Good bit for 3D work

[itamarj]

Hey Brady,
Thanks, now I got it!
I working on the relief right now, and I went with a 0.5 to do rough-roughing and I felt it too strong and because I went with the grains the wood cracks. I read now in other thread that people recommend to go against the grain with the roughing. What are your thoughts about it?

I then changed to 0.25, and I broke the bit too times, I went to fast. I have to say that I didn't have a lot of patience and I learned my lesson.
The path had 0.2 allowance, and because the Z was off a bit few times, I wish I would have left more...

So with the 1/8" I went by the books (almost) and run it at .35" stepdown, 10% stepover and speed of about 1 ips. what do you think about that? (I'm using Walnut)
Is there a good table or source for those parameters?

I feel that the low stepdown creates a lot of unnecessary toolpath - where the bit travel over and over the relief in order to get to the border, or just "clearing" area that have been cleared by the roughing pass. I wish artcam would create a smarter path. Should I go back to use Partworks 3D?
What is the best tool to create 3D reliefs toolpath?


My last question is about leaving the machine to work on it's on. I remember that I've been to a bootcamp and when the subject came up people were concerned with fire. At my Grad school, we use to run a small CNC overnight all the time. A friend of mine also told me that they have a large CNC at school and they leave it to work unattended. Machine a detail relief I feel can take more than 40 hours of work, and it can become significant in my progress. What do you think about it?

Well for the meantime, I installed Icam application on my iphone (only $5), and have a webcam installed near the machine, so I can see the machine running on my phone or on a web browser. Now I feel a little bit safe to get out of the shop for 5 min. can get a snack

[jimmya]

I think if you use a .35 stepdown with an 1/8" bit in walnut, the bit will break for sure. Or did you mean .035?

Jimmy

[Brady Watson]

I read now in other thread that people recommend to go against the grain with the roughing. What are your thoughts about it?

It depends on the wood itself. A raster strategy is usually fine unless the wood is excessively dry. Use 40% stepover for roughing. With hardwoods you need to slow things down. If you have an extra deep relief, with an extra long bit, you MUST slow things down & limit the move speed to keep from breaking the bit in hardwood.

So with the 1/8" I went by the books (almost) and run it at .35" stepdown, 10% stepover and speed of about 1 ips. what do you think about that? (I'm using Walnut) Is there a good table or source for those parameters?

If you run a proper roughing pass, then you should have no problem moving 2,1 or 3,2 on the finishing pass. Stepdown doesn't matter in ArtCAM or PW3D, unless you tell it to machine the relief in multiple passes. This is a waste of time. Rough out & machine the relief full depth. This is where you have to anticipate collet collisions etc.

If you intend on doing some hand carving, scraping and sanding on the relief, then a 20% stepover will get you pretty close in 1/2 the time as a 10% stepover. This is the trade off....If you want a relief that needs minor touch ups, then run 8-12% SO. If you don't mind sanding etc & just want to rough out and get 'close', then a 15-20% is fine. Run tests in software preview of toolpath and scrap material to see the difference for yourself.

I feel that the low stepdown creates a lot of unnecessary toolpath - where the bit travel over and over the relief in order to get to the border, or just "clearing" area that have been cleared by the roughing pass. I wish artcam would create a smarter path. Should I go back to use Partworks 3D?
What is the best tool to create 3D reliefs toolpath?

The finishing pass should always shave off a little material in the Z. If you are talking about the toolpath machining outside of the actual relief, cutting flat ambient area - then the toolpath can easily be restricted using a vector outline of the area that you want to machine. Draw a 2D vector outline and (in ArtCAM) choose the 'selected vector' in the 3D toolpath. The 3D toolpath will restrict the tool to that vector boundary. PW3D will also do this by choosing the 'Use Model Silhouette' option on the material setup page.

The results between ArtCAM and PW3D are identical for most reliefs. It's only when you leverage some of the advanced toolpath options in ArtCAM that you may see a difference in very specific situations - such as machining a dome. For what you are doing, it is a matter of choice. Either will produce good results.

My last question is about leaving the machine to work on it's on. I remember that I've been to a bootcamp and when the subject came up people were concerned with fire.... What do you think about it?

I think that this is entirely up to you. I will not advise anyone on whether to do this or not. I will say that there is always a danger of starting a fire with an unattended machine. There is always the potential for the power to go out, the machine to do exactly what you told it to do - not what you thought it would do, and other hiccups that you just can't plan for. Only after I ran my machine for several years & felt I had the computer, communication and my own programming skills finely tuned, did I consider leaving the machine unattended.

I would focus on optimizing your toolpaths and getting those finishing times down so that you don't have to leave the machine unattended.

-B

[itamarj]

Hey Brady,
Thanks, things are much clearer now, and I start working on the new relief.
I rough it using 1/4" and 1/8" and now I'm finishing it using 1/16" ball nose bit.
I did use several path with stepdown of 0.4" since the length of cut of my bit is .5 and I was concern that in many places I'll have a problem if I'll run it in one path.

But I still predict some problem. The bit is 1/16" but the shank diameter is 1/8", the overall length is 2.5" and the length of cut is .5". Now, in area where the relief is very steep it might create a problem. Artcam will create a path thinking that the bit is 1/16" but when the bit will go deeper then the length of cut the actual bit is 1/8". So i'm not sure what going to happen, it might push the bit and offset the whole coordination.

The depth of my relief is around 2.7" and the maximum LOC that i was able to find was 0.95. Another problem is the overall length. I using the stubby collet and it's a huge help, but again the maximum OAL I was able to find is 3, and it's still a problem (specially since it's 1/8" collet bit).
Do you have any suggestion of how to solve this?

Btw - I were right about the amount of allowance that left after the rough pass - it's much thicker than what I asked Artcam to do. Thank you for this tip!
Here is an image of the work in progress, hope it will help...
http://img59.imageshack.us/img59/9059/photo4lm.jpg