Guilty confession: I have a shapeoko2 gathering dust in my office, I literally haven't even opened the box to start the assembly. Really would rather build the ox as my first foray into CNC. Nice job, looks awesome.

That's easy with the OX. it has an open center so you can just do exactly like the guy in the video did and put the OX on legs to the height you like.

Let me toss out another question to anybody who can answer.
If the software program controls the spindle position, what is the reason for limit switches?
Do most of the other CNC router members here have limit switches on their machines?
Would anybody here be willing to explain how to install limit switches and how to configure them?
OK, I guess that 3 questions. My bad.

I have 1 switch per axis which acts as home+both limits. The optical microsensor switches get the machine positioned to within 0.001 mm. The software doesn't know where the spindle is without the switches. You could try to eyeball it and enter the coordinates but... the results won't be consistent across pieces. Another thing is the motors or software can goof up and crash the machine so limit switches act as an override. I think it's cheaper to add the switches than to be replacing stripped belts, bent parts, broken bits, etc.

I can't really explain how to set up the software. I use linuxCNC with a TB6560 board so my switches come into the board on pins 1-4 of the db9 port on the controller and then go into pin 10-14 on the parallel port and I just tell linuxcnc which pin is which axis and it's both limits + home.

The most common reason for fitting limit switches, not homing switches as described by The Dude, is operator fault. The operator can design a program but often, especially when first starting to design and use CNC machines get the Axis the wrong way around or, as I have found to be most common with my clients, use inches instead of millimeters.

The limit switches are there as a safeguard to stop the machine overreaching itself. Of course some software will allow you to program limits so that the coordinates that are 'over' the limit would be either ignored or an error message appears.

Whatever reason, you are best fitting homing switches AND limit switches to be safe.

Col.

Limit switch, as the name applies, set the limit how far a part can travel. You don't put one switch per axis, you have to put two. One for each direction the axis can travel. On a three axis machine that's six switches. One of the two switches, per axis, can be used as a homing switch as well.

You connect the two switches, per axis, in parallel. Most breakout boards have a terminal for limit switches. Normally three terminals for the three main axis and one terminal is common, or ground. Many breakout boards also have a emergency switch terminal. Not using a limit switch is foolhardy, not using an emergency switch is outright dangerous. On my PhlatPrinter III I have two emergency switches, again, wired in parallel. One on each side of the machine.

Thanks to all of you for your helpful input.Hopfully this helped others as well.

No just one opto sensor per axis. Maybe mechanical switches would be harder because you'd have to trip the switch from the back but those switches are so cheap I'd just use two wired to the same input pin. As people may or may not know, optical switches are far superior to mechanical switches (ie: +/- 0.005" accuracy or better, no switch bounce, no mechanical parts to wear out). I just ripped some out of an old printer and used the reprap gen7 electronics(3 resistors and 1 LED). I hear you can buy a "kit" with everything for all axes for a mere $200 bahahaha

Dude, when I said 'switch', I don't necessarily mean 'mechanical switch'. Optical is just fine but you still need, IMHO, two. One for each end.

As a matter of fact, using an optical switch as homing switch is a great idea because of it's accuracy, as you've mentioned.

Well this build is amazing and Mark you have done a great job. This as far as I can get. Waiting on some parts. So much fun to build.

Chance

Thanks to you man and those great videos you put up. I didn't realize how great they were until I was using them as instructions. Can't wait to get the rest of the parts

@Mopar32985 Good job !

I also expect that everything is in stock to build a Routy + OX. I do not have access to a CNC. Routy will be the mother of the OX.

I'm working on an MDF version of the OX. MDF has great dimensional stability but on a small scale it lacks the hardness of Aluminum, Steel and Garolite. Forces on the parts will cause the holes to deform which results in sloppy linear motion over time. To make up for this in the design, I'm going to pass all of the 'axles' for the V-Wheels through a torsion box structure. This gives them two support points at least 20mm apart. It will act as if the the part was a 1" thick solid block of MDF but it will be made from 1/4" MDF sheets you can get at Home Depot and cut on a 50W laser. The belts will all run outside the aluminum rail so it will be possible to use 9mm x 3mm GT3 belts. The X rails are secured to the vertical torsion box members as well as the outside plate. They are spaced further apart than in the OX design so that the V-Wheels contact centers form a square when viewed from the side. I'm also planning for a taller Z and spaced the Z wheels out further. These two changes combined should give us a very rigid Z-axis.



I'm still finishing up the X/Z axis core. I realize that there needs to be some play to align the X rails to be parallel and match the final width of carriage. Making something thats rigid, long lasting, easy to assemble and easy to adjust (you have to reach all of those eccentric spacers!) is a difficult challenge in wood. But its fun to try

Mark thanks for posting up this design. I recently built a 2x4' shapeoko and I'm not entirely happy with how it scaled up. I setup mine with a 4' X gantry for easier use in the garage. Unfortunately this X gantry twists easily even after adding an addition 20x40 and bolting them together. I'm going to be converting it over to a OX with a 2' X axis and I'm currently in the CAD phase and have a couple questions.

I use Mach3 and I've noticed it would be incredibly helpful to have a Z home switch. My CAM software ends up each job moving the Z to machine zero and then to Y zero. It's really easy to forget to manually move Z up to before ref all home making it really easy to run into fixtures. Has anyone figured out a good way to put a limit switch on the Z axis?

The Z access threaded rod plates have a recess of 16mm for a 5x16x5 bearing and a lock collar is used to keep it in place. Unfortunately the only 8mm lock collars I can find all have a 16mm OD. This will cause the collar to rub against the outer shoulder of the bearing instead of spin freely with the threaded rod. I'm currently planning on using two thin 8mm hex nuts instead of the lock collar. Snug up the bearing with the first and then tighten another nut against it. Doing this on both axis. Anyone see issues with this?

What type of garolite are people using and where are they sourcing it in the US? McMaster has several different grades and I'm not sure which is most appropriate in this use case. Since I have the shapeoko or access to a 4x8 showboat if necessary, I should be able to go slow and either do 1/4" aluminum or garolite. Should I just go straight to the aluminum?

Gareth- Sounds like a great idea. I had an idea a while back of stacking laser cut thin plywood to create a part. If you have a laser you could cut several layers of say baltic birch plywood instead of mdf. If you are worried about the wheel shafts deforming the mdf you could add bronze bearings or even drill bushings. I don't know how long you want it to last long enough to mill out some better ones. I use baltic birch a lot for jigs and fixtures. It is hard and stable and relatively easy to find. You can often find it very thin that is used in making model airplanes. Keep us posted with how you make out. Best Bill

@Robert Hummel Thanks for the link. The sites I was looking at had the same for about $55. Looks like I'll be ordering some aluminum. Any recommendations on bit to pick up for working on this?

One other question around tolerances. The standard v-slot build plates have clearance between wheel holes of v-slot thickness + 20.64. The OX plates had 1-2 millimeters additional. Was this intentional or just sketch up inaccuracies? I'm in the middle of converting the drawings into another cad system which support arcs / circles and can push back up some DXF without the sketch up off by partial millimeters problems.

The bit size depends on, mainly, two things. The part that you are cutting, a hole of 3/16 can't be cut with a 1/4 bit, and how fast you want the part ready. On the PhlatPrinter I have to use many passes to cut hard material and 1/8 is as much as I use to cut. If the material is mounted solidly to the bed and the machine is stiff and the spindle can handle pressure you can use thicker bits and cut with less passes.

If you use SketchUcam in SketchUp, it handles arcs just fine, as long as the arcs are arcs. I wrote just yesterday an explanation about it. http://www.openbuilds.com/threads/routy-cnc-router-v-slot-belt-pinion.27/page-12#post-2079

@JustinTime Sketch up does not (at least last time I used it) handle circles as arcs. Cut a hole in something and it's immediately a set of line segments and when exporting it converts arcs to line segments as well. This can be seen in Mark's DXF files. This leads to several small inaccuracies in the resulting files and potential problems with CAM / machining if you have to many segments per arc.

I'd highly recommend anyone using sketch up for mechanical parts look at Autodesk Fusion 360. It has parametric features more suited to designing things like this and has a free hobby license level and built in community design features. SketchUp is free as in beer, but not open source so there is not really a philosophical reason to stay with it.

I was not referring to bit size, but type as for these plates you have to use 1/8th cutter since M5 holes < 6.35mm. Machining 6061 is it best with a straight flute, o-flute, downcut, uncut, etc… Any recommended or avoided coatings.

I used MArk's drawings as reference in my CAD program but I replaced all the holes with real circles...

Ill have to check out Autodesk Fusion 360.
My current favorite parametrics CAD tool is Moment of Inspiration: http://moi3d.com/
Made by the same dude that wrote Rhino. Outputs to OpenNURBS format and STL.

Had some more parts that came in today. Got some more done on the z axis. Just waiting for some extruded aluminum to come in

Wow. So cool Great job. Can't wait, my parts are shipped.

Please read my post slowly. LOL I said

SketchUp is using segments for arcs and circles but SketchUcam knows when it's a circle or an arc and treats it that way. My circles and arcs come round and I use only SketchUp and SketchUcam.