Saturday, February 9, 2008

Measure twice, cut once, maybe better measure again

A moment of extreme high anxiety arrives. This is one I was dreading, a real no turning back moment, the time arrives to apply a hack saw to the extremely pricey carbon fiber, time to cut the steer tube at the top of the fork.

Another late arrival was the stem. You may be seeing a trend here but I went with the Look Carbostem, again choosing the component manufactured by the bicycle frame manufacturer. This would be my first ever carbon fiber stem. There is a small weight saving but again this was not my main reason for choosing this stem. I was satisfied that this was a good high quality stem. I was pretty sure of this based on how much I paid for it. I did not have a specific ride quality or mechanical function reason for choosing Carbostem. The deciding factor was that it says LOOK right on it. I was building a LOOK, I took this one more opportunity to name brand the bike and to also avoid putting some other name on a highly visible part.

Compare this picture with the Look stem to the previous pictures with the Deda stem and see whether or not you agree that LOOK was the correct stem choice.I stood the bicycles side by side and did lots of comparing. I had the tape measure out and measured distance from floor up to handlebar height, first on one bike, then on the other. I have a couple of spacers on the steer tube underneath the stem and I was able to move the bars up or down by adding or removing spacers. I kept measuring until I had the handlebars at the same height as on the other bike. I had already established the saddle heights as the same, if I get the handlebars the same then the drop from saddle to handlebars has to be the same and the only remaining item of fit should be cockpit length, length from saddle forward to handlebar. This was an important measurement, I had to get it correct.

With this type of fork, it is necessary to load the headset bearings, the bearings that facilitate rotation of the steer tube, the bearings that allow you to steer the bicycle, it is necessary to load the headset bearings by tightening a head cap that applies pressure downwards on the stem to create the bearing load. The stem is not tightened on the steer tube until after the head cap has been tightened.

It is therefore pretty important to get the steer tube length correct. Screw this up and you will be riding without front end bearings. Of course, you could also cut it too short and not have sufficient room above the head tube to attach the stem.

Measure twice, maybe better measure again. Mark the steer tube. Maybe better stand it next to the other bike one more time and take another look.

But finally . . .I purchased the part you see fastened into the vise. It is a steering tube cutting guide, one of the ultimate single use tools. Once you have determined exactly where you want to cut you insert the fork into the cutting guide and line up your intended cutting line with the slot in the tool.

Even the hack saw isn't as simple as it may seem. The recommended blade for cutting carbon is a high tooth count per inch blade. I do not remember the numbers right off hand but I do know I went to the hardware store for hacksaw blades. And obviously, since we are talking about a several hundred dollar part, the recommendation is that you go ahead and splurge and use a brand new $1.79 blade. Do everything you can to maximize the possibility of getting a good clean cut.And here is what came out the other end of the process after a successful cut. The front end of the bicycle has now been assembled.

Several spacers came with the frame. I am not sure how clear it is in this photo but there are two 10 millimeter spacers underneath the steam and a single 5 millimeter spacer on top. Each one of these spacers presents another opportunity to get the word LOOK attached to the bicycle.

Personally, I think with the LOOK stem, the LOOK spacers, the carbon weave of the spacers and the carbon weave of the upper headset, the carbon weave visible on the head tube, and the carbon weave coming into view on the top tube, the whole array of parts comes together quite well and presents an elegant appearance. I think it looks nice.

3 comments:

Anonymous said...

Whew. Glad that worked out -- what's a few single use tools when an entire headset/steering tube assembly is at stake. Ever count how many times your bike says LOOK? Nice bike. ~ TGFR

Anonymous said...

While looking at the previous post to check the appearance of the Deda stem (LOOK was the right choice, of course), I noticed that the Crown Jewel as a Time front fork. Also a nice bike. ~ TGFR

Anonymous said...

I think the title is a little misleading (I was expecting a measurement error), but the tension is palpable. Whew. I remember being amazed that it all came together. I didn't realize how many LOOK parts were involved. I did notice later, however, after riding with you on your newly-constructed bicycle, how many other bicyclists LOOKed at you (or your bike) as they pedaled by.
BB

PS The vice picture adds to the tension. Nice shot.