Boring out a pushbike saddle tube.

[bigegg]

I have a mountain bike.
Very expensive new, but i got it stupidly cheap because some muppet had hammered the wrong size seat post into the seat tube, then cut it off level.

Theres about 10 or 12 inches wedged inside. 22mm ID, 26mm OD (inner tube) and its an alu frame, alu seatpost.

Its been an ongoing project for 3 or 4 (or 6!) years, and i want to get it either sorted, or abandoned.

I've tried heat+cold to break the (assumed) corrosion - in conjunction with a slide hammer. It never budged.

So. I went for more destructive measures.
I drilled down the end of the tube starting with a step drill to keep it centred, then with a 25mm TCT "hole saw". Which drilled out the first 3 inches, leaving a narrow sliver which will easily remove.

I then ordered a 25mm blacksmiths drill and (using a hosepipe to keep the frame cool) managed to get about 8inches down before it bottomed out, still leaving four inches stuck solid: which *still* wont slide hammer out. (I'm using a piece of m24 all thread, made into a tap and welded to the slide hammer).

The TCT hole saw is the chinese type like a forstner bit, not like a core drill, and worked really well, compared to the blacksmiths bit.

So...
I need an extension which will take a 10mm drill shaft - with grub screws to lock it in place (rather than a hex, which would be easy) and be 250-300mm long so i can drill out the last few inches.

Or another idea...

 

[eLuSiVeMiTe]

Just chop down the new seat post to suit the depth you have. I'm assuming you had a decent length 25mm bit?

 

[123hotchef]

cant u cut through the stuck seat post with a hack saw blade both sides the pull the 2 halfs out? one side may be enough to free it up

 

[Welderpaul]

11" is more than enough for the new seat post - cut it down if needs be and leave the stub in there?

 

[Ashley Burton]

Shame it's been cut flush!

 

[Kram]

Any damage on the frame tube from drilling or otherwise? I would be getting it out and using full length it will be stronger. Any photos?

I can make up a drill extension tomorrow if that helps. Is it 13mm drill chuck on the other end?

 

[Brad93]

Is the frame aluminium or steel?

is the seat post aluminium?

If the frame is steel and thre seat post aluminium, you could try a chemical method of removal. You’ll likely ruin the paint though so bike would need powder coating.

 

[a111r]

11" is more than enough for the new seat post - cut it down if needs be and leave the stub in there?

Yep leave it in there. The min. seat post depth needed is quite small, something like 4".

Had similar on a steel frame. I 'ate' the alloy post out with NaOH. Effective but not exactly quick.

^^ Crossed in the 'post'!

 

[bigegg]

11" is more than enough for the new seat post - cut it down if needs be and leave the stub in there?

I've only got 6 or 7 inches of free space - and until i can get the 0.5mm thick remains out, i cant fit another.

 

[bigegg]

Is the frame aluminium or steel?

is the seat post aluminium?

If the frame is steel and thre seat post aluminium, you could try a chemical method of removal. You’ll likely ruin the paint though so bike would need powder coating.

Both aluminium. Otherwise I'd have filled it with boiling NaOH

 

[Brad93]

Both aluminium. Otherwise I'd have filled it with boiling NaOH

Bummer. That’s what I was going to suggest.

 

[Gareth J]

Hats off to you for managing to get it so deep without going off course and poking out the side. I'm sure I would have ended up doing that.

And that would be my concern going deeper still!

 

[a111r]

Is the frame aluminium or steel?

is the seat post aluminium?

If the frame is steel and thre seat post aluminium, you could try a chemical method of removal. You’ll likely ruin the paint though so bike would need powder coating.

Yes that works for steel frames, using strong sodium hydroxide.
To save an expensive paint job:
Plug the seat post with a 'cork', if cut off.
Invert the frame with the BB removed and pour it in.

 

[bigegg]

Any damage on the frame tube from drilling or otherwise? I would be getting it out and using full length it will be stronger. Any photos?

I can make up a drill extension tomorrow if that helps. Is it 13mm drill chuck on the other end?

Theres no damage to the outer tube - bar a little bit of scoring on the inside.

I'm using my big mains SDS drill (with a 13mm chuck) as i'm scared of burning out my milwaukee cordless - it took a good hour to drill out 3 inches with the blacksmiths drill, as opposed to 30s with the TCT hole saw.

 

[bigegg]

Hats off to you for managing to get it so deep without going off course and poking out the side. I'm sure I would have ended up doing that.

And that would be my concern going deeper still!

The drill is following the bore of the centre tube, so actually easier than you might expect.

 

[Welderpaul]

I've only got 6 or 7 inches of free space.

Thats more than sufficient. Seat post will have markings for minimum insertion depth.

Or just use it as an excuse to buy a new bike. N+1.

 

[bigegg]

Thats more than sufficient. Seat post will have markings for minimum insertion depth.

Or just use it as an excuse to buy a new bike. N+1.

This particular bike is the make, model, and year of the one i lusted after in my early 20s, before i got married
I would *very much* like to get it rideable.
Unless anyone knows where i can get a 1992 Gary Fisher "Paragon" in a 17" frame?

 

[Melvyn Best]

Your using 24mm all thread,.? presumably the remains of the seat post have been tapped so you can attach the slide hammer? If that is the case can you place a large thick washer over the top of the frame then put the all thread into the remains with a nut at the top of the threads, tighten the nut then perhaps use the slide hammer whilst under tension .?

 

[bigegg]

Thats more than sufficient. Seat post will have markings for minimum insertion depth.

Or just use it as an excuse to buy a new bike. N+1.

I'm not sure if i could adequately clear out the remains of the bored out bit, without spending £££ on a 26.2mm reamer?

 

[bigegg]

Your using 24mm all thread,.? presumably the remains of the seat post have been tapped so you can attach the slide hammer? If that is the case can you place a large thick washer over the top of the frame then put the all thread into the remains with a nut at the top of the threads, tighten the nut then perhaps use the slide hammer whilst under tension .?

I like that idea: basically using the all thread like a "puller"?

I'll give that try in the AM, although i'm not sure if screwing the all thread in is actually "tightening" the grip like a rawl plug.