First DIY CNC List of dumb questions!!

[Barefootboy4]

I've been surfing this forum and doing my research for 3 weeks so I would not look too dumb with my list of questions. I have my design and would love it if the pro's could review my ideas and see if I'm on the right track. Your input will be most apprecited. Most of my CNC will be in hardwoods for support of my woodworking shop. I want the machine to be robust with a good tool cutting speed. I need to build more on the professional end rather than the hobby/MDF end. I'm going to break down my questions into sections:

1- Frame to be either 3/8" or 1/2" aluminum. Cutting area to be 2' x 4'. Just a basic rectangle with legs and a overhead gantry. I see some people use the 80/20 extruded aluminum. Does the 3" hold up to a heavy cutting machine or I'm I better off using the basic plate aluminum with lots of support?

2- Linear motion to be Hiwin 20mm LGW rails and blocks. Is 20mm tough enough or should I step up to 30mm?? LG rails are classed as heavy duty. Could I drop down to the medium Duty AG class and still be stout enough?

3-Plan to use a Keling Kit KL-4030 3 axis system with 425oz 36vdc/8.8a steppers. Any feedback here would be great. Is the Keling products good? Is 425oz steppers enough? When does one switch over to servo motors. What are the advantages to a servo system over a stepper system other then better torque of the rpm range. This is where I do not want to make a mistake and be under powered! I do not want to wait hours to complete a route process. Please give me some good feedback!!

4- Going with Rotan rolled ballscrews. Is 1/2" 5tpi sound right or should Istep up to 5/8"? Could someone please explain the advantage to multistart over single start. I want to make sure I'm matching my screws to steppers motors.

5- Plan to use my Porter cable 3.24hp router to start and see how it works. My go to a spindle later as I become better.

6- Presently running TurboCad 3d. Plan to go with Mach3 & LazyCam. Have been looking at BobCam. Anyone out there used Bobcam and how well do
you like it?? They are running a special on it right now!

7- I see some people build with pulleys and belts for the motors to leadscrew. Again what are the advantages and what are the correct ratio's, size pully's, etc.

That's enough for one post. I hope a team effort here can keep me on track
Thanks
Steve from Maine

[ger21]

1) pics would help.

2) 20mm is plenty, and the medium duty should also be fine.

3 & 4) Motors, drives, and screws need to all work together. Imo, Gecko drives are a better option. You need to know how fast you want to cut, and how much force you want, and then work from there. 5tpi screws will limit your speed with steppers, as they'll need to spin faster at higher speeds, which is where stppers lose torque. That's one advantage servos have, is that you can spin them much faster with more torque. Multi start screws have fewer turns per inch. Ideally, for a router, you want to be around 1-2 turns per inch, if you want high speeds. Those screws tend to be much more expensive. You can use a belt reduction to get the same effect, but the screw will be spinning much faster, so you need to make sure you don't exceed the critical speed where the screws start to whip.

5) Is that a question? Should be fine to get you started.

6) BobCAD is always on special. Read through the BobCAD forum here and you may see why.

[analogman]

I have a bit bigger all aluminum machine I built a CNC from the Data Cut plans. Works great, but it seems more people are going to JoesCNC for the mid sized machines now. If you can, try to base it on a proven design, it will help to solve some of the problems.

I went Gecko for drives. Very popular for mid sized drives and great support, great warranty. I got my breakout board and motors from Bob Campbell- so far so good! Check on the gecko site - excellent doc on when to use stepper versus servo.

Back when I was building, Gerry recommended the roton acme screws with anti backlash. They work just great. .001" repeatability over the length? Darn close.

If you can afford it, the chinese spindle and VFD is a great option. Fast , strong and quiet.

For CAM I tried CamBam, SheetCam and Cut2d. I did not consider LazyCam because it is no longer supported. I picked Cut2D - very easy to use. 2D only.

[Barefootboy4]

OK,
that's all good feedback. I'll check out these sites. As far as " you need to know how fast you want to cut" is unknown. If you have never built or run a wood cnc router one does not know what one needs. What would you recomend??Give me some ideas.

As far as going Servo motor can you recomend a complete kit from someone with servo, drivers, power supply etc.
Again thanks for the reply

[ger21]

I think you'd be better of building a proven design. Joe's 4x4 can be built as a 2x4. If you buy his plans, you get access to his forum with close to 100 builders of the same machines, and see all the different drive system combinations they are using, and what works and what doesn't.


As for speeds, as fast as possible. 6 years ago, I started to build a machine and was hoping to get 100 ipm. Today, everything is much more affordable and easily available, so I'm currently designing a machine and looking for 1000 ipm rapids, and 300-500 ipm cutting speeds.

[analogman]

Interesting that you selected servos - did you read the gecko document on stepper vs servos? What was the critieria for your decision?

[Barefootboy4]

Well, I guess this is the point of the thread, to get ideas from people who know what they are talking about. I have not read the Gecko but will. So now I have I idea of what I'm looking for in IPM. 500 being something which is a ballpark number. I looked at the Joescnc site but do not like the designs at all! There will be no MDF in my machine. I'm basicly going to copy a k2cnc design I like.

So going back to one of my questions if I'm trying for 500IPM will 425oz steppers or servo's be enough??

[ahren]

You could also build the 2' x 3' machine offered by Fine Line Automation that Nate and I designed, and just extend it to 4 feet in the long direction. (people have built up to 3' x 5' machines using the same parts) This machine can definitely achieve 500 IPM during rapids with the exact motor package you have chosen. Check it out:

http://www.peakeff.com/beta/PostDetail.aspx?PostID=11

This design uses aluminum extrusion, which in answer to your question is a great material for building machines IMHO. Pound for pound, it's usually stronger than bar stock because it takes advantage of larger cross sections. And you can't beat the flexibility

Ahren
www.cncrouterparts.com