My ugly mortises

[Brad Simmons]

So I'm hand chopping some of my first mortises into a pine 2x4 I'm using to build a bench for my lathe. I designed the bench (which could be my first problem) to have stretchers going from the front of the bench to the back of the bench mortise and tenoned into the 2x4's that run from end to end on the front and back...

When chop the mortises the pictures below show what I get. The sides of the mortise split as soon as any pressure comes up to clear out what has been chopped. Obviously the grain isn't being cut, because my mortise chisel is situated vertically.. not horizontally.

So two questions...

1. Is this just a bad design? Are mortises not meant to be chopped with the grain oriented this way?

2. If this is an okay design, how do I avoid the blow out? Just chop down the horizontal sides of the mortise with another chisel?

Thanks!

[george wilson]

Is that pressure treated wood? If so,it is the most terrible stuff to work neatly.

Secondly,mortising across the grain is not the best idea.

Third,that looks like HORRIBLY soft wood,which has no strength about holding itself together. Not the easiest thing to mortise,either. #1 problem is mortising across the grain. Pressure treated wood is also a #1 bad wood to work. I have done it,but your chisel needs to be very sharp,and your technique good for that particular wood.

[Brad Simmons]

It's not pressure treated, but it is a soft wood.

My chisel is sharp... but i doubt my technique is that good... :(

[James Owen]

Some ideas to help clean-up your mortises:

(1) Score the grain horizontally -- fairly deeply (1/16" to 1/8"+) (several lighter passes generally work better than one heavy pass) -- with a marking knife or similar tool. That should reduce/eliminate the blow-out and chip-out going across the grain (in your photos, the "upper" and "lower" parts of the mortises).

(2) Leave about 3/16" to 1/4" un-excavated at each end of your mortises until you get them to depth. Once to depth, then you can cut the remainder at the ends straight down, giving the ends of your mortises clean edges.

(3) Try chopping your mortises in an inverted "V" shape, with the "bottom" of the V in the middle. Then chop out the waste that forms the inverted V and scrape the bottom of the mortise more or less flat. That, combined with the "cushioning" wood (the 3/16" to 1/4") on either end of the mortise will give you nice clean edges, even in splintery, very soft woods.

(4) Make sure that you are using VERY sharp chisels. By its nature, pine/Douglas Fir is a real challenge to cut cleanly, but it can be done, as long as your chisel is sharp. (Sharp = able to peel intact shavings from end grain pine)

[Joe Hillmann]

Go to about 19 minutes in the video http://www.pbs.org/woodwrightsshop/video/3100/3104.html

He shows how to cut a mortise but replaces one side of the wood with a piece of glass so you can see what is happening inside the mortise as he is cutting. It really helps to understand exactly what is happening in there.

[Terry Beadle]

+1 on James's recommendations. Cutting mortises across the grain needs chisel strokes along the mortise line across the grain as James says 'lite cuts' not heavy cuts. That means more of a tap to the butt end of the chisel and not a hit. Test the chisel you are using for the cross grain cuts on a piece of pine mounted in your vice. The chisel should be so sharpe that you make cross grain shavings and not dust. It should easily cut cross grain and not require lots of pressure and certainly not any strokes with a hammer. As James says, pine/fir are one of the toughest woods to cut cross grain. That's why you test your sharpened chisel edges on them. If the chisel won't give you a good controlled cross grain shaving curley, then you need more sharpening effort and maybe some additional 50 to 100 honing strokes on the cutting edge until it does give you good results.

[Prashun Patel]

Try drilling out the waste with a forstner bit first.

Also, I'm unclear on yr design; most of my mortises run perpendicular to the way this one appears to be cut; there doesn't appear to be much meat on the sides...?

[Brad Simmons]

Sounds like I need to do some more sharpening and cut down the sides of the mortises more.

[Brad Simmons]

The design has 2x4's "standing" on edge that "butt" against each other...so that the end of one 2x4 meets the face of another one to form a stretcher from the front of the bench top to the back. I'd take a picture, but I'm not home anymore. Here it is in ASCII looking down from above with each line being a 2x4 and the horizontal lines being the boards being mortised.

__________
| | | |
__________


Maybe this isn't the best way to design the top.. I'm open to suggestions.

[Joe Fabbri]

Are you using a marking gauge to mark the mortises? I assume you aren't judging by the fact that you're going perpendicular to the grain (though I can't tell how long that board is you're using), but it also seems you're just using pencil lines.

Try scoring the lines with a razor blade knife. I'm doing some 1/2" mortises on some sawhorese right now. I'm trying to use up some pressure treated 2x4's I have. Like George says, pressure treated wood, which looks to be Southern Yellow Pine, is difficult to keep from splintering on the edges. The first set I did came out okay, but I think my junky marking gauge with it's finish nail pin was getting dull and not scoring deeply, so I got a few spots of blow out (I'll hide them with the tenon shoulder's though).

Anyway, I made sure on the next set to got back over the marking gauge scoring with a razor blade to cut more deeply, and the mortises are looking pretty nice, considering the wood I'm using.

Also, I'm chopping these mortises with a regular bench chisel. I put a small secondary bevel to strengthen the edge, but I made sure not to try to pry out huge chunks at a time so I don't break my chisel. So, try to go more slowly and take out less at a time. That might help also.

But I suspect, like others have said, going against the grain like that might be hard to do neatly. Also, by chopping that by hand, with the chisel inline with the grain, its seems like you could potentially split or crack the board. Maybe in this case drilling out the mortise would be a good idea.

Joe

[Larry Browning]

You chisel must be sharp enough to easily shave the hair on your arm. At least that what I do. There will be others that will tell you not to do that, but I don't listen! I have bare spots on both arms most of the time!

[Gary Newland]

You may want to use two or three tenons on each cross piece running across the 1 1/2" width of the 2 x 4. Then put horizontal mortices in the main front piece. This will allow the mortices to be with the grain.

____________________
- - -
- - -
- - -
____________________

If this makes sense.

Gary

[Chris Vandiver]

You may want to use two or three tenons on each cross piece running across the 1 1/2" width of the 2 x 4. Then put horizontal mortices in the main front piece. This will allow the mortices to be with the grain.

____________________
- - -
- - -
- - -
____________________

If this makes sense.

Gary

This is the correct way to do it and will solve some of the problems with the tear out seen in the photos. Plus, this method(mortise orientation) provides some actual strength.

[Brad Simmons]

You may want to use two or three tenons on each cross piece running across the 1 1/2" width of the 2 x 4. Then put horizontal mortices in the main front piece. This will allow the mortices to be with the grain.

____________________
- - -
- - -
- - -
____________________

If this makes sense.

Gary

I think I understand you... So on the end of each 2x4 I would have three 1/2" x 1 1/2" tenons with 1/2" from the top and bottom and between each tenon? Again.. in ASCII with a "|" representing half an inch...

|
|t
|
|t
|
|t
|

That's a lot more mortises and tenons!! Maybe I'll just do two instead of three...But this whole exercise was to give me practice while building something that didn't have to be pretty so I guess this works.

[george wilson]

That wood looks like a REAL,REAL,soft cedar which I have some of. It is very light weight,and doesn't hold together very well in the grain for much any type of cutting. It is good for making out of doors things.

[Gary Newland]

226331
Brad,

Here is a quick sketch of the idea. Hope this helps.

Gary

[Brad Simmons]

Awesome! That's what I was picturing. Thank you!

[Tom Millington]

As luck would have it I chopped a large mortise tonight in Doug Fir. It's 3 3/8" tall x 1.5" wide x 3" deep. Using an appropriately sized tool that is very sharp makes all the difference in the world. I've tried the drill and pare routine before but always had trouble getting a square, snug fit. This took 40 minutes to do. I expect the other seven will go faster.

226333226334

[Larry Browning]

I'm actually having a problem with the idea of a double mortise and the orientation of the wood. Isn't this creating a cross grain joint that will fail due to expansion? Seems to me that the first time that 2x4 starts expanding there will be enough stress to break one of those tenons. Plus, getting 2 tenons to line up properly to the 2 mortises is not going to be fun at all, especially for someone who is new to cutting mortises. This just seems like it is going to be an exercise in frustration for Brad.
So what's wrong with a pocket screw? Oh, wait this is the neanderthal forum isn't it? Never mind!

[James Taglienti]

Those double or triple tenons you guys are talking about will be just about worthless in such a soft wood, i would advise against dividing your tenons if you must use that particular wood

[Brad Simmons]

Hmmmm..... This doesn't really have to be pretty so strength is more important than looks. The main stress on this joint is down so I guess a single tenon would be stronger. I'm gonna sharpen my chisel more, knife those cross grain lines more thoroughly and go for it.

Also, I think I should research my design plans more next time.

[Karl Andersson]

Not to beat a dead horse (or thread), but to maintain the most strength in both the striger and the facing board, you should use multiple tenons and mortices - you're basically making a finger joint at each joint. A single large mortice across the grain reduces the continuous long grain to just a small thickness at the top and bottom of the facing board. To save strength and frustration chopping so many mortices, I'd recommend cutting the stringers to finish length, clamping them in place, and drilling holes through the facing board into the ends of the stringers. Make the diameter of the holes over half the thickness of the stringers (3/4 to 1 inch), place 2 or 3 per joint, and glue hardwood dowels in them, then plane flush for a neat appearance. Call them treenails if you're trying to appease the gods of traditional woodworking (but this is for a lathe bench, after all):)

[Floyd Mah]

I have an opinion. As if who doesn't. Having read this thread, I would cut the mortice first, a single one, and maybe only 1.5" width. Having done that, I would then cut the tenon to fit the mortice, since the mortice is in soft and difficult-to-work wood. This would ensure a tighter match than if I cut the tenon and then tried to shape the mortice. I would make the face of the tenon fit more tightly against the end grain side of the mortice, since you might crack or blow out the long grain if the other face were tight. Finally, I would drill a hole on the tenon/mortice joint and draw bore the joint to tighten it, using a harder wood for the pin. The pin would come in from the top and extend through the bottom of the long 2x4. Thus the larger shoulders on the tenon would stabilize the joint and the draw bore pin would tighten it. One problem I see with this design is that the ladder design doesn't have a good provision to prevent racking, so there should be additional pieces added for that.

[george wilson]

Double tenons aren't that hard to fit.You have to do accurate work,of course. I have used them on 2 of my benches. One down in my wood/machine shop,the other upstairs in the jewelry shop. Of course,these benches are both beech wood.

[Chris Vandiver]

Single tenon or multiple tenons or a super sharp chisel aside, your mortise is still oriented in the incorrect direction. for maximum strength(for the type of wood you're using)you would be better served to have a full size pocket to house the 2x4(pocket size would be the width and thickness of your 2x4 and say a 1/4" deep)and have a correctly oriented mortise or two within the pocket(to help hold the frame together). Of course, with this type of wood(new growth hem fir)you are better served doing simple joinery combined with some sort of mechanical fastener.

[Brad Simmons]

I have an opinion. As if who doesn't. Having read this thread, I would cut the mortice first, a single one, and maybe only 1.5" width. Having done that, I would then cut the tenon to fit the mortice, since the mortice is in soft and difficult-to-work wood. This would ensure a tighter match than if I cut the tenon and then tried to shape the mortice. I would make the face of the tenon fit more tightly against the end grain side of the mortice, since you might crack or blow out the long grain if the other face were tight. Finally, I would drill a hole on the tenon/mortice joint and draw bore the joint to tighten it, using a harder wood for the pin. The pin would come in from the top and extend through the bottom of the long 2x4. Thus the larger shoulders on the tenon would stabilize the joint and the draw bore pin would tighten it. One problem I see with this design is that the ladder design doesn't have a good provision to prevent racking, so there should be additional pieces added for that.

What should be added to prevent racking?

[Brad Simmons]

Single tenon or multiple tenons or a super sharp chisel aside, your mortise is still oriented in the incorrect direction. for maximum strength(for the type of wood you're using)you would be better served to have a full size pocket to house the 2x4(pocket size would be the width and thickness of your 2x4 and say a 1/4" deep)and have a correctly oriented mortise or two within the pocket(to help hold the frame together). Of course, with this type of wood(new growth hem fir)you are better served doing simple joinery combined with some sort of mechanical fastener.

By simple joinery and mechanical fastener you mean a butt joint screwed together?

[Brad Simmons]

Not to beat a dead horse (or thread), but to maintain the most strength in both the striger and the facing board, you should use multiple tenons and mortices - you're basically making a finger joint at each joint. A single large mortice across the grain reduces the continuous long grain to just a small thickness at the top and bottom of the facing board. To save strength and frustration chopping so many mortices, I'd recommend cutting the stringers to finish length, clamping them in place, and drilling holes through the facing board into the ends of the stringers. Make the diameter of the holes over half the thickness of the stringers (3/4 to 1 inch), place 2 or 3 per joint, and glue hardwood dowels in them, then plane flush for a neat appearance. Call them treenails if you're trying to appease the gods of traditional woodworking (but this is for a lathe bench, after all):)
I appreciate the suggestion. Aside from trying to go the traditional route, do the hardwood pegs provide greater strength than screws would?

[Chris Vandiver]

By simple joinery and mechanical fastener you mean a butt joint screwed together?

That would be the easiest and would certainly be strong enough. Or you could take it a step further and provide a pocket at each of the 2x4 locations(around 1/4" deep)for added strength. The tight fitting sides of the pocket help to keep the 2x4s from twisting and the bottom of the pocket gives added strength when weight is put on top of the 2x4s. Of course you would then screw the 2x4s into the frame, as well.

[Karl Andersson]

Screws through the facing board into the end grain of the stringers would not be a strong joint - expansion of the face board would eventually pull the screw heads and wallow out the screw hole in the stringer, loosening the screws. If there is a thick deck that provides weight-bearing strength, you could make pocket holes diagonally through the ends of the stringers and screw into the facing board from the "inside" of the joint and you'd probably be OK as long as the deck is glued to the support structure. You don't want the screws to be the only shear strength in the joint (the force downward from the weight and torque of the lathe) - their small diameter would compress the wood fibers around them and the joint would fail - or the screws would snap.

Pegs or multiple tenons (pegs ARE multiple round tenons) give more gluing surface, and their wider diameter/ bearing surface provides better resistance overall to both lateral and shear forces. These two methods also distribute the long wood fibers that make up the strength of the joint more evenly, so they are less prone to failure if there is a "bad patch" of wood, like grain run-out or knots; a single tenon puts a lot more importance on the qualities of the two pieces of through-grain (top and bottom). In this joint where the end grain of the holes or mortices through the facing board meet the side grain of the pegs or tenons, the more gluing surface, the better.

[Floyd Mah]

This thread reminds me of the time that my wife and I took a short cut off the road between Albuquerque and Santa Fe. Just as we got off the main highway and discovered that the new road consisted of gravel, the engine oil light came on. To make a long story short, the oil pump had failed due to plastic pieces of the timing chain breaking and falling into the oil pan (Ford, 1970's, in case you were wondering). We turned quickly, made it back to the main highway and got help. I think your basic design is suited for a temporary resting place for the lathe, but it won't hold up over time if you continue to build it with this plan. Luckily for you, you've discovered early that what you were planning to may not work out or require too much effort to fix.

I would scrap the basic plan to make it with stretchers and a ladder-type construction. Even gluing up 2x4's into a flat slab, maybe with cross pieces screwed on underneath to help maintain flatness would be preferable. It might weigh just a bit more, but you would avoid the racking problem and the problem with the mortice and tenon joints. A surrounding apron of 2x4's or larger wouldn't hurt and would help with attaching the legs.

[Jim Matthews]

The advantage of pegs is if you offset the bores; the hole through the mortised side will be a little further away from the shoulder of the tenon.
When the peg is driven through it "draws" the bores together. It's a strong mechanical joint.

Will a standard peg be stronger than a basic screw, without this offset? I don't think it's significant, particularly if the joint is glued.
Pegs and screws used this way just hold the joint together while the glue dries.

I echo the prior sentiment - your mortising chisel isn't sharp enough to shear the sides, and the frayed end grain is caught when the chisel is retracted.
I do this with a forstner bit and sharp chisel to follow. Remember one thing out of all this - it's MUCH easier to adjust the size of a tenon.

To test the fit of your tenon, apply chalk or soft pencil - the transferred marks will show you where things are too tight.

jim
wpt, ma

[Larry Browning]

How about a half lap type joint? (not sure that is the right name). Cut a notch out of the end of 2x4 half the width of the 2x4 and the same depth as the face frame, then cut a notch out of the face to accept the 2x4. Then simply screw the bottom of the face frame to the 2x4. Easy to do, no racking and plenty of weight support. the only down side is that half the end of the 2x4 is exposed, but I didn't think it had to be pretty. Does that make sense? I do not think I did a very good job of describing what I have envisioned.

[Jim Koepke]

I have not looked at this thread before today.

Just my 226435, a design change may be in order.

Your support may be better if lap joints were used.

The stringers could be mortised into the legs if you want to build a cabinet under the lathe bed.

jtk

[Brad Simmons]

Argh.... I think I'll just run to Habitat for Humanity Restore, buy a solid wood door, screw a couple of 2x4's on their edge to the bottom and put them in the bridle joints I have cut in some 4x4's to use as legs and call it a day.

I really appreciate all the help and input y'all have given here. Hopefully someday I'll be able to return the favor.

[Jim Matthews]

Argh.... I think I'll just run to Habitat for Humanity Restore, buy a solid wood door, screw a couple of 2x4's on their edge to the bottom and put them in the bridle joints I have cut in some 4x4's to use as legs and call it a day.

Now you're talking. Furniture grade is for furniture. Git R-Done for tools...