The word "Spoilboard" in the name seems to be saying that the Bottoming/Planing/Flattening process is being done to the spoilboard(?) But wouldn't that process usually be done to the work piece?

In the CNC world we do use those bits to flatten the spoilboard, to provide a surface that is parallel to the XY axis so that the Z height can be consistent across the entire bed of the machine. That same bit can also be use to flatten/plane a work piece placed onto the spoilboard.

 

Ahh! Of course. That makes perfect sense. Thank you! So - while we’re talking about Flattening bits…

If I’m carving a 1/4”D x 2.5”W dado into a length of 1/2” x 2.5” pine, I expect that I’ll be using a FC bit. Perhaps 3/4” or 1” diameter. And I expect that I’ll be making 2 or 3 passes at increasing depth. But when the dado has reached the target depth…will the bottom surface be smooth? A bit rough? Very rough? Should I plan on skimming it with a Flattening bit when there’s still 1/64” remaining?

 

If I’m carving a 1/4”D x 2.5”W dado into a length of 1/2” x 2.5” pine, I expect that I’ll be using a FC bit.

What's an FC bit? Depending on the material, almost any router bit will leave a smooth bottom, because they are cutting from the side, not the bottom. A downcut spiral is the exception, because it's actually pushing the wood down as it cuts it, which can leave a slightly rougher finish. But if the bit is sharp, you'll most likely get a very smooth bottom finish with any bits.

To add to David's answer, as you use your machine, and periodically cut into the spoilboard, you re-surface it periodically to remove cuts/damage, making it like new again. Some machines with vacuum holddown suck parts down through the spoilboard, and it must be surfaced regularly to keep it smooth and flat.

 

If your setup is exactly perpendicular to the work piece (fully trammed on a CNC) and you're using a downcut bit the bottom should be fairly clean. Sometimes with softwoods you have to experiment with upcut and downcut bits to get the best results.

 

My, my - what a delicious learning curve! Thank you very much, gentlemen!!

FYI - I don't/won't own a CNC set-up. My routing adventures will be rare...brief...and - mostly - free hand. But that's not to say that I don't care about my results, 'cuz I do.

I'm sorry - I made the assumption that the wide, shallow notches that I'm gearing up to cut would almost definitely be done with a Straight Cut bit...But I made a typo and typed "FC" instead of "SC". Sorry. I'll be setting up temp fences to guide the bottom plate, and since there's no profile &/or pattern...I will be using a bearing-less bit. But is there a better choice for the bit? And...

If indeed a bearing-less SC bit is the best choice...how do I decide on the diameter? There are no tight corners or curves, so I'm guessing that the sky's the limit. I could use anything from a 1/4" dia. to a 2" dia.. But a 1/4" bit would require 100 passes, and a 2" bit is probably 'waay too big for a 1/4" shank (and probably costs as much as the machine itself) So I'd guess that a 1" dia bit is about as big as I'd wanna go. But this is 99% supposition; please jump in with your opinions!

 

If indeed a bearing-less SC bit is the best choice...how do I decide on the diameter?

What kind of router do you have, what size collet do you have, and how much do you want to spend. There are no rules dictating what size bit to use in an application like this. If you only have a 1/4" collet, I would not use a bit larger than 1/2". Anything over 3/4" should be used with a variable speed router, so you can slow the RPM down. Larger bits are more expensive than smaller onmes.

 

It’s a Milwaukee cordless. 1/4” collet. Variable RPM.
Yes - I figured bigger bits would be expensive.
But you answered one key question: what dia bit would be a good choice for carving my dadoes? 1/2”. Alright!

Is there a rule of thumb regarding the cutter dia relative to the shank? (Or is it just by chance that your recommended cutter dia is 2x the shank size?)

And...
I see that there are eleventy-nine hundred Flattening bits from which to choose, but it looks like there are three styles:
1) 3 (or 4 or 5) small square blades positioned on edge...parallel to the shank (these seem to be the least expensive)

2) 2 (usually) long blades

3) 3+ replaceable blades positioned at varying & exciting angles relative to the shank (these seem to be crazy expensive)

I am still quite solidly at the toe-in-the-water stage; I don't know if I'm gonna become a regular router or remain a once/decade hobbyist. And I acknowledge that quality tools are always a smart idea...and expandability &/or life-extending features are useful. But I am strongly inclined to stick with one of the #1 options for now. That said, I am curious to learn whether the #1 bits deliver the same result as the #2 bits...since I can buy either for about the same $$.

 

@ronemca ,
if you are going to use your dado-cutting bit for more than one purpose (eg cutting a mortise), be aware that not all straight-cut bits will “plunge”.
For example, your #1 bit will not plunge, because of the central island where there is no cutting blade, and the workpiece must either be entered from the side, or you limit yourself to a shallow cut (like in spoilboard surfacing), whereas the #2 design will plunge (not advisable at that diameter), since there is no gap between the two bottom cutting edges.
The comment does not apply to the #2 you show (probably dangerous to try and plunge), but if you are thinking of a 1/2” bit, it would apply.
#3 will also not plunge.

 

Indeed! In all honesty, the thought of plunging [these bits] never occurred to me. I have a mental image of entering my un-cut board from the side at a depth of no more than 0.125"...carving the entire dado (2.5" x 2.5") then re-entering again from the side at a depth of 0.250. I acknowledge that I may end up dividing the cuts into three passes as opposed to two; it'll depend how the first one goes. But it was always my plan to enter the finished cut from the side for the final skim (flattening/smoothing) And--with that in mind--I may stop a hair higher than 0.250" with the Straight bit so that there's a smidgen left to clean up at the bottom with the Flattening bit.

 

Entering the board from the side will bypass the plunge limitation I mentioned.

I can’t think why there would be a need to use a flattening bit at the bottom of a dado, unless you mean to keep the dado exposed, I.e. you will not use it to house the edge of a board. Even then, the bottom of a straight cut bit or mortising bit should yield a very flat bottom with a final very thin cut, even if in more than one pass to make up the finished width.

The ability to use a bit for more than one task, helps to offset the cost of a decent bit. Once started with using these tools, there is an uncanny tendency to find new uses for them. In my ignorance, the first straight cut bit I acquired was non-plungeable, and I soon found reason to rue the buy.

Talking of costs, your #3 bit, even from a Chinese website, would require a depth of trouser pocket akin to those of fashionable young women, where the pocket is longer than the depth of the shorts.

 

Yes. Not to worrry - that one was never under consideration; it was just an example. But I am encouraged by your assertion that the Straight bit should leave the botttom of the dado smooth. And yes - it/they will be hidden. Great advice! Many thanks!

 

To get the best possible finish, you might want to do a very shallow finishing pass. Say 0.5mm/0.02".

About using a cordless router - I recommend using a corded router. If your battery dies and you don't stop it in time, you will very likely break the bit.

 

Wow! Break the bit? Why? The motor will stop essentially instantaneously if the battery is disengaged or the switch is turned off, so I expect the same will occur when it (the battery) falls below the minimum threshold. But please expand upon your warning - that's an angle I hadn't considered.

 

Sorry for so late, I should email notification working.

Yes but your machine will keep moving. Since it is not cutting, you would try to drag the bit through the wood. Something has to give.

 

Phil, I think things have changed with the new batteries and brushless motors. Ron’s router is rated by Milwaukee as having the power of a 1 1/2 hp corded machine, and good for 250 board feet of edging on a single charge. He already has a bunch of Fuel batteries. I really don‘T see him running out of juice for the average amateur routing operation, particularly what he has in mind.

I don’t have a cordless router, so cannot speak from experience, but none of my DeWalt cordless tools have ever let me down mid-cut.

 

Oh, I fully believe the power is there. How do you do a job longer than the battery can run? Is there a way to monitor the battery state and do a feed/hold and battery swap when it drops low? I dunno, seems like a needless complication when you have wall power at the machine.

 

A "spoiled" or "spoilboard" in CNC machining is a sacrificial board that is attached to the CNC machine's bed. It's used to protect the actual machine bed from damage caused by the cutting or engraving tools. If the CNC tool accidentally goes too deep or there are any issues during the machining process, the spoilboard takes the damage instead of the machine's bed. I am using archiver macos. These spoilboards can be replaced or resurfaced as needed, making them a cost-effective way to maintain the CNC machine.

 

Welcome to the forum @benmi34r

 

G'day Ben, welcome to the forum.
Would you like to introduce yourself in the "Introductions" section, so we can understand a bit more about your router uses?

 

Well...it actually happened. I was testing the process on a scrap piece & the machine stopped. Nothing exciting occurred - it just shut down. I was quite surprised. But as soon as it happened I pressed the TEST button on the battery and it was dead. So that answers that question! I snapped on a freash battery & resumed like nothing had happened.