Detailed documentation of my next build

Document your personal work here. Show photos, movies, and share your secrets.

Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp

pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

Idris wrote:Very tidy looking work there pmg, I'm impressed.
My workshop definitely is not :) Always have to do a thorough cleaning before layup to get rid of all the dust that assembles.
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

A lot of planer work

So, using the planer to bring the cores to their final thickness is the next task.
Like all other I use a selfmade negative profile thingy. It is basically a solid bottom part, variable distance pieces and a wooden plate on top. In this picture, you can see several of the distance pieces with their numbers (height in mm). In the middle of the ski, there are some "0" distance pieces.

Image


So for this ski, I was aiming for a 2,5 - 12,5 - 3 shape. As the planer always messes up the first and last 5cm, I need some extra wood at the tip and tail, so the core itself is planed nicely. Well, I just use the sawn off pieces of the core (they are fixated by double sided tape):

Image


The first 2/3rds of the planing are done just like this. Some chips get under the middle of the core, but I don't care for now - precision comes at the last few mm.
About 2/3rds of the planing done - see how the first 5cm are messy:

Image


When its time for precision, I attach the core to the wooden plate with double sided tape. I am aware that the double sided tape is about 0.1mm thick, well - I really don't care about this :)

Image


Some passes later (at the last 3 I only take away very little material, like 0.2mm per pass) the core is finished:

Image


The same is done with the second core of course, and: the sidewall pouring mold. It is planed to the same thickness as the core:

Image


Here you can see that its not perfectly even. Must be because the 6mm plywood on the bottom hasn't the same thickness everywhere. I did some quick sanding after taking this picture to even it. (it was a 0,2mm difference).
For the next mold that gets planed I will change my sequence: planing the top part first, and then gluing together all 3 parts. Well, always improving.

The result of this ski so far: A big bag full of wooden chips.

Image
Last edited by pmg on Fri Sep 26, 2014 2:16 pm, edited 1 time in total.
OAC
Posts: 961
Joined: Thu Jul 23, 2009 9:34 am
Location: Sweden
Contact:

Post by OAC »

Nice work and journal! This must be a very expensive ski in terms of labour. :)
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

@OAC:
Yes, it is a lot of work, but as it is a hobby aiming to give me good skis to ride on, why noit? If I was trying to sell the skis I would surely try to keep it less time-consuming.
On the other hand, it is the first time I built this ski model. If I do it again, it will be way less work: templates done, pouring mould done... saves at least 1/3rd of the total time if not more. Guess its more like 2/5th.
the.quass
Posts: 122
Joined: Mon Mar 04, 2013 12:02 am
Location: Melbourne, Australia

Post by the.quass »

Looking forwards to seeing the pouring mold!
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

Pouring the sidewalls - Preparation

Tomorrow will be pouring day. So I did the preparations today.

The wood cores have to be sealed so the PU does not react with the humidity in the wood. I seal the whole core so no silicone from the mold release agent gets into the wood. For sealing, I use epoxy:

Image


The mold is also coated with epoxy. Afterwards, release agent is applied to the mold. Then, one core is pressed on the mold using the 15mm thick plywood that I cut out of the top mold plate:

Image


A closeup of the ski end:

Image


So, tomorrow we will do the pouring. the process is simple: Taking the needed amount of Task 12, put some black color in part B, degas both parts in vacuum, mix the parts, degas the resin for about 16 minutes. This will leave us 4 minutes to pour the PU properly.
We - yes, a friend will help me. As I want the PU to be in vacuum for as long as possible, 2 persons pouring will reduce the time the pouring itself takes. At the first ski, I will try 16 minutes from starting mixing to starting pouring, if everything is easy, I can increase the time before pouring starts.
User avatar
falls
Posts: 1458
Joined: Tue Oct 27, 2009 5:04 pm
Location: Wangaratta, Australia

Post by falls »

Do you just rely on the viscosity of the PU to match the thickness of the core when you pour it? It seems if your pouring mold has been profiled to the core shape the the PU wouldn't be able to level out.
I guess I will wait for the next update and see :)
Don't wait up, I'm off to kill Summer....
User avatar
chrismp
Posts: 1443
Joined: Fri Feb 13, 2009 9:00 am
Location: Vienna, Austria

Post by chrismp »

Looks like he's clamping it down onto the router sled. That should make the top surface level again.
User avatar
falls
Posts: 1458
Joined: Tue Oct 27, 2009 5:04 pm
Location: Wangaratta, Australia

Post by falls »

I see. Thanks
Don't wait up, I'm off to kill Summer....
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

chrismp wrote:Looks like he's clamping it down onto the router sled. That should make the top surface level again.
100 points for you :)

Haven't been able to pour yet, was away for a good week. Hope to find the time for it tomorrow.
Last edited by pmg on Tue Oct 14, 2014 12:53 pm, edited 1 time in total.
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

Pouring the sidewall

For this ski I tried Smooth on Task 12 as sidewall material. Lets see how it performs on snow. Regarding pouring I can say that its quite a ****, as it is much more viscous than the other PU's I have tried so far. But the cured resin is really nice in terms of destruction.

So, lets have a quick look at some of the pouring equipment:

Image


From left to right you see the vacuum pump built into an old computer case, my selfmade degas pot, mixing pots and the 2 pouring "bins".

I don't have any pictures of the pouring, because we did it as fast as possible. So let's describe it:
The correct amount of part A and part B are put separately into mixing pots, and black colour is added to part B. Then, the 2 parts are degassed: They are put in the degassing pot and vacuum is applied (the bubbles get very big and "explode").
Then the 2 parts are thoroughly mixed and then put into the pouring bins. These are put into the degassing pot again and the resin is being degassed for about 12 minutes before pouring.
And then, pour it before it cures :)

After pouring, it looks like this:

Image


By using a torch to remove surface bubbles, I was able to get a nice result.
After pouring and curing, the extra PU on top is removed. I use one of my absolute favourite tools for this: a stanley surform tool. I do this before taking the core out of the mold:

Image


Taking the core out of the mold work very easy thanks to the beveled mold sides. The first mold I built had straight sides, it was quite some work the get the core out.
After a bit of work on top and on bottom as well the cores are finished:


Image
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

Pressing preparation - adjusting the press mold

We use an adjustable mold, as we are still quite new to skibuilding and try a lot of different stuff. Lets have a look at it:

Image


Its basically a thick plywood board as bottom, and on top there is a tip shape (in the left foreground) and another plywood board for the whole camber section. While adjusting the mold, the bottom board is screwed on 2 thick pieces of wood. The reason for this is that the camber would pull the bottom board up a bit and make everything unprecise. With the 2 thick wood pieces the bottom board stays flat - as it will be in the vacuum press later.

So, the first real working step is to determine the middle of the ski. I have a look how I want the tip to be by pressing down the base with the edges:

Image


So I know were exactly the middle of the skis will be - lets mark it:

Image


Now its time for the camber. What I do (and forgot to take proper pictures) is to put a distance piece under the middle and screw down the ends of the plywood board. But not just the end, I do it on several points until the plywood board has the camber/rocker shape I like to have:

Image


When this is the way I want it, its time to add a lot of distance pieces under the plywood board. I just put them in carefully until they stick:

Image


(in this picture you can see that the board is held by screws in several places)
When they are put below the plywood board and fixed with some gaffa tape it looks like this:

Image




Attaching base and core

I use simple hardboards where everything is put on:

Image


The base is attached to the hardboard with a method I use for the first time with this ski - lets see how it works.
I use some spare pieces of base, attach them to the lower side of the base with some gaffa tape and screw it into the wood:

Image


Then the core is put on top. I take great care that base and core are aligned precisely:

Image


Time for the 4 noses on each core: they are used for keeping the core in place. They are screwed down, and I form a "notch" for each nose with hot glue. This keeps them in place quite exactly:

Image


The release agent I use is quite simple: wrapping foil. Its attached to the hardboards:

Image


When all this is done, I put everything back on the mold to see if everything works as I want:

Image
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

Layup and pressing the ski

today was pressing day. I didn't take any pictures because I did the layup alone and didn't want to take the camera with the gloves full of epoxy.
I used triax carbon (450g/m²) as fibres. The top is done with a thick layer of fabric with a nice imprint. I mixed 800g of resin for the ski (dimensions: 185 long, 132-98-120), could have done with 100g less.

There are only 2 pics:

The workshop right before layup. base and cores were cleaned carefully. After putting everything in place like this, I started to mix the epoxy.

Image


And a view into the press. It is a vacuum press with a heat box on top. you can see both in the picture:

Image


I use a very slow curing epoxy to ensure even temperature distribution through the ski. The good thing about the slow curing epoxy is that there is lots of time for the layup - no need to hurry.
Tomorrow or on sunday I will see if everything went as planned - thats the time I like and hate about ski building the most - not knowing for sure if the ski will be the way you want it to be.
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

Had a look at the pressed ski yesterday - unfortunately no pics, because I lent the camera to a friend for a week.

My method of holding base and core in place really worked well, its set up quite quick and obviously reliable. Will keep in doing it like this in future.

Though without picture, the next step is:


Sealing the surface

This is a real hard part: The ski is out of the press, and I want to cut it out right away. BUT: The uneven surface after removing the peel ply is tricky. Carbon dust gets in there so deep it stays, and all the nice colours are darkened. So it's time to be patient and put some finish on the surface. I just put an epoxy coat on top. Not a perfect solution, but the best I had at hand.
Tomorrow its finishing time, can't wait to see the final result.
pmg
Posts: 479
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Post by pmg »

Finishing the ski

First, lets have a look how the skis look fresh out of the press:

Image


IMO one major issue with finishing a ski is the glass/carbonfibre dust flying around everywhere. So I built some small helpers that clean most of it away during finishing.

First, the jigsaw is used. Would love to have a bandsaw, but I don't. I built the jigsaw into the table with an attachment for the vacuum cleaner:

Image


In the table:

Image


Skis after cutting them out roughly:

Image


Now its time for my favourite tool: My belt sander built in the table. The vacuum cleaner attachment works damn well, hardly any dust escapes it:

Image


In the table:

Image


All excess material grinded away at a 90° angle:

Image


Last, the sides are beveled using the router. I use a self-built depth setting (the 2 screws in the white plastic block). Like this I can set exactlx how deep the router cuts into the sidewall.
The half round wood is really handy, especially when having a camber ski. No need to press down the camber thanks to that small piece of wood.

Image


So, the skis came out the way I wanted, but there is always a BUT, isn't there? In this case I was a bit too eager to finish the ski and sanded the tips a bit too hard, causing the edges to overheat and delaminated a bit... damnit! Well, first aid is a re-glueing of the tips, but that won't hold forever. So I will build a tip protection that also holds everything together. In general, for the next ski I will either pre-bend the edges vertically or flame them in the tip area, so they loose all their tension and stay in the shape the mold gives them.

Here's a pic of the re-glued tips:

Image
Post Reply