I recollect seeing that Record, at least, provided plough irons especially sized
for plywood.  That beloved article, the Record 42 drawer bottom groovong plane,
certainly had an alternate set of irons available for just this purpose.  How
much better to have an iron perfectly sized for 6mm ply than having to grind
your own or fiddling with the wrong size groove.

As for accuracy, we all know that in an era of stamped or sheared blades, they
were never accurate to the degree we take for granted in our CNC made world.


Richard
who is currently discovering that a 43 works well when applied to vertical
timber.





> On 29 Aug 2021, at 14:21, Christian Gagneraud  wrote:
> 
> Hi Galoots,
> 
> I recently bought a set of Mathieson plough irons.
> They are all in very good condition, marked from 1 to 8, all with the
> same stamp at the same location "ALEX. MATHIESON GLASGOW".
> This looks like an original set to me and by the look of it, they have
> been barely used.
> I'm thinking of making a nice box for them, to go with a Mathieson No
> 4 plough plane I'm restorating right now.
> 
> The sizes puzzle me, it looks almost like a metric set, as I can't
> make any sense of the imperial sizes.
> 
> Here are the figures:
> Number    mm    inch    mm    Error (%)
> 8    15.44    0.607    15    +6.6
> 7    13.05    0.509    13    +0.7
> 6    11.83    0.465    12    -2.0
> 5    9.78    0.385    10    -2.2
> 4    8.21    0.33    8    +1.7
> 3    7.04    0.277    7    +0.3
> 2    4.97    0.198    5    -0.2
> 1    4.00    0.158    4    +0.0
> 
> I can't make any sense of the imperial sizes (eg, numbers are not in
> 8th or a 16th of an inch), but the metric sizes almost match, except
> for #8 maybe.
> However this doesn't sound like a convenient set, the size progression
> is really odd: 4, 5, 7, 8, 10, 12, 13, 15+? The #8 is off by 3/16th of
> an inch
> And then if it's metric, why some random numbers instead of the size in mm.
> 
> Hum... Anyone seen something like that?
> 
> Will post photos soon.
> 
> Chris.
> 1 AM, Monday here in locked down NZ.
> 
> PS: I tried to measure the imperial sizes with a wood/brass stanley
> caliper (thank you galootaclaus), but had to resort to my digital
> caliper.
> 
> 
> 
> 
> 



-- 
Yorkshireman Galoot
in the most northerly county, farther north even than Yorkshire
IT #300