[ahren]

The carriages have an adjustment in the bearings that allow them to be snugged against the steel, and even pre-loaded a little bit. Cold rolled steel is remarkably accurate from the mill. It is spec'd at +0 / -0.004", and that's between different pieces of steel. Within a single piece (which you adjust the carriages to), deviations in the 1/4" dimension are often less than 0.001".

This z axis is the one used in the 2' x 3' plans (and upcoming 2' x 4' R&P plans) from cncrouterparts and fine line automation, and has proved itself on many different machines -- check out the build log section of my website, and you'll see a lot of them!

Hope that helps,

Ahren
www.cncrouterparts.com

[jsheerin]

Doing test moves I get repeatability in positioning to less than 0.001" - basically 0 as far as I'm concerned. Cutting I'd say I can typically can be within 0.005" or less. However a lot of other factors go into that - backlash of the screws, deflection of the cutter, material movement for soft materials (wood), the steppers possibly missing steps due to bad speeds and depth of cut, constant velocity mode in mach3 potentially rounding corners depending on settings, accounting for exact tool size, etc.

How do you think it would move around? Like the rail moving on the 80/20? I have not seen that at all even when accidentally crashing a 1/2" cutter into one of the 80/20 bed rails at 200ipm (which then stalled the router and tripped a circuit breaker). The one part that I have had move on me were the adjustable bearings on the thickness of the steel, but I've only noticed that on my z axis.

[viroy]

Wow I didnt think that would be achievable without having a constrained spherical rail.

[viroy]

This is for Gio666:
For the X-Axis 25mm leadscrew, here are the dimensions I am looking for... the travel can go all the way to the bearings, and I dont mind it being 40" instead of 39.5" if it is easier on you... just add the extra length to the 1/2" shaft for coupling.

[jsheerin]

You can achieve very precise, repeatable results with lots of different systems. It's repeatability and precision under load that are a different story, and how much load. For hobby machines, the cold rolled steel rails are great. However I'm currently working on replacing them with THK rails for higher load capacities and less problems with adjustment. But I'm also stepping up to a 5HP 3ph spindle, 1kW servo motors, etc. so the forces involved will be much higher.

[viroy]

Now that you mention spindles... I have not even started looking at router products yet. I would really like to tap threads in aluminum holes with the CNC if possible... is this common?
I need a motor that can cut alot of aluminum with no problem, and if possible also thread holes. To thread, the motor has to be reverseable right?
I dont mind manually switching out bits.
If the right motor for threading is like 3x more cost than something for just milling, I would rather save the money and tap threads by hand like I do now... although after an hour or two of threading and a broken bit later, I may decide someday to expand the Z-axis and add a 2nd motor just for threading.

Also, is Mach the most recommended CNC software? I'm curious as to what software people are using for similar and different cutting scenarios/motor setups.

Why would you go with servos instead of steppers under a heavy load?
I thought steppers have more torque but less speed than servos?

Just meandering thoughts.

[jsheerin]

I have no direct experience with this as a disclaimer, but I think you can tap in two ways - with a tapping head or via rigid tapping. A tapping head automatically reverses the tap, I believe. Tapping heads can be pricey - look up a tapmatic on ebay. Rigid tapping would, I believe, require that you can reverse the spindle and probably that you have feedback on the spindle - some type of encoder. So you could drive the spindle with a servo motor, for example. Both of these are more milling applications as opposed to routing and you'd want much slower speeds. You might want to look at a milling head. I've posted several times on this just this week I think. I'm working on building myself a separate drilling / milling head for my next router. Oh, and another way to do this would be thread milling. But just to warn you, thread mills are expensive.

Steppers vs servos - there are some good faq's on this. I suggest searching for them. But briefly, stepper motors have torque curves that fall off as speed increases while servos stay closer to constant torque as speed increases, so the rpm where you get the most power out of the two types of motors is different. A servo motor needs an encoder on it to function while a stepper doesn't. Because of this, you can possibly achieve more accurate positioning, or at least know when your machine has a positioning error so you can try to fix it with the servo. You could argue that a properly designed and run stepper motor machine would never lose position, but I'd say that's not extremely likely to happen. We're usually pushing the limits of our machines. I think in general servos will become more appropriate as you need higher output power, but the setup becomes more complicated and they're more expensive. If you get good at scrounging on ebay you can do okay though. I bought a used 1kW AC servo for $20+$25 shipping a few weeks ago, but I haven't researched enough to buy a used controller for it, so at the moment the controller will be around $300 and the power supply will be around another $200-$300. That's for one motor. However this is vastly larger than what a machine like the one you've been looking at would need. Along those lines, I'd have strong reservations about your machine design giving you satisfactory performance doing a lot of tapping and milling. A bridgeport milling machine does those jobs very well with around the same travels or less than what you're talking about, but it weighs around 2500 pounds. If you want to shave away at some aluminum once in a while with a router that's one thing, but if serious milling and tapping are going to be a primary function for your machine, you might want to beef up your design a bit. My machine is much more rigidly built than yours, and it is very marginal for milling aluminum - surface finish is not the best. I just wouldn't want you to build something and then be disappointed in its performance.

Mach3 and EMC are the typical control software choices. EMC is linux based and open source. Personally I use Mach.

[viroy]

Gio666:
Here is the Y-Axis, also 25mm please.
The nut for this will not bolt to 8020, rather I will need it to turn 90 degrees. So some kind of flange mount that I can create a bracket for connecting to the Z-axis plate is needed. The Z-axis plate I speak of is the center yellow peice in my drawing that connects the blue Y-axis bearings, to the purple Z-axis (post #71).
Once again, I dont mind it being a little bit longer to make things easy on you... just add the extra length to the 1/2" coupling shaft please.

[viroy]

Ok I have been thinking alot about whether to go with this design or trying to stabilize the Y axis more... I cannot think of a better way to stabilize the Y axis without compromising the 2 Y shafts alignment and possibly introduce binding.
I considered independent shaft mounts on both ends of an 8020 beam, but I cannot guarantee they will be 100% parallel like that since one may bolt in slightly different than the other. To use 8020 as a primary gantry support, I believe I would have to make shaft mounts that are connected to each other via an aluminum support to hold their relative positions exact.
Any ideas on how to design a more robust gantry?

[jsheerin]

Here's my suggestion. As always, I'd say go with supported rails if possible, but I think you said earlier you already have your rails? If so, the unsupported y rails would probably be the limiting factor in this design.

When bolting stuff to 80/20, if alignment is critical you can align it, clamp it, and then bolt it. Or bolt lightly, tweak, tighten, tweak, tighten, etc.

[viroy]

The 2 Y-rails I have are just 20mm stainless rods, literally just the rods with good bearings for them... so I have to create a mounting system for both, and have it match the Y-leadscrew mounts.

I like the design and will give it a shot...
I have 2 questions:
1) The X-axis leadscrew is shown mounted on the outside of one rail.... are there supposed to be 2 leadscrews, one on each side? Or will just a single LS on the side actually work ok like that?

2) What is the best way to mount fabricated aluminum parts to 8020? just drill holes and order their T-slot screws/bolts? I cannot find the right part in autoquoterX, not all parts have a picture to go with.

[jsheerin]

That was supposed to be with dual lead screws, one on each side. I left out the detail on the far side. You could put the screws in different places - that was just an easy way to draw it and would work.

I typically just drilled a hole in the part I was mounting. I usually used carriage bolts with the head in the 80/20 groove as they're much cheaper than the 80/20 hardware. Sometimes I had to buy the 80/20 stuff though. For example one of my Y limit switches - I just used two pieces of aluminum angle to make a bracket to mount the switch. You can't really see the surface where it's mounted to the 80/20, but you can see the end of the carriage bolt sticking out of the bottom of the angle piece:

[viroy]

jsheer:
In the pic above... is that 3"x6" ??? I cannot figure out what model # that is.

[viroy]

Think this is a better design to go with??
I was thinking of attaching the x-leadscrew by adding 8020 beams vertically, between the y-rail mounts and the x-rail mounts.... they will connect under the work bed.

[jsheerin]

Yes, my machine is all 3060, 3030, and 1530.

[viroy]

Sweet, somehow I missed the 3060!
Ok here is a nearly complete gantry re-design.
What do you guys think?

[viroy]

Some more pics

[jsheerin]

Are you trying to go with one screw in the center to drive the gantry? If so, that's fine. Otherwise I'd say all that stuff hanging down looks like a lot of extra material adding cost and weight that isn't necessary. If you drove it from the sides, all that would be gone. That would add the cost and complexity of another drive system but would double your force available to accelerate that axis and would remove the extra material cost and weight (leading to lower acceleration) of the structure needed for the center drive.

[viroy]

This design I did with a single leadscrew in mind.

To be honest, I really dont know much about a dual leadscrew setup. I understand the mechanics... but it seems difficult, and expensive requiring 2 leadscrews + motors + bigger PSU. Would I have to get a special controller for that? Speed is not a major concern, but if it will increase accuracy and repeatability by atleast 30%... I would probably change my mind.

If speed & torque is the only advantage of a dual leadscrew, I would rather save cost and wait a little longer for milling to complete.
If I do go with a single leadscrew, do you think that gantry design will be stable and secure enough to not bend/rock/twist under load?

[m1911bldr]

I cut only wood - don't have a spindle that will slow down enough for aluminum (yet) - and get .003-.004 accuracy for the inlays I cut. The leadscrews are 3/8-10, there are opposing nuts on the lead screws to adjust backlash, and the motors are all Hobby CNC 305 oz-in. The drive is a Soigeneris box with a Smoothstepper and G540 inside. It runs with Mach3 using the USB port. I can rapid at 100+ IPM but the skinny leadscrews whip at speeds over 80 IPM. The second motor on the X axis is not connected, it used to be but the X motors always fought each other. It's not in the pictures but there's a timing belt between the two X motors, at first intended to keep their steps synched, but now it drives the second screw off the one motor. The single X motor will still drive the gantry with enough force to break off a 5/16 dowel like it was butter (how do I know??). I can get .001 if I adjust the leadscrews so they're under tension and the opposing nuts are adjusted VERY carefully. I cut inlays for custom cutting boards and I have to keep pressure on them while the glue's setting or the air pressure trapped under them will push them up out of their pockets. If you plan your leadscrews for 5/8, 3/4 or 1", you'll get higher speeds and still have plenty of power without huge motors.