Starting a 4 axis CNC Router Table

[Gir]

Hey guys, I'm a bit new to the forums but have been lurking around for a while. I've been interested in building my own CNC router table for a while and I'm finally ready to dive into it!

My goal for this project is to route mainly 3/4" MDF, but other hardwoods will be thrown in there from time to time. I'm looking at creating a usable routing space of 28"x18"x3". All these dimensions are somewhat flexible, but around what I'll need them to be. The table will be made from MDF.

As for budget restraints, I'm looking to keep it pretty cheap. I, like everyone else, would love to make it fast, but that can be sacrificed a bit to achieve a cheaper design. High accuracy would be great, as I would like to someday get a proper spindle to route PCB's, but if it runs the cost too high I can skimp on super accurate.

My first goal is to figure out what kind of stepper driver and motors I should use. I was looking at using the 185 oz-in Nema 23 (or equivalent) for X,Y, and Z, and then use maybe a 100 oz-in motor for the 4th axis, as I understand spinning a block of wood shouldn't take a whole heck of a lot of force. As for the drivers, I would really love to build my own. I could probably design my own, but it seems like it would be a lot more work than I'm looking to get into. If you guys feel it's really worth laying the cash down on a commercial driver, that will be considered.

On the mechanics side of things, I'd like to go with the v rollers and lead screws-or any other cheaper method that will achieve similar results-for all three axis. The router I'll need to purchase and will obviously go for lowest bidder; if it spins I'm happy.

As for my tools, I have only but the basic woodworking tools: table saw, jig saw, (soon to have) drill press, really crappy router from the 70's (will upgrade soon), and other various hand tools. I am currently co-op'ing at Wallops Flight Facility right now, which happens to house one of the largest machine shops on the East coast... so I might be able to pull some strings and get a few crucial parts milled from scrap aluminum... MAYBE.

Anyway, sorry for writing a book! I hope you guys can help me on my adventure! I'll start posting some 3D models of what I'm thinking about this weekend!


Tyler

[ger21]

Motors are so cheap these days that it really doesn't make sense to go with anything smaller than 250 -300 oz. And I'd go with the same size for the 4th axis. And it's really almost impossible to beat the HobbyCNC boards for the price.

[jdell42]

I think your on the right path with the V Bearings... If I had to build a new router from scratch and I only had hand tools and a small budget I think would give those serious consideration. Those give you a good value and offer adjustement depending on how you mount the angle for them to ride on.

Acme lead screws are also cheapest and probably easiest to incororpate in a hand built design. There are a few designs out there JGRO and one by hack (I think) who use standard tools or bolt together designs... you may want to look at those but modify the bearing design a bit to suit your needs.

Agree on the HCNC setup. Its cheap and quick to get going. The kit is a good value.

[Gir]

Motors are so cheap these days that it really doesn't make sense to go with anything smaller than 250 -300 oz.

After looking around on ebay I found 3 285 oz-in motors that weren't too costly. I think I'll go with those.

And I'd go with the same size for the 4th axis.

Why go with such a powerful motor for just spinning it? It seems like an area to reduce costs a bit. I don't mean to say you're wrong or anything, I would just like to understand why.

And it's really almost impossible to beat the HobbyCNC boards for the price.

They do seem to be at a pretty good price. Earlier I was looking at the Linistepper board which would run me $90 for a three axis, but it looks like I can get a 4 axis HCNCPRO for $106. Sounds good to me!

To make it easier to assemble, I was hoping to just directly connect the stepper motor to the lead screw. What type of attachment should I use? I've seen several out there, but I'm not really sure which is better for what.

Really quick, what is the difference between a lead screw and an acme screw? They seem to be the same. Thanks!

[jdell42]

Originally Posted by Gir To make it easier to assemble, I was hoping to just directly connect the stepper motor to the lead screw. What type of attachment should I use? I've seen several out there, but I'm not really sure which is better for what. Really quick, what is the difference between a lead screw and an acme screw? They seem to be the same. Thanks!

Try these for the connection.. more expensive than a lovejoy.. but less slop.
http://www.dumpstercnc.com/acme_couplers.html

Another solution is lovejoy connectors. Do a search on those. You can get them from Enco.

Lead screw is generic term.. ACME screw is a specific type of leadscrew.

[Gir]

Lead screw is generic term.. ACME screw is a specific type of leadscrew.

Ah, thanks. That clears up my confusion.

Try these for the connection.. more expensive than a lovejoy.. but less slop. http://www.dumpstercnc.com/acme_couplers.html

Those look pretty easy to machine yourself. I might be able to use some excess delrin from back at school and have a friend mill a few. Can you use a normal tap to thread the acme screw in or is it special?

Thanks for the ideas, btw!

[EDIT]
Looks like ACME screws have their own threading. Any idea where to get a tap or is that pretty much left to DIY?

[ger21]

Originally Posted by Gir Why go with such a powerful motor for just spinning it? It seems like an area to reduce costs a bit. I don't mean to say you're wrong or anything, I would just like to understand why.

Your talking $20 difference, and I think you'll need more torque than you think. A 4in diameter part will only have half the force at the circumference of a 2" diameter part - a 6" only 1/3. Depends on what your doing with it, but a 6" diameter part wiull only have about 2lbs of force at the circumferernce with a 100oz motor, and that's before it starts spinning. Once it's spinning, the torque will drop off fast.

Numbers are assuming direct drive, btw.

[Gir]

Okay, that makes more sense, Gerry. Thanks!

[jdell42]

Originally Posted by Gir Ah, thanks. That clears up my confusion. Those look pretty easy to machine yourself. I might be able to use some excess delrin from back at school and have a friend mill a few. Can you use a normal tap to thread the acme screw in or is it special? Thanks for the ideas, btw! [EDIT] Looks like ACME screws have their own threading. Any idea where to get a tap or is that pretty much left to DIY?

Dont bother an acme tap will be expensive. If you want cheaper look at the lovejoy solution.

Here is a link to a site that sells ACME taps as an FYI.
http://www.newmantools.com/taps/acmetap.htm

[BobF]

Some on the boards have made Acme taps from a scrap of lead screw. You won't tap steel with it, but soft materials can be cut.

[Gir]

This morning I whipped up a few models for the Z axis, so here's what I came up with. I haven't quite figured out how to attach the rails (epoxy, screws, both, and where?), and the rod in the middle there is going to be my acme thread. Feel free to tear my design apart!

[jdell42]

You may want to consider some adjustment in the y direction (left to right). If yo go bigger on the rails you can add coutersunk screws so they are out of the way of the bearings.

Have you considered V-bearings vs. the popular skate rail design? I think the skate rail design is tough to implement if you are builing by hand. The V-Bearings allow for lots of adustment. IMO