Hollow mortice chisels and auger diameter

[PaulO]

I got a new (to me) hollow chisel morticer last week, a Sedgwick 571. It came with a mixed box of mortice chisels, some Wadkins, Ridgeway, and a bunch of Chinese ones. All of them were pretty abused, with blunt chisels and augers showing signs of blueing.

So I decided to buy a few new Draper Expert ones based on the recommendations here. The problem I am having with them is that the tip of the auger appears to be slightly larger than the chisel. So as I cut the mortice, slight scallops are left in the walls. This would be fine for blind mortices as they would be covered by the shoulders of the tenon. But I am concerned about the finish of through mortices.

So, should I
a) Reduce the diameter of the tip of the auger? I plan on doing this by applying a diamond stone to the outside of the auger while it is running (so not taking any metal of the chisel, but reducing the auger to match the chisel)
b) Cut my mortices undersize and take a cleaning paring cut with a hand chisel?
c) Buy a different brand of mortice chisel?
d) Stop being so fussy?
e) Something else?

Thanks for your help

 

[woodbloke]

I am concerned about the finish of through mortices.

Paul - As you say, for blind mortises the edge of mortise isn't too much of an issue as it's covered by the shoulder of the tenon. Through mortises though are another kettle of worms as in my experience it doesn't matter how careful the set up, the edge of the mortise will always have a degree of a 'zig-zag' edge from the hollow chisel, which will show on the final job. The only way to cut a mortise to ensure a dead smooth side (for show joints) is with a router, after which the corners are cleaned up with a chisel - Rob

 

[wizer]

Couldn't you mortice to a few mm from the bottom, then do the rest with chisels?

 

[woodbloke]

Couldn't you mortice to a few mm from the bottom, then do the rest with chisels?

Tom - it's not the depth of the mortise that's worrying Paul but the top edge on the surface - Rob

 

[wizer]

oh I see, sorry I was thinking about tearout on the bottom edge.

 

[OPJ]

Are you sure the auger is that much larger than the chisel? Sounds to me as though the auger might be slightly bent (or, perhaps not seated correctly in the chuck)?

 

[ProShop]

PaulO,
Is the Sedgwick 571 the version with a chuck or is it the collect version ?.
If it's the collect version it may be due to wear & tear, the collects are not the fit they used to be. When the grub screw pinches the bit against the collet causes a misalignment if the collect is worn, meaning the bit can & does spin slightly of center causing the problem you describe. If it's the chuck type it could be that the motor is slightly of alignment with the cast mounting therefore making the bit again run of center to the chisel causing the same issue.

We use the Draper Pro version as well and some older Ridgeway and also some Clico all did the same thing, so I doubt it's the bit & chisel.

We took ours to a engineering firm and got them to machine some new collects and to check the above alignments. It's been a great machine since.

Hope this helps

 

[PaulO]

It's the collet version. Sounds like I need to machine up some new collets, and see if that helps.

 

[custard]

While searching I came across this old thread. Through mortices can be done neatly and efficiently with a hollow chisel morticer.

1. Japanese style augers probably aren't the best for through mortices, the single cutting edge does a great job in clearing chips quickly, but in my experience they're rarely axially concentric with the chisel and often have a cutting path that lies slightly outside the chisel path, leaving shallow "gutters" down the walls of the mortice which can be visible on the outside face of a through mortice. The "English" style augers (such as Clico) tend to run truer although even here there can still be problems unless the Jacobs chuck or collet are in good condition.

2. For through mortices you need the auger clearance to be as small as possible while still allowing decent chip clearance. The normal clearance advice, around 2-3mm, is too much and 1mm or even a touch less is better and will usually remove any "guttering" problems. I suspect that clearance advice tends to be aimed at softwood joinery rather than hardwood cabinet making.

3. "Through mortises though are another kettle of worms as in my experience it doesn't matter how careful the set up, the edge of the mortise will always have a degree of a 'zig-zag' edge from the hollow chisel, which will show on the final job." This comment just isn't correct, decent tooling on a decent machine should allow the chisel to be set perfectly square with the back fence, which will remove any hint of "zig-zag".

4. It goes without saying that maximum chisel and auger sharpness is needed for successful through mortices.

5. You should aim for an acceptable through mortice straight from the machine, but if all else fails you can cut a through mortice with an auger and chisel that are 1/16" smaller than the final dimension, then replace with the correct size chisel without an auger, and use this to pare the walls precisely and cleanly. Alternatively you can use a smaller chisel throughout, but that will mean resetting the fence. In either event you'll need a bit of dowel to periodically push the chips up the inside of the chisel in order to clear them through the chisel slots.

6. You do have a little bit of "wiggle room" in that very, very small shortcomings in the side walls of a through mortice are often obscured during the glue up and finishing, so aim for perfect at arms length, not perfect under a magnifying glass!