The use of thumb planes

[xy mosian]

Hello,
I am in the final wood shaping phase of a carved bowl I am making. Like an idiot I did not completely finish the inside before starting the outside. To get a good finish to the inside I am having to resort to holding the bowl with my left arm and using a scraper with my right hand. While I have been doing this I was thinking of alternative ways of achieving a a better surface, from somewhere I came up with Thumb Planes.

I have never handled a thumb plane and would like to ask a question, or two, of anyone who uses them. If I may be terse.

How tricky, or not, are they to use?
Are there any unseen benefits to using them?
What are the downsides or problem areas?
Are there any difficulties in adjust them?
How useful are they on an inside curve that doesn't match, greater radius of course, or even flat?

If you use any of these small planes I would like to hear of your experience please.

Thanks, xy

 

[JohnPW]

I've made a few wooden thumb planes for instrument making. They are small, 40-50mm long, shorter than my thumb.

They're not tricky to use at all. You're only removing narrow shavings and it doesn't take much effort. Obviously the blade has to be sharp and at the right depth.

On my planes and most of the commercial ones I've seen, there's no screw adjustment for blade depth, so you have to use the tap-and-try method which might need a bit of practice if you havn't tried it before.

The commercial ones are quite expensive though.

To get a smooth finish, I would think the curvature of the blade and sole would have to match the curvature of the inside of the bowl quite closely, and even then you'd probably have to finish off with a scraper.

 

[JohnPW]

If you can fix the bowl still (improvise something from scraps and f cramps), that would make it lot easier using the scraper!

 

[xy mosian]

John,
Thank you for your reply. I have, of course, been squizzing around the 'net and have to agree "The commercial ones are quite expensive though.". I am not phased by tap-and-try adjustment, so I guess I'll have to attempt to make one. Your note about the match of the curve is very much what I was expecting so a very useful confirmation of that. I am happy enough to finish with a scraper but at the moment I am taking more off than I would like.
The snag I have, with clamping the bowl, comes from the shape. The top is rectangular, about 8" square, the outsides slope down to a small foot at about 45 degrees. I can clamp a board straggling the bowl but that fouls my working space. I am managing with the scraper but my thumb is beginning to complain. Anyway making a small plane with double convex sole could be fun?

Thanks again, xy

 

[xy mosian]

John,
I have just found your plane making wip. I had looked, but not that far back, How time does fly! Very helpful, I like the drilling through the mouth and the starting of the mouth, on the sole, to prevent breakout.
xy

 

[Shrubby]

Xy - to hold your workpiece try a sandbag with a grippy rubber mat on it. Alternativeley draw round the bowl on to a board and cut out the shape giving you a recess to drop the bowl into, the board can be clamped to your bench
Matt

 

[xy mosian]

Hi Matt,
Thanks for the ideas.
I have actually managed it by resting one side of the, 5" or 6", deep bowl on an elbow height bench, using my left arm to hold the thing in place. Taking excess wood off, with a curved scraper, a little at a time seems to have worked. I am just about at the stage where more work will bring less return, and risk the possibility of duffing it up as well.
I gave up on the thumb plane idea as the curvature of the surface changes too much. the grain is taking some reading too.
xy