Spoil board surfacing cutter

I bought this cutter for surface spoilboards in a timely manner:
https://www.amazon.com/gp/product/B071748JQN/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

What speeds and feeds do you reccomend on the XXL w/ a Makita router head?

Also, do i need to plunge off of the spoil board surface and work into it, or can i lightly plunge into the board to skim off the top coat?

Surfacing, esp. with a large endmill, demands a light touch — start at the highest point — take the lightest cut your tool can reliably take (equal to chipload or a bit more) and cut the entire area.

Jog the Z axis down to the cut surface, reset the zero, and run the file again — repeat until the entire surface is faced off.

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Maybe this is a seperate topic… So i’ve always struggled to wrap my mind around chip load, proper feeds and speeds, etc. when using mills (mainly manual bridgeports) throughout my career. Typically i just wing it by setting cut depth to half the cutter diameter, cranking the RPM up to something that sounds good and then adjusting my feeds until it produces a nice looking cut with a sound that doesn’t run chills down the spine.

If MDF has a chip load of .025-.027 for a 1/2" or larger cutter, per internet search.
If i have a1" cutter like the one i linked that i purchased on amazon that doesn’t give any RPM or feedrate specs, how do i go about determining my RPM’s and/or feed rates?

I realize there are these equations, but if i only know chipload, how do i get the others?
Feed Rate = RPM x number of flutes x chip load
RPM = feed rate / (number of flutes x chipload)

If i just assume i run my makita at dial 1, which i think is 10k, that would tell me that:
Feed Rate = 10,000 x 3 x .025 so my feedrate for that big cutter should be 750ipm :astonished: :astonished: :astonished: That seems way to fast for a big dang cutter like that, even if i’m only taking .020" off.

Don’t believe everything on the internet :slight_smile:
Did you mean 0.025"-0.027" maybe ? 75ipm feedrate sounds more like it.

If you start from chipload, then you need to choose an RPM value (somewhat arbitrarily, but a better way is to maximise it to reduce cutting forces), then compute feed rate (as you did)

Here’s my take on the whole thing, including chipload values that sound reasonable to me (and most of the community, since I mostly sourced them from here)

https://shapeokoenthusiasts.gitbook.io/shapeoko-cnc-a-to-z/feeds-and-speeds-basics

I don’t have values for 1/2" cutter, but somewhere between the 1/4" values and twice that, would seem like a reasonable starting point.

Anyway, at the very very shallow depth of cut typically used for surfacing, it won’t matter much and you can usually go faster than what the equations say, since there will be very little force on the cutter/machine.

EDIT: and for surfacing the community consensus is :

  • RPM in the 16k–20k range

  • Feedrate in the 80–100 ipm range

  • Depth per pass in the 0.01–0.05’’ range

  • Plunge rate is mostly irrelevant for such shallow passes, any value will do.

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@Julien I’ll read through your link and see if that helps cement this topic in my brain any better.

I guess i just get spooked when running cutters with such high feed rates, especially on benchtops machines like a Shapeoko. Just last night i was boring out some holes and profiling for my spoilboard setup and and i was running a1/4" bit at 16k RPM and i had the feedrate at 40 and i felt uncomfortable.

Please always start with the Carbide 3D tooling for which we have feeds and speeds in Carbide Create — they’re quite conservative, but also reliable.

Another link (or rather link to links) which may help you is:

It is a good thing to treat the machine with caution, and any published feeds/speeds with skepticism until they are proven out with a test cut.