One of the reasons I decided to do this 'doublet Diary" was because when I got started there wasn't much out there geared toward gettign a fellow started. That included some of the basic stuff like pattern drafting and the like. So, I will periodically be posting "Tips O' The Moment" for the newbie garbmongers among us. The rest of you can skip these posts if you like or laugh at the way I do things.
Here's the facts... despite certain key similarities, we all tend to take slightly different paths to arrive at roughly the same destination. That is to say: This is how I do it, I'm not an expert, just experienced. Do it my way, don't do it my way, it's your choice. The success or failure of your sewing project is in your hands. I'll tell you my route to the summit but you have to climb the mountain yourself.
Enough metaphors! Let's sew!
TIP 1: That's not a big roll of toilet paper or a really small kitten. It's my eleven pound 6-month-old kitten Dusty illustrating the rough size of a roll of butcher paper I picked up at my local Costco warehouse store. If you don't have a Costco, go to Sam's Club or Pace or whatever. Odds are they sell this stuff by the roll. I think it cost me ten bucks two years ago. My wife & I both use it and we still have this much left. If you don't use it to light the woodstove or as a cat toy, it'll last you awhile.
Even if you are using a commercial pattern (and there are several good ones out there) don't cut out the flimsy tissue paper pattern that comes with it. Trace your pattern pieces on heavier paper (like butcher paper) and cut those out, saving your tissue pattern for the next time you want to make a garment and this time want an extra two inches on the left front piece or whatever. Everytime you alter your pattern from what it was, trace out a new one or you'll be sorry. Each minor alteration requires minute changes at other points that you may not be aware of until its too late to go back (ie after you've cut the expensive fabric.)
TIP 2: Which brings me to another point: "Do as I say, not as I do..."
I mentioned earlier being reckless and not doing a muslin for this project. I can get away with this because this will be the umpteenth doublet I've made. Even that's not really a good enough excuse, though, because even the most experienced tailor makes mistakes once in awhile. Even the pros rarely just sit down at the machine and wing it. I'm doing it anyway because the entire outfit is really a prototype for another outfit. I am confident enough in my abilities to anticipate problems and know that I have the MacGuyvering skill to roll with it and still turn out a suitably wearable garment. It's a gamble, but I feel pretty comfortable making it. Also, the mistakes are learning experiences and I have plenty to make before I put shears to velvet.
Don't do this until you're experienced enough to make the gamble with your eyes open. Fabric dollars add up fast and mistakes can be costly if you don't know how or can't correct them after the fact.
All that said, I advise making a complete mockup of your garment in muslin and trying it on before you cut even so much as the lining fabric. Better yet, make it out of scrap canvas in a weight and give similar to the final fabric you're going to be using.
If it's a doublet or slops, put it on, walk around in it. Do the things you think you're likely to need to do when you're wearing the final product. Can you reach? Stretch? Bend? Squat? Climb Stairs? Do jumpingjacks? Run a marathon? Fence? Swing from a chandelier? Quaff and ale? Fit your cuirass over the doublet? Fit your billowy shirtsleeve through the armhole?
Think of everthing this garment has to put up with and design and alter your design accordingly. You'll feel where it's tightening across the shoulders as you make a few parries and thrusts with your rapier. You'll notice the tightness and lack of give in the crotch as you try to bend down and pick up the cloak you threw across the puddle for your lady. If it's tight, loosen it and try again. Keep making alterations and new mockups until it feels wearable and you're sure the butt isn't going to tear out when you bend over. Then pull the seams and use that one as your final pattern.
HERE is a link to the Sempstress' website. She's great! This is where she explains in great detail how to make your pattern from scratch. I recommend this for your second doublet. Make the first one with a commercial pattern and wear it for awhile. Figure out what you want from it. Then go back and make it up from scratch.
Let me know how it turns out!