Official Luthiers Forum!

I'm new to this so please excuse my dumb questions.

First, what approximate feed rates are expected using a cnc router with say Hard maple, using a 1/2" or 1/4" bit at 1/8" depth passes? Other hardwoods? What speeds are you running the router using a speed control? Any ones experience with this would be greatly appreciated.

My reason for asking is, I see so many trying to get high speed rapids. I can see the need for the rapids if in production, but how does that equate to actual cutting other than getting from point A to point B quicker?

The machine I am currently building is within my budget and the lead screws have their limits. After a lot of testing of my X axis, I'm questioning my choice? I get very consistent runs at 45 IPM anything over this It gets funky as the IPM increases. I don't want to continue with this build until I have sorted this out, as I don't want to have to tear it down completely in order to replace all axis screws.

So again thank you in advance for your knowledge and sharing of info.

Mike

_________________
I'm outside looking in, just farther from the window than most.

I think the focus on rapids is less due to usefulness and more due to the fact that you can still get a pretty high rapid speed on a machine that might not be able to cut very quickly. That only helps much if you're doing a lot of quick passes (ie: drilling, production slotting, quick paths with different tools).

In an ideal world (high rigidity) you'd be running a 1/4" at 1/8" depth at 10,000RPM and 120IPM and a 1/2" at 1/4" and 240IPM. Those are aluminum feeds and speeds, as a start. You can run more depth in wood without melting chips or more RPM to take a load off your axes, so you could run at 50IPM with a 1/4" at 10K RPM and not burn anything, for example.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thank you Bob,

I think I'll stay on my track as it is without the expectations I had. I believe that I will find this will suit my needs at present. If not, then I'll reevaluate these areas.

Again Thanks

Mike

_________________
I'm outside looking in, just farther from the window than most.

For a small quantity work, 40 ipm is fine. I don't run much above that on my K2. It's plenty fast to be much more efficient than manual work...!

Trev

_________________
http://www.PeakeGuitars.com

Thanks Trev,

That makes me feel much better about my decision at this time.

Again, if after I get farther along and see I need to change this, I will work it in. I also plan now to incorporate the idea of change into the build to minimize the destruction to accomplish the upgrade reconstruct if needed.

Again Thanks.

Mike

_________________
I'm outside looking in, just farther from the window than most.

You can do quite well at low speeds, and you'll learn all kinds about economy of movement. And a second set of 'hands' is still bonus time for you even if it takes two hours to save you one hour of work!

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks Bob,
That actually makes sense about the 2 hrs, vs 1 hr and the extra hands

Thanks again.
Mike

_________________
I'm outside looking in, just farther from the window than most.

What is the consensus about cutter diameter vs depth of cut? Should you use a 1:1 or 1/2 cut depth : dia?

_________________
tim...
http://www.mcknightguitars.com

The rule in metal is 1/2 diameter depth of cut. In wood the rules are different.

In metal the problem is chip evacuation/recutting/melting/welding and cutter beam strength/breaking/chattering

In wood it's about chatter/vibration, chipping, splitting, heat, and hold-down.

You can run cutters at 4X diameter in wood (as a practical maximum) but the deeper the cut the more issues you'll have with heat causing scorching, cutter forces causing splitting, side-pressures causing parts to move, and grain chipout. Which of those issues you run into most depends on the cutter size. The larger the cutter, the less likely I am to run it deep.

Grain chipout, for the most part, can be avoided via cutting strategy. Side-pressure can be dealt with via fixture design. Scorching is a feed/speed issue (bad chip evac can cause the cutters to get much hotter as well). Cutter forces causing the work to split/snap is one you only run into if you have all those other ones completely solved

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Hey Tim,

It depends on your machine, the part you are cutting, and the way you are holding the part. If your machine is not very stiff, or the part you are cutting is fragile in some way, or your jig does not hold very securely, then you probably want to go with less depth of cut...and vice versa.

If you can take a full depth pass comfortably, then go for it.

_________________
http://www.PeakeGuitars.com