# spoilboard vs bottom cleaning vs surfacing router bits



## Mike_C (Jul 11, 2020)

I have seen several designs for these bits.

my main use is slab flattening or occasionally creating an odd angled chamfer.

can someone enlighten me as to the differences between the "4 wing style" and the "full cutter" style as per photos below?


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## mgmine (Jan 16, 2012)

I can't tell you the difference but I can say that each time you make a pass it will leave a small ridge. The ridge can be removed with a belt sander or hand planing


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## difalkner (Jan 3, 2012)

I use one like the yellow flat bottom bit, 1.5", to surface my spoilboard. It shouldn't leave a ridge; make sure your router/spindle is properly trammed.

David


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## lowracer (May 22, 2015)

Hallo, which one would last longer?


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## difalkner (Jan 3, 2012)

I've been using my flat bottom bit for the past 4 years to surface the spoilboard and occasionally flatten a rough piece. It's still cutting plenty good 'nuff for me.

David


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## dovetail_65 (Jan 22, 2008)

I have both type router bit one in a 3" version and neither leave a ridge. If a ridge is occurring tramming of the router is almost certainly needed. I use a glass plate and dial indicator for tramming to get rid of the ridge I might see on large surfaces.

For me and my use there is no functional difference between the end result for bit types you show.


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## Mike_C (Jul 11, 2020)

I would assume there is some issue with chick clearance? or maybe the ones with multiple cutters are easier to sharpen?


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## dovetail_65 (Jan 22, 2008)

Mike_C said:


> I would assume there is some issue with chick clearance? or maybe the ones with multiple cutters are easier to sharpen?


I could see where theoretically the 4 edge could be better with chip clearing, for me being only a one man shop with a 3HP dust collector on my CNC machine that I rarely run faster than 300 ipm(usually never faster than 175 ipm) I find the collector clears the chips faster then the bit can produce chips at the rate I cut anyhow.

For people cutting at 600ipm or 1200 ipm using larger bits with deeper cutting paths then chip clearance may become an issue.

Most chip clearance discussion and issues are actually for the pros. In my experience no type bit, lessor quality or designed bit, hardly any issue at all with a CNC, can't be over come by doing one thing and that is slowing down.

Even at 60 ipm being one guy I can never outwork the machine for my work. Clearance and all those calculations I used to fret over as a newb now after 17 years in CNC never enter my mind. Most home or garage CNC workers or smaller shops will tell you this, that the sound the machine makes during the test cut tells them to immediately to increase or reduce the depth of cut or tool path speed and they do it by ear on the fly. I use the bit I have on hand I think is best for the job. Then I make a test cut and use sound to tweak the settings for speed and depth to get the best cut, indirectly giving me the correct chip clearance for the job.

I think many guys here feel what I am saying, they can hear the right point for their CNC machine and that's better than any paper calculation on chip clearance ever can give. Chip clearance is a starting point at best for our type machines(well mine anyhow).

In short, regarding the type bits and their differences for any profile, I would go with the best deal, least expensive over all that look to give the same edge we want. I do not think too much about chip clearance when purchasing the bits anymore. Many bits I have do the same exact thing, but use different tech, just like these 2 bits. I generally purchase the cheapest bit with decent reviews and my brand loyalty has lessened over the years too.


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## harrysin (Jan 15, 2007)

For planing I prefer to use a dish cutter as it's more tolerant to slight tilt of the router, whereas bottom cleaning bits that I used to use can cause lines where the corner digs in.


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## dovetail_65 (Jan 22, 2008)

harrysin said:


> For planing I prefer to use a dish cutter as it's more tolerant to slight tilt of the router, whereas bottom cleaning bits that I used to use can cause lines where the corner digs in.


That works, but for a CNC Spoil board I do not recommend using that type bit for the sole purpose of stopping ridges.. Those bits cut flat, they don't leave ridges. It is not the bits that cause those ridges and if they did who would buy them and what purpose would they serve. I suspect as long as the bit is not defecteive for the msot part the ridges come from jigs, fixtures or CNC machine that are not set up perfectly, trammed or otherwise. Or from a the routers themselves that simply do not have balanced enough collets or have slop in the plunge mechanism or jig or fixture mechanism, I am talking very small tolerances. The wider the bit the tighter the tolerances need be.

If I get a ridge on my CNC spoil board I know for a fact my machine needs tramming. I adjust and adjust until that ridge disappears and I never had an instance where I could not get that ridge to disappear with a cnc machine with a decent quality spindle.

Now on a jig or fixture sometimes even a regular router right from the factory the tolerance just aren't there for most to adjust out a small .003 ridge due to imperceptible flex, or the router not being 100% perpendicular to the surface or very slight movement of the entire router as the router moves along the fixture or the collet not being balanced enough etc, etc.

I always say if it works to get the end result we want, then do it. There is no right or wrong in woodworking to me as long as an operation is safe. If using the bowl bit works for a given project to make it flat great.

For a CNC table application I go for the dead flat tables(as flat as I can get using my machinist levels). Believe me I have skipped that step and not done enough to ensure the table had no ridges or wasn't flat and too many times in the end it came back to bite me. I never found it to be the bit causing the non flat or ridge issue on my table either. If the use of a dish bit is to hide an accuracy or precision issue, ie hiding a CNC table's true flatness that isn't actually dead flat(which is actually an indication most times there is another issue somewhere else on the CNC machine), some other project, probably 3d bas relief or projects where you want to cut through your material and not cut into the table itself(or as cut in as little as possible)are going to be effected most. Ask me how I know that. Hand routing with jigs and fixtures I don't see any issue using the Dish bit for most work though.


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## harrysin (Jan 15, 2007)

It's for the very reasons you give that in my opinion the dish cutter is more tolerant.


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## LeftFinger (Mar 21, 2019)

How much overlap harry?


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## difalkner (Jan 3, 2012)

harrysin said:


> in my opinion the dish cutter is more tolerant.


For hand use, yes. For CNC, no. If you're not able to use a flat bottom bit because it leaves ridges then going to a bit that doesn't produce ridges just hides a poor setup on the CNC; you haven't 'fixed' anything but have simply masked the problem. That needs to be corrected such that you can successfully use a flat bit or a rounded dish cutting bit.

David


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## harrysin (Jan 15, 2007)

I pride myself on the fact that I have the ability to turn errors into features!


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## harrysin (Jan 15, 2007)

LeftFinger said:


> How much overlap harry?


Just so that there is a seamless transition.


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## J0seph (Dec 2, 2011)

I use a 2 1/2" spoil board bit and do not get any ridges on a 5x8 table. It takes about 18 minutes to surface my table. I do have a 4 hp spindle and not a router. If ridges should appear, it is time to check your settings. Learn to use your machine by tinkering with it. I can remember the first time I attempted to set the tram on my machine. I was terrified I would mess something up. After the first time ( and many attempts) I have no fear to adjust my machine and to maintain it properly. Just my experience.


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## Skullface (Aug 17, 2021)

difalkner said:


> I've been using my flat bottom bit for the past 4 years to surface the spoilboard and occasionally flatten a rough piece. It's still cutting plenty good 'nuff for me.
> 
> David


Mine did last for 2 and a half years, and I had to replace it with a new one. Use spiral compression router bits to cut the plywood cleanly on both edges without pulling it out. The sharpness of the upcut and downcut flutes of compression router bits. As a result, the flutes compress the plywood as they cut it in both directions. The only thing that I don't like to do, is to clean after I do the work. You need some special solutions to clean that dirt, therefore I prefer calling a professional service from Commercial Cleaning Services in Portland, Oregon — Cleansolution, to clean it for me.


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## old55 (Aug 11, 2013)

Welcome to the forum @Skullface


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## jw2170 (Jan 24, 2008)

Welcome to the forum @Skullface


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