Cutting frame down

(Sorry if this gets posted twice, seem to be having issues posting)

I have another question for you guys! I asked over a week ago about finding a unicycle short enough for me to ride and you guys were super helpful. I found a lightly used 16" Corker CX on Craigslist for a great price.

I had the seat post cut, but I still need the frame shorter. I know from reading a post here this can be DIY, but I lack the tools and know-how to do it. I have asked two different bike shops here and they said they cannot do it. They both said I should take it to a welder. I didn’t totally grasp why, but I think it has to do with the seat post clamp (which is integrated). I guess I don’t understand why the frame can’t be cut and a new clamp put on?

What do you guys think?

Even with an integrated seat post clamp it doesn’t have to be taken to a welder, but you will need to buy a regular bike type clamp. First of all, you need to work out how low you need to cut the frame, ideally leaving a couple of inches to give enough room for the clamp and a bit of adjustment. A pipe cutter is great to cut this down, as it’ll leave a straight smooth cut, however a hacksaw and a steady hand will be just as good.

Once you’ve got the frame at the right height, you will need to cut a slot out so that the top can squeeze in enough to hold the seat post. Drill a hole about 1/8" dia around 1" from the top of the frame at the back*. Then use a hacksaw to cut a slot about 1/8" wide all the way down to this hole.

I don’t have a Sun frame here to measure, but there are a few ‘standard’ diameter seat post clamps. If you can accurately measure then you can just order a clamp in the size you need, but if not, take the frame to your local bike shop (lbs) and see what fits.

STM

  • Check for L and R markings on the cranks or pedals to work out the front or back of the frame if you’re not sure. Don’t worry if you get it wrong, the whole wheel can be rotated if necessary.

While I have no problem with using a pipe cutter for cutting seat posts (as long as you grind the edge after) i would not suggest using one for a frame as it tends to squish the end that is getting cut.

Most bike shops have a hacksaw guide for cutting seatposts which would be perfect for getting a nice strait cut on your frame. Assuming that you have a bike shop that will allow you to use some of their stuff bring in the frame clamp it in their guide and just hack the top off.

Cut a new notch, sand down any burrs and you should be good to go.

I don’t know for sure but I think that Sun unicycles probably have 22.2mm seatposts which are quite small by todays standards and you might have some trouble finding a suitable post clamp. Your best bet for finding one that small is a bike shop that deals in BMXs and or childrens bikes. Last time I needed a post clamp for a post that size they just gave it to me for free.