What to use for template?

[sabinoerc]

I agreed to make my daughter some floating shelfs which look like pic. She has a similar alcove next to her fireplace.
I'm not a great woodworker but good enough to make these. I fab'd some custom support hardware to mount them and happy with that.

The problem I have is getting the shelf trimmed to the wall and fireplace.
The walls aren't square - which I was expecting and made the shelfs long with expectation I'd need to trim them to minimize gaps against the wall.
The right side is a bit greater than 90 to the back wall and the fireplace side is a bit less than 90 - so may be lucky enough the shelfs can be trimmed to have a small gap and still get them on supports (as opposed to both sides being less than 90 to the back wall). - But it's hard to measure exactly with just a square.
So I'm thinking I need to get some material for templates that I can place where the shelfs will go and scribe the wall profile - and cut as a template to use for trimming the shelfs.
I was thinking of thinnest plywood I could find but just curious what more experienced wood workers would use.
I'd appreciate any thoughts or advice in general.
Thanks

 

[mike93lx]

Narrow strips of material (think yard stick width) and a hot glue gun can make some really good perimeter templates. I've also used cardboard strips and a stapler

 

[jar944]

Some flavor of a stair tread jig would also work

 

[niget2002]

Cardboard or posterboard

 

[SaintPanzer]

I would use a joggle stick.

A Quick Tick Stick - Small Boats Magazine

I quickly traded my joggle sticks in for tick sticks. I preferred having some irregularity on the edge to register the stick without having to eyeball markings along a stick with a straight edge; a few swipes with a rattail file made shallow grooves that would be traced along with the edge...

smallboatsmonthly.com

 

[drmarkr]

https://a.co/d/6xpjTvK

Use this is an excuse for a new tool!

 

[Damon L.]

I have a set of stair tread jigs that use a 1x2 for the center "stretcher". Easily adaptable to any length by swapping the wooden center piece.

 

[rkevins]

the plastic cardboard like material like yard signs work

 

[The Cobbler]

Narrow strips of material (think yard stick width) and a hot glue gun can make some really good perimeter templates. I've also used cardboard strips and a stapler

this

 

[rust in the eye]

Wouldn't it be easier to simply transfer the angles (like tile setters do) then measure and cut?
Looks like you are seeking a tight fit, I hope the walls are flat, if not you'll be coping too.

 

[BlindViper]

If the rear wall is fairly straight you can put a framing square in the corner. Then say your shelf is 14" deep, measure at 14" on the square how out of square it is. Then transfer this to the workpiece.

 

[sabinoerc]

Wouldn't it be easier to simply transfer the angles (like tile setters do) then measure and cut?
Looks like you are seeking a tight fit, I hope the walls are flat, if not you'll be coping too.

I started off by attempting to hold square in corner and measure but the corners are ~rounded and couldn't get the square into corner. I couldn't get the measurements this way repeatable.
The back walls are pretty flat but the side walls aren't great.
I made a "angle measure" by screwing together two straight 36" steel rules with a thumbscrew and rounding off the edges. This worked better but showed the side walls have a bit of a contour + still wasn't great repeatability on the measurement.

I'm about 2hr away from my daughter's house so had hoped to get something good enough I could cut with confidence and bring the finished shelfs to her house. I didn't feel good about the measurements,

So decided to finish them at the house and trace the contour of the side wall onto something so I can figure out what cut to make.
The shelfs have to slide in from the front - so I can't have anything "concave" out.

I bought some 1/4" plywood and cut to same width as shelfs. As I have to hold the template in place with one hand and scribe with the other (at heights from 1' from the floor to 7') - I wanted to be conservative and get something with some rigidity for the templates.
I also made an adjustable rigid "length" tool (shelfs are ~5' long) to get a good width measurement so to set where to make the cuts on both ends.

I appreciate all the thoughts and suggestions. Thanks!

 

[nadogail]

The contractor who replaced our Master Bath tub with a large shower brought a bundle of battens, Snips and a glue gun. He assembled templates from the battens, stuck them together with the Hot Melt Glue and took the templates to the shop where the slabs were cast from acrylic, trimmed to fit and then assembled into the finished shower on site.

 

[no704]