help a new frame builder, question on seat tube reaming.

[spinzman1]

I am new to building frames, I have built a few but always end up with a problem reaming out the seat tube. I am using a 27.2 seat post, and I am using an expansion reamer in a hand held air drill, and it takes forever. I would like to know what more experienced builders are doing, what tools and processes you are using. Even when I am done, the seat post is very very very tight. Any info would be fantastic. I have used Tru Temper tubing, and am at the moment using Nova Cycles externally butted seat tube on the frame I am working on right now. Thanks in advance.

Mike Foster

[bencooper]

How much reaming are you having to do? Ideally a frame should need little to none - if you have to do a lot, it indicates that it's deforming - and then reaming too much will thin the walls.

I have a 27.2 spiral reamer that I quickly put down, just to smooth off the inside - doesn't need more than a few turns.

[spinzman1]

I am able to start the reamer at around 26.9mm, and having to go from there. I don't know that I am having a lot of deformation, I think it is more the back side of the weld that I am having to ream out. I think that my reamer is probably not the right tool for this job. It cuts very slowly. I have looked for a 27.2 spiral reamer and have not found one, I think I would be better off with one like that. Where did you get it?

Mike Foster

[e-RICHIE]

spinzman1 please add your first and last name here, and to all posts on the FrameForum.
Thanks.

http://www.velocipedesalon.com/forum...rum-36866.html

[John Winston]

External butted seat tube: do you have the tube 'backwards'? Sounds trivial but......it can happen.

[spinzman1]

I don't think that I have it backwards. the only flared end is on top.

Mike Foster

[bencooper]

Ah, that sounds okay - mine is a Silva one from Ceeway.

[echelon_john]

An expandable reamer is fine, but put it on a t-handle and do it by hand; no drill! Speed is probably way too high, and it's not cutting into the material you want to remove. Also use plenty of cutting oil. If you have a specific point that's distorted, creating a lump on the inside, you may need to emphasize the tool's contact with that high point. Again, impossible with the drill.

[spinzman1]

Thanks John, I had not considered a T-handle.

Mike Foster

[Rody]

Spinzman1,

Firstly, please adhere to the rules of the forum and place your first and last name in your signature line.

What are professionals doing? NOT using externally butted seat tubes, they are inadequate for long term performance and durability.

Read this first...

Groovy Cycleworks 330-988-0537: Creating the spine of the frame...

It discusses how to create a thicker top portion to the seat tube that is highly accurate and less likely to deform, requiring less post fabrication reaming.

Next, ditch the expandable reamer and spend the money on an accurate tool. Joe B can hook you up with a nice spiral reamer ground to the exact size you want.

Look here... Bringheli Parts

cheers,

rody

[Will Neide]

I have the Cyclus reamer. I don't recall it being too expensive and it does a great job. The T-handle is nice.

[spinzman1]

Thanks for the info John and Will.

[DeeDub76]

Rody can you elaborate on what makes externally butted seat tubes inadequate?

[Mark Kelly]

using Nova Cycles externally butted seat tube on the frame I am working on right now.

I am able to start the reamer at around 26.9mm, and having to go from there.

Assuming you mean this tube, something doesn't add up.

The stated dimensions are 28.6 OD x 0.8 / 0.6 / 1.0 WT, yet they call out a 27.2 seat post.

28.6 - 2 * 0.8 = 27.0; which gels with you needing to start the reamer at 26.9.

I thought tubing that size took a 26.8 seatpost.

[Will Neide]

Assuming you mean this tube, something doesn't add up.

The stated dimensions are 28.6 OD x 0.8 / 0.6 / 1.0 WT, yet they call out a 27.2 seat post.

28.6 - 2 * 0.8 = 27.0; which gels with you needing to start the reamer at 26.9.

I thought tubing that size took a 26.8 seatpost.

It's externally butted at the top, so the OD at the top is 29.2 for that particular tube.

[Eric Estlund]

Mark, that Columbus tube uses the .8 at the bottom, and the 1 is the flaired 29.4 top.

Some TT externally butted tubes are for 26.8 seat posts. Otherwise it sounds like a boat load of distortion (or blow through?) or an upside down tube.

[spinzman1]

Assuming you mean this tube, something doesn't add up.

The stated dimensions are 28.6 OD x 0.8 / 0.6 / 1.0 WT, yet they call out a 27.2 seat post.

28.6 - 2 * 0.8 = 27.0; which gels with you needing to start the reamer at 26.9.

I thought tubing that size took a 26.8 seatpost.

Hey Mark, I don't have the frame in front of me but I do know the O.D. At the top is 30.0mm

[spinzman1]

Thanks for the input guys, it is very helpful. I am not really having much distortion, it is the back side of the weld that I am having to grind out, not so much of the actual tube itself.

[Amaro Bikes]

Rody can you elaborate on what makes externally butted seat tubes inadequate?

I'm also curious to know why external butting is not adequate. Enlight us Rody!

Thanks for the input guys, it is very helpful. I am not really having much distortion, it is the back side of the weld that I am having to grind out, not so much of the actual tube itself.

Well, if you are not having any distortion, then you wouldn't even need to do any reaming at all... Distortion usually ovalize the tube, so you would only ream certain part of the tube, and if it's too much you're weakening this specific section on the tube (by making it thinner). If you mean that you're having to grind penetration inside of the tube walls, I'll assume you're tig welding, and apart from saying it sounds to be a bit overcooking, I would recommend you either go faster or use heatsinks as this will help keeping things tight and nice (not just distortion wise, but also purgue point of view)

Cheers

[bencooper]

Just as a contrary (and not to make any comment whatsoever on the workmanship of anyone here), I've seen several frames which have the plug-in top piece, where the top piece has broken off. They were ones where the join was about level with the centre of the TT, so the upper part was getting little or no support from the stays, and because it was internally butted the seatpost wasn't reinforcing it either.

Basically, any method built badly can fail ;-)