New Part: Bicycle seat (1 of 3)

posted in: Carbon Fiber | 2

In this new post, I will try to show the work to a piece of carbon fiber. Specifically a bicycle saddle. The process will first modeling and machining of the Model, or a 1:1 copy of the final piece. In this part, modified to facilitate fiber laminate, the mold will fiberglass, or a negative copy of the final shape. Into this mold I will laminate carbon fiber, which will get the final piece, which will cut and clean it, after sand it. I will try to describe this process. I hope you find interesting.

This is the 3D model, which I download from Grabcad page.


This 3D model, I’ll have to modify it to create the piece who uses as model. This modification consists in modeling a “skirts” along the perimeter to facilitate fiber laminate. The glass fiber, as the carbon, is a fabric of interwoven fibers that are steeped in resin to catch the mold shape where applicable. The problem is in the corners or angles very prominent, since the fiber will tend to take the form of primordial material, peel and not copy touches the surface as we intend to replicate.
A favorable geometric makes this process much simply. While surfaces may take many forms, this is perfectly valid:

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In the picture you can see the surfaces I said before and surfaces that are actually the seat. So it will be very easy to apply the fiber as it will tend not to peel off. I have not generated surfaces tangent to the saddle , for the simple reason that well , with the generated edge will be very easy to define the limits of the piece once cured resin in the final piece. This model will be what will be machined with CNC and sand it to leave the perfectly smooth finished surface.

The machining will be done as usual in two main phases : The first phase of roughing and finishing second. In the middle I decided to enter a phase of 3D contoured to define the boundary of the part. Later I’ll show you in detail.

All machining, depending on the program , took one hour and a quarter, so I tried to save time by modifying the machining. Finally these are the details:

Roughing: depth of cut : 6mm with a strawberry roughing D10mm four lips. Feedrate 1000mm/min . Later I found that this is excessive , and I’d rather take a little more time for not to force the machine.

Finish: with a spherical cutter D10mm I found that the finish is much better than with the spherical cutter D4.5mm , so if sticking past 0.5 mm. While it is true that this phase will last nearly 50min . The main fear was that I was overheating engines , because after all machining time , get hot enough, not so much that they can not even touch his hand , but enough to burn enough. I estimate about 60-70 º C will research on this topic, to see if normal operating temperatures . Progress is 1000mm/min although I think at this stage could have increased this speed to 1300 or so.

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This is the stock. It consists of two blocks ureol, glued with loctite (more than enough, in principle) bolted to a martyr of MDF with three sheet metal screws thread. MDF plate is screwed on the table.

This time I placed the part zero at the geometric center of the model, and test whether it would be more comfortable. I discovered that this was a mistake, but I willjustify later.

The roughing, To not model the stock, was made delimiting a perimeter which the tool should not exceed. In that way,the CNC will machine all on a permanent material, sculpting the model within the stock. This entails some risks, as hereinafter will see.

This is video of the first entry in the stock, and the first stage roughing machining. I Notice that the machine works forced, maybe those are too 6mm deep. In other mechanized, with 5mm and 700mm/min was pretty good, but it would take more time, of course.
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Still, the machining is having good looking … until I get to the penultimate level.

turns out there was a movement, ONLY ONE, a repositioning tool, to finish a level, which left the limit imposed, and in the simulation do not get to see. Result, the tool try to move down 50mm normal movement speed until Z = 0, and then move to start the level. Then, the tool crash into the material, and try to move forward, bending the entire structure, folding everything and blocking engines. That scared me enough, I gave escape in a hurry, and all was stopped. With some effort I managed to get the tool out of his hole, but not before taking off the two stocks glued with loctite. So, I had a complicated time.

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Damage Inspection: The stock was separated, but it’s not serious at all, because it can be reattached in virtually the same position, and if not, we are still at the stage of roughing, it can handle certain errors. Engines, were forced, but apparently still working. The CNC, it seems that has not broken anything, no cracks in frame or has broken anything mechanical, but the Y has caught slack. I need to fix it. It is not serious, but it bothers me to have it. I will fix it when i finish this part.

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I got to fix the stock, and as I did not want more problems, and for only 5 mm, I’ve cutted the excess with a chisel, not to have useless pieces of material that do nothing but annoy.

But here is not all, I have lost the origin in Z, so i need to redo zero and hit play again….

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Buuuut … had also lost the origin in the X and Y axes. Sure , the machine could not move , but the program did not know and continued execution. And of course , gone to to make their tour, and has gotten half ka tool around the strand , great, just what I need . Being optimistic , that I can then fill with putty bodybuilder , and leave it functional . is not such a problem .
Now is when I regret having put the origin where I put it, as I said before . Because now what? as I will reference about a point that no longer exists ? complicated issue
The only solution that occurred to me was referenced with respect to a fairly definite gap, looking for the coordinates in the code ( 25,000 lines of code ) and know that this point had the specified coordinates . After losing more than an hour or so, I’ve gotten back to doing zero, and make sure everything is where I left off . Now is when I push play button and pray that all goes well !

The contour phase, as I said before, went very well, despite having to redo zero:

And now, tool change and finishing stage. This is safer, I hope everything goes well!

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Well, finished the stage roughing, finishing begins, and here and smoothly. Only with strawberry D10 spherical finish is impressive. I hardly have to be sanded to leave the polished mirror. That if he has taken nearly an hour and a quarter, quite hot engines, but still do not know if its normal operating temperature.

Now ready for sanding, putty and let her polished mirror. I started by sanding and applying a little bit of putty, but i haven’t got enough, and will I need to get more. Later I’ll hang more progress with this piece.

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2 Responses

  1. Jesus

    La temperatura de los motores nema no deberá de exceder los 80 grados centigrados, aunque es normal que la alcance en mecanizados 3D.
    Mecaniza unos pequeños disipadores y los atornillas en la parte trasera e instalale unos ventiladores de 12 o 24 v de pc orientados a los disipadores y walaaa no pasan de 45 grados en mecanizados de 8 horas en una nave de techo de chapa en verano, un saludo y espero haberte ayudado.

    • ostervi

      Muy buena idea! Si consigo trabajo como para tener que dejarla funcionando mas de una hora, ten por seguro que recurriré a lo que me dices. Gracias!