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Prototyping. How To Avoid Huge Mistakes With 1 'Dead' Technique!

Ever heard of a 'pre-mortem'?

Chances are, you probably haven't. Post-mortem, sure, the process of dissecting exactly what went wrong after someone's ultimate demise.

But a pre-mortem on the other hand, is simply a shift in perspective, or a change in the order of things that can make a huge difference to your bag making and general leathercrafting success.

''It's not like having a time machine to prevent future problems, but it's the closest thing to it..''

In simplified terms, pre-mortem is business jargon for imagining that a project has failed in a number of different ways, so that creative minds can come together and figure out solutions to these hypothetical failures before they arise.

So how would you use this on a leather bag, a leather wallet or even a leather watch strap?

My version of this is called 'pre-mortem prototyping' and it's simply a process of picking the trickiest parts of your project, or the parts you are unsure about, then creating them with the leather, reinforcements, and even the hardware you will be using in the finished piece.

This allows you to see and prepare for mistakes ahead of time before you actually make them. It's not like having a time machine to prevent future problems, but it's the closest thing to it.

Sure, it's great to create your design from Salpa (cheap bonded leatherboard), card, craft foam or other materials that mimic reinforced leather, but this only gives you a very rough overall feel for the look of the completed design.

So, for the latest video course I'll be teaching 'The Cutler Briefcase', I have used pre-mortem prototyping to test out a short section of an inner bag seam with piping and edge binding.

Now had I gone ahead with this combination on the real bag in real life, what would have gone wrong? Take a second to study the above images closely to see if any problems stand out to you.

Ok students, gather round the table, put your aprons and masks on with a fresh scalpel in hand please, let's dissect the design death of this particular part.

Problems noted:

  • Distance of edge from stitches is too great which could lead to issues flipping the bag or create excess wrinkling in the corners.

  • Skive width on the 'panels' either side of the piping is too short causing the leather to resist bending correctly. This prevents the piping from being level with the external panels (looks sunken in).

  • Light brown thread on tan leather doesn't provide a particularly interesting look and isn't in keeping with the contrasting theme of the bag.

Ok, so wider skive needed with shorter height from the seam and a thread colour matching the canvas lining we're using. Got it.

leather bag piping edge binding
A close up macro shot of the updated design. Better

However, we really should see how the theoretical updated design works when we add in another variable: a naughty corner!

Oh dear.

So the front 'pre-mortem prototype' of a case corner shows a glaring issue. A fold in the canvas lining at the apex of the bend.

Take a second to think how would you would remedy this issue and why corner attempt #2 doesn't have this issue anymore.

If you guessed 'use a larger corner radius' or similar, well done. The pattern was altered to employ a more gradual curve in the corners so that the canvas has more room to make a turn without creasing and bulging.

This may have been fine with a soft suede lining, or any other material for that matter, so this is why it's important to prototype with the final material selection. So test what you'll finally use.

leather bag piping edge binding

Next we will focus on the handles and their overall design.

These handles are my version of a simplified rolled handle. No round leather cord, rope or rubber cable here.

The design takes inspiration from a particular tool in my workshop that has a similar curve to the end.

This needed to be prototyped to provide practicality, strength and aesthetic appeal. But handles can take quite a while to create when made in their entirety. So I have chosen to test out the end of the handle on the left hand side:

leather bag handle saddlestitch prototyping
Rolled strip handle test followed by various design tweaks before settling on the completed shape

Once the handle design and shape has been selected, I can then get an overall feel by recreating it with craft foam and card. A visual check-up if you will:

bag pattern making prototyping

Lastly, this particular bag has an internal divider that partitions off a laptop compartment. This will be made of canvas on both sides, however canvas lacks the structure to do this, even when two layers are laminated together.

leather bag canvas saddlestitch prototyping

The final combination of materials utilises a layer of stabiliser sandwiched in between layers of canvas.

Finishing off is a top leather binding to tie in the design with the rest of the bag whilst adding extra stiffness and protecting the raw canvas edge.

This was a rare one-and-done test where I was pleased with the outcome and no changes were necessary. This is unusual however.

So in conclusion, making a leather project from scratch straight from your patterns without prototyping parts can be a time consuming and costly way of finding all your mistakes after hours of work.

It is much better in my opinion to test complex parts that you are unsure about with the materials you intend to use.

Do you have any prototyping tips or tricks you would like to add? Comment below!

Thank you for reading,


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11 comentários

Shayne B.
Shayne B.
27 de fev.

Beautiful work, Philip. Would you mind sharing the size of the stiching iron and thread you used for this project? And perhaps the weight of the leather? I'm still trying to figure out what I like, in terms balancing these three factors. Thank you!

Respondendo a

Hello Shayne, thank you. Difficult to answer (in part due to memory!). There is more than one stitch spacing used in the project and multiple leather thickness too. You will see this quite often with advanced projects, including multiple glues, edge finishes, reinforcements, even threads. All the info is in the course and will explain this further. Cheers.


I love this website

Leathercraft Masterclass
Leathercraft Masterclass
03 de jan. de 2023
Respondendo a

You're very welcome! Glad it was helpful for you 👍


In software development we use something similar to this approach to predict bugs. This test design technique is called “error guessing“

Leathercraft Masterclass
Leathercraft Masterclass
20 de jun. de 2022
Respondendo a

That's very interesting! Thanks for sharing 👍


18 de jun. de 2022

Thank you Philip for sharing your creation and prototyping processes. I have been stuck many times on unthought issues that left me with sleepless nights. After reading your article, I just decided to act as a grown up and follow your advice instead of plunging head first in my coming projects. Than you for all this! 😉

Leathercraft Masterclass
Leathercraft Masterclass
20 de jun. de 2022
Respondendo a

Wonderful to hear! Let me know how you get on 👍

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