Feed rate fundamentals

[Anonymous]

I'm working with a shopbot to carve some guitar bodies(how original right...) and i've been very excited about the progress I've made.

i'm new to the cam part of things, and i still learning some of the parameters, definitions, so on.

What are good rules of thumb for Lead-in, lead-out rates for the x and y moves?? 75% of my cutting feed rate??

What are good rules of thumb for ramp and plunge feed rates?? I'm using 3/8" and 1/2" diameter cnc bits and the machine is pretty robust.  Most of my cutting speeds are set between 120 and 150 in/min.

On one of my first runs i noticed that although the cam simulation looked very smooth and uniform in speed, in real time it was not the same thing.  For instance a 2d adaptive milling operation for a pocket was about 5 times longer on the machine than in the simulation.

My lead-in and lead-out rate were pretty slow, making the whole process look jerky.  I didn't set these in fusion myself, I think Fusion calculated them.

thanks in advance for any help climbing up the curve

joe in WI

[RandyKopf]

@Anonymous

I got a moment so I'll toss in my 2 cents 🙂

Great questions you are asking about feed rates. It is relative to what you are doing. There as so many factors involved. The goal should be to become familiar with what works well for you for what you are doing.

It is easy to say this material and cutter should always be used with this spindle RPM and feed rate. but in reality it all varies relative to how much volume a cutter is expected to make. A very shallow cut may be able to cut at maximum rates where under maximum (axial) cut depth and step over (radial) cuts likely need reduced feeds. Typically the RPM doesn't need changing but feeds do need adjusting.

As an example in typical machining you typically have the following factors for the most part in order of importance:

1) Material you are cutting.

2) Cutter selection. i.e 1,2,3 or flutes etc and cutter material High speed or Carbide

3) Machining strategy - I.e. Roughing, Semi Finish, Finish tool paths.

4) How your part is held down.

5) Rigidity of the machine

6) Horsepower

7) Available Spindle Speed

8) Available Feed rates

9) Coolant

10) Chip evacuation

In your case if you are machining wood there is a huge difference in machining walnut vs pine. That is true from a hardness as well as grain perspective.

Are you needing to rough the main shape of the part. In your case the basic shape of the body. Or neck.

Do you also need to do fine detail work like slots for inlays in the fret board.

With just those factors 1 cutter is likely not going to do everything. So you find a cutter that works for each type of cut you would be making. And try   to use the largest tool possible to cut the most material possible. And when needed use smaller cutters for more detail.

There is no absolute right way to do something. It's a matter of working with what you can with the least amount of effort to get the job done.

Most cutter manufactures provide suggested cutters for materials. And the operation you are doing. And they provide speeds and feeds as a starting point.

As you use a tool and cut strategy keep notes of what works so you can apply those settings for future jobs. Fusion has the ability to save operations as starting points with all you settings. Evertually you will have more than just a favorite set of cutters but also the matching machining strategies as well that includes operation types and speeds and feeds and they can simply be applied to new parts and geometry very quickly.

Hope this helps and keep asking questions!!

[ian1196]

Here is my two cents also. The odd woods you plan to use may machine oddly. Therefore to risk splitting, start with about 1/3 the tool diameter especially on the edges. Some of those oily woods will handle a full tool width. Clearance is important. Many 4 flute mills may look like they will have enough clearance but they will smoke. A vacuum is great because it does two things. It prevents slap cutting of chips. It pulls heat away from the tool. Air is better if someone else cleans the shop. If you buy carbide, get the shiny ones. The grains are smaller and gives a sharper edge. Put a little baby oil on the tool when you finish. It will prevent the surface build-up of wood resin making it sticky. When you wipe the oil off, it will keep the tool clean. Now, worry about chip load and feed rate. High surface speed is your friend. Feed rate is a try and see since I do not know your parameters.  If you are taking a final finish cut at router speeds, you can usually cut at least 100 ipm.  Look up Delrin and use it as an average.

[Anonymous]

This current project is made from a lighter ash tree grown in the south, not quite as heavy or as hard as a northern ash tree.  Not oily at all, machines pretty nicely.

I'm using 3/8" or 1/2" amana carbide end mills for most operations, at 10K rpm.

My cutting feed rates are at 120-150 ipm depending on the operation.

I'm taking .120" or .150" depth cuts for most operations as well.

My questions were more pointed at some of the non-cutting feed rate speeds, such as lead-in and lead-out, and the   plunge and ramp speeds.

The shopbot has a 1.00 hp spindle, with 1/2" collet, relatively robust machine.

thanks in advance for sharing.

joe

[ian1196]

You numbers look good. If you have a feed override, start a little slow. Make your first parimeter cuts clockwise  to avoid splinters. You have parallel and perpendicular grains, plan accordingly. Remember, all guitar bodies resonate. You do not want that when you are making it. I would imagine Eric Clapton's latest guitar was carved from a CNC router in a few minutes. When your machine is taking an hour to make the body, remember this. Jimi's guitar was probably made using multiple router box templates. It probably still took over an hour to carve the body. Good luck.

[Anonymous]

Thanks for the reply and comments,

I get it, you can't rush the process, I was just trying to be time efficient on the machine, so it the tool just 'hovering', and I was like ...what the heck.

Still have so much to learn...

thanks again

joe