Shims - they're just bits of tubing, right?

[jazzibizznizz]

Here's a problem I wonder if anyone has had any experience of.

I've got some forks which take a 1 1/4" steerer, but I need a 1", so I need a shim. There are shims on ebay, and Pace also make some, which are 1 1/4" to 1" selling for £20. Plus postage.

Here's the rub:

Steerers are all standard tube sizes. An inch and a quarter tube will have an internal diameter of one inch or inch and one eighth. So why pay over twenty quid for something that I can get from a steel or aluminium stockholders for the price of a pint?

Does anyone have any experience of home-made shims?

 

[Leighcal]

My guess is shims are made for the job, they fit tight and are milled so they fit tight. Ok you might get something you think is right from a steel place but just that 1mm off and it putting extra stress on that part of the frame. Do you really wan to risk damaging or even snapping your frame? I know I wouldn't

 

[legrandefromage]

Quality of materials counts, a soft shim will deform

 

[jazzibizznizz]

Good point and given that the fork is quite a critical place you wouldn't want to mess with it. If it goes wrong, your face will meet the ground at an alarming speed. But sizes are what they say they are - one inch is one inch, 31.8mm is 31.8mm and so on, and that's standard across the board regardless of who has made it. So is there any margin for error? Are they just charging extra because they've cut it to length for you and cut a split in it?

 

[daugs]

Re:

its been said really, its materials, being hard enough alloy, although some "cheap" shims are probably worse than good tubing and the accuracy of the tubing ie the machining, we know about seat posts and the difference 0.2mm makes or doesn't in certain circumstances. As to sizes, measuring accurately is probably the key, 31.8 could be anything from just over 31.75 to just under 31.85, depends on the quality. As to allowable tolerances ? never tried it. I've got a 1 1/8" to 1" shim on one of my marins, on basis couldn't find the right tubing with both internal and external dimensions accurate enough, but didn't pay £20 for it, but then not Pace.

 

[mattr]

Pace will probably have bought tubing to a specific dimension with detailed tolerances, made out of a specific material and possibly machined it to a more precise size.

If you haven't got those details, you might be best stumping up the 20 quid. Failed forks cost a lot more than that.

 

[Rampage]

Good point and given that the fork is quite a critical place you wouldn't want to mess with it. If it goes wrong, your face will meet the ground at an alarming speed. But sizes are what they say they are - one inch is one inch, 31.8mm is 31.8mm and so on, and that's standard across the board regardless of who has made it. So is there any margin for error? Are they just charging extra because they've cut it to length for you and cut a split in it?

If you buy some tubing from eBay then sizes seem to be +/- 0.2mm, it's not uncommon for me to receive 28.6mm bar that measures 28.45 or worse, it's usually undersize not oversize. I also have a 3 meter length of aluminium, tubing that has a wall thickness of 1mm more on one side than the other. If it is for Pace forks then you'll also need the shim for the crown race, which are machined to +/- 0.01mm on the important diamensions.

Compared to the steerer adaptor shims I sell on eBay (only two left, they are this price because someone wanted me to make some for him, I charged him this price and made some extra and I can't sell them for less than I charged originally him!). They are perfectly concentric, sizes are +/- 0.015 on the important diamensions, and have the safety bit at the bottom to stop it pulling through the crown.

Cheap off-cuts vary massively in quality, I have to anodize a piece before using it to check its ok. As do some of the big companies, like Cane Creek.

I almost never use tubing as it varies so much. It shows black lines when it's anodised, and the weld lines are visible, you can even see the weld lines sometimes when you machine it.
(weld lines are part of the extrusion process of tubing, it's not welded like some steel tubing is)

 

[jazzibizznizz]

Ok, some good points. It has always been a question that's niggled at me and now I've got some informative answers so thank you everyone. This wasn't really about whether or not to stump up £20 for a piece of metal - in the overall scheme of things it's not that much, and compared to what it could cost you if it were to go wrong you can't put a price on it. It was more about whether or not it was truly necessary. Within a couple of miles of my house are dozens of stockholders and fabricators who could all easily supply me with something that will 'do the job', but now I know it's not as straightforward as I first thought.

Thanks again for all your help, and Merry Christmas!

 

[paddy311]

Re:

Most stuff has already been said - but I'd like to add this.

To some extent shims are just bits of metal yes. But you have to look at the application when deciding whether to use one.
e.g. I have made shims in the past for handlebars - to get 25.4 mtb bars in a 26mm road stem for example. I make them in brass sheet and roll them. The brass is hard as hell and works well. Worst case if it fails - the bars slip and spin round a bit. Not life threatening - and TBH it would never happen.
Tomorrow I'm going to cut up a 1" fork steerer tube to make a shim for a front brake cable stop to be mounted on a stem. I'm using one of these:

And shimming it to mount on the stem - because the steerer tube is too short to get a normal cable stop between the nuts on the headset.
It will be totally fine - 'cos its just a cable stop.

Your steerer tube shim thing though - Fk that . It's just too critical to mess with.