Couple of questions for a newby

[automationsteed]

Hi all, fairly new here and have a few questions. Firstly, I would like to build my own CNC router setup for sign making, anyone doing that as a hobby here. I would also like to make a few bucks out of it if possible, extra money is always helpful, anyone have any luck in that regard.

I am an Engineering Technologist working for a Fluid Power company in Edmonton. I program PLC's and HMI now so the electronics should be fairly easy for me, I would like to use Mach3 for software, I have access to a manual mill and welder (I can weld and manual machine) and would very much like to make a cnc unit.

My thought is to make a 48" X 36" inch machine out of steel and aluminum. I want this unit to be fairly ridged to be able to etch 1/4 aluminum sheet on occasion as the shop frequently makes panels and uses colored tape to detail the schematic on the panel, which I think is pretty low tech.

I want to have a fairly decent speed out of the unit, so I am leaning towards rack and pinion on the X & Y axis and acme on the Z axis. I will be using linear bearings on solid steel rod material, (3/4"d on X, 1/2" on Y) which should minimize sag.

What do you think of the design so far, this is just the start, I have only just started this rendering.

Automation.

[dustin1706]

Hello from another Albertan!

Etching aluminum is really no problem even for a router made from MDF. That being said, a unit made from aluminum and steel will be able to cut aluminum as well, albeit slowly. Also, you never really indicated how much you plan to spend on this router. The cost will be your limiting factor for a lot of the stuff.

Welding a router table seems to be frowned upon when you talk to DIY machinists as it is difficult to get things perfectly square with absolutely no warpage from heat input. It seems most people go with a welded steel table, then make the router table itself from 8020 extrusions. Rack and pinion for the X and Y is a great idea. you will have to decide for the Y axis, if you are putting a motor on each side of the gantry, or just going with one in the center. you should take a look at some commercial CNC tables online and see how they are set up. Generally the Y axis R&P is driven from both sides of the gantry, while smaller leadscrew machines are driven from a single motor under they table.

I think that you should forget the unsupported rails completely, except for the Z. The Gantry with the Z slide and router/spindle is going to be fairly heavy, and unless you are going to find some seriously thick rails, they are going to flex. The way the joes 4x4 hybird and the shopbot, among other machines get this done is by using V-Rails, mounted to 8020 aluminum extrusion. PRSalpha CNC Routers

Or, if you want to go with the rails, go with some supported rails. They really aren't as expensive as one might suspect. If i had known they were as cheap as they are, I may have gone that way on my Joes build rather than the V-rail. Glacern Machine Tools - Linear Rails and Bearings

For the Z, I'm not sure if you have access to cheap aluminum at work? If you do, you could easily mill yourself a nice Z slide. Otherwise, I found that by the time I priced out the aluminum, bearings, screw etc. It was cheaper for me to buy one from K2CNC. If you do go K2, don't pay list. They go for about $300 on ebay, and if you email them they will give you a better price than the list. CNC Routers, Routers for Wood, Routers for Plastic and CNC Plasma Cutter

Then you need to decide on a router or a spindle/VFD. if you want to cut aluminum well, you need to turn fairly low RPMs. A spindle will do this, but is significantly more expensive. The cheap route is a regular router (I use a craftsman) and a SuperPID which will allow you to run your router at lower speeds. www.SuperPID.com - Super-PID Closed-loop Router Speed Controller

Then you need your steppers and drivers. With a table that size you can probably go with Nema 23s with a G540 if you like, or if you want to have more torque than you'll ever need, step up to Nema 34s with gecko 203v's and a Break out board.
CNCRouterParts Actually, you could go with (or make your own version of) their rack and pinion drive. CNCRouterParts

Then remember that you will need bits and software as well. The Vectric line of software is very popular with home users it seems. V-CarvePro specifically lends itself very well to sign making.

I'm no pro, but I just went through the same ideas that you are before settling on a joes 4x4 hybrid. We kinda get screwed in Canada, as UPS shipping is retarded and a lot of ebay shippers won't ship UPS, or charge ridiculous fees. The biggest thing I learned making the JGRO from scratch is that exact dimensions don't matter at all. All that matters is that you have no flex, and that your axis' are exactly perpendicular to one another.

Retailers I did have good luck with for service and shipping include Moore Gear(gear rack), Superior bearing (v-rail & bearings), VXB(bearings), K2CNC, CNCrouterparts. If you need any 8020 extrusion, you can get it at Fastenal in Edmonton, but check prices with a few stores because some of them will try and rip you off.