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Boring a Tapered headtube bottom flange to taper?

5K views 51 replies 22 participants last post by  mtnbikej 
#1 ·
So my bike looks like it has a tapered headtube - so I went and bought an upgrade fork than has a tapered steerer.

Taking a closer look at the headtube, there appears to be a flange on the bottom to fit a 44mm headset bottom cap - which I find rather strange.

I am aware that there are headsets available for 44mm to 1.5" tapered steerer - but I would rather not fit a traditional headset since this will further lift the front of the bike (the upgrade fork is longer already, I wanted to change the geometry a little on purpose)

So the question is - can I machine out the flange without destroying the frame?

Here is kinda what the headtube looks like
Line Parallel


The bike is a Scott Spark 29er Team, 2012

Should the headtube be butted, or is it usually just straight tube?
Knowing that the resulting ID of the headtube may differ to standard, a custom bottom cup may be required, which I am ok with.
 
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#3 ·
Probably won't destroy it, but might make it useless.

No offence intended, I think I understand "what" you are trying to do, but I can't figure out why. Can't you change geometry of the bike without modifying the frame? I would rather modify the fork (internal spacers) or some other removable piece.

I would imaging that Scott put many hours and many $$$ to design and engineer the frame, but it's your bike, do what you want.
 
#5 ·
Probably won't destroy it, but might make it useless.

No offence intended, I think I understand "what" you are trying to do, but I can't figure out why. Can't you change geometry of the bike without modifying the frame? I would rather modify the fork (internal spacers) or some other removable piece.

I would imaging that Scott put many hours and many $$$ to design and engineer the frame, but it's your bike, do what you want.
So what I am trying to do is remove the flange that has been left in a tapered headtube so that the headtube can actually take a tapered steerer
 
#6 ·
Are you sure that it won't take a tapered steerer? I thought they came with straight steerers, but would take tapered as well. This article seems to suggest so, but I haven't found definitive specs.

But in any case, don't go boring out your headtube.

Edit: Here's the 2012 Spark manual. It's not model specific though and the headset info says it differs by model. It seems very possible though that you have something like a press fit reducer on the bike now to run the straight steerer. I'd ask your shop if you can't tell.
 
#7 ·
Thanks for the links!

Had a look through the manual, like you said there appears to be 2 variations on the headsets. One being tapered, the other 1 1/8 straight. In both cases the headtube looks like its tapered.

On closer inspection, mine appears to not have a reducer per se, but the headtube itsself has a flange on it that acts as a reducer - the hole at the bottom of the headtube is 44mm (same as the top)

The headtube appears not be just a tube, but rather a tube with the bottom bent in again to form a reducer. The diagram in my 1st post shows a cross section of the headtube only

Hope this makes a little more sense!
 
#10 ·
I don't think there's ever a time when it's a good idea to modify a head tube. A head tube failure could easily put you in an ambulance.

In my opinion, if there were no way to make it work without cutting into the frame, I would sell the tapered steer tube fork and buy a straight steer tube fork.

Safety issues aside, even if you got it to work and it never failed, I bet it would be prone to creak, bind, be out of alignment, etc.
 
#12 ·
#15 ·
thats why I shop on amazon or rei... I just simply return the tapered fork for a straight one...

Wouldn't that be the solution ? can you get a refund on your fork ?
Perhaps if he has not modified the fork, the manufacturer would be willing to swap out the CSU for a straight 1.125".
 
#16 ·
The difference between a Cane Creek 40 external cup lower (to fit a 44 diameter headset and 1.5" steerer) and a zero stack lower is 8mm. If you are worried about raising the front by that much, you could shorten the fork travel by the same amount and keep the same basic geometry. Sounds a lot better than trying to machine your headtube...

You would need a Cane Creek ZS44|EC44/40, Chris King InSet 7, or equivalent.
 
#21 ·
Thanks for all the feedback - here is some more info



Thanks for taking the time to give that feedback, hopefully these pics are better:

Side view, front view
Front top with headset installed, ID=44mm, OD ~50mm
Bottom view with internal headset cup installed: id=44mm, OD ~65mm

Wood Bicycle accessory Bicycle frame Bicycle part Bicycle
Carmine
Wood Hardwood Wood stain Bicycle accessory Plywood
Material property Cylinder Circle Silver Steel


Appreciate all the frank feedback - In no rush to fit the new fork.
The 44mm to traditional 1.5" cup is the easy solution, and 8mm is probably ok for geometry - can always give it a try.

Boring the bottom of the headtube would be an additional 'project', something nice to do.

From what I understand, this frame came in a version with the same headtube already bored out at the factory - not something that I just want to do without getting as much information as possible.

While I accept the risks, I would rather learn from others than learn by breaking a perfectly good frame.
 
#23 ·
From Park Tool, the Onepointfive standard has cups that press into a head tube dia of 49.6mm. If your current bore on the bottom there is for 44 (actual 43.9), I don't see why you couldn't bore out 5.7 mm. It doesn't look like it would make the head tube excessively thin, because it looks like the head tube is made to be bored for either 43.9 or 49.6 mm, and in this case the bike build was able to get away with a 1 1/8 fork and semi-integrated headset, so they just bored it for 43.9 and did that.

I say do it. Hah. Something like this isn't as stupid as some of these people might make it to be, but I'd reckon most of them wouldn't be able to machine it themselves anyway.
 
#24 ·
From Park Tool, the Onepointfive standard has cups that press into a head tube dia of 49.6mm. If your current bore on the bottom there is for 44 (actual 43.9), I don't see why you couldn't bore out 5.7 mm. It doesn't look like it would make the head tube excessively thin, because it looks like the head tube is made to be bored for either 43.9 or 49.6 mm, and in this case the bike build was able to get away with a 1 1/8 fork and semi-integrated headset, so they just bored it for 43.9 and did that.

I say do it. Hah. Something like this isn't as stupid as some of these people might make it to be, but I'd reckon most of them wouldn't be able to machine it themselves anyway.
From the manual the same headtube comes with either 44mm or 54mm bore - so thanks, thats the confirmation I was looking for.

Is there anything special about boring a heatube?

Of course alignment and final measurements will need to be spot on
 
#25 ·
Well on doing some more research, it looks like that 49.6 mm is also for an external cup. I think it would raise the stack less than the one for 44 but maybe not much. The fully integrated headsets for 1.5 steerer is 52 or 54 mm dia, which is maybe pushing it on this head tube. You would have to do the measurements and judge for yourself. Really, I say just keep it at 44 and use the headset for that diameter unless you really trust your judgement.
 
#29 ·
Punch out the current headset cup and have a look around to see what's going on there, if the headtube really is one piece or there's an adapter pressed in.

If you do decide to go ahead with the bore, and you really really want a zero stack headset, you should know that FSA makes a zs49/40 bottom cup. So there's no need to bore all the way to the zs56 standard, going from 44 to 49 seems quite safe to me considering the wall thickness seen in the photos.

FSA Gravity 2 ZS49/28,6 - ZS49/40 Steuersatz günstig online kaufen - bike-components
 
#34 ·
What are the IDs and ODs you're quoting?

I thought the OD for a 1-1/8" steer tube was 1-1/8". And for tapered, it necks up to 1.5" at the bottom. Which is still about 38 mm, so less than 44 mm. I think you need to pull your headset and see what's going on in there.

Personally, I'd be disinclined to do this. Fit specs are often very tight-tolerance, so unless you're set up to ream and hone too, and you can get really good concentricity, I see a lot of ways for this to work out poorly. I'd be more inclined to make an adapter or my own bearing arrangement.
 
#37 ·
Are you ever planning on selling this frame after you make chips? Are you going to disclose that you hacked up this frame on your lunch hour at work?

Like I said at the start of this thread, I understand what you are trying to do, I just don't understand why?
 
#39 ·
OP, the company did not lie, the HT is a tapered capable one, just not an internally capable one, but an external 44 cup will allow the use of a tapered steerer fork, which you seem dead set against. Looking at your pics it does look like the HT is very thick and it's very possible what you say about it coming bored 2 different ways from the factory, still I wouldn't go doing it myself, not with the tolerances and alignment needed or end up having it not line up with the upper cup and not without confirmation from the manufacturers or consulting a reputable frame builder.

I observed a similar occurrence the other day on a straight steerer Reba fork, it has the crown the size that would fit a 1.5" steerer, so was also wondering if to save cost they only produce one size crown, designed to fit a 1.5" steerer and just machine to suit what steerer is being pressed in. Sure does make it not look so funny if you had a straight HT frame and one of these forks and then bought a frame with tapered HT, but didn't want to buy a new fork.
 
#40 ·
Not as fun and might give you fewer options for thr fork down the road, but you might get the height you want with an external lower cup, cutting the steerer tube down and using a stem with a low stack height? I think riders go for these lower height stems when the st is too short, but it might also get you close to where you want to be.

http://forums.mtbr.com/29er-components/low-stack-stems-860525.html
 
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