Newbie CAM questions

[WoodSnarfer]

Hi...this is my 1st post to any board on cnczone. I've read about 10 hours worth before posting, so I apologize in advance if these questions have already been answered...I found a LOT of information I needed, but have some lingering questions regarding CAM I'm hoping some folks could help me with:

Question #1:
If you design your own CNC router, how do you "calibrate" the mechanical aspect of the system with the electronics and the control software? In other words, if I design a system using servos driving ballscrews via stepped-down belt-driven gears, how will the servo driver "know" to pulse the motor x times in order for the ballscrew to move y inches? Do I have to very carefully match my motor, gearing and screw pitch to the driver and software? Or, do you input this information to the CAM software? Or, is there some sort of calibration routine that you run when setting up the tool?

Question #2:
Is CAM software aware of the tool's bit size and profile? For example, in my CAD program I can round over the edge of a part with a 1/2" round profile. When routing this part, the centerline of my round-over bit might be 1/4" outside the actual part being routed. How do you tell the tool path generator to position the router bit on this vector? I'm hoping that it isn't up to me to figure out the offsets for the tool!

Question #3:
When doing a CAD drawing, I can show a pocket of material removed from the part I am designing. For example, I might want to start with a block of wood, and hollow out the inside, to make it into a box. In CAD, I'd draw the box already hollowed out. How do you tell the CAM software to actually move the tool back and forth, to hollow out the box? Otherwise I picture the tool simply cutting the outline of the box and leaving a big hunk of material inside.

Question #4:
Same question, but this time regarding cutting depth. In CAD, I can show the outside edge of a part notched out by 3" deep. Of course, I don't want the router to plunge into the edge of the wood 3" deep and try to cut it in one pass. How do you tell the CAM software to take multiple passes and increment the depth each pass?

Question #5:
I'm imagining that I can take my CAD drawing, export it to the CAM software, and then turn on my CNC router and go take a nap. From reading (a lot of) stuff here, I bet my imagination is way off. Say I want to do something like a nice 3-D carving for a fireplace mantle. If it takes me 12 hours on TurboCAD to draw, am I in for another 12 hours setting up the CAM routine? Or is it more of a few minute "tweak" exercise in CAM before going to the router?

Question #6:
Any suggestions (for a hobbyist) of a 'best in class' CAM package to do 2-D and 3-D woodworking?

My game plan is to really understand the software, electronics and math/physics behind the mechanicals before I even think about designing the motion system. I've played quite a bit with TurboCAD, so I'm comfortable doing the up front design work. My goal is to build something very similar to this:

Beezer's CNC machine

Beezer, if you are reading this, awesome job...it's an inspiration to me.

Thanks for your time.

-Chris

[Bubba]

WoodSnarfer
I will attempt to answer your questions as best I can as noted below each question. Please realize this is based on my experiences and system. My total system includes acad for the cad package, Sheetcam for the cam, and Turbocnc for the controller driving gecko drivers into servo motors. Depending on exactly how you set up a system may vary some of the paramaters, but the principle will be the same. Hope this helps with some of the problems.

Question #1:
If you design your own CNC router, how do you "calibrate" the mechanical aspect of the system with the electronics and the control software? In other words, if I design a system using servos driving ballscrews via stepped-down belt-driven gears, how will the servo driver "know" to pulse the motor x times in order for the ballscrew to move y inches? Do I have to very carefully match my motor, gearing and screw pitch to the driver and software? Or, do you input this information to the CAM software? Or, is there some sort of calibration routine that you run when setting up the tool?

You will tell your controling software "how many steps per inch" based on the location of the encoder and the pitch of the ball screw, reduction of the motor etc.

In MY case, I chose to mount the encoder on the end of the 5 turn/ inch ball screw and the encoders are 500 line (2000 pulses per revolution in quadrature). Therefore, it will take 5 turns of the screw to make 1 inch and 2000 * 5 pulses of the encoder to make 1 inch. This is 10000 pulses per inch and we invert that to get 0.0001"/pulse (step) which will be entered into the configuration file of the controler software. If you mount the encoder on the servo shaft, you will divide the above calculation by the reduction ratio of the system. For example, if you had a 4:1 reduction, then you would enter 0.0001/4 = 0.000025 "/step.

Question #2:
Is CAM software aware of the tool's bit size and profile? For example, in my CAD program I can round over the edge of a part with a 1/2" round profile. When routing this part, the centerline of my round-over bit might be 1/4" outside the actual part being routed. How do you tell the tool path generator to position the router bit on this vector? I'm hoping that it isn't up to me to figure out the offsets for the tool!

This will depend on the CAM software that you use. For example, if you use ACE; YOU will have to do all the necessary offsets in cad and put the toolpaths on a seperate layer for Ace to convert to Gcode. As stated above, I use Sheetcam and here, I just have the actual outline for each "process" on a seperate layer, tell Sheetcam which tool to select, the type of path to take (Inside offset, outside offset, No offset, or a pocket) and how deep to make the cut. There are other variables that can be set as to how deep. how fast etc that can be give for the program to do its job. Sheetcam is great for 2 1/2 D work and there are others out there for the true 3D work (read $$$$$)

Question #3:
When doing a CAD drawing, I can show a pocket of material removed from the part I am designing. For example, I might want to start with a block of wood, and hollow out the inside, to make it into a box. In CAD, I'd draw the box already hollowed out. How do you tell the CAM software to actually move the tool back and forth, to hollow out the box? Otherwise I picture the tool simply cutting the outline of the box and leaving a big hunk of material inside.

See Question #2

Question #4:
Same question, but this time regarding cutting depth. In CAD, I can show the outside edge of a part notched out by 3" deep. Of course, I don't want the router to plunge into the edge of the wood 3" deep and try to cut it in one pass. How do you tell the CAM software to take multiple passes and increment the depth each pass?

See Question #2

Question #5:
I'm imagining that I can take my CAD drawing, export it to the CAM software, and then turn on my CNC router and go take a nap. From reading (a lot of) stuff here, I bet my imagination is way off. Say I want to do something like a nice 3-D carving for a fireplace mantle. If it takes me 12 hours on TurboCAD to draw, am I in for another 12 hours setting up the CAM routine? Or is it more of a few minute "tweak" exercise in CAM before going to the router?

My Several hour cad is transformed into Gcode "usually" in less than an hour (I usually have to go back and change the cad because of my stupidity:})
Then I put it in the machine (Takes a while to get the raw material setup PROPERLY)
Hit the enter key and change tools when asked. Length of time to do the job depends on complexity, # of tool changes, speeds, feeds, etc


Question #6:
Any suggestions (for a hobbyist) of a 'best in class' CAM package to do 2-D and 3-D woodworking?

Personally, I am sold on Sheetcam for the Cam and Turbocnc for the controller. They have been very forgiving in my learning curve and very easy to setup and use:}) Obviously, I am biased but after playing around with several demos of various software, I find this combination works for ME. YMMV

(Usual disclaimer)

Bubba

[ger21]

Originally Posted by WoodSnarfer Hi...this is my 1st post to any board on cnczone. I've read about 10 hours worth before posting, so I apologize in advance if these questions have already been answered...I found a LOT of information I needed, but have some lingering questions regarding CAM I'm hoping some folks could help me with: Question #1: If you design your own CNC router, how do you "calibrate" the mechanical aspect of the system with the electronics and the control software? In other words, if I design a system using servos driving ballscrews via stepped-down belt-driven gears, how will the servo driver "know" to pulse the motor x times in order for the ballscrew to move y inches? Do I have to very carefully match my motor, gearing and screw pitch to the driver and software? Or, do you input this information to the CAM software? Or, is there some sort of calibration routine that you run when setting up the tool? Question #2: Is CAM software aware of the tool's bit size and profile? For example, in my CAD program I can round over the edge of a part with a 1/2" round profile. When routing this part, the centerline of my round-over bit might be 1/4" outside the actual part being routed. How do you tell the tool path generator to position the router bit on this vector? I'm hoping that it isn't up to me to figure out the offsets for the tool! Question #3: When doing a CAD drawing, I can show a pocket of material removed from the part I am designing. For example, I might want to start with a block of wood, and hollow out the inside, to make it into a box. In CAD, I'd draw the box already hollowed out. How do you tell the CAM software to actually move the tool back and forth, to hollow out the box? Otherwise I picture the tool simply cutting the outline of the box and leaving a big hunk of material inside. Question #4: Same question, but this time regarding cutting depth. In CAD, I can show the outside edge of a part notched out by 3" deep. Of course, I don't want the router to plunge into the edge of the wood 3" deep and try to cut it in one pass. How do you tell the CAM software to take multiple passes and increment the depth each pass? Question #5: I'm imagining that I can take my CAD drawing, export it to the CAM software, and then turn on my CNC router and go take a nap. From reading (a lot of) stuff here, I bet my imagination is way off. Say I want to do something like a nice 3-D carving for a fireplace mantle. If it takes me 12 hours on TurboCAD to draw, am I in for another 12 hours setting up the CAM routine? Or is it more of a few minute "tweak" exercise in CAM before going to the router? Question #6: Any suggestions (for a hobbyist) of a 'best in class' CAM package to do 2-D and 3-D woodworking? My game plan is to really understand the software, electronics and math/physics behind the mechanicals before I even think about designing the motion system. I've played quite a bit with TurboCAD, so I'm comfortable doing the up front design work. My goal is to build something very similar to this: Beezer's CNC machine Beezer, if you are reading this, awesome job...it's an inspiration to me. Thanks for your time. -Chris

1. You input all the hardware information (screw lead, belt reduction...) into the machine control software (Mach2, TurboCNC) and it tells the motor drivers (Gecko, Xylotex...) how far to move the motor(s).

2. If you're talking about using a typical router roundover bit, Then most likely, you'll have to figure that out for yourself. Most CAM software I've seen will figure toolpaths for straight or ballnose bits, but I doubt roundover bits. Typically CAM software will "roundover" the edge of a part by making many passes with a ballnose bit.

3. Most CAM software will handle pocketing automatically. You might want to look at SheetCAM, currently free during beta. http://www.sheetcam.com

4. See above. Typically, for basically flat work with holes and pockets, All you need is a 2D .dxf and something like SheetCAM, which will let you specify depths and cut directions.

5. With the right software, it should only take a few minutes to setup. For good cheap 3D CAM, look at MeshCAM http://www.grzsoftware.com

6. For hobby level woodworking, I'd recommend the two programs listed above, SheetCAM for 2D (2.5D), and MeshCAM for 3D. Each are about $150. They both have Yahoo groups for support (both are excellent), and more info.

One thing about 3D stuff. Most CAM programs need to import models as .stl files, so make sure your CAD software can export as .stl. MeshCAM can also read 3D.dxf files, but ONLY if they contain 3D faces ONLY.

[WoodSnarfer]

Thanks for the help, Gerry and Bubba. I appreciate it...it cleared things up for me. Now off to the CNC wood router board to ask a few more questions over there.

Regards
Chris