Christopher Aldgate – '.a frame build'

{} .a 2016 – Frame repairs. {}

Venge

So 2016 begins with the delivery of several smashed frames! A fairly standard mid-range Scott Pro One, which appears to have been broad swiped by a vehicle, although this is speculation.  It has two fractures across a seat and chain stay, and also a rather nasty bend to the rear hanger. This should be super easy to mend.

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The second frame has a more sever break but is a rather high end S-Works Venge. It was recovered by the Pro who destroyed it whilst racing. His account was that he was rear ended by another rider, the impact was apparently not that heavy but the damage is considerable. Not sure how far I’ll get with this frame. the entire rear triangle has been destroyed, the impact seems to have concertina the frame cracking the top tube and BB area as well.

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The first stage is to realign the frame sets, which I’ll achieve with some 5 min structural adhesive, and considerable care and attention. Secondly missing material and the crack line will be filled with a mixture of milled carbon powder and resin. The area will then be heavily sanded to remove as much dead carbon as I can from the area that I will re-apply more carbon. It’s worth remembering that generally the failure occurs to the resin matrix, so I need to make sure I return structural integrity and cover any small cracks that may have propagated. Fortunately the Venge has a very thin black topcoat and cracks appear as white lines, I’m fairly confident that I can see the areas that require attention. This is not the case with the Scott, which has a very thick white topcoat designed to cover up unattractive carbon work and blemishes.  The damage however is very different; the break to the Scott seems clean and as far as I can tell, less likely to have caused residual damage.

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The damage to the Scott has been realigned and filled.

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Likewise this image was taken during the process of realigning and filling the rear triangle. Interestingly whilst Specialized replaced the Pro’s frame immediately they asked him to swap out the seat post, clamp, fixtures and fittings. I’m thinking it will be fun to try to fabricate as much of these replacement parts myself, I may even attempt the seat pillar and a set of bars to marry up to the head tube area.

After the realignment the structural layers of carbon are added and sanded to marry up to the tube profile. The image below shows the tube before the area gets sanded back to receive the top layer of carbon.

Scott Rear stay base layer

Scott rear stay sanding

After sanding I wrapped the tube with a thin layer of uni directional carbon which unless i decide to paint it, will be the final layer.

Scott wet lay up Rear Stay

And the final layer – it’ll be polished with some wet and dry and a touch of polishing compound.

Finished Scott

scott-1

So because I found a crack on the S-Works at the point the chain stays meet the BB shell, I want to sand back and encase the whole BB area just in case. Also, I feel the finish will be a lot more attractive. I began by sanding the BB shell. The top coat and paint layer are impressively tough!

SWorks BB sanding

You can see the layup schedule Specialized used…

SWorks BB Sanding3

I’ve also done a lot of work on the top tube, rear and seat stays.

Carbons

After sanding back the cracked area on the top tube, adding some bi-axial cloth and three layers of Uni directional carbon, the last layer I chose to add an aesthetic layer which will be repeated elsewhere. I hope the finish will make this otherwise standard Venge stand out!

SWorks TT wet Layup

SWorks TT sanding

Working around the rear stays there are a lot of cable holes and areas I don’t want resin to wander into. To these areas I’ve added a release wax and some filet wax to ensure I can remove any waste material easily.

Release wax

SWorks wax on rear stay

I think I mentioned that in addition to the other six breaks in the frame, I found a crack on the stay joint depicted above. Just to be sure, and to achieve the same finish on either side, I’ve wrapped both sides. I’m less concerned by this crack, I suspect the drop out will be mounted high into each stay. I think it would be unlikely to completely fail. Better to be safe however…

I added layers of bi-axial / uni directional carbon and then wrapped the areas in a carbon ribbon to increase the pressure on these tricky angles.

SWorks dropout first layer

SWorks Drop out

The peel ply is added before the compression layer.

SWorks Peel Ply

After a light sand you can see the fix. I’m please with it and confident the area has been restored.

Dropout

I’m taking some time to cut the carbon as neatly as possible, I find this guillotine blade is really useful.

Cutting carbon

And the now structurally sound stays, which were once cracked in half… rebuilt! Once the rest of the frame is sound again, there’s just a decorative finishing layer to follow.

SWorks Seat stay structural layers

The finished seat stays.

rear stays

I’ve reinforced the carbon around the bottom bracket / chain stay area. Mainly with a  Bi-axial (or 0/45 degree unidirectional)  cloth. I’m going to finish the area with a wrap of higher quality fine twill carbon. I’ll need to vacuum bag the entire frame for this layer however, compressing around the tricky multiple tubes is not easy.

BB shell

I spent some time cleaning up the top tube decorative wrap, which I think looks really nice. I’ll also add a boarder strip, trying not to get the original paintwork covered in resin.

TT

TT detail

What it will look like.

TT with boarders

Resin

Vacuum Bagging

So for the final layers to the bottom bracket area, I thought I’d use the opportunity to re visit the vacuum bagging process. It’s quite labour intensive and to date I haven’t managed to document the process as fully as I would have liked.

The process is used to squeeze the carbon cloth together whilst wicking away excess resin and thus bonding the layers into a composite material fit for purpose. In truth I usually try to complete all the layers that would go into completing an area of the frame within the window of full resin curing – with the intent that the area is compressed into one full cured layer. As I understand it the resin will continue to cure over the course of a week or so, this is the sort of time frame I usually give myself to complete.

Obviously in this case I’m restoring a broken area of composite that is several years old so I’m not hoping to achieve the above. In order to gain a good bond however, all surfaces are washed with a solvent cleaner or acetone and then lightly sanded to both be sure of the removal of grease, and to add a tooth to the surface.

Cleaner

To generate the pressure required to bond the carbon and wick away the excess resin, on this frame I’ve so far used several layers of tape that are stretched tightly. With oven heated higher temperature prepreg carbons, this is often achieve either within a vacuum bag, with the air drawn away by a pump, or with shrink tape that reduces by 5% when heated.  A full vacuum achieves 14.7 PSI, however this is difficult to achieve, so realistically 12.9 PSI is the sort of target i’m likely  to hit. I believe tape will achieve a lot more than this so whilst it looks a little DIY, tape or latex strips stretched over the surface are more than adequate. Issues arise with this method however when the surface area is not round, then of course equal pressure can not be applied to all areas. In the bike building industry silicone inserts are used to round off or filet areas.

Anyway… the first stage is to cut the bag material. The bag material I bought is sealed on to sides, effectively a long sleeve.

Vac Bag 1

Bag Size

A bagging tape is used to seal the open sides. Once applied it is important to take time to press out and stretch away any areas of kinked bag or air bubbles. A  full seal is essential.

Bag Tape

So this is the bag… the next stage is to insert the hose that’s connected to the  vacuum pump.

Bike bag

The hose connection. The lower portion of the connector punctures the bag is supposed to self seal. I tend to use the bagging tape however, just to ensure a full seal.

Hose connector

Vac Pump

The vacuum pump I use.

Before bagging the frame it’s wise to round off any sharp corners, head tube and BB shell. The bag can easily get punctured if you’re not careful.

Foam inserts

I tend to fill out the BB shell and head tube with foam inserts.

Soft ends

Once ready to bag the frame, I need to insert a breather cloth that allows the pump to draw the air from the area of the bag the wet carbon is in.

Vac Bag2

Vacuum Bag Full Frame

You can see that the breather cloth also wicks the excess resin.

BB Shell2

And this is the finished carbon work with a layer or two of top coat. I’ll continue to build up the top coat to get rid of those super small blemishes.

bb

I had to marry up the semi transparent black paint and matt finish but I faded the finish to reveal more of the carbon work. You can see this in the down tube below.

HT

The finished frame. If you look closely you can see the carbon rebuild work around the entire rear end and bottom bracket area.

Fixed frame

So you can see in the blow image most of the areas that needed re-building including the crack across the top tube. You can’t see the crack propagating into the bottom bracket area or the crack around the dropout.

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Upon completion I’m a bit undecided as to what to do with this frame . After building the TT frame I had wanted to build a full aero bike for myself, but as space is limited I think I’ll utilise the aero origin of this frame and build it up as my main road frame for a while. An all rounder.

I managed to pick up a set of aero handle bars and a TT aero bar for just over £80. Perfect material for a little chop shop activity.

So…

tri bars

So the two things I want to do are mount the aero bar, which of course functionally offer the rider a complete different riding position, and also mount the arm rests.

I’d be nervous drilling into the current carbon wall of the handle bar, I wouldn’t say I fully understand the structural integrity of the bar layup design. When ridden the torsional forces must be considerable and I don’t think it’s obvious how the design will have countered the stresses.  My intention then is to bond/wrap the bar onto the handle bars and surface mount a fixing on the top grip..

I spent a few hours with the bars attached to my current road bike to ascertain a comfortable riding position. And of course this can be altered with the fore and aft position of the saddle.

First job is to strip back the top coat and paint work.

Sanding

A couple of handy Garmin/computer fixings offer the opportunity to test the position. Also a TT seat post usually has two distinct flip positions to really increase saddle position from normal capacity.

Bars

Mounted bars

The bonded bars have a really nice aesthetic. I’ve used a 5 min structural adhesive to create the first fix, I’ll subsequently do an all over bar lay up of carbon to both secure the fix and also add some additional rigidity.

Bonding

This is the kind of finish I aiming for, nicely presented by Livi…

Livi

Also, whilst mending the frame, I’ve been trying to purchase the missing frame fixtures and fittings.

Hanger

More to follow…

I’ve recently had to fashion a new mech hanger to adapt a frame to receive a SRAM red group set. Poor images but…

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One response

  1. Geoff Fletcher

    Love your enthusiasm and confidence Chris. Good luck, Geoff.

    Like

    February 27, 2016 at 8:55 pm

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