What value first in feeds and speeds? And what about Inventables bits?

[JohnnyLong]

Hi! I’m new and still trying to learn as much as possible, so I’m sorry if I use the wrong terms and such…

I’ve read a lot of articles about feeds and speeds, because I live in Africa, and my bits are pretty precious because I can’t buy them here. I want to do everything I can to extend their life.

From what I understand, it’s very important to get just the right chip size to remove enough heat and get long tool life, clean cuts and fast job times. (Thanks to this article for that.

I understand the concepts, and I’m even OK with measuring chip sizes if I need to but when I sit down to a project in VCarve, I’m at a loss. I guess I’m just missing something.

For example, VCarve has the tool database with parameters like spindle speed, feed rate, plunge rate, etc. I thought all of this was tool-specific, like these parameters are fixed based on the manufacturer’s specs, but the VCarve help document says, “…The Feedrate and Plunge rate you should use will vary depending upon the material being machined and the tooling being used.” This is confirmed in the tutorials where the user monkeys with these tool database settings prior to launching a job.

So that’s where I get all tangled up every time I look at all the speeds and feeds formulas. What comes first? Richard Shannon in the above linked post gives these formulas:

If you know Feed and RPM………Feed Rate / (RPM x # of cutting edges) = Chip Load
If you know RPM and Chip load ………….RPM x # of cutting edges x chip load = Feed Rate (IPM)
If you know feed and Chip Load ………Feed Rate / (# of cutting edges x chip load) = Speed (RPM)

So, that’s my first question… When you sit down to work on a job, what number(s) do you start with, and what parameters do you typically change?

Is it the cutting speed of the material? If so, what source do you use to determine that?

I’m just trying to understand the process.

Lastly, I have a bunch of Inventables bits from their shop, but there aren’t any detailed specs about speeds to run them, etc. I stumbled on a post referring to that at some point but I can’t find it anymore.

Thanks so much for the help. I’m anxious to learn but very protective of my bits.

[MalcolmStanley]

Crossing streams

A guide to understanding basic Feeds and Speeds

Lets talk about the feeds and the speeds, and the birds and the bees. First I want to say hello to everyone, this is my first post on this forum. I wanted to write a topic that I hope will contribute to helping people who are new to machining by providing a better understanding of how a tool works in relation to the material. Disclaimer: Please understand that my experiences and theories are based on personal experience with large commercial CNC routers and not with the X-Carve; however, tooli…

I think this is the core discussion thread for this topic.
I’m trying to figure it out too.
I have a linked dicussion at Repeatable process for setting Feed Rate and Depth of Cut in Easel and elsewhere with a spreadsheet calculation tool that may or may not help.

your situation is … interesting,
The guidance so far has been to experiment with materials and zero in on what your machine can do.
We’ve documented in the spreadsheet the ideal speeds/feeds for the spindle rates for the deWalt: an XCArve cannot acheive the optimal settings so you are left with a need to compromise in one of several directions.

if you think of feed rate, depth of cut, and spindle rate as an iron triangle, all inter-related,
then I guess it looks like this:

• The spindle on a deWalt goes at 16k RPM minimum.
• The feedrate for a spindle at that rate is unachievable, so go as fast as you can: in a hard wood the target rate is somewhere around 60 inch per minute if that is achievable
• to push the spindle faster, make depth of cut shallow. The rule of thumb is half of your tool diameter: for a 1/4" bit use a 1/8" DOC, and do so on.

The easel program uses preset feedrates and DOC based on the material.
these are in the spreadsheet.
I am still trying to make sense of them;
they seem arbitrary if you consider material hardness to be important.
for instance, here is a list with the hardness rating for the woods:

Two woods with very different hardness ratings will have the same settings.
This implies the settings are a bit arbitrary and experimentation is required to get it optimal.

in this context, tool life is going to be difficult to optimize for.
we are running tools at the wrong speeds to keep them cool, so the bits will burn out sooner than in a more controllable situation.
there seems to be an assumption this is unavoidable;
the advice is to buy the clearing bits in 10 packs,
and be very deliberate in the settings you use.

I hope this helps.