Pathfinder build (SQD) project week 1.
Making the patterns…..or not.
Blog time : it’s early May 2021 and i’m in the first actual week of the Pathfinder project build , what i’m doing or at least trying to do is make patterns of the frame parts from the drawings so that i can use those to help me see how best to use the plywood. I should explain so….the boat is built around a series of frames set on a base that is flat across it’s width, the outside line of each frame being a series of straight lines that join at the stringers/chine points and on top of some of those is a curved crown which gives the deck (foredeck) and transom their curves. Several of the frames aren’t made out of one piece of plywood but rather are made up from a bottom cross web, 2 sides and then a top/crown piece ; after that there are doublers and so on.
On the bench/blog.
Well, i had a long day in the workshop starting fresh at the point i left it the day before – with the bottom web and sides made for the most complex of the frames (frame no 2) and just the difficult top piece to do ; difficult in that it has a curved top edge and bottom edge and then the inside curve also has to flow into another curve that brings the top piece into the side of the frame. I had to ask the designer’s group page about defining and drawing those curves but in the end that was quite easy because i had an old alloy batten that was perfect for the job. At the point where i had the curves drawn and flowing into each other nicely i thought ‘i’ll just cut the pieces out, marry them all up and then treat myself to a coffee break and a slab of moist cherry cake’ which is when it all seemed to go wrong because my pieces didn’t line up properly and that was dispiriting because i’d done the job as accurately and diligently as possible.
Before i explain what went wrong i thought i would do a quick photo shoot of the job thus far :
The bottom cross piece is quite simple because it’s basically 2 parallel edges and just with a simple chine point but here are the more complex side pieces for frame no 1, one already cut out and the second one all marked out and ready to cut. The material , by the way, is the orange corrugated plastic that my shelter roof came in.
Marking out the top piece of frame no 1 with my alloy batten pinned to the workbench with some flat nails. In this picture the centerline is obvious as is my datum line which is a line i ‘moved’ up the page if you will from the actual measurement datum which for all of the frames is the waterline. Even at this stage of pattern making i’m running out of usable bench space so sometime soon i’m going to have to continue the job outside -certainly with the wider frames and the transom.
Marking out the crown curve, the curve of the underside of the frame and the side curve that brings the underside curve into the side pieces…..my guide for that was the top rim of the yard bucket which seemed ‘about right’. At this stage all seemed well and good as it looked like the actual drawing and so i was feeling pretty confident.
All the pieces cut out , the side pieces nicely matched up with the bottom cross web and the first change of angle at a chine point…..but the tops of the side frames didn’t then match up with the sides of the top piece and by enough margin that i thought i must have made an error somewhere even being very careful about my measurements. It kind-of looks about right in this view but isn’t, so i figured that rather than measuring everything again and trying to find my mistake i would just go and take a break for a while , check admin stuff and in my case go and see if anyone had commented on my question about defining and marking out those shapes.
A few days prior to this i put up a question on the group about how to define and mark out those curves, particularly the top one which defines the curve of the deck. On frame no 1 the curve is defined by a series of measurement points which i just had to mark out and then draw the curve using an old and springy sail batten as my guide. I had it in my mind that i had to calculate something like a section of a cone which is something i think i’d seen on another boatbuilder’s website for the 2 ends of a curved cabin roof ; the answer came back that all i had to do was lay a batten across the 3 points of contact and just draw the line along the curve of the batten. As it happens though i was back on the designer’s (John Welsford) FB page reading through some of the responses when another member alerted me to a potential problem with the measurements on that and another drawing. It turns out that the numbers have come out so fine on the drawings that John’s 5’s 7’s and 9’s all look alike and i’d misread a critical measurement point as 590mm when it should have been 550mm. As soon as i got back to the workshop i marked and cut some new side pieces and the ‘unfit’ was made even worse because then i was compounding the mistake with a mis-measurement (my error) in the top piece.
At the end of the day i had patterns for the pieces of frame no 2 (plus one piece for frame no 3) that didn’t look right at all, in fact even worse than before my coffee break. I could have been pretty dispirited about that because it would then have felt like a whole wasted day but it wasn’t because it’s been another day of learning how to do the measuring and marking out which at least is starting to make sense.
Tools and techniques.
I did say that i would talk about the tools i have been using, especially anything that iv’e bought for the project and then any points about the actual techniques that are new to me and that might be relevant to another beginner so…..
In the complete frame photograph above there is what appears to be a tape measure running down the side of the bench and that’s new – what that is is a sticky backed steel measuring tape that iv’e stuck down to that side of the bench and it runs from (my) right to left. Iv’e got another one (left to right) on order which will go along the front edge of the bench as well. I found that super useful as it doesn’t get in the way….it’s thin enough that that the plastic just slides straight over it and i often pick up a measurement along it with my dividers to transfer onto the pattern piece.
I also bought a new long measuring straight edge that is 1000 mm i think , that’s the one next to my old yellow straight edge which only has marks at 2mm, the new one is in 1mm markings and a lot crisper too. I use the tape measure very little and in fact only to rough out the measurements on a whole sheet of material to work out how much i need to cut and bring inside to work on. The black square is what i use to mark out my centerline at 90 degrees to my datum (waterline) mark. It might seem very ‘minutiae’ to mention my marking out tools but iv’e found that it makes a huge difference which pencils and markers i use on different materials ; for most jobs on the light plywood i now find that a ‘B’ pencil gives me the best combination of a dark line that is still sharp, one the plastic that doesn’t work so a 0.5mm pilot pen does that job and then my cutting lines are marked in using a fine Sharpie marker….although that looks thick it really helps in the photographs to show what is going on.
That’s about it for today, tomorrow, as i write, i’m going to try something different in that i’m less sure now about the value of making frame no 2 out of lots of separate pieces ( 5 to begin with ) and John did mention making some frames all in one piece so what i may do is make a pattern in one piece using some of the covering material that my plywood came with.