Need Help!- New engraving with CNC mill

[bherr]

As noted I'm a newbie to engraving and need some insight. I'm using BobCad Pro X, engraving software and of course the BobCad ver.20.7. The engraving I'm working on is only 4 inches across and about 1.25 inches in height. I'm using a .241 ball mill with a .0622 step over and milling to a depth of .0625. Rather than getting a nice cut, I'm getting sections that are not being milled on the X axis path. The engraving is small and is oval shaped with some lettering engraved down into the aluminum. That's the 1st issue and second the program is over 5000 lines of code and my Heidenhain controller only can handle 999 lines of code. The NCnet lite 4.0 doesn't do drip feed and the ver 20.7 doesn't do drip feed. I found the 4.1 version for $198, but man I'm just a small shop (ME) and right now that's alot of money. anyone know of a free download/shareware program that is as good as the NCnet lite 4.0???? If there isn't any free stuff, does anyone know if I can increase the RAM (memory) in the Heidenhain??

Thanks in advance.

ben

[Cartierusm]

Sorry don't know about the software problem but as for the engraving I might be able to help. When desinging the part did you run a simulation to see if the cutter was cutting all the sections? I just did some text for a part I was making and I know nothing about envgraving nor do I have an engraving bit so I made the letters as big as I could while still being able to have a 1/4" endmill fit inside the lines. When I had the text smaller certain parts of the lettering were not getting cut because the cutter would not fit inbetween the lines. What I think is happening is the bit you're using won't fit within the size of the lettering you have desinged so the program only tries to mill out where the cutter will fit into. Right now I dealing with the same thing how to do small text without having to use a ton of specialized bits.

[bherr]

Originally Posted by Cartierusm Sorry don't know about the software problem but as for the engraving I might be able to help. When desinging the part did you run a simulation to see if the cutter was cutting all the sections? I just did some text for a part I was making and I know nothing about envgraving nor do I have an engraving bit so I made the letters as big as I could while still being able to have a 1/4" endmill fit inside the lines. When I had the text smaller certain parts of the lettering were not getting cut because the cutter would not fit inbetween the lines. What I think is happening is the bit you're using won't fit within the size of the lettering you have desinged so the program only tries to mill out where the cutter will fit into. Right now I dealing with the same thing how to do small text without having to use a ton of specialized bits.

Cartierusm,
Know what you mean about the small letters. I think if I make the step over very small, maybe about .005 I'll be able to pick up the small sections I'm missing. when you're working with a graphic that is only 4" long and 1/25 " in height, it doesn't leave much room to play with. guess I'll just have to keep on trying different step overs until I get the results I'm looking for.
ben

[Torchhead]

Engraving with a rotary engraving bit (v shaped) has several challenges.

1. You need high spindle speed because the actual cutting portion of the bit is small. 10,000 to 50,000 RPM depending on material/depth

2. The material has the be PERFECTLY flat because ANY varience in depth results in a widening or narrowing of the cut. for every .010 deeper you cut you can get from .006 to .010 more width on the cut....clearly visible. If you cannot provide absolutely flat and even thickness material and cut surface you have to do what the do on commercial engraving machine and build a spring loading floating head and depth limiting nose piece that drags on the material and keeps the depth of cut even regardless of the material height.

True engraving fonts are single stroke fonts but don't have much character. You can use regular fonts but you need to cut "online" in the CAM.

Sample of conventional fonts on Stainless Steel pencil using rotary engraving setup and floating head.

[Cartierusm]

Torchhead, I'm using a home built CNC Router, using a porter cable router. All aluminum machine very rigid. When I made my original Pendent Control Pendent Control Finished I used a baic 60 degree wood router bit to cut the lettering in aluminum. Worked all right because I was going to, and did, fill in the letters with paint, but the lettering walls were not very smooth. What would you suggest for an engraving bit for that router to do aluminum? Thanks

[Torchhead]

Use a real engraving bit like the ones at:

http://www.bitsbits.com/

60 deg works for most thin lines. Router may have more bearing run out than you want for ultra fine work but having the right bits helps a lot.

Tom Caudle
www.CandCNC.com

[Cartierusm]

Thanks Torchhead, got another question. I make guiatars and I'm using Artcam and it doesn't seem to want to create a tool path in the inlay function for some fancy text, english fancy lettering. I'm assuming it's the same reason we mentioned in this thread where it knows the bit we have can fit in some areas. What do most people do to over come this. It will only be cutting in hardwood and i have bits as small as 1/32". Should I be looking at smaller bits? Will endmills work in wood and should I get some super small endmills for that kind of work? Thanks again.

[Torchhead]

Get super small endmills at Think and Tinker or BitsBits. 1/32 bits are huge for doing small inlay. You may need to look at the .015 0r .010 end mills. At the cost you need to have your feeds and speeds setup right before you start to cut....breaking 18.00 bits is not fun. Another thing you can try is buying some the PCB drill bits off ebay in tiny sizes. It's less trama to break a 50 cent bit! It's not hard with ArtCAM or even SheetCAM to define the same object in multiple cuts. Use a bigger tool to cut out most of the pocket and run one or even two smaller tools to do a profile cut the cut out the detail. I know ArtCAM supports inlay pattern cutting.

Your challenge is that tiny bits need to spin REALLY fast. A trim router or VS rotozip tool has close to the 30,000 rpm you need. Dremels may have too much radial play and snap tiny bits like they are free!

Tom Caudle
www.CandCNC.com

[Cartierusm]

What about a porter cable router, I think mine is 22,000 rpm? What feed speeds should I start at like 1 ipm?

[bherr]

Originally Posted by Torchhead Engraving with a rotary engraving bit (v shaped) has several challenges. 1. You need high spindle speed because the actual cutting portion of the bit is small. 10,000 to 50,000 RPM depending on material/depth 2. The material has the be PERFECTLY flat because ANY varience in depth results in a widening or narrowing of the cut. for every .010 deeper you cut you can get from .006 to .010 more width on the cut....clearly visible. If you cannot provide absolutely flat and even thickness material and cut surface you have to do what the do on commercial engraving machine and build a spring loading floating head and depth limiting nose piece that drags on the material and keeps the depth of cut even regardless of the material height. True engraving fonts are single stroke fonts but don't have much character. You can use regular fonts but you need to cut "online" in the CAM. Sample of conventional fonts on Stainless Steel pencil using rotary engraving setup and floating head.

Torchhead,

I'm milling the piece mentioned in the original post, spindle speed is 1000 rpm's and I'm getting a pretty nice cut. I do notice some fine lines that are present between the toolpaths. I'm milling in T6061 aluminum. My step over is .005 and I guess If I'm going to get a perfect cut I'm going to have to reduce the step over, which I was hoping to not have to do as this engraving is currently running 26,601 lines of code and takes about three hours to mill at a feed rate of 35. Once I'm finished I'll try and fine sand the lines to see what happens. If I can't get it looking nice I'll have to change the step over distance from .005 to .002. there's another two hours milling time.

Ben