I’m working on my first metal 3D-printed parts, and I’m planning to use 316L steel and weld it with columbus tubes.
I’m having trouble designing the seat lug. I’m not sure how much support the seatpost should have. Is the 3D-printed part enough, or should the seatpost also be supported by the seat tube?
The inside diameter is 31.8 mm, while the outside diameter of the shell is 35 mm. The thickness is 1.6mm.
I couldn’t find any designs showing the solution. I’m considering changing the design so that the seat tube goes through the lug, allowing the seatpost to have contact along its full length. However, I do like the look of the lower tube surface being flush with the lug.
Additionally
What tolerance should I use for the seatpost?
What tolerance should be maintained at the joints with the other tubes?
Thanks for any advice on how to finalize this part.
My seatclusters/lugs are designed to slot into a 35x0.9 tube. As you can see, the 3d printed part extends into the tube. On this part, the seattube is only in contact with the lug, but there’s about 100 mm in total that’s in contact. I size the internal bore to be nominal size (in this case 31.6), and this works out fine for post-weld reaming as I’d do for a regular frame. But you may experience a different amount of distortion depending on the joining system you’re using.
I’ve added the additional supports to help keep roundness, but I’ve never made any without these, so I have no idea how much difference they make. They only take a few seconds to remove, so I just keep including them.
007: 1.7mm wall, inner diameter 31.6, 1 3/8”x.035” seat tube butts the bottom, with a small alignment ring. I had to do some reaming for a good seat post fit. Note, the top opening warped closed a bit, so for the next version I added some sacrificial pins between the clamp at the slot to keep it round. This bike is built and great.
009 and 010: Similar to 007 but with more sleeve inside the tubes and the sacrificial pin to keep the opening round. Wall thickness is 1.7 at the bottom and 1.2 at the top. These parts are in the mail.
I’ve found things end up a little bigger than designed. So if you have a sleeve with an OD of 6mm, it may end up between 6mm and 6.1mm, with variation. My first round of sleeves I made .025mm less in diameter than the ID of the tube, and had to file them to fit. The second round I made .05mm less, but haven’t received those yet.
FYI Protosoon recommended a minimum wall thickness of 1.2 to avoid warpage. This is a part they were having trouble with that I had to redesign. Those web walls are .5mm (which worked fine on other parts).
