Tips for Planing Very Hard Wood

Some years ago, as a gift my wife gave me a nice piece of purple heart (peltogyne spp.), approximately 36" x 8 3/4" x 7/8", and it's been waiting for the right project to come along.  That time is finally here.  I knew this stuff was going to be hard to plane, but I really didn't know just how hard.

Three pieces of purple heart on top of some cherry

This purple heart is incredibly dense - the board was very heavy.  My project needs pieces about 12" long - one 8" wide and two pieces 5" wide.  I crosscut the board into shorter lengths before doing any flattening.

Tip #1: It's key to have a VERY sharp plane.  I started by sharpening the planes I planned to use, and I probably got them as sharp as I've ever gotten them.  I've come a long way in that regard.

The Stanley #4 next to the diamond plates and strop

Tip #2: It's also important to make sure the plane is set up properly.  When the iron engages the dense wood, there is a lot of resistance and you don't want your iron to shift on you.  For metal planes, the iron should bed nicely on the frog and the lever-cap screw should be tightened properly so that the iron and breaker don't move when in use.  For wooden planes with cambered irons, make sure the iron projection is centered and is as coarse or light as you want it.

Tip #3:  Remove as much material as possible with coarser tools before trying to smooth the surface with a finely set smoothing plane.  Because I had a lot of twist to deal with, I was able to use the wooden jack plane to remove some.  And I had the iron set for a MUCH lighter shaving than I usually take with the jack.

Using the jack across the grain, but I also used it with the grain

To remove some coarseness left by the jack and to get closer to my layout lines, I used the wooden try plane that has a more gently cambered iron that was freshly sharpened.

Using the try plane to get close to the lines.  I think the heft of the try
plane helped a lot in getting through the dense wood.

Tip #4: When you're ready for the smoother, set the plane to take VERY light shavings.  Even then it was tough to plane consistently from one end to the other.  Skewing the plane also helps get the plane through the dense wood.

I had to press down fairly hard on the front knob to keep the iron engaged

See-through shavings

Pretty darned thin, but it takes a long time to plane

Here's the thing: planing a thousandth of an inch at a time will take a very long time.  This is why it is so important to remove as much material as possible with coarser tools.

I also did a little scraping with the #80 cabinet scraper - freshly sharpened - to level any remaining unevenness.

Scraping for final flatness

Tip #5: Don't remove more material than you have to.  When I drew up the plan in Sketchup, the PH boards were 3/4" thick.  But it won't hurt anything if they are a little thicker.  (It also wouldn't have hurt if the back side that won't be seen was left with a big twist, but I flattened it anyway.)  These pieces will finish out at approximately 13/16" thick.  It wasn't worth the effort to bring them down to 3/4" and I'll never notice the difference.

I'm interested to hear other people's thoughts on this.  Please comment if you have something to share.

This PH was definitely the hardest wood I've ever planed.  Fortunately (or maybe unfortunately), my current project won't require any mortising of the PH.  I'll need to saw some short tenons and pare shoulders, so I'll see how the chisels do. But the planing was a great learning experience and will give me more confidence in the future when working with harder woods like this.