I want to remove about 5mm of HT on a frame (it’s okay if it is a bite off of each side). I have the Park facing and reaming tools, but that is a very big cut to do by hand. I also have shop-made tools that will let me run the Park facer in my lathe, but still think that could take forever.
Tools at my disposal: benchtop milling machine (Emco FB-1), 10-inch lathe (Emco Compact 10), 4x6 bandsaw, Park HTR-1, files, vises etc.
The frame is painted, and I’d like to keep it that way. It has a Paragon externally tapered HT, which seems to be 2mm thick even in the thin portion (it measures 48mm external diameter). We’re doing this because the HT is a hair too long for our target fork, even with a Cane Creek “slam set” and short stack stem. I think I can afford to remove a few mm at the top and bottom of the Paragon HT while keeping plenty of meat.
Ideas that I’ve thought of:
Put frame in vise, mark the cut line, rough file to that line, face to final dimension. Alternatively do the same thing with a small angle grinder. Upsides: lots of control. Downsides: taking solution far from faced and counting on the Park tool to get it back there.
Do it in the lathe using the Park facer with a steady diet of cutting fluid and just accepting that it’ll take a while. Downsides: this probably puts a lot of wear on the facing tool.
Mount sideways on the milling machine table with some finger clamps. “Face” using a long endmill side cutting. Face properly by hand when complete. Seems good on paper, though I don’t current have an endmill with a 2” long cutting face.
I think the lathe is the safest option with the least amount of setup time (since you already have the tools), and I’d rather risk dulling a sharpen-able tool than potentially risking the frame in some of the other operations.
If you set things up using an end stop and plan to leave ~.020” for final facing anyways, I bet you could get away with using a short endmill to “face” half of each end of the headtube, then flip the frame over and do the other side/half.
I would mark the line you’re going to with a sharpie and get most of the way with a grinder, but just sanding with a flap disk, not a cut-off wheel. If the line marks all of what you want to remove then you know you’re OK if you’ve left a bit of sharpie there all the way around. Get it as flat as you can with the grinder anyway to make things easier, then use the facing tool by hand.
I don’t know what tools you have but I’d go with this method probably. You don’t even need a 2” cutting face, you can do it in multiple cuts. Just the overall length needs to be sufficient.
Tramming it in might be a bit of a challenge though…
I’d be worried about the cutter catching on a relatively thin tube. Especially since it’s unlikely that your setup is going to be really rigid. Angle grinder/file/powerfile to get close, then finish with the hand tools. If you’re trying to save the paint, go nice and slow so as not to ‘burn’ the paint.
To be honest, I’d probably just take the hit and do it all with the handtools. It won’t take that long to do, and sure, it might wear the cutting tools, but that’s what they’re there for!
This! I use a bench grinder and remove portions of the HT end bit by bit around one end at a time. Followed by the usual facing. Just take care on how hot you get the HT ends as you don’t want any paint getting burned. I’ve done a few with sawing off a mm+ sliver then facing but the grinder is faster and there’s less chance of the paint getting scratched. Andy.
Yes. Leave it as is, particularly because you have to ask the question. The 5mm on a head tube is nothing to sneeze at when the whole of the design and rider position are factored in. You can do a lot more damage trying to remove this measurement than you’ll gain if you even can accomplish it.
Sorry Richard, but doing nothing isn’t an option. I appreciate the message.
For full context I designed the frame, know my fit, and it’s a MTB. It was built by a friend as a prototype for a larger run and the head tube was made slightly too long due to a communication/spec issue. That’s okay and it’s why we prototype
I appreciate the ideas and think I’ll do the rough it in with files/grinder approach and finish with the facing tools.
Upvote for the hacksaw, file, and face approach. But 5mm on an MTB? If the fork is anything over 100mm travel I imagine changing a little fork pressure will change the average hand position more. Also, I guess you’re using a bar with some rise?
In hands on rookie, hacksaw and some sort of blade guide followed by the headtube reamer treatment. You want to make the straightest cut possible by eye. The guide could be a simple tube block. Go slow.
I have done it with a hacksaw, but that can be risky on a painted bike. I have done more hacksawing than most people, so it may be even more risky for most people. Hold the frame in tube blocks as close as possible to the HT for rigidity because one of the risks is the saw jumping out of the kerf due to resonance vibration.
@Fuzzmuffin This isn’t to fix rider fit. I agree with you that 5mm would be nothing and is correctable in other ways. It is to fix fork fit – the planned 170mm head tube became 190mm, and our target forks have 225mm (SID) and 230mm steerer (Wren, already trimmed) lengths.
So the math for the 230mm steerer fork is 14mm stack height (EC44 lower, ZS44 “slam” upper) and 30mm Deity stem. That would fit on a max 230-30-14+2=188mm maximum headtube, so we’ll need to trim a little bit, but could get away with less than 5mm. Fitting the SID is nice to have but not necessary and would require a deeper cut but got me into the thought process of how to do it.
I’ll just using the hand facing tools if 2mm ends up being all that is necessary.
The Paragon externally butted head tubes to my eyes have plenty of reinforcement to remove 4mm from each end (8mm total) should we need it. The thin part of the tubing is still fairly thick at over 2mm, so we have a little more leeway if necessary.
The drawings are fixed and this won’t be an issue when more of these frames are made.
