Instructables

Step 2: Carve & Cement the Bike Frame Rests

DSC06496.JPG
DSC06497.JPG
Take the 3" length of 2" diameter pipe & split it length-wise. You end up with (2) 3" long half-pipes. These will be used to rest the bike frame. One will be the rest for the bike's bottom-bracket shell, & the other will be the rest for the down-tube (the frame member that runs from the head-set down to the crank). Lets start carving & assembling the down-tube rest, since that will be easier than the bottom-bracket rest.

Start carving one of the T-fittings so that the 2" half-pipe can be cemented parallel it. You want to begin carving the branch of the T that runs perpendicular to the other two. You want the low spots on that branch to be pointing toward the straight-through branches so that when you cement the half-pipe it will be parallel to the straight-through direction. Look at the photos to see what I mean.

Begin rough cut carving with a tool that can remove a lot of material quickly. (I started out with the hack saw, then tried a bolt-cutter, & finally went out & bought a Dremel Tool. I've always wanted one, & justified the purchase based on the money I'm saving by not buying a bike stand.) Be careful to not remove too much material during the rough cut. Dish the shape out to match the curve of the 2" half-pipe. Match the half-pipe frequetnly to your carving as you progress in order to tell where to carve & to maintain the parallel of the two pieces.

As you get closer to the final shape & it becomes more difficult to tell where to carve, start using the dry-erase marker as an indicator. Cover the outside of the half-pipe in the dry-erase color & let it dry. Then fit the half-pipe into the carved area & rub it around a bit. The dry-erase color will come off on the high spots that need to be carved down. In addition to carving down the high spots, keep checking that the pieces are fitting parallel. If they are not, you may need to remove a little more than just the dry-erase color in some spots to bring them back into parallel.

As the fit gets closer to the final shape, remove less & less material each time. Eventually you will want to switch to a file & finally sand paper. You will never completely fill all the gaps, & you don't need to since the PVC cement will soften the plastic material & bridge small gaps.

When you think the fit is close enough, clean the parts thoroughly in preparation for cementing. Make sure all of the PVC particles & dry-erase color are removed. (I don't think it is necessary to use PVC primer, since this bond doesn't need to hold water.)

Now comes a critical step. Since we are not fitting these parts usign their insertion fittings, we must make certain that the cement is applied in the correct place & that the parts are aligned properly. Set the parts on a clean flat work surface in a well ventilated well lit area. Observe all the precautions on the PVC cement label. Apply a thin layer of cement to the surface you have just carved and to the outside of the half-pipe where it will contact. Bring the two parts together & smear the cement around slightly for no more than 2 seconds - making sure you end up with them properly aligned before they begin to harden. Hold the parts together for at least 30 seconds more. Then let the cemented assembly sit for at least 2 hours. After at least 2 hours, you can add another light coat of cement to the joint to help fill it in & reinforce it (this isn't necessary with pipes inserted into fittings, but since this is a surface-to-surface fit, every bit helps).

Next, lets assemble the cross-fitting & the bottom-bracket rest. Hold the cross-fitting up in a position like the letter X (not like a + sign). The 2 branches pointing down will join to the legs of the work stand. The branch pointing upper-left will join to the front-tube support. The one pointing to the upper right will be carved to hold the bottom-bracket support.

Start by placing the remaining 2" diameter by 3" length half-pipe in the upper crotch of the X with the open side facing up. You could cement it in place right there, but there would only be 2 tiny contact points - not very strong. Since the upper-left branch is going to hold the pipe for the front-tube support, our only choice is to carve into the upper-right branch. Go ahead & carve away, using the same method used on the front-tube support. As you carve, make certain the half-pipe is aligned straight up (with the cross-fitting remaining in the X position) & perpendicular to the branches of the fitting.

It is OK to let the half-pipe rest against the upper-left branch of the cross. As a matter of fact, it is probably preferable & will lend strength to the final assembly. This bottom-bracket support will hold most of the weight of the bike - it will need all the strength you can give it. This is why we started with the front-tube bracket - so that you could get practice carving & cementing. As you carve away, watch to see how small the gap in the crotch of the X is getting. You don't need to completely close it off, but let it get small enough that it will hold some PVC shavings from your carving without falling through. Later we will use some of the shavings to help reinforce the joint.

Continue to carve until the fit is good & the gap in the crotch of the X is small. Finish sanding & clean up the area - but save some of the PVC shavings for later. Set the parts on your clean flat work surface. Apply a thin layer of cement to the surfaces, including where the half-pipe will contact upper-left branch of the X. Bring the two parts together & smear the cement around slightly for no more than 2 seconds - making sure you end up with them properly aligned before they begin to harden. Hold the parts together for at least 30 seconds more. Then let the cemented assembly sit for at least 2 hours.

After at least 2 hours, you will lay the X down on the work surface & sprinkle some of the PVC shavings into the gap in the crotch of the X on one side. Then dribble a small amount of cement into the shavings. Sprinkle some more shavings into the cement & press them in with a nail or a stick. Let it sit for at least 2 hours, then flip it over & repeat the sprinkling, dribbling, & pressing on the other side. You can also coat the other parts of the cemented joint with another coat of cement to make sure it is strong. Just be certain not to dribble cement into the branches of the fitting that will later need to have pipe inserted.

Now you're done with the most tedious & time-consuming part of the build. From this point on, we will progress quickly & begin to see the stand take shape.
 
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ponkan5 years ago
Where you talk about whittling the T to fit the half-pipe, there's practically no better way to fine-tune the fit than by wrapping the half-pipe in sandpaper and rubbing. Start with something rough, like 80 grit wet-dry (wet it to ease the process), to really remove material, and switch to finer grades to refine edge. A plausible progression might be 80, 160, 320, and if you're really serious about a smooth edge before cementing, 600 grit.