Newbie- CNC Newbie Questions

[Smokingman]

I am very new to CNC, in fact I just got my first one this week. I spend the past few months doing research and trying to learn everything I could before I purchased.

This is what I ended up getting:
KG3925-G
0.75" top
8" Z-axis
HST 3HP 18,000rpm Spindle
RhinoCAD
RhinoCAM



OK, so maybe it's a little overkill for my first CNC. I couldn't help myself.

After reading everything I could get my hands on and using all the software and going through the tutorials, I thought I knew everything I needed to know to figure out how to use this thing properly. I'm learning quickly that there are a few holes in my knowledge.

Although I've been able to design and cut several small projects successfully, I have a few questions I hope someone can help me with.

Feeds and speeds:
I know, big subject. I come from using power tools by hand in my shop. I can feel how fast I can push a router through a piece of wood and listen to the sound to know if I'm going to fast. It seems this experience doesn't help much using a CNC.

I want to know if I'm doing the math right, and this I understand what everything means.

Using the formula:

Feed Rate(ipm)=RPM * [# of flutes] * [Chip load]

Using a 1/2" 2 flute bit in Mahogany cutting 1/2" per pass at 8,600 RPM with a chip load of 0.018" should equal:

8,600 rpm * 2 flutes * 0.018" = 309.6 ipm

That seems awfully fast. Am I doing this right? Also, is this the "proper" speed, or the max speed?

Drilling:
I need to be able to drill deep (up to 2") holes and various diameters (1/8", 3/32", etc). What is the best way to do this? Do I need special bits? Can I simply mount a drill chuck to my spindle? Is that even possible? Or should I just walk the piece over to the drill press?


Final Note:
The guys at K2 were great. Very helpful, and I got my CNC in about 3 weeks. The initial setup was a breeze. I know some people have complained about getting noisy units, but mine is whisper quiet. The loudest part of it (when not cutting anything) is the cooling fan on top of the spindle.


Thanks in advance to anyone who can help with my questions!

[jalessi]

For drilling deep holes use G83

YouTube - cnc mill g83 g code

YouTube - cnc mill g83 g code

[jalessi]

https://www.onsrud.com/xdoc/ChipHardwood

[koshersteel]

please keep us posted on how you evolve with this machine. I am about to order an almost identical setup.

[ger21]

Originally Posted by Smokingman Using the formula: Feed Rate(ipm)=RPM * [# of flutes] * [Chip load] Using a 1/2" 2 flute bit in Mahogany cutting 1/2" per pass at 8,600 RPM with a chip load of 0.018" should equal: 8,600 rpm * 2 flutes * 0.018" = 309.6 ipm That seems awfully fast. Am I doing this right? Also, is this the "proper" speed, or the max speed?

Manufacturers chip load is usually a starting point. You're machine will dictate how fast you can go. 300ipm is not too fast, but it'll seem pretty fast on a small machine like that. On most small machines, spindle HP will be a limiting factor in regards to chip load. But with the HSD spindle, you shouldn't have a problem. As long as your machine is rigid enough to handle the cutting forces at higher speeds and chip loads. A general rule of thumb, for longest tool life, is to cut as fast as possible while still getting acceptable cut quality. You may be able to cut even faster, especially if you're ding rough cuts and quality isn't as important. You may have to cut slower to get better quality. Keep in mind that increasing RPM will have the same effect as slowing the feedrate, but will save you time. The main thing that chip loads help with are tool life. Generally, the higher the chip load, the longer the tol will stay sharp. Lower chip loads result in hotter tools, and heat is the main factor in tools getting dull.

Drilling: I need to be able to drill deep (up to 2") holes and various diameters (1/8", 3/32", etc). What is the best way to do this? Do I need special bits? Can I simply mount a drill chuck to my spindle? Is that even possible? Or should I just walk the piece over to the drill press?

A drill chuck at high rpm is very dangerous, unless you can find one that is balanced for high rpm use. Otherwise, it'll probably shake like crazy. 2" holes are tricky. The easiest way would be to route them as deep as the bit will allow, and fnish on the drill press. Usae an 1/8" bit, and G83 peck drill as Jeff said. for the larger holes, use the same bit and helical G2/G3 cuts. Using the largest bit that will fit in the hole will allow you to go deeper, as larger diameters come in longer lengths.

[Smokingman]

Thank you so much for replying ger21!

That's the type of information I needed and explained in a way I can understand. Being new to all this, it seems counter intuitive to push your tool faster through the material to increase the life. But now I think I understand it.

It's seems to be a matter of dissipating heat. Moving the tool faster doesn't allow as much heat to build up on the material and tool at a given spot, and a higher chip load provides larger chips. The larger chips having more mass can remove more heat from the tool. Slowing down the spindle and slowing down the feed rate will give you larger chips (better heat removal), but increases the contact time between the tool and the material at a given spot (thus generating more heat) so it's less ideal. Right?

As for the drilling question, I guess I was over complicating the issue. I only foresee drilling 3 diameters of deep holes, 1/8", 5/32", and 1/4". So I just bought an ER25 collet for each diameter, mounted a drill bit and ran the spindle at 3,000 RPM. Using G83, it made perfect holes.

[jalessi]

Smokingman,

Happy to hear that worked for you.

Jeff...

[Smokingman]

Koshersteel,
Since this is my first CNC, I really don't have anything to compare it to, but I can say I LOVE IT!.

I've been CADing and cutting everything I can think of to see the limits of what I can do. Doing this is helping me learn RhinoCAD/CAM, Mach3, and how to do things in general.

Here are a few things I've learned that I'm sure more experienced users will think are obvious, but experience is one of those things you get just after you need it.

• I first used Mach3 with a mouse, but I found it a bit awkward so I tried a touch screen. Much better! I put a 17" touch screen on a swivel arm mounted to the CNC table and it works great. The only problem is the jog controls. A keyboard is still needed until I get/make a pendant.
  
• K2 setup the Mach3 profile, but didn't set it up to stop on tool change. I found that out the hard way. Going from surfacing to v-carving without changing tools doesn't work so well.
  
• The spindle takes some time to spin up, so it's a good idea to add a spin-up delay.
  
• The gantry extends quite a bit beyond the table top in the home position. Make sure you don't put it too close to a wall because can and and will scoot 400lbs of table across the floor when it hits the wall!