Improving the Human Power Feeder

amana-tool-grooving-cutterThere are many important factors on getting a nice, clean cut at the router table or shaper. Cutter design, flute direction, spindle horsepower, size and depth of cut, workpiece control (featherboards and hold downs), grain direction, and machine calibration just to name a few.

I was reminded of another factor the other day when I was milling parts for cabinet doors on the shaper. I noticed the edge along the panel groove of my stile was getting some tear out.

If I was on my router table, I would be thinking about grain direction or if I’m cutting too deep. Possibly my bit edges are getting dull. The other telltale sign to pay attention to is the audible feedback from the router itself (for a further look at router bit use, Tools Today has a nice informational page).

The problem on a shaper is (unlike a router table) there’s rarely an audible sound which tells you that you are going too slow or too fast.  The motor typically doesn’t bog down and change pitch. Especially on grooves only ¼” wide and 3/8” deep (which is nothing for a decent sized shaper). On small cuts like this one, there is virtually no resistance regardless of how fast you feed, so its up to me to be cognizant of my feed speed.

Wait…feed speed. Of course! I was getting tear out because I was feeding too fast! It was getting late in the day and I was hurrying. The next stile I slowed down and the cut was much better.

You can get quite technical if you so desire when looking at achieving proper feed speeds. The following equations are how one would go about it.

Chip load = feed rate IPM / (RPM x number of knives)

RPM = feed rate IPM / (chip load x number of knives)

Feed Rate = chip load x number of knives x RPM

Chip load* – the size of the wood chip being removed by one of the cutters or blades.

RPM – Revolutions per minute. The farther from the center of a spinning circle you get, the faster that point goes. I.e. your router has a 20,000 RPM setting. That means the spindle is humming along around the edge of the collet at close to 30 MPH . However, spinning a 3” panel raising bit at that setting would mean the farthest edge of that bit is going 178 MPH! It’s why many routers and shapers have variable speeds. To accommodate different diameter cutters.

Feed Rate – usually in IPM or inches per minute. How fast or slow the workpiece moves against the cutters.

*The variable that’s a little more difficult to find is the Chip Load. Good news is Amana Tool provides us with these charts for most of our items. An example can be found here and here.

Getting technical is all well and fine if you have a power feeder or CNC where you can precisely set the feed speed, but what if your feed control is of the two-armed variety?

Experience is the best guide. Not what a new entrant to woodworking wants to hear, but there is truth to it.

But don’t let that slow your woodworking roll. There are some tricks we can employ whether we have experience or not. Something that can help new folks build that experience up without wasting a mill full of wood and help experienced folks have a bit (pun intended) better day in the shop.

European groover shaper cutters work a lot like a dado stack. There are scorers on each edge to score the cut, and rakers to clear out the wood in between. Most router bits lack this advantage to score the cut. They essentially have just a flat set of rakers.

On longer workpieces, the grain might go in several directions along the cut line. Further necessitating the need to score the cut. The limitations of a router bit slot cutter are tough to overcome in these instances. So, when I need to avoid tear out, I turn to my circle marking gauge. It works wonders as a scorer.

 So, when I need to avoid tear out, I turn to my circle marking gauge. It works wonders as a scorer.
I did a quick, not-so-scientific exercise with poplar stiles. I cut four grooves with my slot cutter on the router table. I scored two of the four slots. I then went fast enough to stress the router motor on one non-scored and one scored. I then slowed to the point where I would risk burning the wood on the other scored and the other non-scored groove.

See photo results:


As you can see, there was a lot of tear out when I went fast on the non-scored workpiece.

Yet going fast on the pre-scored piece gave nice results. So, it’s no surprise that when I slowed down on the other pre-scored piece, it also looked good. However, the big surprise came when I slowed down on the remaining non-scored cut. It looked just as good as the pre-scored! Granted, this is fairly straight-grained poplar and not curly maple. But knowing we have a nice option for those hard-to-tame woods can give us more confidence at the router table.

The takeaway from this exercise is, if you want to hurry up and do good work, slow down! Or grab your marking gauge…

I hope this tip helps. It has certainly saved this two-handed power feeder more than a few redo’s over the years.


Brandon Larkin
Larkin Woodworking


This entry was posted in Router Bits, Shaper Cutters and tagged , . Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *