Mortising for Monsters

How would you make a 2-foot mortise in a giant stick of Ipe wood? We don't learn that here, but we do learn something about why Ipe is so tough on tools. July 3, 2008

Question
Does anyone have any suggestions for through mortising a 24"x24" ipe squared log? The mortises are 8"x14" by 24" deep. They need to be relatively neat and line up perfectly through and it is very hard wood.

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
Why do you want to do this? It's hard to imagine that a two-foot deep mortise would be any better, structurally, than one half as deep. Timber framers use a chainsaw-based mortising tool, but I don't think they'll do that sort of depth.

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From the original questioner:
A portable chain mortiser did not work, and it has to be a complete through mortise for the application.

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From contributor D:
One of my fantasy pieces is a Tori gate that would require huge mortises and timbers. So, while I sidestep any sort of answer to your question, I will ask where in the world did you get that timber?

I have an electric chain saw mortiser and while it does cedar just fine, I would think it would only smoke on ipe. What research I have done on the big Japanese work suggests large chisels and lots of time. They mostly use softwoods - fir being one of the favorites.

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From contributor Q:
That is some really tuff wood. Maybe hog out the majority of it with forstners bits with bit extensions long enough to get through the piece. Then clean up the corners with the chain mortiser and some big timber framing chisels.

You could clean up the mortise with a power plane that can cut right up to the edge. The power plane I have would fit right in those mortises.

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From contributor J:
Is it critical that the cut surfaces be flat and straight all the way through? You could use a router and template to cut a neat rectangle on each side, a couple of inches deep, and slightly overcut everything in-between.

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From contributor H:
Could you perhaps saw it then re-glue the sections for the mortise with a void?

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From contributor C:
This is an incredibly daunting task. What is the need for the internal perfect surfaces? I finished a large timber gate in front of my house recently 14 x 12 timbers. It was a lot of work in cypress five years air dried. It turned out beautiful. Find a big old fashioned industrial machine shop they will have drill presses big enough to drill through.

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From contributor A:
Ipe is about the hardest of the readily available commercial woods. Its Janka hardness is over 3500 (white oak is about 1600). The wood incorporates silica as it grows, i.e. microscopic particles of sand.

High speed steel can work ipe, but it dulls tools very fast. If you are using a chain saw, you'll need to touch up the teeth every couple of minutes with a file.The same goes with a forstner bit.

When working with ipe, don't let your cutting tool overheat. You'll lose the temper in the steel and goodbye tool. Watch the cutting action carefully. When the going gets rough, stop and sharpen your cutting edge(s).

Contrary to expectations, ipe actually works well with hand tools. It is slow, and, like the edges of power tools, needs frequent sharpening. However, there should be no trouble finishing off the edges of either mortise or tenon with a sharp chisel. Ipe requires patience.

One last word: ipe is toxic. Protect yourself with mask, gloves, and long sleeve shirt. If you doubt this, do a WOODWEB search on ipe.