new to cnc'ing metal, have a few questions

[Dyer13]

Hi. I am new to cutting metal on a cnc. At school, I have access to a Light Machines prolight 1000. I have cut numerous things on the cnc machine so far, but I have never cut any metal on it. I am doing a basic flat design for a classmate, who wants paintball gun grips cut out of 1/4" diamond plate. So here is my question. I need to know what a safe Z-step depth is. I don't know how much to cut off per pass. I also need to know the speed/distance the table should move in the X and Y directions, sorry I do not know all the terminology yet. I am going to be using a 1/4" endmill. Finally, what should I set the spindle speed at?

Thanks, I hope you understand what I am asking.
Dyer

[InspirationTool]

You need to learn "speeds and feeds". Google around and you will find it.

Stock material and cutter material define tip speed in surface feet per minute (sfpm).

sfpm and cutter diameter define rpm.

rpm and chip load (ipt) define feed (ipm)

You should be able to cut at least 1/8" deep in one pass on that machine.

How do you like that machine?

-Jeff

[msomerville]

Is the tool you are using carbide or HSS?
How many flutes on your tool?
As far as the distance in X and Y, I don't know the distance you need to travel so I can't really help you there.

[Dyer13]

ok, I googled speeds and feeds, and I found a couple good sites, mainly a wikipedia site. I found a bunch of equations to find the spindle speed to run at. My drafting told me to just be safe and cut it at about 50 or 60 ft/min. So I guess that solves that problem. Then I used the equation to find the spindle speed: (4x50)/.25=800 RPM. I don't really know where the 4 came from, my teacher told me that was just a constant, so I used it. I don't know the chip load of the 1/4" HSS endmill. It has 2 flutes.

Jeff, I really like the machine, but I don't have anything to compare it to, since its the only CNC mill that I have ever used. I actually had to fix it to be able to use it. Before I fixed it, it sat at the school for at least 8 years since the last time anyone used it. The software for it frankly, sucks. I am used to programs like autocad, inventor, solidworks etc and the programs that are with it are very basic by today's standards, but the machine is a bit old. I don't know if it will work with windows xp, but if it does, I would really like to upgrade it. I am using windows 98 with it right now. To be able to easily cut out 3d parts instead of basic engraving/flat parts, my teacher had to buy a program to convert stl files to NC code. Then, since the program's NC output was different from the format the cnc control program uses, I had to write a program to take the NC txt file to the format that the CNC control software would understand and work with. There are still some bugs in it though, and it sometimes seems to have a mind of its own.

[msomerville]

Do you go to a local trade school?
Just asking because we had a CNC at my trade school, back in '97, but the machine sat and was hardly used because the teacher didn't know too much about it. We also had a lathe that wasn't working right, but he didn't do anything to fix it because it was out of his comfort zone. Although I would hope that most schools would realize the importance of a teacher having that knowledge.

Anyways back on topic I did a short search and found this site for American Machinist. It should help you out.

One thing is for sure is don't use feet/minute it should be inches/min.
RPMs are too slow. Even if you are using High Speed Steel I would start out at maybe 1300RPMs and 6 in/min. try cutting .06 deep first.
If it is carbide I would probably run about 2300 RPMs 10 in/min. start with the same depth and work from there.

If you see any blue chips while you are machining with High Speed Steel that is bad and you need to back off the RPMs or Feedrate or both.

http://www.americanmachinist.com/Cal...eedsFeeds.aspx

[Dyer13]

No, I am actually a junior in high school. I guess I am the only person in a long time who had the patience, know how, and the technical skills to do anything with it. The cnc machine is in the drafting/3d modelling/architectural room, and the teacher just started teaching the classes that involve those topics last year, since the teacher before him retired. We also have the prolight cnc lathe, but I don't know how to use it yet.

[InspirationTool]

Dyer, the new windows software for that machine is supposedly pretty good and I've heard it's not that expensive.

I'd contact light machines, http://lightmachines.com/

-Jeff

[The White Fox]

You seem to be heading down the right path to find the info you're looking for, so I don't have much to say. Do not forget the beloved Machinint Handbook.

For what it is worth, you teacher telling you to use "4" in the equation for rmp's : 12 (inchs per foot) / pi = 3.8197......
So, 4 is acurate enough, it's what my boss uses, I like using 3.82

SFM with HSS tooling for medium soft steel is about 100
Remember, as a rule of thumb, use at least .001 chip load per tooth

[JWB_Machining]

White Fox, really .001 chip load? Some times when I use that my cut doesn't sound so hot. I've been using 0.5% of my Diam and even then find myself dialing down. Is there like a threshold where I could be going too slow?

[foam27]

Your best bet is to ignore all formulas, theories, etc...

Listen to the mill, feel the metal, and be one with the mill.....may the force be strong within you.....

....and pray for protection of your face, chest and throat.......

[JWB_Machining]

haha That's how I machine. Unfortunately when the Computer is spitting out the controls instead of me turn the knobs I'm fearful. Hence you can often find me ducking behind something with a full face protective shield and my hand on the feed hold button when I do my first run of things. Thank god we have an old bridgeport when doing things manually is just easier.

[ALLtra Mach]

Originally Posted by foam27 Your best bet is to ignore all formulas, theories, etc... Listen to the mill, feel the metal, and be one with the mill.....may the force be strong within you..... ....and pray for protection of your face, chest and throat.......

How do you "feel" the metal in a CNC?