[longassballs]

If nothing ever clamps to it, is it necessary to be perfectly square?

It’s so easy & quick to use a rotary saw (with a diamond wheel for carbon) I’m wondering why all the recommendations are to use a saw guide and a tungsten carbide saw blade? Sure, using a rotary saw will never be perfectly straight and perpendicular but it’s close after sanding and if the top cap is only ever clamped to a spacer or stem, does it need to be?

Please correct me

Topic

[matthewn5]

Quote:

if you are cutting the steerer down to a mm below the top of the stem

You must leave at a short length of steerer to allow a thin spacer to sit above the top of the stem – it is simply not safe to cut the steerer lower than the top of the stem and can lead to sudden failures. If you’ve done what you suggest, you will have most likely voided any guarantee you had on the fork.

[longassballs]

For future reference…
For future reference…

[b]USE A HACKSAW & SOME FORM OF SAWGUIDE WHEN CUTTING A STEERER TUBE[/b]

?

No I didn’t fuck it up but I was playing devil’s advocate when I said using a rotary saw was quick and easy. Sure its easy to cut but it isn’t easy at all to cut straight. It was actually only when I failed to consider the steerer plug, realising I had to knock another 2mm off, that cutting became tricky. No longer having the length of tube to rest my hand on made a straight cut very difficult. Only using the face of the cutting wheel as a sander let me get away with it – but only just. When I do it again I’ll definitely use a tungsten carbide blade and a guide!

[mtbtomo]

I use an old stem clamped on
I use an old stem clamped on to the steerer as a guide. Doesn’t have to be factory square, I’ve had it a few mm off over the years and it’s fine – so long as you can still preload the headset. Once cut and fitted, a 5mm spacer above the stem usually helps with the gap needed between steerer and top cap too if the cut is a bit wonky.

[mtbtomo]

The rougher/coarser your saw,
The rougher/coarser your saw, there is more chance of fraying the steerer tube too, the guide stem helps from this perspective as you finish the cut. Or insulation tape. I’ve had steerers where a whole shard has split off over an inch down the steerer when I havent used tape or a stem to hold it together ?

[Dingaling]

Don’t forget to seal the top

Don’t forget to seal the top of a carbon tube with superglue!

[Nick T]

Basically the less square the

Basically the less square the cut, the less leeway you have for preloading the bearings. Tightening the top cap pulls the steerer tube up towards the cap, which puts pressure on the bearings. Say you have a standard 5mm spacer on top of your stem – if you cut the steerer a few mm off square then you’re more likely to top out the steerer when it pulls up, thus be unable to tighten and not put enough pressure on the bearings.

A precise 1mm extra all round the top of the stem to sit the spacer on gives you 4mm of tightening potential. Every mm off square reduces this potential

[Pilot Pete]

Yeah, badly worded, apologies

Yeah, badly worded, apologies. I meant the clamping force around the steerer by the stem bolts after pulling the slack up in the bearings using the top cap either on the stem or on a spacer above the stem.

If the cut isn’t square, with no spacer above the stem, the upper stem bolt may clamp over the top edge of the steerer, which could cause problems.

That was quite hard to write what I meant for some reason!

PP

[Drinfinity]

I wrap masking tape around

I wrap masking tape around the tube and cut to the edge with a regular hacksaw, and tidy up with fine sandpaper.

With an alloy steerer, I use a plumbers pipe slice which gives a nice easy clean cut. 

[srchar]

But the top cap doesn’t touch

But the top cap doesn’t touch the steerer. If it did, you wouldn’t be able to preload the bearings.

[Pilot Pete]

You don’t need a correct

You don’t need a correct hacksaw blade, a normal one works. I’ve used a hacksaw with a guide, and a table guided hand saw with the forks clamped to guide the cut. No special blade in either use, cuts nice and clean, no fraying of fibres etc etc.

The idea of it being square is to allow the top cap to clamp down evenly to pull up the slack in the bearings. Slightly off probably won’t stop that happening, especially if you are going to put a spacer above the stem, but if you are cutting the steerer down to a mm below the top of the stem, an off square cut could compromise  the clamping force applied with the stem bolts.

PP 

[longassballs]

You’re right – it’s just that
You’re right – it’s just that I don’t have a saw guide or correct hacksaw blade ?

[Rod Marton]

No, it doesn’t have to

No, it doesn’t have to perfectly square but it has to be reasonably square. More importantly, you don’t want to cut too much off and I would be more confident of that with a hacksaw and guide than with a rotary saw. And it isn’t exactly the most time-consuming of jobs, anyway.

[Author]

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