Round Top skis 19/20

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Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

side wall glue up went well and so I sent them through the thickness planer on my cradle. I might have to run them through again as the cores are ~11mm thick in the centre with the tips being ~3mm. Unfortunately the depth gauge on the planer is in inches with only 1/8" gradient between them. So, not as precise as I would like.

Either way, edge bending and applying edges to base this weekend. then I have to make sure that plugging in two heating blankets and vacuum does not trip the breakers in the garage...

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Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

things are moving along. I have drilled the holes in the vacuum table to pass the wires from the heat blanket out to the power source. I then caulked the heck out of the wires/holes so I hope that they will hold up to the vacuum for the hour it will take to press the skis.

I have found a source for Entropy Epoxy, triaxial fibreglass, carbon fibre cloth and all sort of vacuum press supplies here in Canada. If you are interested in any of these materials I would check out Composites Canada. I have been dealing with JP and he has been very helpful with answering questions and getting me set up with my order.

I should be pressing my first pair of skis in the next week or two. Several large snow storms are heading our way so ski building will be on hold until the powder is gone.

Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

After a lot of procrastination and self doubt i finally sucked it up and pressed my first pair of skis on my own set up. While the skis didn't turn out 100% perfect I think for a first attempt on a new system all on my own i think it was a success and i learned a bunch of lessons along the way.

1. A big pain point was the "lid" of the vacuum table. It is basically a wood frame with the silicone blanket attached to it. It is not attached to the table so i have to lift it on and off while using it which results in too much time and opportunity for things to shift on the mold.
2. Do not cut all of the materials close to final size before pressing. While fiddling with the lid i must have shifted the veneer of one ski backwards so the tip of one ski has fiberglass exposed.
3. Regulate the temperature differential between the bottom heat blanket and the top blanket. I use a flat mold but still wanted camber so I was using a heat differential to achieve this result. For the first attempt a camber of 8mm might be a little excessive but this first pair will be used at the ski area so i am not too worried about it.
4. Mix up a little more epoxy at the start. I used a volume measurement for this pressing which seems to have worked out but it was a close thing at the end. I used 1 cup of resin and 1/2 cup of hardener for both skis, i used a foam roller to apply the epoxy which resulted in very little squeeze out but everything seems solid. I think next time i will use a little more epoxy just to be on the safe side.

I am sure there are other things I would do a little differently but on the while the whole process was pretty easy. I was worried about nothing.

So, I used the Entropy CPM with slow hardener, 22oz fiberglass and cherry veneer. The bottom heat blanket was set to 82 Celsius and the top was set to 45 celcius (the differential obviously too much). I held the heat for 60 minutes and then turned down the heat to 30 Celcius on both blankets and kept the skis under vacuum for another 2 hours just to be on the safe side. All of this resulted in a pair of flat skis with 8mm camber and a gentle early rise tip of 48mm. The final dimensions are 133-98-118, with this shape and camber they should be lively on the slopes...or really hard to keep in a straight line!

Bases in the mold:
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All clamped up and vacuum running:
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Fresh out of the press:
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Tip shape is looking good:
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mammuth
Posts: 436
Joined: Tue Oct 28, 2014 3:48 am
Location: somewhere in the alps

Re: Round Top skis 19/20

Post by mammuth »

Dont know the resin you use, but if it needs heat to cure you did create a half cured ski on one side (45 degrees....).

You dont necessarily lower the temp on one side to get camber, you can change your timing too. So one side kicks in and hardens up before the other side does.
Tom

Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

Darn it! I didn't even think about that which is causing me a little concern for their durability. However, I will get them tuned and mounted to see how they ski, they are my first pair made solo on my own set up so I certainly wasn't expecting a perfect pressing right off the bat (although secretly I was...). Plenty of mistakes and plenty of changes for the next pair.

So, for the heating I assume I should ramp up the bottom blanket to 82C (I am using the Entropy CPM/CPS combination) and then 10/15 minutes later get the top blanket up to 82 as well. I wonder how others with vacuum tables who only heat from the top time their process.

I guess I will do some more searching/reading on heat differential and timing as it relates to camber while I make changes to the set up and get the next set of cores milled up.

Jonrezz
Posts: 43
Joined: Thu Feb 13, 2020 1:14 pm

Re: Round Top skis 19/20

Post by Jonrezz »

Congrats on your first pair! they look great!

Did you perform the layup over the mold? I would recommend performing layup on a cassette on a flat surface, then transferring the whole thing to the mold once ready. I've tried it both ways and having it all flat while stacking the layers makes it so much easier to align everything. once it's all in the mold and you're ready to pull down, I'd just press the middle of the skis down with your hand to help everything stay in place until the bag pulls the tip and tail against the mold.

Looking forward to hearing how they ski!

Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

well, they are good from far but far from good 😁 I am sure they will ski just fine at least for this season. Even with all of the flaws in the ski it was good to get over my fear of messing up and just doing it.

I did the lay up in the mold. It was pretty straightforward really. I had bent tip and tails of the cores so that they laid pretty flat on the bases (which were also bent to shape). Although I am not sure how it happened but one of my side walls did not quite make it out over the edge so I have a pretty exposed edge on one ski. Since I tele this will be on the outside (as I said, if they last this season I will be happy).

I think that once I mount the lid for the table on hinges it will make keeping everything aligned much easier. Also not using parchment paper over the aluminum will help with that as well. I just need to get some release wax for the mold for the next pressing.

I will be dropping them off at the ski shop today for the tune and then I will wax and mount the bindings before trying them out this weekend, although I will have to see if my old skins will fit...but that is a problem for future Pat.

pmg
Posts: 465
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Re: Round Top skis 19/20

Post by pmg »

Hi,

regarding core shift during layout/pressing. My method to avoid this is as follows: I use 3 thumbtacks glued to the base to keep the core in position during layup. the core then can't move more than about 0.2mm without getting resistance from the thumbtacks.
Maybe this can help you to avoid that problem in future.

Image

Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

Thanks for the feedback, that is a really interesting idea! I suppose you have not experienced any issues with the tacks incorporated in the ski. Although I also assume you would have to create a small recess in the cores to account for the head of the tack. I will explore trying this in a future press.

Although I honestly don't know how this happened as I was using the 2 peg method to locate the cores on the bases, through all of my dry runs it looked good and if they shifted so far the ski should have been really out of shape, so it is a mystery at the moment. I am chalking it up to another lesson learned.

Either way, I am starting to implement some of the lessons learned and get set up for my next pair of skis.

pmg
Posts: 465
Joined: Sat Dec 01, 2012 8:59 am
Location: Sonthofen

Re: Round Top skis 19/20

Post by pmg »

Yes, a small recess for the thumbtack head is neccessary of course. I make this utterly simple: I take a 10mm wood drill but run it turning left (the way you would turn a screw out) so it does not really drill but just "smear" the wood of a bit.

Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

Another flaw and lesson learned from my first pressing. The centre of each topsheet seems to be crowned. I assume this means that the vacuum was not pulling enough or I did not use my j-roller aggressively enough to really flatten the skis. The bases are (surprisingly) over all very flat but the tops not so much.

Next time I will be clamping a steel platen on each ski to try and they them flat.

They are back from the ski shop with a nice tune and wax. I will start applying Spar Urethane to the skis tonight and they should be ready to ski by the weekend.

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chrismp
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Re: Round Top skis 19/20

Post by chrismp »

Wheatlpa wrote:
Wed Feb 17, 2021 1:06 pm
I assume this means that the vacuum was not pulling enough or I did not use my j-roller aggressively enough to really flatten the skis.
Did you put a breather fabric over the skis during pressing? Just asking because it's hard to tell from your pictures and this might be a reason for the lack of pressure in the middle of the skis.

Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

Yes, I had my skis in the press, then a sheet of perforated release film with the breather fabric on top. The breather fabric extended onto the table over the holes in the mold where the vacuum port is located. Oh well, I will pay more attention to the flatness of the top sheets when the initial vacuum is created. It seems like one ski is definitely more crowned than the other which is fairly flat aside from near the edges.

I weighed both skis last night before putting on the bindings this morning. one ski is 1.552kg and the other is 1.538kg. I don't think that is too bad for a first attempt.

I have coated them with a Spar Urethane and they look pretty good, I am only going with one coat because 1. I am impatient to try them out and 2. they are a beta test and so I don't know how they will stand up to skiing. I will be testing them out this weekend which should have some new snow and groomers which will put them through their paces.

Image

mammuth
Posts: 436
Joined: Tue Oct 28, 2014 3:48 am
Location: somewhere in the alps

Re: Round Top skis 19/20

Post by mammuth »

You created a resin trap. Topsheet folded over the side works good to keep resin trapped with vacuum ;) One solution is to have the fibres still sticking out so the resin can flow along the fibres to get sucked out.
Tom

Wheatlpa
Posts: 62
Joined: Fri Feb 12, 2016 11:14 am
Location: Sutton, QC

Re: Round Top skis 19/20

Post by Wheatlpa »

mammuth wrote:
Fri Feb 19, 2021 2:10 am
You created a resin trap. Topsheet folded over the side works good to keep resin trapped with vacuum One solution is to have the fibres still sticking out so the resin can flow along the fibres to get sucked out.
Ahh, that makes sense. The last pair I pressed were on a friend pneumatic press so we cut the materials very close to the final shape. For the next try I will leave a lot more on the sides. I also think I will have to use a little more epoxy for the lay up. I applied it all with a roller and so only used 1.5 cups of epoxy for both skis.

I did get to ski my new skis this morning. We have not had any new snow lately so I stuck to the freshly groomed trails. The skis carve really nicely, it has been a while since I have been on skis with this much shape so I had to adjust my stance. The rear ski did chatter a bit and they did get tossed around when I got into the refrozen ungroomed stuff so maybe not the best for eastern hard pack but they will probably handle spring snow and powder nicely.

Changes for the next version of these skis will include a couple of layers of carbon fibre to increase the torsional rigidity and maybe use maple and ash for the core instead of ash and poplar which will add some weight and stiffness. The camber is pretty high (8mm) so I will try and get that down to 4mm and see what these changes do.

On to the Mk-II version!

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