2manyoranges
Old School Grand Master
- Feedback
- View
Not strictly retro but a warning to all spanner-monkeys.
I recently was putting together a jump bike for the Grom, and ordered a machined stem from a high end manufacturer in the 'States. Lovely thing, very light, great anodised colour. I was very happy when it arrived. As usual, I put it on the bench to check it out, looking at threads etc. Stems are SUCH an important part of a bike, and highly stressed. You just don't want to be fretting about stem failure as you enter a rock garden at Warp 6 (I canna hold her Cap'n...) or experience bar rotation - or worse. And it's the worse I want to focus on here.
After seeing that all the threads and bolts were good and that they hadn't shipped a 31.6 body with a 35mm plate (has happened) I was absolutely aghast to find that the machining had left an ultra-sharp lip facing INWARDS on the inside radius of the bar clamp of the stem body. This was raised by .75-1.0mm and really, really sharp - enough to slice my skin as I pushed my finger round it. Contrast HOPE stems, where they know that a stem should have a chamfered edge all around the bar clamp, so that no stress risers occur as the bar flexes in use. This is vital with carbon bars in particular. Mr K Bontrager used to pay HUGE attention to these kinds of micro-physics of designs - and HOPE and Cy Turner and Dan Stanton (Cotic and Stanton respectively) have taken that knowledgeable craft tradition forward.
Cold forged stems, rather than billet-machined, tend to have nice round radii to the clamps - and frequently are stronger than machined stems, since the forging gives directional grain to the alloy. They look lumpy compared with machined stems, but the material physics is preferable. RACEFACE do nice cold forged things. But we have a weak spot for HOPE products in our stable, and I do like a nice HOPE stem - brilliant engineering pedigree.
On this stem, had I not spotted the lip, this would operate as massive stress riser in an aluminium bar. On a carbon bar, it would have cut into the bar significantly, caused very early failure of the bar - very very scary indeed. It was easy to remedy - a small round file gave me a nice finish, and I carefully chamfered both sides of the bar clamp, and on both sides of the stem. This kind of thing should not happen these days, and using a high end producer like HOPE is vital insurance against poor design and QC.
Worth checking.....
I recently was putting together a jump bike for the Grom, and ordered a machined stem from a high end manufacturer in the 'States. Lovely thing, very light, great anodised colour. I was very happy when it arrived. As usual, I put it on the bench to check it out, looking at threads etc. Stems are SUCH an important part of a bike, and highly stressed. You just don't want to be fretting about stem failure as you enter a rock garden at Warp 6 (I canna hold her Cap'n...) or experience bar rotation - or worse. And it's the worse I want to focus on here.
After seeing that all the threads and bolts were good and that they hadn't shipped a 31.6 body with a 35mm plate (has happened) I was absolutely aghast to find that the machining had left an ultra-sharp lip facing INWARDS on the inside radius of the bar clamp of the stem body. This was raised by .75-1.0mm and really, really sharp - enough to slice my skin as I pushed my finger round it. Contrast HOPE stems, where they know that a stem should have a chamfered edge all around the bar clamp, so that no stress risers occur as the bar flexes in use. This is vital with carbon bars in particular. Mr K Bontrager used to pay HUGE attention to these kinds of micro-physics of designs - and HOPE and Cy Turner and Dan Stanton (Cotic and Stanton respectively) have taken that knowledgeable craft tradition forward.
Cold forged stems, rather than billet-machined, tend to have nice round radii to the clamps - and frequently are stronger than machined stems, since the forging gives directional grain to the alloy. They look lumpy compared with machined stems, but the material physics is preferable. RACEFACE do nice cold forged things. But we have a weak spot for HOPE products in our stable, and I do like a nice HOPE stem - brilliant engineering pedigree.
On this stem, had I not spotted the lip, this would operate as massive stress riser in an aluminium bar. On a carbon bar, it would have cut into the bar significantly, caused very early failure of the bar - very very scary indeed. It was easy to remedy - a small round file gave me a nice finish, and I carefully chamfered both sides of the bar clamp, and on both sides of the stem. This kind of thing should not happen these days, and using a high end producer like HOPE is vital insurance against poor design and QC.
Worth checking.....
