Thursday, April 3, 2014

Paragon Ti tricks

I've pushed through a few of Mark's two piece yokes recently, in Ti and Steel, so I thought I would share my thoughts on the fabrication process with these.

The Paragon Yoke is a two piece design, with a nicely profiled exterior shape and a relieved interior for lighter weight.  It forms a male plug end for the chain stays to fit a .875" x .035" tube and has enough forward material to adjust the overall length of the finished chain stay for a variety of wheel sizes.  Originally designed as an elegant and stiff piece to allow 29+ 3.00" wide tires plenty of room without crowding  the chain rings, I've also found that it is well suited on smaller width tires when mated with a belt drive chain wheel, which typically takes a bit more real estate.

I've had numerous folks already ask if it is possible to braze the two halves together.  The pieces form a meticulous fit with zero gap or room for a brazing material to flow, so I do not feel that brazing is a suitable option to join the two halves reliably.  Here is the process I used for tig welding the pieces.

I approached the steel and the Ti using the same process, just to insure uniformity in results.  That being said, the first thing I did was fixture the individual pieces to the mill table to be able to create channels for gas flow throughout the yoke.  Once clamped securely in place, I ran a .125" ball end mill through the three square/tapped junctions that are found on the inside of the pieces, leaving the solid end sections intact.  With the inside now channeled for purging, I mated the two individual sections in the vice, and using a small bit, drilled a single hole in each of the bottom bracket and chain stay ends.  The yoke was taken out of the vice, blown out with filtered air, and then surface sanded with 120 grit shop roll.  I then hit all the weld areas with a fine stainless wire wheel, a grey Scotchbrite wheel, then scrubbed with soap, water, and a rinse.

Once rinsed, the pieces went into the ultrasonic for 20 minutes at 120 degrees, along with a couple pieces of filler rod.  The items come out of the ultrasonic, are rinsed in hot distilled water, then dried in the bake box at 250 degrees.

While drying, I took two simple air needles (like the kind you use for filling up balls) and created a Y shaped purge hose that is attached to a Parker micro valve, for precise control.

With the pieces totally dry, they get a quick wipe with Acetone and then are clamped together for tacking.

I made a quick sketch with dimensions showing the location of the thicker sections of the yoke, and used those reference points for the first tacks, to insure that I could put enough heat into them to hold alignment once the welding really got going, reducing the probability of blowing a hole in the thinner wall of a high dollar piece.  I ended up with fourteen tacks in all, working alternately back and forth around the piece to keep it all aligned.

To weld the yoke, there are two primary concerns; seeing the mating line, as the machined surface camouflages it well, and insuring that you can create good gas coverage for the longer beads.  I accomplished this by taking two parallels wrapped in foil to protect their surface, clamping them to the yoke, and then placing everything in a vice at a slight upward angle.  Fortunately for me, the thickness of the yoke matches the diameter of a #12 cup and lens perfectly, so that you simply have to keep the torch at a right angle in the channel and your electrode will be spot on center to the seam.  A little foil at the end of the parallels creates a nice dam.  As it is positioned in the vice slightly uphill, as you weld up the channel, the gas will cover your active puddle and slowly dam up and keep a pool of argon present to continue to shield the bead as it cools, allowing for long runs.  You can see the basic set up below...the bead is pure silver, though it is reflecting a rare bit of Ohio sunshine from the adjacent window :)

The process is repeated for the interior sections, using the parallels as we go.

Filler rod is added to all the externally mated surfaces.  The actual male plug sections that fit into the chain stays were fusion welded to the shoulder, to prevent interference with the tube id.

Of note is the inside profile of the bottom bracket end, it's a bugger to get your torch, filler rod, and still create sufficient shielding at a good torch angle.  One of the few drawbacks to the design in Ti.

 The most difficult aspect of working with this product is fixturing it so that the mating chain stay tubing can be fabricated for both bend angle and length to the dropout accurately, keeping the yoke square and aligned to the bottom bracket.  I machined an aluminum block that fits the yoke profile with slotted bolts to allow fore/aft adjustment on the mitering plate, probably the most time consuming aspect of fabricating with this product.

A steel yoke in the fixture, ready for the next step...

As this product has a fixed shoulder at one end, mating it to plate style dropouts is preferred, as it will allow a little wiggle room at the axle end.  If you are a masochist or just really like a challenge use a hooded dropout and be prepared to be able to fabricate a mating tube section that is EXACT in bend angles and length, then replicate it for the other side.

Put some serious heat and filler into the tube/yoke joint, as there is sufficient material to take it.  

Other interesting notes....

The 4130 yoke, once welded, is super hard.  Two points to adhere to for coping...know the point you'll need to push the cutter through and weld up to that point and not beyond.  The hole saw will engage one side of the yoke's profile fairly easily, the other is a bit of a tough job.  To get through the more difficult arm, I ran the saw backwards and let the teeth cut a small groove in the surface, then ran the saw forwards, allowing the groove to keep the teeth from wanting to skate or flex.

I choose to use a detail belt sander and smooth off the weld bead on the Ti yokes, as I was planning on masking it to leave the inside face where the tire is located bare, with Cerakote on the rest, the customer's name negatively masked on the outside face to show the polished Ti.  Just remember to keep the belt dead flat so that you do not get into the base material...not an easy task.

Welding to the bottom bracket, the inside edges of the yoke arms can be tough to sneak into with a good torch angle.  A large cup and screen that allows maximum electrode extension is really nice, giving good access and gas coverage...

So that's about if we could just convince Mark to make a nice piece to fit true Fat Bike tires, that would be SWEET!



Sunday, February 23, 2014

Jeroen's 29+ retro neon eye burner fabrication...

So, with the blessing from my doctor and physical therapist, I began working in the shop this last week.  I've got a lot to do, building three bikes and a frame before the show in three weeks, gonna be tough.

Jeroen is on the build list but is a ways down, however, we are doing what we can to get him into a Groovy build asap.  You see, has is quickly losing a key physical attribute for mountain biking that we take for granted...his sight.  Hindered with a degenerative eye disease, he has continued to ride the last few years using the periphery of his vision as the central focus is gone. He has ridden amazingly well, navigating his way through Colorado and Moab trails better than I, but unfortunately, life is changing for him so it is my hope this build will give him hope and inspire others.

Here's the rundown...this bike is to be a steel 29+, which is a wheel size that is about a half inch bigger in diameter than a standard 29er and has a width of 3.00", giving it a nickname as a "mid-fat" wheel size.  The goal of this build was to create a bombproof chassis with a wheel that can roll and float over obstacles that Jeroen may not be able to navigate with the same precision as others but still have that cross country handling and feel.

The materials selected include a mix of True Temper OX Plat tubes, curved and shaped on the main triangle and straight gauge 4120 for the rear end.

I usually start with the seat tube.  In this case, I wanted to create shorter stays with a little extra clearance, so I choose to roll and shape this hardened tube.  Curving/rolling OX Plat tubing is not easy, as if you get too aggressive, it can fracture at the stress points.  For success in creating the oval shape without fracturing, I filled the tube with cerobend, rolled it in a die one size up (1.375 for this 1.25 tube), and got a nice round to oval shape for the tire clearance.  I also put in all the braze ons before welding up the tube, so that no introduced heat stress will mess with the alignment of the frame once out of the fixuture.

Once all the tubes were mitered/coped up, I began working on the dropouts for this build.  Jeroen is a child of the 80's and I wanted to create a dropout that was similar to some used in that period that would be incredibly strong.  As I am also looking to use this dropout in the future for a single speed and a Rohloff build, it had to meet the criteria of having enough horizontal motion for tensioning as well.  I drew up the design and then the fabrication plan and got to work.

The dropouts were machined on the mill out of 4130 plate...

and the hoods were created out of 4130 tubing, bored to the correct inner diameter and then cut and shaped to fit the profile of the plates.  I will likely leave the derailleur tab on the other builds just to give the possibility of using it with a derailleur as the mount is fairly low profile and unobtrusive...

Welded up and ready for action...

I'll be using a Yoke on the rear to help achieve room for the tire and a large chainring for the 1x10 setup with a standard 73mm bottom bracket.

What's tough is about to come, creating chainstay profiles that are a fixed length, come straight off the fitment on the yoke and fit precisely to the hood on the dropout.  To accomplish this, it took bending the .875" diameter tubing in three planes; one bend to move it out laterally even with the 135mm axle, a second opposite bend to bring it back straight in line with the droput, and a third bend to bring the end of the tube up to the hood to compensate for the bottom bracket vs axle height, otherwise know as bb drop.

Once bent, I created a sub assembly for the rear end and welded it up using the fixture I created earlier, noted in the blog.

With the sub assembly done, I meticulously cleaned all the tubing, fit it into the fixture and welded it all up.  Lots of folks always want to know machine settings..."what do use for max amperage, pulse settings, slope up and down?"  Here's the skinny, this was all welded with the amperage set on 80 and running hot and fast, allowing the dipping of my filler metal to create weld bead pattern.  No fancy settings, no fancy machine, just plane welding, controlling the puddle with the angle of my torch, rate of filler, and overall heat input with the remote pedal.  Practice is what you need to know, not how to manipulate machine settings.

The final aspect was creating the seatstays and then post fab finishing, which consists of reaming the seat tube, facing/reaming the head tube to fit the headset, and tapping the bottom bracket and derailleur.

The final fab'd frame, ready for the paint booth to come.


Monday, February 17, 2014

Fixture time...fitting a paragon yoke

Another fixture today... the new yoke requires a fixture to hold it securely for mitering and affixing to the chain stays, so I machined up a quick adapter for my Anvil fixture. 

I laid out the coordinates on a scrap piece of aluminum and then went to work as the human CNC...not as efficient as the computer, but it cleaned up with a quick pass of the drum sander and fit nicely.

The new piece holds the yoke symmetrically and allows for adjustment fore/aft/lateral to achieve perfect alignment. Cool. 

I received some good news today. My doctor has released me to do light work in the shop although I still have a few more weeks before I'll be returning to heavy lifting and the fire department. Looking forward to feeling productive again 

PS... don't get old it really sucks.

Thursday, February 13, 2014

Slotting seat tube binders...

Mined another unpublished vid from my laptop for your viewing pleasure...

Monday, February 10, 2014

Bending thin wall tubing...tubing rollers

The last month has been really difficult for me...the herniation of a few discs in my back has kept me out of the FD and the shop for weeks. I've been focusing on hitting the physical therapy hard and in the last week really felt like I've turned a corner. I actually have been getting out in the shop a little bit to work on a personal project, a new tubing roller. 

My current roller was made for shaping tubes for chopper frames and while very effective, is large and not easily adapted for differing tube diameters. 

I had purchased a cheap Harbor Freight roller a few years ago simply for the dies, as 120 bucks for three die sets is dirt cheap. However, as a roller it is an ineffective tool on cycling tubing, either hardened steel or ti. There is a significant user driven adaptation for this tool to make it better than originally designed for, much of the insight coming from an off road forum and pushed by Troy of SWAG Offroad. Reading through the thread the mods they were making were simple but had much improved results, so I embarked on a project to adapt this tool to my needs. Borrowing some ideas and making a few modifications of my own, I really like how the end result turned out. I added a 4 ton hydraulic press, expanded wings for greater rigidity, and ceramic coated the roller pins for decreased friction. 

I rolled out a few seat tubes and have nice transitions, so it looks like it was a successful effort. 

Looking forward to getting cleared to return to work full time, lots to do and only a month before the show...gonna be busy.


Tuesday, January 21, 2014

Bending thin wall bicycle tubing...

One of the most asked questions on the builder's forums is how to bend tubing without kinking, wrinkling, or collapsing it.  Folks are always quick to throw out the frozen soapy water, pack it with sand, or stuff it with welding/brazing rod tips.  These will work fine in a hobbyist situation where only a few bends need to be made, but for a professional shop, accuracy, efficiency, and repeatability are mandatory.  

I took a few of these impromptu videos with the intention of stringing them together into a tutorial, but they have set alone and lonely on the hard drive for too long. So, here ya go, the first of a few videos on techniques to bend thin wall tubing into clean, flowing shapes.

Using an air over hydraulic dedicated tubing bender...

As always, any questions, please let me know.