CNC manufacture bike part

i have a seatpost needs replacing, and GIANT tells me it no longer manufactures them. Unfortunately the seatpost is an aerotube and can’t be replaced by anything off the shelf i have seen. if you know of any kind of modification kit please let me know.
My question is would it be possible to get a CNC machine to fabricate an aluminium copy of the seatpost?
(I guess the starting material would have to be a fairly widthy aluminium cyclinder.)

@LukeForward could help?

Don’t @Taiwan_Luthiers have a CNC too?

I do not own a CNC machine, but I can get access to one if necessary.

I need a CAD drawing of the items in question. If the item is simple I will machine it manually, if it requires CNC I will ask my neighbor CNC shop for help. Now if you only want one, the price per unit will be high because you will be asking for a fixture be made to hold the part(s) you want to make, time it takes to translate the CAD drawing into G codes, etc. which is likely to take time. It is actually less work (per part) to make 200 parts vs. a few.

So if the part is simple it is often faster and more economical to machine it manually.

If you do not have a CAD drawing, one will have to be made. There are costs associated with that, depending on the complexity of the item (I believe it’s a minimum of 8000nt per part).

If it’s a simple seat post I may be able to machine it manually. Andoization is available too, for a cost. The main difficulty here is if your quantity is too low they tend to overcharge you on this, assuming they even accept the job.

Easier to find it second hand. What you need?

Is it this one?

I’d say use an adapter sleeve. To improvise a weight carrying part is always risky.

  1. taiwan luthiers: thanks for the repsonse. is it possible to machine an aero tube shape manually? apart from this aspect it is just a tube, very simple.
  2. Darsabule/Liub: nope it is a giant 6300 6700 model seatpost. My friend has just shown me a taobao site with good price.
  3. Luke forward. Can you get an adaptor sleeve for a skinny aerotube shape? can you give me a link?

thanks for the answers

I’m not sure what an aerotube is, when I googled the word all I get is air tubes for air vents… I seriously doubt they make bike seat posts out of it.

However to answer your question, I can machine 6061 aluminum or even alloy steel if you want, but I doubt the part is made out of alloy steel because it would be heavy. I do not currently have a lathe, however I can use a rotary table to machine round objects.

sorry my mistake, using jargon… aerodynamic shape, streamline shape. the cross section for the tube is a teardrop shape. can you machine that?

Normally this is a CNC operation, but I’ll see what I can do with a rotary table, I think a rotary table can machine this shape fairly easily. Is this teardrop shape cosmetic or does it need to conform to a very tight and exacting tolerance?

I’ve shaped aluminum using woodworking techniques before, if the tolerance requirement is not very exacting this is a good way to machine irregular shape manually without CNC.

Do you have the old, broken part I can use as a basis for comparison?

Thought you have a round tubing seatpost with aero top section like those in
the early days. Without a sample photo we can only guess. Assuming you have a GIANT Vector seatpost, it is always possible to buy old new stocks overseas. It’s hard to believe it’s out of production as it was long standard spec before D-fuse seatpost was introduced.
Back in Australia, I used to invest a bit over cracked, rejected-from-warranty, victim-from-garage-roof frameset/bicycle to salvage parts like seatpost, forks, headset, hangers. I did sold Vector seatpost and a few other proprietary parts. I was a rogue mechanic anyway. I later quit this business as the profit is literally none.

Assuming it’s a Vector seatpost, I strongly advise you not to get involved. Reasons as follows:

  1. Vector seatpost is notorious for slippage.
  2. The cross section is very critical.
  3. The saddle clamp area is whole another story.
  4. As mentioned, it’s a weight carrying part. Your profit will definitely not able to cover the worst scenario.
  5. The reason for replacing is still unknown. If it is due to a previous failure, the cause has to be found before going any further.
1 Like

I googled vector seatpost.

It looks like all the parts involved is carbon fiber. I’m not equipped to deal with it.

6160 aluminum will most likely handle any strain you can throw at it, it’s a very strong material. Unless you need to bear many tons of force, 6160 will work. If you have to bear many tons of force, then pre hardened 4140 will usually do the trick (they are used to make gun barrels, receivers, drive shafts, truck axles, etc. and can handle tens of thousands of psi of force).

If you need me to machine a teardrop shape, and it must conform to a very exact tolerance, then unfortunately I can’t do it. If the material is 6160 aluminum I can ask my neighbor if I can use his CNC machine for this work, but I must have exact dimensions, CAD drawing, etc. because otherwise I’m just sitting there guessing what the final dimension is, and if I’m wrong then I’d have to start over (and the guy uses his machine to make part which me makes money doing, so any interruption costs him money).

If the part is carbon fiber, then nobody is going to be able to make it for you. Almost every CNC shop I seen machines only 6061 aluminum. Carbon fiber requires a mold to be made for it.

@serendipityfox Could you please post a photo of the frame showing the model name and seat post insert point?

Let’s hold up for now… there is a second hand part from taobao at a good price (just like dasrbule suggested) - if this doesn’t work for any reason i will come back to you.
You have given me some very useful information taiwan luthiers, because i want to go into this aspect and find out what can be done with machining. CAD and CNC are definitely ruled out as too expensive.
Of course we are talking about aluminium not carbon. Is 6161 strong enough.
Tolerances… within 1mm each side. Of course i have an original to model.
Luke forward -
kink not necessary

6061 is used for bike parts and they are strong enough unless you are trying to jump off a 4 story building with it.

CNC is not necessarily expensive but it takes time to set up so if you only wanted 1 or 2 it’s not worth their time. If you wanted thousands of them then it’s very cost effective because there’s almost no manual work apart from feeding and cleaning up after the machine.

That part looks like they were made by forging or extrusion.

You can contact some chinese factory and act like you are into selling bike parts and want to order 10000 pcs, but want to check the sample first. This would be a good way to get your part cheap. There are thousands of machine shops competing for your business there…

Then again you may just buy a new bike alltogether because it will take a bunch of time and energy. Buying a new bike alltogether is maybe an eassier thing to do, imho.

This only works for available, open stock items.
A company will not tool up to create a one off “sample” without a fairly large order to back it up.
Also, generally a douchey move allround.
Buy an available seat post or hang that thing on the wall.