What Should I Build?

[DroopyPawn]

I've been wanting to build a CNC router for at least 5 years now. I come back here from time to time to look at new threads, check out all the latest pictures, etc. I've just never actually started building.

I've collected a few parts. Here's a partial list of what I have.
A pair 54" supported shafts (1/2" I think) with 2 pillow blocks on each rail.
A pair of 40" unsupported shafts with 2 pillow blocks on each.
A K2 aluminum mount for a router. I've had it so long that I don't remember which router. Probably a Porter Cable.
A 12" acme screw with derlin nut.
One of those expensive ballscrews with the fancy nut thing. I'll probably sell it on eBay to get funds for the other parts I need... more Acme screws, bushings, bearings, MDF, wood, aluminum... whatever.

I even have a little Taig CNC milling machine. I killed the driver board at least a year ago. I bought another board to replace it but I've never gotten around to getting it running again. I could use the CNC stuff from the Taig to get my CNC router going.

So basically, I think I have the X- and Y- axes covered. I know I need to get lead screws for them. I'll do that. I'm thinking 1/2-10 ACME from Enco.

I asked a friend across the road if he wants to help me put the machine together. He doesn't think he's smart enough to help but offered me some space in his workshop while I get mine finished up. Mine is built but I need to finish running the electrical work.

I think I just need a little push and some tips on where to start. I've looked at a bazillion pictures of CNC routers in the last few years. I think I'm ready to start.

[DroopyPawn]

Oh yeah...

I wanted an opinion on this. I saw this picture on eBay and it got me to thinking. I wonder if this arrangement would work.

I was thinking of mounting a Z-table on the Y-axis. This table would hold the router and would be lifted/lowered by 3 or 4 acme screws. The 3 or 4 acme screws could be positioned at the corners of the z-table and would all be turned by a single motor with a geared belt.

The reason I might want to do it this way is that the table could be hinged and could swing upside down to allow easy access to the router for tool-changing. I could rig some sort of clamp system to make sure the table doesn't move while in its locked-for-cutting position. This would keep the height of the entire machine lower I think.

My Y-axis bars are about 1.25" thick so I don't think there would be much deflection. Correct me if I'm wrong. And anyway, I'll be doing mostly 2.5-D routing.

Could this work or have I lost my mind before I even start?

[DroopyPawn]

I want to order my ACME screws. I'm looking on Enco at
http://www.use-enco.com/CGI/INSRIT?P...PMAKA=408-0220

The normal price is $21.95 for 1/2-10 6' RH Oil Finished Steel rod. The online price is only $9.39. I plan to get 3 of them now. One for my x-axis and 2 for later use. Or maybe I'll cut and grind one down to 4 feet for my y-axis. Is that price too good to be true or am I looking at the wrong item?

The 3-footer is only $5.99 online (normally $14.95).

Finally, I'm illiterate on ACME rods. What exactly do the number 1/2-10 mean? What's the difference in that and 3/8-10 or 1&1/8-5 for example? Which is best for CNC routers?

[CarveOne]

Originally Posted by DroopyPawn I want to order my ACME screws. I'm looking on Enco at http://www.use-enco.com/CGI/INSRIT?P...PMAKA=408-0220 The normal price is $21.95 for 1/2-10 6' RH Oil Finished Steel rod. The online price is only $9.39. I plan to get 3 of them now. One for my x-axis and 2 for later use. Or maybe I'll cut and grind one down to 4 feet for my y-axis. Is that price too good to be true or am I looking at the wrong item? The 3-footer is only $5.99 online (normally $14.95). Finally, I'm illiterate on ACME rods. What exactly do the number 1/2-10 mean? What's the difference in that and 3/8-10 or 1&1/8-5 for example? Which is best for CNC routers?

The price is real. I ordered three 1/2-10 rods for my Solsylva 25x37 build almost two years ago when they were on sale for $7 each. They are not precision rods. Mine were straight enough, but a small serpentine squiggle is noticeable due to them being roll threaded instead of cut or ground threaded. One of mine had roughness on the flat top surface of the threads which I block sanded off easily with 400 grit wet/dry sandpaper glued to a small block of red oak scrap board. Didn't take anything but the burrs off.

1/2" diameter rods with 10 threads per inch. (10 revolutions for one inch of travel) These have one thread groove. 5 threads per inch will give 2 inches of travel for 10 revolutions. Relative to the 1/2-10 rods, these are "twice as fast for the same rpm".

CarveOne

[DroopyPawn]

So should I consider a bigger, faster ACME screw? Maybe 1-5? I understand that stepper motors work better at lower speeds. 1-5 would cut the speed in half. Of course, if I understand it right, it would also cut my machines accuracy in half - or would it matter much?

If I go with something other than 1/2-10, will I be able to easily find nuts for it?

Also, I was wondering about material. I'm considering, before I start on my big machine, doing a smaller one. I wonder about what material to use. I don't want to do an aluminum machine right now. So what's the difference in building it from MDF or good quality plywood. It seems to me that plywood would be stronger than MDF. But I see more MDF machines than plywood ones. Am I wrong?

Another question... Should I build the axes in X-Y-Z order or should I start with the z-axis and work downward? It seems to me that if you went with making skate bearings from angle aluminum, that they need to fit on the "rails" perfectly. That means the dimensions of each axis need to be really tight. What if my y-axis needs to be 32" wide but I cut it 32.25" wide? Will the gantry move horizontally? How accurate does it really need to be?

[CarveOne]

Originally Posted by DroopyPawn So should I consider a bigger, faster ACME screw? Maybe 1-5? I understand that stepper motors work better at lower speeds. 1-5 would cut the speed in half. Of course, if I understand it right, it would also cut my machines accuracy in half - or would it matter much? Keep in mind how heavy the 1" rods will be for the length that you will use. The mass will be a factor in how fast the motors can accelerate and reverse direction. If you have more backlash in the system than the calculated accuracy numbers of the rods you will never see the inaccuracy in actual operation. Rods are generally better than the published accuracy specs. It's hard to achieve zero +/- zero backlash. The inaccuracies in various parts tend to average out algebraically more often than to add up in either direction from zero. If I go with something other than 1/2-10, will I be able to easily find nuts for it? Anti-backlash nuts for larger than 1/2" rods can be ordered as custom parts from DumpsterCNC if you supply a sample piece of lead screw that Tim W. can use to make a tap with. See the FAQ page on his site for details about custom parts. Also, I was wondering about material. I'm considering, before I start on my big machine, doing a smaller one. I wonder about what material to use. I don't want to do an aluminum machine right now. So what's the difference in building it from MDF or good quality plywood. It seems to me that plywood would be stronger than MDF. But I see more MDF machines than plywood ones. Am I wrong? MDF is just lower cost, and is smoother on the surface than all but the best grade of plywood. Take a look at the Rockcliff, Jgro, and Joes 2006 forums for MDF builds. It makes good machines but there are some benefits and drawbacks of using it. MDF needs to be sealed with paint of some kind to keep out moisture. Another question... Should I build the axes in X-Y-Z order or should I start with the z-axis and work downward? It seems to me that if you went with making skate bearings from angle aluminum, that they need to fit on the "rails" perfectly. That means the dimensions of each axis need to be really tight. What if my y-axis needs to be 32" wide but I cut it 32.25" wide? Will the gantry move horizontally? How accurate does it really need to be? On my second build (my own design) I started with the X axis (long axis) rails and added the Y axis (gantry), and finished up the Z axis last. Now I'm adding the Y axis lead screw assembly. It's possible to build it in whichever order you want to. There are cases where you need to custom fit the Z axis onto the Y axis rails.

CarveOne

[DroopyPawn]

The shafts of my y-axis plus the aluminum end plates weigh about 30 pounds. That's before the bearings are added and the z-axis and router is mounted. Is that going to be too much weight for an MDF or plywood machine?

[CarveOne]

Originally Posted by DroopyPawn The shafts of my y-axis plus the aluminum end plates weigh about 30 pounds. That's before the bearings are added and the z-axis and router is mounted. Is that going to be too much weight for an MDF or plywood machine?

No, I don't think so. My own gantry is at 85 pounds now and that includes the entire gantry with everything that adds weight on the X axis rails. Mine is all steel and aluminum construction. MDF can really add up also. Just make your base strong enough to handle the loads and use fully supported rails.

CarveOne

[DroopyPawn]

If I buy 6' acme screws for my x-axis rails that are 54" long (because I can't find 54" acme screws", is it ok for the extra to stick out the end? Or do I need to cut off the extra. What about bearings on the non-motor end of my screws? Necessary or not?

If I decide to build one from hardware store parts first, say a 3'x3' machine, how much can I expect to spend on it, not counting the computer parts (PC, drivers, power supply(s), etc.)?

If I do build the 3'x3', one first, I could use it to cut nicer parts for the 54"x40" machine. Right?

I'm so excited about this that I actually went out last night and started finishing my workshop. Running power, moving stuff to make room, etc.

[DroopyPawn]

Also, would this be a good start on the z-axis?

http://cgi.ebay.com/Linear-Slide-Rai...d=p3286.c0.m14

[DroopyPawn]

I bought some tool holders for my Taig CNC mill. When I need a tool change, I just unscrew the current tool and screw on the next one. Takes just a few seconds to change tools and they're all zeroed in at the right height. Can you get the same kind of thing for routers like Porter Cable et all?

[CarveOne]

Originally Posted by DroopyPawn If I buy 6' acme screws for my x-axis rails that are 54" long (because I can't find 54" acme screws", is it ok for the extra to stick out the end? Or do I need to cut off the extra. What about bearings on the non-motor end of my screws? Necessary or not? Having about 18" (?) of rod sticking out will be a safety issue but may not be a problem if you screw a bright red or yellow rubber ball onto the end of each rod. You wouldn't want to get impaled on one, especially if it is turning. I would cut off the excess myself. You can always use the short pieces for a Z axis lead screw. You will need bearings on each end of the rods. If I decide to build one from hardware store parts first, say a 3'x3' machine, how much can I expect to spend on it, not counting the computer parts (PC, drivers, power supply(s), etc.)? That's hard to say. Make a list of everything that you think you will need that costs any serious amount of money at all and then check the list against prices on a Home Depot or Lowes web site. It's easy to eat up a $400 to $500 budget just for the hardware materials. The better you are at scrounging and bumming stuff off of friends the cheaper it will be. It will also take longer to build it. If I do build the 3'x3', one first, I could use it to cut nicer parts for the 54"x40" machine. Right? Right, as long as the parts for the larger machine will fit within the working area of the smaller machine. Lots of people do this. Some will cut parts for friends who want to build one. I'm so excited about this that I actually went out last night and started finishing my workshop. Running power, moving stuff to make room, etc.

I know what you mean. After getting halfway through my first CNC build I built a 30' x 40' workshop to put around it.

CarveOne