex in any configuration. There are much better alternatives, like the Workbee, but even designs using C-Beam shouldn’t be made any larger than 1000 mm in any direction. The V-Slot profiles just aren’t stiff enough for anything serious in lengths more than 1000 mm.

There have been endless debates on the OB forums about how to strengthen the C-Beam, but nothing has ever been conclusively proven to improve them. It’s just a fact that the OB extrusions are light duty, and you can’t make a silk purse out of a sow’s ear…

If you want a good, stiff design, you have to use much heavier 80/20 or Misumi extrusions that are twice as thick and better designed, or use multiple extrusions to support each axis.

Also, the polycarbonate wheels used in the Ox and other OB designs are not very stiff or stable, and wear out quickly. Linear rails or linear slides are the way to go for large machines. The OB lead screws are also just barely adequate for up to 1000mm, anything larger and they just don’t cut it. And when was the last time you saw a commercial CNC machine with belt drive? NEVER. There is a reason for that.

I have to laugh every time I see someone building a 1500mm or larger Ox based design. It’s ludicrous.

Having said that, in the smaller sizes, they are cost effective and good enough for hobby use, providing you take small bites and don’t push the envelope too hard.

MG