planing technique advice please!

Afternoon all!
I've just b******ed up the replacement bottom rail of a sash window I was making.
It's 3.5 inches wide and I needed to reduce the thickness of the wood I'd bought by about 5/16 across the whole of that width.
My powerplaner's base is about 2.5 inches wide so I cant do it in one pass across the whole width - I tried working from both sides and then got into a mess - I've ended up with a much thinner piece :-(
I don't know why I didn't stop when I hit the scribed lines! - some sort of "well if I do it gently it'll just take out the high points in the middle" muddled thinking.
I have got a big hand jack plane but the sole plate on that is slightly narrower than the power plane - however - would I be better off using that for final cuts?
So - what's the technique/best tool to do this job? - I haven't got access to a thicknesser...
So annoying - I have to wait until Monday to get more wood ... Oh well - there's plenty of leaves need raking up!
TIA
Barley Twist (Please put out the cats to reply direct)
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If the iron is sharp then yes, more control. If you have scribed lines and check regularly, don't try taking off more than the thinnest shaving each time and don't expect to do it in 2 minutes it will be ok. I have a No7 jointer I use for jobs like this and it works well, just keep moving the plane over the width, if you go hell for leather on one side you will end up with a ramp and a succesively narrower shaving.
Remember, check often.
Peter
--
Peter Ashby
School of Life Sciences, University of Dundee, Scotland
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Why not treat yourself to a belt sander.
You can buy them quite cheap ( Screwfix/ebay etc) and they are brilliant!
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