Ouch. I broke my mortiser!

[Nathan Conner]

So, maybe someone with some experience with this mortiser can tell me what I was doing wrong? This is a Delta 14-650 I picked up from a guy on Craigslist. It was a few years old, but looked lightly used.

I was cutting 1/2" x 3" or so mortises in some 2 1/4" thick Alder. Brand new chisel (still had the wax/rubber coating on it) and the first time I've used a mortiser at all.

I found that it was tougher to cut them than I thought, and I was having to put a bunch of downward pressure on the handle to get the chisel/bit through the wood. No problem, just more work than I expected. It seemed to be cutting fine - no tearout with a backer board.

The issue was in getting the chisel back OUT of the newly cut hole. I had to clamp the mortiser to the work table, and REALLY put my back into getting the bit back out of the wood. My shoulders and triceps are killing me after cutting 30+ of these guys. When I cut the initial hole, it was a real bear to get the bit back out, but if I took nibbles after that, it was a breeze, so I cut both ends, and then nibbled down the workpiece towards the other end. That seemed to fix the majority of the problem.

But about 1/2 way through my cunning plan, I was pushing up on the handle and the fence (the 3/4 post that goes through the column, actually) snapped in half right at the column! I wasn't hurt, and the piece was fine, but...what was I doing wrong? I'd tried waxing the chisel, tried some SlipIt on the chisel, made sure it was cool between cuts, made sure everything was square and plumb as I was working.

I was able to get the fence clamped to the table and get it working again without too much issue, but it looks like Delta doesn't sell that part any longer (the fence/post is a 1-piece casting), calling it "Unavailable - obsolete", whatever that means. And the 651 seems to have a square post instead of the round one.

Is the issue just a bad casting? Was there a magic trick to getting it back out of the wood after the cut? Anyone know if the Jet fence (they seem to have a round post, too) would fit this guy? Maybe someone sells a nice sliding cross-vice I can use to replace the fence? It was really handy to have the fence, and I don't mind extra setup now, but it'd be nice to know I was doing something dumb. I've only got about $50 into the mortiser, including 7 bits, but...well....yeah. I'm sure there's something someone knows about it.

[Mike Goetzke]

I only had a mortiser for a short time, but, from your description it sounds like at least two possible problems:

1) even though it was new the bit might be dull, mine were on my 651 and I had to sharpen them (Rockler/others have sharpeners).

2) it was never hard for me to pull the bit from the work piece - sounds like your bit wasn't square to the wood.

Just my opinion, but, I believe the fence/rod are made to keep the wood steady for cutting. Probably not designed to hold excessive force of pulling the bit from the wood. Saying that though, hard to believe with the x-section of that rod it would have failed.

Mike

[Michael McCoy]

I have the 651 also and agree that bits do not come out of the box ready to use. I do a lot of mortices and don't bother clamping the stock. I just hold it firmly by hand and that lets me do a slight up/down motion after the first cut and the chisel will let loose.

[Charles Lent]

First you need to know that "out of the box" mortise bits aren't really sharp. Just like chisels and other cutting tools you will need to sharpen them before you use them. Woodcraft, Rockler, and many other woodworking outlets sell a special cone shaped diamond cutter for sharpening them. Don't attempt to sharpen them by removing metal from the four outside surfaces of the chisel. The most that you should do to these is to polish them to a near mirror finish to make them slide through the wood easier, but do this with a very minimum of metal removal. Sharpening the end of the chisel mostly helps you plunge the bit into the wood and polishing the outside of it helps you get it back out. The drill bit will also need to be sharpened, but only the bottom cutting edge. When you install the bit be sure to set it to be about 1/16 lower than the bottom of the square chisel part. I frequently lock the drill bit in place using a nickel as a spacer between the chisel shoulder and the chisel's chuck. When the drill bit has been secured, I then remove the nickel, raise the chisel the remaining distance, and lock it in place. This provides the needed gap between the drill bit and the chisel. The drill chuck will need to be "very tight" or it will slip.

The larger the mortise bit is, the more force that will be required to plunge and remove it, but it shouldn't be as difficult as you have been experiencing. I frequently rub paraffin wax on the outside of my bits in between strokes if the effort to plunge and remove seems to be increasing.

Charley

[Jeff Duncan]

Just a couple thoughts in general....first when using the mortiser once you cut the first hole, your next cut should be right next to it. In your pic it looks like you cut your holes with spaces between them? This just makes for more work than needed. Cut the first hole and then work your way across.
Second.... the opening in the chisel should face towards the first hole. Or put another way when your cutting the second hole the chips should be directed toward the first hole.
Third....as already alluded to you should make sure your chisels/bits are sharp. But at least as important is that they are set correctly. The Bit has to engage the wood first then the chisel cleans up. If your chisel/bit aren't set correctly you'll have problems.
Lastly concerning the excessive upward force needed to remove the chisel....well I have to admit I don't have an answer for that. Mortising with a small machine does require a good amount of bicept use. Especially 1/2" mortises in hardwoods, your pushing the limits of these little guys with that kind of work, but it should handle it. I'm just surprised it required enough force to break that part. Could have been a weak spot on the machine or????
JeffD

[Kirk Poore]

A couple of comments:

First, the only time I've had a chisel stick in the wood is when the wood was not held down firmly, allowing one end or the other to tilt so that the hole was now not parallel to the head travel. Since you were clamping the work down firmly, and were having consistent problems, I think Mike Goetzke is on the right track that the chisel may not be straight when compared not to the work but to the travel of the head. I'm not familiar with that mortiser, but assuming it has a chisel collet, I'd take that out and make sure there wasn't something in the collet or between the collet and the head that was putting the chisel at an angle. If you can't see anything, put the chisel back in and measure the chisel angle vs the travel direction and see if there is a difference. Do it with both the left/right and front/back chisel surfaces.

Has this happened with other chisel sets? Maybe your chisel is bent slightly, though this is hard to believe.

I don't think you should have been able to snap a 3/4" cast iron rod unless something was really wrong.

Second. I disagree with Jeff about making holes right along side each other. Since there is no wood one side of the chisel, the pressure on the other side might make the chisel deflect, leading to a hole that isn't quite straight. Making spaced holes, then coming back and cleaning up the remains in between would avoid this deflection.

Good luck...

Kirk

[Warren Clemans]

You probably already dealt with this, but the only time I have issues in removing the bit from the work is when there's a bit of space between the top of the workpiece and the hold-down. That allows the workpiece to rack slightly when the chisel rises, causing it to jam. I can't see how the sharpness of the bit could affect your ability to get it out...you're not cutting anything on the upstroke. I'm reluctant to put any lubricant on the chisel for fear of interfering with the glue that I'll ultimately use to create the joint. I have no idea what could cause your fence post to break...sorry.

[Frank Drew]

Nathan,

I have to think that the casting had a pre-existing weakness to break the way it did.

But one of the main reasons I prefer horizontal slot mortisers to hollow-chisel mortisers is because the former present fewer of the issues you've detailed.

[Dale Lesak]

I polish the sides of my chisels and it seems to help a lot. I also use slip-it . It seems like the softer woods grip the chisel more then the hard woods. also check that your chisel is square and the sides parallel. I had one that had a slight taper to one side and was a bugger to get back out. Dale

[Bruce Gray]

From the photo, it looks to me like your workpiece is not clamped down adequately. ...it's only clampled at one end. That would mean that, when you try to raise the mortise bit, it will lift the work slightly ( to contact the "fingers" on the mortiser. This racking will jamb the bit. I would assume that the reason that the casting broke is because of the huge upward force that you applied to get the bit out.

I have the same mortiser, and always clamp the workpiece on both sides of the bit for the first hole.

[John Lucas]

Add one more thing to all the good advice above. When you make the mortise, make it in a series of plunges so that the waste can be totally removed as you go. If you do it this way, you will feel when the moritse work is getting too tough to work. I dont think you should have to work hard at getting the handle back up.

[Bob Vallaster]

Quoting: "I had to clamp the mortiser to the work table, and REALLY put my back into getting the bit back out of the wood. My shoulders and triceps are killing me after cutting 30+ of these guys."

You broke it the old fashioned way: overload. If such force were required, Delta would have shipped it with a longer lever (and beefed up the parts, and charged more...).

Cast iron doesn't like to bend, so it broke.

Charles provides a good checklist.

No one has remarked this so I will. I gather these were through mortices. That's ambitious, especially so if the sides of the chisel are not polished and haven't been confirmed to be at/under the width of the front(lower) cutting edge. An alternative is to cut 55-60% depth from either side---no blowout and far less drag on retracting the chisel.

Two have speculated the rod must have been inherently weak or flawed. Perhaps, but your narrative reads like it gave up only after abuse.
Within the last week I made adjustments to the home-brewed counterweight (cast iron sash weight) which helps me lift my drill press table. By 'adjustment' I mean I removed excess weight by hanging it over a hard edge and struck the overhang with a small hammer. The cross section was in excess of 1", fractured straight across, and looks like your broken rod. You said it broke "right at the column"---that's predictable. The edge of the hole in the column served as the hard edge (maximum point load) and your grunting on the lever provided the force. Same same.

If that were my -650 (I have one and like it), I'd look for a machinist to cut off the 3/4"dia stem, then put a 1/2-5/8" recess where the stem used to be. Make provision for a set screw to trap a new rod. Take a 3/4" rod of appropriate length and flat the length as on the broken stem. Then reduce one end to match the recess mentioned above.
Or search eBay for bits of someone's dead -650.

Good luck.

BobV

[Greg Hines, MD]

Kind of off topic, but I have read that you should cut mortises with a hollow chisel mortiser as the OP describes, cutting a series of individual holes with some meat between them, and then going back to clean them out. The rationale, as I understand it, is to prevent the tendency of the bit to follow the path of least resistance, if you have nothing to support it on one side.

Just another reason I use a router and mortising jig to cut mortises.

Doc

[Bart Leetch]

This is a good example of when you think it isn't working right STOP DO NOT CONTINUE WORKING. Ask the questions that you need answered then don't just continue on risking breaking the tool & possible injury.

If you even begin to think your forcing the issue you probably are.

[jerry nazard]

Good thread - I'll add another 2 cents. I have a PVC nozzle attached to my machine that runs to my central shop vac. This keeps the chisel and workpiece chip free as I am mortising. No clogs, no mess, and I can see what I am doing.

-Jerry

[Simon Dupay]

in high school we had the same machine and i did the same thing you did and broke the same part.

[Nathan Conner]

Hey, guys, what a great bunch of advice! Let me clarify a few points.

I tried, at first, to bore through a chunk of Oak. It worked like a champ. It was only when I went to the softer Alder that I had issues getting the bit back out. The softness may have been the issue. Also, the bit was not polished on the outside - that may or may not have made a difference? I was always using a backer piece of ply to make sure I didn't blow out the back, but 2 1/4" deep may have been a bit of a stretch.

When I started, I was chopping out the starting hole, then leaving about 1/4" of material between each hole as I moved down the mortise - this helped the tendency for the bit to bend towards the empty side. But this proved to be too much work. After the piece broke, I completed by chopping the first, then the last, then taking small (1/4") nibbles along the length. Like that, it was a breeze on the down- and up-stroke. And I didn't care if the bit wandered to the side a bit.

I kept compressed air handy as I was working and blew the chips out each cut. I like the idea of some PVC hoooked up to the cyclone or the FesVac, though. That may help out.

I don't think the piece was ever racking. I have a cute pair of bruises on my left hand from keeping the workpiece lined up and tight to the fence. But it may have been slightly. Even when I let the piece pull up against the hold-down after cutting and used both hands to pull the bit out, it was a bear.

So, in general, I'm taking some good advice away from this, as I knew I would.

1) Sharpen the chisel, polish the outside
2) Use a light amount of a lubricant
3) Quick-clamp the piece to the work table for safety and ease.
4) Verify all the set up steps on the machine - square, plumb in all directions - before starting. (I just did "chisel square to the workpiece" and "chisel square to the fence")
5) If it feels like something's wrong, it probably is. I tell my wife I can bench-press 8,500 lbs :), so if I have to break a sweat and swear under my breath to get a piece of metal out of a piece of wood, I'm probably working too hard.
6) Use pocket screws instead of M&T.

Ok, so that last one just slipped in there. I'm sure with more practice, I'll have this working smoothly. Luckily, I was able to get everything finished, even after it had broken. I may have it repaired by a machine shop, or I may try to repair it myself with a different fence, but a pair of clamps and some hastily-machined spacers seemed to get me functioning again.

Thanks again for all the advice, guys. I'm surprised again at how much there was and how quickly it arrived. Well worth the $8,500 a year I spend on membership. (Again...ask my wife!)