Barto Cycles | Making my first ever full suspension mtb frame

[AleixBartoCycles]

Hello guys!

My name is Aleix and i am from Barcelona. I’ve been riding bmx and mtb all my life, digging trails (worked at La Poma Bikepark) and after studying mechanical engineering i have decided to gather all my effort and make my own frames in my free time.

I’ve worked at a Bamboo Bicycle manufacturer for a couple of years and i am now starting a new career at a composite manufacturing team that makes cool racing stuff so that’s my professional background. I studied machining for 4 years and manufacturing in general so touched a bit here and there on all possible ways of making stuff.

Being new here, i thought it would be great to document my first build struggles as i develop the skills, design and make the tooling, the frame and anything related with the process.

So here’s the frame!

I’ve named it “The Hammer” since it just sounds metal and it is a tool that works great for everything plus it always comes handy when things go south. I live in Barcelona so the mountains around here are Mediterranean, which implies dry conditions, very rocky (sharp knives) and heights of up about 500 meters~. I would consider myself a pretty gravity focused rider, so the bike is designed around the use of double crown forks, and giving it a try at the more recent geometries proposed for people the likes of Aston Mtb and Cahal = Long Boy. My bmx background is whispering behing my ear to not do it but i am not listening and going full for it.

The frame is made to run 27,5” front and rear. With 160mm vertical at the back, plus a 180mm front forks at 63º Head Tube angle which equals to 160mm of vertical travel aswell. Chain stays are 480mm and Reach 490mm. I used linkage X3 for the kinematics plus Fusion 360 for the 3D modelling. The Bottom Bracket Height sits at 310mm at 30% SAG which might prove a bit too low for the frame since it is basically a Balfa BB7 / Appalache Real affair result…

I have found a European supplier for the Tubing, which is 25CrMo4 and i am using:

• TT = OD 40mm wt = 1.5mm
• DT = OD 35mm wt = 1.5mm
• ST = OD 35mm wt = 2mm which will be reamed to 31.7mm post welding
• Head Tube and Main Pivot housing = OD 48mm wt= 2.5mm. Both will be reamed to ZS44 to run regular ZS44 1 1/8” headset angular contact bearings. The idea is to get two Headsets and have all the bearings done.
• The gusset tube i am still leaving room for improvisation, might do some curved cool stuff, don’t know atm.

Ah yes… The Swingarm

I was reading “The Racing Motorcycle Volume 2” by John Bradley, trully worth reading! and came around the 5xxx series aluminium. Doesn’t need Heat Treatment (my wallet loves that), only thing is you must be creative with it since it only comes in sheet, plate or round stock. I checked with my local laser cut supplier with whom i’ve been working for a couple of years and they have tons of this stuff for the Ship Building Industry. Got to work with the sheet metal design in Fusion and come to something which i like! it is also a little shoutout to my first dh bike, a Chumba Racing F5.

I am currently designing a One off adjustable Jig for future projects. Thought of doing a fixed coordenates one welding some tubes together but i prefer spending the extra time and design something that i will only make once and then insert add ons as i go.

Stay Tuned!

Kind regards,

Aleix Bartomeus

[AleixBartoCycles]

Update!

After doing some research for linear rails and welding tables, following inspiration on Peter Verdone’s Samantha Frame Fixture system i came to the conclusion that for now that level of equipment is out of my economical reach.

Went back to the drawing board and applied all i’ve learned from the Main Fixture i’ve already built and improve upon that system, using the 45 x 45 mm square tubing and the bolt on adjust-ability. This time i have improved upon the concentric relationships where the important coordinates like pivot point etc are to be hold.

Apart from the laser cut pieces, there’s only lathe work which is what i have in the garage and have capabilities for.

We keep going

[AleixBartoCycles]

UPDATE DAY!

All the aluminium bits for the swing-arm arrived and i immediately realized i made a costly mistake. I designed all the interfaces with a system of teeth that engaged in a self-jigging way (or that was what i told myself). Low and behold It doesn’t work since the teeth are way too small for any meaningful holding force when tacking. Also by cutting the thick 10mm plates with the laser, the plates distorted really bad that i render them useless and i destine them to the coupon God.

The obvious course of action was to redesign the sheet metal parts to lower the amount of welding needed and i eliminated the idea of the teeth profiles. As a bonus i specified a water jet cut for the thick 10mm plates so heat distortion is out of the question.

At least i have a nice mountain of coupons for setting up the machine before welding the final part so they will amount to something in the end. You live and you learn!

Here are the new layouts for the V2 Swingarm with hand bending in Mind:

All is in 2mm wall thickness.

Kind regards,

Aleix Bartomeus

[earle.b]

Looks great.

[AleixBartoCycles]

Update!

After double checking the jig i had made a mistake. I realized that i had machined all the adapters and support turrets for the frame parts (Head Tube, BB, etc) to final size without taking into account the post weld reaming. So i went to the lathe with my dad and reworked a couple of things like the Head tube Tower and BB92 adapters to 43,5 mm and 40,5 mm respectively.

I also made the new Support tower for the Main Pivot Housing!

Also got the new Main Plate for the Bottom Bracket, Main Pivot Bearing and lower Shock Support which so all coordinates are perfectly related to each other.

Next thing is the to finish the Swingarm Fixture and get the new aluminium which is being quoted as of now!

[AleixBartoCycles]

Merry Christmas to everybody!

Well, i’ve got the laser and water jet parts cut 5 minutes before my supplier closed for the holidays. What seemed like mission impossible finally is done. After overthinking about the project, i decided to make my life easier and cut the jig for the front triangle out of 12 mm thick 5083 aluminium plate. By doing it like this the table style jig is actually pretty simple to work with and the space i save in the new workshop is really worth it. The ability to take measurements from a flat table is also a great solution, checked everything 3 times in order to confirm that my frame center line was perfect and all came out within 0.02mm which is good enough!

With the frame jig table, the new v2 swingarm also came out perfect! the tabs i design for hand bending worked better than expected, even though i first bent it the wrong direction, i was able to bend it back the opposite direction without cracking the piece! The shock and rear axle plates fit perfectly that i barely have to touch it with a file for the welding set up in the jig.

Next week i’ll machine the missing parts for the swingarm jig plus the table jig which we have laying around somewhere. The idea is to weld both the front triangle and the Swingarm before the end of the holidays, little by little!

Have a nice day

[crowe-molybdenum]

this is super sick; Im really into the design and would be keen to hear about a couple of things, as I’m hatching a similar design of my own, which ill pop a thread up for when I start making some parts.

• how are you planning on managing chain length, growth, retention etc, and clearance against the swingarm? it looks like maybe a pivot-centric idler and the chain stays above the stay the entire time?

• which specific 5XXX alloy (s?) are you using, im guessing maybe 5083? (which i have access to here in nz) and have you done some comparative engineering vs 6061 or 7075 or something known to make a plan for strength, fatigue life, etc?

cool build, love the name, and pivot location especially. im a bit nervous about that butt join in the DT, but im a nervous guy..

[AleixBartoCycles]

Hey man! Appreciate the interest!

As you suspected, the Idler sits concentric to the main axle to make my life easier. I made a 15mm 6082 solid axle and the pulley out of a bmx racing hub driver so i can either change the teeth and/or replace when worn! Making an interchangeable idler pulley with the Shimano HG splines would’ve been too costly.

The Main axle has a collar with which i can preload the headset angular contact bearings and then the collar is tight via a m6 bolt in order to prevent it from loosening once set up. The Idler is held by a 8mm bolt so whenever i need to replace it i don’t need to get the axle out of it’s housing.

In response to your question about the aluminium swingarm, 7005 would be the way to go in the future but it’s not easy to come by (or i haven’t searched deep enough yet) but after some research, i found out that the 5xxx series alloys have a pretty decent strength and more importantly, they don’t loose it when welded. That meant that for example, if i welded some 6xxx series alloy (which ends up at 60% of it’s original strength post welded) i would need to add more material in order to account for the lack of heat treatment. The 5xxx ended up stronger than 6xxx post weld and even then i went overbuild.

The main plates (10mm thick) are 5083 and all the other sheets are 2mm thick 5754. I’ll be welding with 5356 rods.

Hope i clarified most of your doubts, happy end and start of the year!

[AleixBartoCycles]

Down tube!

Top tube gusset

Down tube - Head Tube gusset

Frame almost ready for welding. Just missing now the shock mounts and the seat tube gusset. All to the mitering done with a grinder for the heavy cuts and hand files for the fine final dimensioning!

Wish you all happy end and start of the year!

[AleixBartoCycles]

Front Triangle not my best welding but it came out straight

[AleixBartoCycles]

Update day!

How are you guys doing? After overthinking the Swingarm Fixture and loosing sleep i finally decided to just go for it and build it AS SIMPLE AS POSSIBLE.

So this is what i came with:

Thanks to my buddy’s machined table i could align everything and it came out spot on! Checked the alignement et every step of the process and it delivered.

The machined barrels i made for both the swingarm main pivot axle and the shock eye, self align when pressing them to the 45x45mm square tubing. Since this fixture is half way between a one off and an adjustable one, i have hopes for it in the future if designs have to be changed and adressed. I am happy since it has room for add ons and it is a solid accurate foundation for the rear axle.

I have started to document all the process on youtube:

Aleix Bartomeus | Barto Cycles

So feel free to go check it out! There i’m going to cover everything in more detail.

Kind regards!

[AleixBartoCycles]

We made it!

Swingarm is welded, only missing the cable holders for the brake and rear derailleur lines. Which i plan making out of U bent 2mm thick aluminium sheet strips i have spares.

This was my first time Tig welding aluminium, so it’s definetly ugly AF, but it sure is strong. Has at least double the thickness at the corners since my filler game was not there. After running at least 100 kilometers of beads, to my absolute surprise it came out straight, so the fixture did a great job keeping things from distorting to much. I double and triple checked everything along the way and i sequenced the welds to account for even distribuition of heat.

Did numerous stops to let the heat dissipate and when welding the 10mm plates to the 2mm thin sheet i preheat the thicker material with a blowtorch. No cracking anywhere to be seen 1 day after.

I have ordered all the remaining parts to complete the build, so soon i will be able to show a finished piece! Now i am contemplating all the little details, like cable guides, water bottle cage placement, etc.

Units are grams

The super scientific double arm bend test to see lateral stiffness came out to a satisfactory “PDSIS” Pretty Damn Stiff I’d Say, can barely make it move, probably i need to go more to the gym but i am happy!

Now i just need to machine a couple of adapters for the main pivot axle on the lathe later next week, finish some details, and most important ream everything to nominal size for the Head tube, Main Pivot Housing, Press fit Bottom Bracket and make a bb custom chain guide to get the chain to wrap around the front sprocket a little more.

Cheers!

[Luniz82]

Hi Aleix,

finally I get to typing an answer in your thread, been silently following your progress for a while now

I really like the fact that you referenced the BB7earlier, having ridden two BB7’s yself in the past! Yours is maybe a reverse BB7, or a 7BB then with the alu swingarm and the steel front triangle

I’m excited to hear how it rides, and how the swingarm holds up to fatigue! The Aluminium plates in the multi part swingarm of teh BB7 were famous for cracking around the cuntersunk bolt holes…

Anyway, keep us updated, I really enjoy reading about that “martell” you’re building!

[AleixBartoCycles]

Hey man,

Appreciate the interest! And really cool that you know the catalan word for the name of the bike!

I had the idea of doing something similar to the original Balfa’s but proper alignment with different plates and standard bolts could’ve been difficult to achieve (even if i used centering pins), and it would have added complexity. I prefered to go for the one piece design instead. After all the welding i had to do, i took many notes to redesign it completly.

I am working to make V2 with separate welding sub-assemblies, something like the 2 arms first, the dropouts and main plates, and the bridge/ center box, resulting in as much weld bead reduction as possible to lessen the overall heat input. I prefer to fight less distortion next time and have a more agile welding session haha.

I am having trouble finding any supplier that can sell me small quantities of 5083 rectangular tubing in H14 condition, which it exists but in asia they demand minimums of half a tonne which i am not going to order obviously. But now it is a good time to really up my game with industrial origami style construction and design something with more bends instead of welds. Have any of you experience working with Xometry? my supplier near Barcelona outsources the sheet metal bending and i am finding very attractive that Xometry has all the services in one click.

Cheers!

[AleixBartoCycles]

Update!

Just finished the Front Triangle this afternoon .

Reaming by hand took most of the day since i’ve used adjustable reamers. Got the PF92 to 40.98 mm, Both the Head Tube and the Main Pivot Housing to 43.99 so pretty stocked! Also i bought a cheap seat post that i was missing in order to have it as a go-no-go tool. I know, my welds are awful, i’ll be getting more practice for V2 i promise .

Nice

I am pretty happy also with drilling two holes on the top tube for riveted nuts that hold the cable guides (from an 2011 Demo 8 nontheless).

The reaming of the seat tube also went perfectly and the seat post goes all the way.

Before finishing with some wd40 and some scotchbrite i got the frame back to the jig to check for alignment and everything came out straight! I only had to slightly adjust the shock mounts with a hammer and some love, how fitting…

Soon i’ll be also finish the last touches on the Swingarm to make it a bit more appealing. And i just need to machine the two cone adapters for the main pivot axle, the lower chain guide, and a swingarm plate to hold a chain guide to avoid unwanted movement at the idler.

Almost there guys!!

[AleixBartoCycles]

We have a finish bike! went for a quick test ride before the rains and nothing out of the ordinary!

Pretty Stoked! This has been a childhood dream accomplished for me. I love it! Cannot wait to get more practice with welding and strive for better quality but overall she’s strong. Pedals amazingly which i was surprised given it’s antisquat predictions in the pc. The rear axle path truly is a super power, haven’t ever ridden a high pivot before, but i get it now. Shock activation is with light finger pressure. I am surprised on how stiff the bike is, not in a bad way, but really spot on. The aluminium swingarm has hold up amazingly!

Stoked!!

[TDB]

What an incredible thing! Congrats, enjoy!

[Luniz82]

@AleixBartoCycles

IMG_29431920×1280 518 KB

What a machine! It looks like a freight train But somehow it looks a lot longer tnan your numbers suggest it is. Maybe because the complete frame profile is quite low… But I like ist, it definitely looks fast!

[AleixBartoCycles]

Honestly, it rides so much more agile than i anticipated, doesn’t feel as long as it is! Steering is really responsive and it is true that you lean more than steer. She absolutely rips! Will be updating soon!