004 – Jesse’s Gravel Frame


To continue from my last blog post I would like to include a music suggestion. This time I have chosen Bookends by Simon and Garfunkel.

This frame is my first build for a customer, Jesse. I have spent a lot of time refining all the finer details of the design that I created for 002 and 003. I hope I can detail and discuss a lot of these in here without getting too carried away!

The Brief

  • Gravel frame for races and touring
  • Specific fit geometry from provided info
  • Many mounts for cargo cages and bags
  • Custom paint job
  • Reduce frame weight from previous builds

The Geometry

004 – Frame Geometry

For the geometry I began with the data that Jesse had provided me from a bike fit he had previously. I started by plotting his handlebar, hoods and saddle position into CAD. Then I started to bring in the handling geometry that I felt would complement his fit and expected riding. 

All of this is a balancing act of a million different criteria and is still something I am working to get a better understanding of. My mind likes to see objective data to support any engineering decisions but handling and comfort can become very subjective. This is very difficult to work with in my head but it is a challenge I am really enjoying and can’t wait to work with more customers and get an understanding of how they like to ride and how I can implement their desires.

For 003 I built around the suspension forks but this time I have built around a set of Columbus Forks. I tried to be fairly conscious of the trail value that would result from the combination of all the front end geometry. I don’t know if this is the best thing to focus on but again the subjectiveness of all of this is fairly challenging. For the rear geometry I made the seattube angle a little smaller to move the rider weight back as I felt on 002 that it was too far forward and this should help to provide a comfortable long distance bike and provide confidence on uneven ground. The chainstays are 10mm shorter than 003 so the intention is for all this to balance out and create a balanced, comfortable ride.

All of this is very subjective and tricky to talk about without riding the frame. So I think I will leave it there before it becomes too speculative. When Jesse has had some time to put the frame through its paces I will get some feedback and see if we can verify some of my geometry.

The Tubes

The tubes need their own section here because I spent a lot of time refining all the processes involved in making them. All of these refinements will lead to higher compaction, strength, accuracy and reduced weight. All of the work paid off in the end so let’s get into the improvements and the challenges required to make these improvements.

46mm Mandrel with freshly made bottom bracket

The first improvements came from a very kind favour from Emily and Jimmi from Attacus. I met them at Backyard Bike Shop when Nic assembled 003. Emily explained that her dad used to run an engineering company and has a lathe if I ever needed it. So I thought it would be rude to refuse the offer! I am still figuring out how to say thanks properly, I have a few ideas. Emily’s dad produced a 46mm mandrel for making PF30 bottom bracket shells and a 3 part headtube mould with 44mm and 56mm ends. To add to the amazing work he even provided the material, so I now have some long term, accurate, reliable stainless steel mandrels for creating the press fit sections of future frames. Thank you Emily and co!

Continuing with the roll wrapped tubes the next improvements came with the front triangle tubes. I refined my compression tape wrapping machine which was an incredible headache but now I can reliably apply even tension to the tape, 003 had some lumps under the paint caused by the tape losing tension. With this settled I produced a toptube and downtube with a tweaked layup on the toptube to try and reduce weight. The final tube for the front triangle was the seattube, this time I created a long slightly tapered mandrel with the intention to bond in an insert of 27.2mm internal diameter for the seatpost. This is a much better process than previously as a straight 27.2mm mandrel at more than 600mm long is a nightmare to demould, on top of this the material can be focussed where it is needed so the lower section has a thinner wall.

Chainstay after trimming the flash

The rear triangle tubes are all produced using clamshell moulds and inflatable bladders. I first made a new mould for the seatstays as the previous one was just 3D printed and was suffering pretty badly. A crack in a mould trying to hold in high pressure is a recipe for disaster. With that I proceeded to improve the bladder production process. This involved a lot of CAD and an enormous amount of research into silicone and various other rubbers. They are a tough beast and creating items from them is a very different ball game to composites. Still much to be learned but I am happy with the knowledge I now possess for the bladders and the full result of the tubes. The reliability of the bladders and the new moulds allowed me to increase the pressure used when curing so that helped to really reduce the weight of the tubes.

Inside the chainstay. Great compaction, no wrinkles, pooling or other defects. The internal layer is a stitched biaxial (or non-crimp) fabric.

All of these weight savings are marginal. But as we all know, marginal gains have won many races. But 5g off a tube here and 10g off a tube there all add up. With that the tubes were done. Months later than I had hoped but I had no intention of providing my first customer with something subpar, so the effort was worth it.

The Ancillaries

New dropout plates with refined design.

The dropout plates are the only extra parts for this frame design. But I still had improvements I wanted to make to them. My main issue with them on previous frames was the heel clearance. This is fairly dictated by the plate style dropouts from Paragon as they do add width to the rear. However I found some ways to gain some room and as an added benefit it looks better.A quick redesign and a different jig set up made all this knit together.

The Full Assembly

With everything complete and a few improvements to my frame jig a started mitering the tubes together. My previous mitre work has been far from perfect but these mitres are a lot better and use less adhesive. With everything tacked together I took the frame out of the jig and test fit tyre clearance with an actual wheel and checked the alignment. 

This is the hardest mitre on the whole frame. The downtube has a funky cross section and the headtube tapers so its a really tricky one. But I am super happy with how it came out.

At this point I had routed sleeves for cables to come from the downtube all the way to the rear for the derailleur and brake. However I realised that providing an option for which way to route the cables would be better. So I removed the front section of the sleeve and created a routing port at the bottom of the downtube. Now the holes at the headtube end can lead to whichever side the builder desires. Whether it be for different brake lever configurations or just for aesthetic concerns of cables crossing the headtube.

I filleted and shaped the joints which used a lot less than 003 as there isn’t a big wart on the headtube for the cable port and I didn’t fill in as much between the chainstays this time as it created too much of  a shelf and reduced tyre clearance.

Excuse the living room paraphernalia. Filleting all complete and ready for layup.

From there I prepped for the final layup. Most of the schedule was the same but I reduced the length of some of the layers to just try and tweak the weight down. The big change to the layup was in the consumables I applied. I cut the peel ply a lot more accurately this time and experimented with using infusion mesh linking into the breather ply to reduce the kind of print through and wrinkling caused by the breather. The usual solution is to use a thinner breather but I can’t find any in small enough quantities for me. The woes of not being able to use a scrap or two from work! This solution worked relatively well apart from one section of infusion mesh that didn’t have enough release film under it and had to be sanded off.

The main downside to this is that the resin didn’t instantly get drawn away from the part and flowed into areas I didn’t want it to go to. Primarily it snuck into the headset and bottom bracket areas, which ruined my nice accurate pressfits dimensions! This was a tough lesson learned and really sucked. I walked away for a few days and came back ready to tackle it properly. With a fresh mind I designed some tooling to ream the pressfits out accurately, I removed the resin that had intruded into the areas and continued with the build. This has reduced the accuracy of them but they do just receive pressed in cups so it’s still within tolerance, the main result is that it has marred the polished surface inherited from my new mandrels. Mistakes suck, but they are wonderful learning experiences.

The Finishing and Paint

Looking back to the previous frames I think that both paintjobs have their individual merits but both have parts that detract from the overall finished look. So I began by spending a few days going back and forth with a guide coat of paint and finding any low spots and getting the lines of the frame just right. This is not a process I have ever had any professional experience with so unlike the composites sections, I lack the confidence to know exactly what result a certain action will produce, but I’m learning the ropes.

Primed frame ready for colour

With the frame primed and ready I moved on to interpreting Jesse’s brief for the paintjob:

“Finish and paint… I’m looking for something playful, just like the bike and what it’ll be used for. Maybe a 2 color soft serve ice cream swirl of mango and boysenberry – with sprinkles. Just an idea.”


I had been mulling this over since our first conversation and discussing it with more artistically in tune friends. But the final decision was mine and after a few sketches and drafts I think I had an idea which I could produce and fulfil the brief, various ideas could have been done by more skilled painters but design for manufacture is a big part of my engineering mantra so I tried to do the same with paint.

If you have figured out why I recommended Bookends at the start of this write up, then well done, it’s quite obscure. The song “Punky’s Dilemma” (Side 2, Track 2) has a line: “I’m a “Citizens for Boysenberry Jam” fan.” Disregard any meaning of the song in this context, it is simply the only time I have heard of a Boysenberry! So it was one of the first things I thought of when designing this paint job. I also happen to really enjoy this album and it has some good memories for me.

So, I decided to produce a design with a deep purple and mango in an explosive and random pattern over the whole frame. I had then thought to do the sprinkles cascading down from the top of the frame as if they were sprinkled on like a topping. But once Jesse and I saw the purple and mango look we feared that the sprinkles could add too much visual confusion to it all. So I had a small rethink and applied them inside the seatstay, chainstays and fork legs. My partner and my friends were initially a little apprehensive about adding the sprinkles but I wanted to stick to the vision and the brief. I think holding my ground was worth it as it adds something fun to build and draws your eyes to the inner corners of the frame. I don’t think I would have ever come up with an idea like this independently so I am really thankful to Jesse for the inspiration and the freedom to create something unique, it’s been a really enjoyable process.

With the paint and the clearcoat on the final frame weight is 1100g. So still a little heavy but I think I will always be limited by the tube to tube construction. A reduction of nearly 200g from the previous frames is fantastic though and the work has paid off. The paint job added nearly 100g but I think it’s more than worth the weight.


As this is my first build for a customer there has been a large amount of paperwork and payments to set up which is something I have neglected until now. I have spent my entire life buried in bike technology, engineering and composites so all the business running stuff has been an uphill battle. This was all exasperated by the fact that Jesse lives in California! It’s made for an interesting time communicating and converting costs to dollars and discussing travel or shipping plans. But as I write this now the frame has all the customs documents ready and is sitting in a box ready to be shipped in two days. Fingers crossed!

With the experience of selling to someone in a different country as my first build I feel that building a frame for someone in the UK will seem like a breeze. Much like a lot of things in my life I have done it the hard way first, but it’s a fantastic way to learn something quickly and have good experiences that can be taken forward into future situations. Jesse should receive his frame soon and with the parts list we collaborated on he should have exactly the bike he wanted. I will wait with baited breath for his Ride Review and try and get a few words to put on here about it. 

Thanks for reading all this. I have tried my best to summarise 3 months of work. The next builds will be a bit shorter as I have really developed a lot during this one. See you round!

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