Mortises cut with a hollow-chisel mortiser?

[Mark Berenbrok]

I've previously cut my mortises with a plunge router. The sides of the mortise have always been smooth and clean.

To get some additional depth and get away from the screaming router, I bought a Powermatic 701 bench-top mortiser. It got good reviews when introduced a few years ago. I have not used a hollow-chisel mortiser previously.

I've sharpened the chisels and bits and adjusted the mortiser according to Roland Johnson's article in FWW #185 and made some 5/16" test cuts in yellow pine (1" deep). The results have been consistent, there's no smoke or excessive noise, and the chisel advances and retracts smoothly. However, the sides look kind of rough.

How smooth are the sides supposed to be?

[Roger Newby]

Yellow pine is one step above bubble gum for milling. Try some poplar for openers and the move on to some of the better hard woods such as walnut or maple. I'm sure you'll get a smoother cut from the harder woods

[Paul Ryan]

The sides are going to be kind of rough. A router will give you much cleaner mortises. I usually clean up the sides of mine with a chisel it only takes a second or two. No need for a mallet with the chisel just use your hand strength. But as long as the tendon fits snug it doesn't matter how clean it is

[Frank Drew]

Mark

If the hollow chisel is even ever so slightly out of parallel with the table's fence (thus, the work piece), you'll get some scoring in the sides of your mortise. It's difficult to eliminate entirely all the irregularity, especially when compared to a router or slot mortiser's slick cut.

[John Thompson]

As stated... you are going to get some roughness as in a slight ridge from one plunge to another. Clean it with a chisel which only takes a few moments. I have an Industrial floor mortiser (any floor model with XY table works here) that I reverse the direction when I get to the end to straddle the ridge with the middle of the hollow chisel. With and XY this onlt takes a few seconds as the main mortise is already cut and all you are doing is the same thing you do with a chisel by hand.. paring the ridge off by simply turning your right-left wheel and making a quick plunge as depth stop stays set to original plunge.

Good luck with your machine and BTW... the mortises will work fine even though not baby butt smooth.

[Peter Quinn]

We have a floor model chisel mortiser at work and it leaves a bit of roughness, but it doesn't affect fit or joint strength. My boss would probably kick my butt if he caught me cleaning the mortise walls with a chisel. Can't see it, doesn't affect anything, why bother. So I don't let him catch me. Not sure it really matters but it feels good.

We use a Bridgeport with end mills for most big mortises, and it makes the chisel mortiser seem crude in pretty much every way including smoothness of mortise walls, but it does the same job.

[Cody Colston]

My boss would probably kick my butt if he caught me cleaning the mortise walls with a chisel.

LOL, it's amazing how unimportant some things become when there is time and money involved.

I have a friend who works for a furniture maker. When he was going through his apprenticeship, his boss jumped him out for using a brush to spread glue for an edge glue-up. The boss said a thin line of glue was sufficient and that the clamp pressure would spread it without taking time to do it with a brush. To this day my friend doesn't spread glue with a brush and they make high-end furniture.

Hobbiest woodworkers (like me) have the luxury of time that professionals don't.

[Tom Hintz]

As mentioned, getting clean cuts in pine with a mortiser is a VERY tough job.
Second, I would rather have some "texture" to a mortise (roughness to some) as it just gives the glue a little more tooth to bite into. If anything, that slightly irregular surface adds strength to the joint. If the tenon fits the mortise with a slight press fit, nobody will ever see the inside unless they blow it up anyway.

[Chris Friesen]

Second, I would rather have some "texture" to a mortise (roughness to some) as it just gives the glue a little more tooth to bite into.

For pva and poly glues the bond is chemical so you generally want the thinnest glueline possible. The ideal glue joint is a perfectly flat planed surface glued to another perfectly flat planed surface. Extra "texture" will only weaken the joint because you're adhering disturbed fibers.

For an epoxy joint the rules are different...there you want the glue line thickness to be a few thou.

[Mark Berenbrok]

Thanks for your responses. I made some additional cuts in mahogany and the sides were a little cleaner. I cut open a mortise and everything was straight and true. Since I wasn't having any performance issues like chattering, binding, or smoking, and the inserting and retracting were smooth, the rougher sides must be the nature of the beast.

[Howard Acheson]

The smoothness is somewhat dependent on how sharp your chisels are. I have seen most professional shops hone the four sides of the chisel using their waterstones. Hone them to the same degree of shine as you would your hand chisels and plane irons. Honing the outsides of your chisels is probably more important than sharpening the insides.