Narrowing Chisel to Fit Groove Cut By Plow
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Does anyone have advice on making the blade of chisel narrower, when it is just a bit too wide to fit in the groove cut by a plow? For example, a 10 mm chisel will be too wide for a groove cut by a 3/8 inch cutter, if both the chisel and the plow cutter are right on specification.
Don’t do it, just use a smaller chisel and go in passes.
Chisels can vary ever so slightly between brands in my experience, especially on the cheaper end, and all manufacturers work to a tolerance of some kind.
I would use what I had, rather than start tweaking chisel widths. It’s hard to do that cleanly and accurately without a mill.
Darren.
Hej John,
All my left hand plough plane blades are off; most of them too narrow. My ¼” blade is around 6.25 mm, while my ¼” mortice chisel is the stipulated 6.35 mm.
The discrepancy has had no impact on grooved mortice and tenon frames. First, the shoulders, the hunch and the panel will conceal any deviations, and, second: My mortices tend to end up a tad wider then the nominal ¼”. My sawn tenons will always have to be adjusted to the mortices, which takes care of any potential. Split cut tenons tend to end up towards the loose, but never more than that the joints will be stable, once glued.
In your case the difference on each side of a groove would be 0.01″ – too small to be of any relevance, I think.
From Mr. David Charlesworth I learnt that making a loose tenon can be a good addition to a mortice guide. The attached photo shows a ¼” one that fits quite comfortably in a groove that is 0.1 mm too narrow. In addition too helping me keeping the mortices square and true, I use these loose tenons to find where in the groove to start chopping.
Sven-Olof Jansson
London, UK; Boston, MAI’ve modified a 10mm bevel-edged chisel to get an 8mm blade, and it was pretty simple (though I didn’t try to reinstate the bevel). I used a grinder wheel to remove the bulk of the waste, working from both sides of the blade to keep everything centred and cooling the steel periodically in water, and finished off with a diamond file.
The key to getting accuracy, it seemed to me, is to creep up on your blade width. Don’t charge in and try to take off too much material at once.
If it is really an issue, then another option is to put a small shim around the fence of the plough plane, cut the main groove, remove the shim and then plane again to finish off. If it’s just a small amount, then maybe a sanding block with a shallow slope to center it in the groove, worked in the area where you want to chop the mortise. You can also chisel the mortise with a smaller chisel, and then pare to match the width of the groove. But I also don’t worry about that small difference.
Colin, Czech Rep.
Sven-Olof,
Thanks for your reply.
That loose tenon looks nice. Did you mark your work in ink? That looks good too.
John McDermott
Williamsburg, VirginiaPeter Fitzpatrick,
I tried your approach, only with a rotary motor tool (e.g. a Dremel). Light passes, same number on each side, pausing frequently to check. I cleaned up the swirl marks and adjusted the bevel on my diamond stones. It worked because I only had to take off about 0.5 mm.
@Colin, Sven-Olof,
I went to the trouble to do this because I want to use just one chisel to square the ends of the mortise. I am barely out of beginner status and have a tendency to mess up unless things are simple.Another solution would be to buy a new Vertias plane with metric cutters, but The Management won’t authorize it 🙂
Well John, the truth is that I’ve tried loads of ways to enhance the visibility of my knife lines, and eventually found something that works. Pigma Micron PN pens leave ink lines that are good enough for most work, and where knife/gauge lines are required these pens leave a very narrow enchanement. Blue masking tape is my second aid to improve visibility. Please see attached photos (which also show that some white oak does away with earlywood). Unfortunately I can’t remember the name of the gentlemen advocating this method on YouTube.
A link to a comment on tolerances and precision of plough plane blades.
Sven-Olof Jansson
London, UK; Boston, MA
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