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15 April 2016

Ask Mitch - Gap between Frog and Iron

Good afternoon. I really enjoied your videos about No.4 and no.5 planes restoring and fettling. It helpred me a lot on working with a new No.5 Anant AA plane i acquired a month ago. Now i have the best  jack plane for a fraction of the cost of a premium plane, assuming i have to use a new iron and iron fact i installed a new quangsheng blade thast is made of good steel, and retains a good edge.  Followed your instructions, i obtrained a good work horse ( sole was almost flat, needed only ten minutes of lapping).
Only doubt still remained concerns blade bearing on the frog: if i look at my plane against a good light source, i can see a tiny gap between the blade and frog surface.  I know blade is flat  because i checked it on my diabase master plate, and have worked also flat my frog surface, as you tought us on videos. Does this gap affect performance ? Now i’m planning to buy  a No.4 wich is a finer plane..what i have to do if i discover this small gap again?
Many thanks, Carlo

This is no problem, and simply caused because you are clamping the flat iron against a concave chip breaker. Both pieces flex a bit, each one according to it's physical properties. The chip breaker is made concave (mostly flat, but with a deviation of some sort at the working end) in order to enable a tight fit against the back of the blade at it's extreme tip.
It might seem unimportant to flatten the blade with this in mind, but, doing so will ensure two, full width, contact points against a flat frog (that doesn't quite work out at the top of the frog, because of it's shape, but it does maximise contact).
The flex in some thicker irons will be so small as to not allow light through, but it will be there all the same.

Cheers, Mitch

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