12-Degree Versus 20-Degree Cutterheads for Poplar

A discussion of whether to use 20° or 12° cutterhead angles for machining Poplar. January 25, 2010

I have just purchased my first moulder (a 1995 model five head Scmi Superset). It came with a full set of FS Tool heads that have four twelve degree pockets. I am wondering if it is at all possible to machine poplar paint grade moulding with 12 degree, or do I need to just buy 20 degree heads right away. I know I will need them eventually, but trying to keep my costs down up front. I am a small cabinet shop slowly looking to break into the moulding business. Right now I have a customer who needs 3,000-5,000 of paint grade case, base and crown every two months or so. I realize this is not much, but I have to start somewhere. If anyone needs twelve degree heads, maybe we could work out some sort of trade for 20 degree heads?

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
This is an ongoing debate. I think even Weinig has switched and started suggesting 20* pockets now for most woods. But just some advice before you go out and buy new heads. We run 12* on everything, poplar too because it’s what we have. This finish is just fine. We do have nice moulders (non jointed) but I would go ahead and start production with what you have - the 12* heads. Yes there is the horsepower issue. Less used with a 20* but if all you have now is 12 and your machine is set up properly, proper dust collection and feed speed and you will be just fine.

From contributor T:
Contributor J has it right. The 12 deg. is best for poplar. I think the reason mfg. recommend 20 deg. heads is the horsepower, or lack thereof, issue associated with mass produced moulders. Never trust a salesman to tell you what he thinks you need. In addition who says you’re never going to cut oak or maple someday. Use the 12's, they are what I use and I cut a lot of poplar.

From contributor R:
The total geometry of the cutting tool is what provides you with the best finish and the longest lasting tool. This geometry is made up of the hook angle, the back clearance angle, the side clearance angle and the cutting tool diameter.

When we look at cutting different types of wood, we need to understand the material. The softer the wood is to cut, the more you want your tool to slice at it; the harder the wood, the more you want the tool to scrap at it.

With this stated, I normally use a 20º hook on poplar and soft cutting woods and 12º on harder to cut woods. Since the hook angle is only part of the overall tool, it is not uncommon to use a variety of hooks. For example, when I use 20º hook for poplar, I grind my back clearance around 27º. If I use 12º hook, I grind the back clearance between 30-33º. The bottom line is this, if you find a combination that works and you get the finish on the material you want, then there is no wrong tool. I always suggest that you try a few different combinations until you find the one that works the best for you.

From contributor M:
Or add dual angle heads to your collection that have both 12 and 20 degree pockets.

From contributor J:
Remember knives must be ground at the same angle as they will be run or the profiles will not be accurate!

From contributor Y:
12 deg. is for hardwoods. 20 deg. is for softwoods. Poplar is actually a hard wood but I mainly use 12. It depends on the knife stock you use also.