Estimating router feed rates & depth of cut??

[ian maybury]

Most of my routing has been of the try it and see variety. I've figured out that there's a sweet spot in terms of rate of wood removal for a given cutter - that if i feed too slowly i get burning, or too fast and i can hear the router loading up. Also that the cutter can get quite hot and bothered if there isn't good chip clearance.

Trouble is i don't always get it right - and i'm a bit impatient with taking multiple passes. I tend to go cautiously with 1/4in cutters for fear of breakage.

Has anybody come up with a reliable rule of thumb for hitting the sweet spot in terms of depth of cut and feed rate for a variety of cutter types?

ian

[glenn bradley]

Most of my routing has been of the try it and see variety. I've figured out that there's a sweet spot in terms of rate of wood removal for a given cutter - that if i feed too slowly i get burning, or too fast and i can hear the router loading up. Also that the cutter can get quite hot and bothered if there isn't good chip clearance.

Trouble is i don't always get it right - and i'm a bit impatient with taking multiple passes. I tend to go cautiously with 1/4in cutters for fear of breakage.

Has anybody come up with a reliable rule of thumb for hitting the sweet spot in terms of depth of cut and feed rate for a variety of cutter types?

ian

To succeed at this, get over your impatience. This isn't a race and your machines are not industrial grade :). I follow a rule of thumb picked up somewhere along the line of removing a profile no more than a square 1/4" per pass. This means that a 1/4" straight bit would be limited to a cut of 1/4" deep per pass. A 3/8" sraight bit would be limited to an 1/8" deep cut per pass. You have to use your judgement on profiles that do not translate easily but, you quickly develop the idea.

Some woods like cherry and maple are burn prone due to makeup. slower speeds (even on smaller bits) will reduce burn tendency on these woods. If you go too slow, you will get a rough finish. Even if you carefully found the perfect speed and feed rate for a given batch of material, the next batch would be a bit different; its wood. Charts with basic guidelines are the best we can hope for until we develop our own 'feel'. Even then we can still get surprised by some over-sugary hard maple or some irregular consistency walnut.

Here's a general speed chart:

[Jeff Duncan]

Experience, IMHO, is more valuable than any chart were one to exist. In woodworking there are so many variables it's difficult to establish hard and fast rules. Your experience is building with each project and it will only get easier with each new project. Take it slow and easy and only push when you feel able.

Good luck,
jeffd

[Bill Huber]

I agree with the experience with it, now the chart is good for knowing the bit speed but there is still nothing that tells you the feed rate. For me it is feel, I let the bit work and push only enough to keep it working. Now I know that if I am taking off a lot of wood I need to go slow and maybe even do it is 2 or more passes.

[Jim Rimmer]

I agree with the previous posts. It is an experience/experiment thing and it will change from one piece of wood to the next (in the same species). I couldn't tell you how many times I've been routing (or sawing) a piece of wood that may be the 3rd or 4th or more in the sequence and suddenly encounter more resistance and the thought goes through my head "What the heck is going on?" It's the nature of our hobby and you just have to learn to deal with it and enjoy the challenge.

[Neil Brooks]

I make sure I have at least one piece of scrap, from the working species. Before I put a profile into actual stock to be used for the project, I practice on the scrap.

Usually, that gives me eight or 12 edges. I can normally get it right before I have to cut fresh faces, on the scrap piece ;)

[Larry Edgerton]

I make sure I have at least one piece of scrap, from the working species. Before I put a profile into actual stock to be used for the project, I practice on the scrap.

Usually, that gives me eight or 12 edges. I can normally get it right before I have to cut fresh faces, on the scrap piece ;)

This is my method as well.

Also, for me my ear is the most important indicator of if I am doing something wrong, but I have no way to pass that to you, only time and an empathy for your machines will do that for you.

Another rule, and of course there are exceptions is I try to never make a cut that is over half of the bit cutting diameter on an outside cut. In other words if I have in 1" bit I want to limit my cut to 1/2" or less. So if you are doing pattern work try to precut close to the line and use as big of a diameter a bit as you can.

Using routers is different than say a tablesaw, it takes some time to become one with the router. I would not want a novice to watch me to learn. But the limits of what it will and will not do will come in time, and then when you know what that bit is going to do before it gets there you will know what I mean.

Larry

[J.R. Rutter]

Important for cnc, not so much for hand feeding because of additional variable like pitch build up, dullness, species, etc. But, here is a reference that might be interesting:

http://www.cncroutershop.com/technical-info/calculating-feeds-and-speeds

[ian maybury]

Thanks again guys. Sounds like i'm not the only one that's not quite certain how a given cut is going to go, but having a test piece makes a lot of sense. Thanks for the write up too JR - i like if i can to combine a technical basis like that with the feeling and experience all say is so important too.

It's not a case of running maths every time - more of using it to gain some sort of understanding of the broad effect that changing one or more variables is likely to have before using the old gut computer. :)

ian

[Kent A Bathurst]

I follow a rule of thumb picked up somewhere along the line of removing a profile no more than a square 1/4" per pass. This means that a 1/4" straight bit would be limited to a cut of 1/4" deep per pass. A 3/8" sraight bit would be limited to an 1/8" deep cut per pass.

Well, shoot, Glenn................That's so simple even I will be able to remember it. Thanks. ;)