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Old 10-04-10, 07:59 AM   #1
mrbUSA
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Cutting a steer tube with a pipe cutter

I finally achieved a perfect fit on my newly built CR1. The steer tube needs to be cut about 2" and I was wondering if after measuring and scribing the CF tube, I could use a pipe cutter, tightening and turning until it's severed.

Will a pipe cutter work on CF? If no, I assume a fine TPI hacksaw is the option?

Thanks,
Mike
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Old 10-04-10, 08:15 AM   #2
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Use a hacksaw. You may also want to leave extra room in case you change stems in the future. They are not all the same 'stack height'. This is more a problem if you're cutting to the very shortest stack possible. You'll want to keep a minimum of 5mm above the stem.
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Old 10-04-10, 08:16 AM   #3
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NO! No pipe cutter EVER on steerers regardless of material. That kind of load on CF will ruin the fork. On AL or steel, it puts a bulge in the material which makes fitting the headset or spacers impossible without further filing or grinding.

A diamond coated saw blade, and a mask are needed. You do not want to breath that stuff. Go slow and rotate the fork as you cut, lest you tear fibers off the fork. We use a special guide here in the shop-you need to make that cut as close to perfectly tangent as possible.

Good luck.

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Old 10-04-10, 08:22 AM   #4
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Thank you for the input and firm warning! Sounds like something I may want my LBS to do with a Park Took Guide as well. I wanted to complete the entire build including cutting the tube by myself though.
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Old 10-04-10, 08:35 AM   #5
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Cutting a carbon steerer with a pipe cutter is a no-no as you have been told. However a good quality fine tooth (32tpi) hacksaw is more than adequate and nothing more exotic is required. Measure at least twice before cutting anything!

Use a radiator clamp as a cutting guide and go slowly. Wrap a turn or two of masking tape around the cut line to keep the edges from fraying. You can work outside to avoid the dust and a dust mask is a worthwhile precaution but cutting one steerer isn't that big of a deal.

Also, as recommended, cut the steerer at least long enough to require a 5 mm spacer ABOVE the stem. That assures the stem is fully supported by the steerer. Also, since the headset adjustment will be made against the spacer, having the steered cut absolutely square isn't that important. Work carefully but don't agonize over a very slight deviation.
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Old 10-04-10, 08:59 AM   #6
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Also, as recommended, cut the steerer at least long enough to require a 5 mm spacer ABOVE the stem. That assures the stem is fully supported by the steerer. Also, since the headset adjustment will be made against the spacer, having the steered cut absolutely square isn't that important. Work carefully but don't agonize over a very slight deviation.
Good advice. A tiny caveat is if a True Temper fork is being fitted. They use a bonded-in insert which requires a very precise tangential cut to make it look neat and relieves the need to run spacers on top of the stem, since the insert is designed to take the load.

However, as HillRider stated, forks equipped with expander plugs may require a spacer above. It is also worth checking to see if there are any warranty guidelines requiring the fitting of a particular brand of stem, or the avoidance of certain brands due to clamp design. This is a good time to full read and comprehend the instructions even if you aren't normally the type to do so. :-)
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Old 10-04-10, 09:00 AM   #7
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Also, if it is a threaded fork, screw the race onto the fork before you cut it. That way, after the cut, your race will clean out the threads, making reassembly much easier. Without doing this, you could ruin the threads.

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Old 10-04-10, 09:01 AM   #8
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^^^^It's a carbon steerer! No threads. But good advice for steel steerers, no doubt.
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Old 10-04-10, 09:32 AM   #9
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Seems from the start, as I read the 1st tool choice...

the mechanic part of the owner is not as high tech as their tastes.

the steerer tube needs to be square across the ends and just whacking it off with a hacksaw

is rather difficult to cut straight with, freehand ..

A bike shop will have a steerer tube cutting guide to do it right

why not let someone else , the bike who is better equipped do that job.

rather than messing up an important component that you risk your neck on being right. ?
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Old 10-04-10, 10:40 AM   #10
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Quote:
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....the steerer tube needs to be square across the ends and just whacking it off with a hacksaw is rather difficult to cut straight with, freehand ..
Well, I certainly don't recommend doing the cut freehand but a radiator clamp tightened over the steerer will provide a very clear edge as an accurate cutting guide.

And, further, if you cut the steerer long enough to require a spacer above the stem, the top of the spacer, not the steerer, provides the surface that the top cap presses against for headset adjustment. So, the steerer being cut at exactly 90 is not a big issue.
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Old 10-04-10, 11:02 AM   #11
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A radiator clamp is one option and a wrap of masking tape applied so that the free end lines up with the start as it comes around is another way to create a cut and file guide. Or a wide strip of printer paper wrapped around and taped so it forms a cylinder will provide a nice square cutting guide. The masking tape and the radiator clamp both have the advantage of supporting the fibers at the cut to help avoid splintering out of the resin matrix.


For home use a fine tooth hacksaw blade also works just fine. The trick is to use a new or near new blade and basically let the weight of the saw do the cutting. Don't apply any additional force. You can also avoid pullout splinters at the end of the cut by first cutting a shallow scoring cut all the way around the tube and only then work straight down to finish the cut. The scoring cut should be about a millimeter deep. Again, the secret is support and guide the saw well but with only very little pressure into the cut. And take fairly slow strokes when cutting anything plastic so the cut doesn't overheat.

Other than this do it outdoors and you'll be fine. If it's a bit windy wear a dust mask. The carbon and epoxy dust isn't good for you by any means but it's not hard to avoid inhalation or eye contact. Just wear a mask, vacuum your clothing and wash your hands, forearms and face after the cutting and sanding.
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Old 10-04-10, 11:06 AM   #12
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Quote:
Originally Posted by mrbUSA View Post
I finally achieved a perfect fit on my newly built CR1. The steer tube needs to be cut about 2" and I was wondering if after measuring and scribing the CF tube, I could use a pipe cutter, tightening and turning until it's severed.

Will a pipe cutter work on CF? If no, I assume a fine TPI hacksaw is the option?

Thanks,
Mike
I used a chop saw. I used minimal pressure and took my time. I then polished the cut on a wire wheel.

Don in Austin
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Old 10-04-10, 11:34 AM   #13
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Don, you must have used a VERY light touch with those power tools. The wire wheel in particular could have pulled splinters out from the matrix at the cut line in a flash if the tube was not presented to the wheel at just the right angle. Both those tools would be the last resort in my books.

Not to mention the dust from the cut and wire wheeling would have been all over your shop.
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Old 10-04-10, 11:53 AM   #14
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breathing in Carbon fibers as a sawdust has been found to have the same effect,
in the lungs as asbestos.

so cutting under a stream of water may be safer, as the fibers won't go into the air.
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Old 10-04-10, 01:14 PM   #15
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Get a like thisTube Cutting Guide
Or if you happen to live in my area I would be willing to cut it for you.
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Old 10-04-10, 02:17 PM   #16
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It would seem to me a diamond bladed tile cutter works well.
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Old 10-04-10, 02:27 PM   #17
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I use an automotive hose clamp as a guide and cut with a 32 tpi hacksaw. Then I square up the cut end with a flat file. The top of the steer tube needs to be about 1/8 inch (3 mm) below the top of the stem when fully assembled.
I recommend using a compression plug that offers the most support on the backside of the steer tube. Set the headset pre-load with the cap bolt. Set the pinch bolt torque with a 1/4 drive torque wrench with no more than 44 INCH pounds or 5 nm of torque. Don't use torque specs shown on the stem.
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Old 10-04-10, 04:28 PM   #18
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Quote:
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breathing in Carbon fibers as a sawdust has been found to have the same effect,
in the lungs as asbestos.

so cutting under a stream of water may be safer, as the fibers won't go into the air.
In looking around it seems like it's not as bad as that. One MSDS sheet I found online went into all manner of POSSIBLE effects but I think it must have been an early one since they really didn't know and all the warnings were "might cause" and "may result in..." and similar phrases. Nothing else I found that had MD behind the author's name suggested that it was as bad as asbestos by a long shot. After all, if it had been shown to be as bad we would not find it in readily available products like we do. An irritant sure. But a long term health risk? Other than in forums such as this one and the model airplane ones where everyone just assumes that it's deadly I'm just not seeing the material that suggests that anything more than a dust mask and a good vacuum and washup is needed.
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Old 10-04-10, 04:46 PM   #19
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Ok, wish this thread came up earlier... I picked up a cf fork with aluminum steerer tube last month for the road bike I just built from scratch and I DID use a tube cutter with a very sharp wheel. I don't know if I just got lucky or what, but the cut came out very clean, very straight. The mechanic at my lbs said "everything was good" when I had him do a final tune-up before taking it out on a 1/2 century. I agree, you might get some deformity from the pressure of a tube cutter if the wheel is 'dull', but I believe it would be an indentation rather than a 'bulge' (note to bikewise), I don't mean to be impertinent, and am in no way or manner a 'mechanic', so did I just get lucky or does the quality of the tool and the quality of the material determine the quality of the outcome?
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Old 10-04-10, 07:40 PM   #20
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The big issue with a dull cutter wheel would be that the tube is pinched between three wheels. The cutter and two wider idlers. A dull wheel requires a LOT more pressure to get a cut. In a bad case it would be enough pressure to flex the tube enough to cause delamination.

Same with the wedging action of the wheel on the fibers to each side. The first layer cuts clean but then as you continue to push the wheel in further you are wedging the outer surface fibers with an extreme amount of pressure. LIkely your tube has some minor delamination that extends into the tube by some number of millimeters. But since the end of the tube for the first inch or so is not a loaded portion you're getting away with it and very likely won't ever have an issue. But regardless, anything that wedges into carbon fiber is bad. You may have got away with it but I sure would not recomend that you make a regular practice of using such a cutter.
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Old 10-04-10, 08:51 PM   #21
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Quote:
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The top of the steer tube needs to be about 1/8 inch (3 mm) below the top of the stem when fully assembled.
Not quite. There must be a 2-3 mm gap between the top of the steerer and whatever the top cap is pushng against. That "whatever" can be the top of the stem OR the top of a spacer above the stem. I much prefer to cut the steerer long enough so a spacer is required to obtain the gap. That way there is no unsuported part of the stem above the end of the steerer and no chance that the top pinch bolt of the stem can squeeze the very end of the steerer.
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Old 10-04-10, 09:29 PM   #22
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A cutter guide is 12 bucks from bike Nashbar. It may actually be cheaper then buying a tube cutter. Just use the guide. It is super easy to do.
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