Round Top skis 19/20
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
Re: Round Top skis 19/20
Made my final pair of skis for this season over the weekend. This time a pair of powder skis with dimensions 140/109/123 over all length of 183cm. After the base/edge gaps from the last pair I was a little nervous about how these were going to turn out but after reading one of Vinman's posts about having to straighten the coiled edges I spent time making sure they were as straight as possible before bending them to shape. It seems to have worked as I had very minimal gaps and then only near the tip and tail at the serious curves.
That is not to say there were not some issues. I finally bought a temperature gun to see if the heat blanket control temperature match the actual temperature...turns out that the top blanket was showing 82 degrees on the PID but was in fact 97 when measured with the thermometer. I assume that the bottom blanket which was inside the vacuum was the same so now I will have to adjust temps by ~15 degrees so I am not totally over shooting the mark.
Once hit the 40 minute mark I turned off the heaters but left the skis under pressure for a couple of hours until they had cooled off to garage temps. Once out of the press and the flashing cut off (which with the excess carbon fibre was a lot tougher, I went through 2 jigsaw blades!) I had a final camber of 6mm (not what I was aiming for but better than 10mm), tip height of 50mm and tail height of 20mm. The skis weighed 1.905kg and 1.899kg so not bad really. Unlike the last pair the bases were also very flat which I also think was caused by the coiled edges not being straightened out before use.
The only serious issue with this pair is that one of the skis has a twist in it. I have not started to research why this might have happened but I am assuming that they might have been a little crooked in the press, or maybe it was the CF as I have not used full sheets of this stuff in the previous two pairs of skis.
Either way, they did turn out very nicely, unfortunately I will have to wait until next year to try them out.
ski build information:
cores: poplar/ash with white oak side walls
Thickness: 2.7/10.2/2.7
two layers of 22oz FG
two layers of 3K carbon twill
Camber: 6mm
dimensions: 140/109/123
That is not to say there were not some issues. I finally bought a temperature gun to see if the heat blanket control temperature match the actual temperature...turns out that the top blanket was showing 82 degrees on the PID but was in fact 97 when measured with the thermometer. I assume that the bottom blanket which was inside the vacuum was the same so now I will have to adjust temps by ~15 degrees so I am not totally over shooting the mark.
Once hit the 40 minute mark I turned off the heaters but left the skis under pressure for a couple of hours until they had cooled off to garage temps. Once out of the press and the flashing cut off (which with the excess carbon fibre was a lot tougher, I went through 2 jigsaw blades!) I had a final camber of 6mm (not what I was aiming for but better than 10mm), tip height of 50mm and tail height of 20mm. The skis weighed 1.905kg and 1.899kg so not bad really. Unlike the last pair the bases were also very flat which I also think was caused by the coiled edges not being straightened out before use.
The only serious issue with this pair is that one of the skis has a twist in it. I have not started to research why this might have happened but I am assuming that they might have been a little crooked in the press, or maybe it was the CF as I have not used full sheets of this stuff in the previous two pairs of skis.
Either way, they did turn out very nicely, unfortunately I will have to wait until next year to try them out.
ski build information:
cores: poplar/ash with white oak side walls
Thickness: 2.7/10.2/2.7
two layers of 22oz FG
two layers of 3K carbon twill
Camber: 6mm
dimensions: 140/109/123
Re: Round Top skis 19/20
hi!! nice job man, it looks great.
from the process i think we are handling quite similar way... just i was wondering how do you apply the heating blanket from the bottom of the base. it goes everything to the vacuum bag... so i can't imagine how you do it from the base of the ski. From top it's clear, that once the bag is closed you can apply this blankets from top... but the bottom from the sk?
that would help me a lot to figure out how to do it.
would you say that hot box would do the same if envolved system=?
thanks,
Sergi
from the process i think we are handling quite similar way... just i was wondering how do you apply the heating blanket from the bottom of the base. it goes everything to the vacuum bag... so i can't imagine how you do it from the base of the ski. From top it's clear, that once the bag is closed you can apply this blankets from top... but the bottom from the sk?
that would help me a lot to figure out how to do it.
would you say that hot box would do the same if envolved system=?
thanks,
Sergi
Re: Round Top skis 19/20
Hi Sergi,
Really sorry for the late response, I will blame the pandemic and the fact that once I built the last pair of skis I needed a year to ski on them before building more pairs.
So, adding heat in the press was pretty easy. I just drilled a hole in the table in front of the tip mold and passed the wires through. Then I filled the holes with silicone and I have not had any leaks yet.
Now, if you are also asking is this a good idea...I am reconsidering it. I press with a flat plate and was hoping to use heat to form the camber but I have discovered that the thermocouple that comes with the blankets is not accurate, or at least does not tell me what is happening in the middle of the blanket. All four skis I have made (I just pressed my first pair in 2 years last week, more on that later) have a whole lot of camber. for the 2 pairs I made specifically for groomed runs, spring corn and steeper chutes it wasn't a huge deal. The powder skis on the other hand...a 7mm camber not what I was aiming for. So for the next pair that I am in the process of making I will limit the heat from the bottom blanket to roughly 40c and generate most of the heat from the top blanket (I am still using Entropy CPM/CPS with an 82c curing temp).
Again, sorry for the long gap in updates I hope you were able to take the leap and start making skis.
Really sorry for the late response, I will blame the pandemic and the fact that once I built the last pair of skis I needed a year to ski on them before building more pairs.
So, adding heat in the press was pretty easy. I just drilled a hole in the table in front of the tip mold and passed the wires through. Then I filled the holes with silicone and I have not had any leaks yet.
Now, if you are also asking is this a good idea...I am reconsidering it. I press with a flat plate and was hoping to use heat to form the camber but I have discovered that the thermocouple that comes with the blankets is not accurate, or at least does not tell me what is happening in the middle of the blanket. All four skis I have made (I just pressed my first pair in 2 years last week, more on that later) have a whole lot of camber. for the 2 pairs I made specifically for groomed runs, spring corn and steeper chutes it wasn't a huge deal. The powder skis on the other hand...a 7mm camber not what I was aiming for. So for the next pair that I am in the process of making I will limit the heat from the bottom blanket to roughly 40c and generate most of the heat from the top blanket (I am still using Entropy CPM/CPS with an 82c curing temp).
Again, sorry for the long gap in updates I hope you were able to take the leap and start making skis.
Re: Round Top skis 19/20
After a 2 year gap I am making skis again. The first three pairs that I made on my new set up all had some issues but for the most part ski well and served as great learning opportunities. The first pair that I made I am still skiing on and they performed very well in the spring corn last May while on a 2 week trip through Colorado and Idaho. The second pair I used a different weight of carbon fibre which resulted in a pair that were way too stiff for my telemarking needs, I have given them to a friend to ski on and provide some feedback. The last pair were supposed to be powder skis but also way too stiff and the early rise tips did not rise enough for comfortable backcountry fun. The MDF tail mold also cupped due to the heat of the press resulting in a slight twist in the skis. These have been sent off to my brother who is bigger than me and skis resorts so he should be just fine with them.
The latest project was using the same powder ski template but different material. Now that the borders are opened again I can source much better fibre glass and carbon fibre (not to mention all the other stuff). I have also rebuilt the tip and tail molds out of plywood with a different geometry trying to get a better rise for tips and tails which I think I succeeded at. I also rebuilt the planer sled which I think resulted in better thickness control. So here is the run down:
Finished Length: 183
Dimensions: 143/111/123
Core: 2/10.5/2 mm
Core Material: Ash/Poplar with Ash side walls
Core length: 142.7cm
Core weight, 702 g and 706 g
Topsheet: Bubinga wood veneer
Ski weight: 1.940kg / 1.951kg
Boot centre = 54% of running edge of 135 which is 73cm
19oz Fibreglass
5.8oz Carbon fibre 0-90 Plain weave
Epoxy: Entropy CPM/CPS 2 cups/1 cup (way too much epoxy for this press)
Press time: 50m after the 82c was reached. Then the skis were taken out immediately but still resulted in too much camber
Resulting camber: 7mm
Tip rise: 50mm
Tail rise: 15mm
I was not happy with the camber but on the plus side the flex was really nice and smooth. As chance would have it the last big dump in Vermont was last weekend so my ski partners and I were out last Sunday searching for untracked snow. I took a chance with the new skis and was very happy with the way they skied. the front of the skis had a great flex which floated me up and the tails have a nice pop to get me in to the next turn. Helpful in the tight trees we were skiing. They will do nicely in rogers pass next week!
The latest project was using the same powder ski template but different material. Now that the borders are opened again I can source much better fibre glass and carbon fibre (not to mention all the other stuff). I have also rebuilt the tip and tail molds out of plywood with a different geometry trying to get a better rise for tips and tails which I think I succeeded at. I also rebuilt the planer sled which I think resulted in better thickness control. So here is the run down:
Finished Length: 183
Dimensions: 143/111/123
Core: 2/10.5/2 mm
Core Material: Ash/Poplar with Ash side walls
Core length: 142.7cm
Core weight, 702 g and 706 g
Topsheet: Bubinga wood veneer
Ski weight: 1.940kg / 1.951kg
Boot centre = 54% of running edge of 135 which is 73cm
19oz Fibreglass
5.8oz Carbon fibre 0-90 Plain weave
Epoxy: Entropy CPM/CPS 2 cups/1 cup (way too much epoxy for this press)
Press time: 50m after the 82c was reached. Then the skis were taken out immediately but still resulted in too much camber
Resulting camber: 7mm
Tip rise: 50mm
Tail rise: 15mm
I was not happy with the camber but on the plus side the flex was really nice and smooth. As chance would have it the last big dump in Vermont was last weekend so my ski partners and I were out last Sunday searching for untracked snow. I took a chance with the new skis and was very happy with the way they skied. the front of the skis had a great flex which floated me up and the tails have a nice pop to get me in to the next turn. Helpful in the tight trees we were skiing. They will do nicely in rogers pass next week!
Re: Round Top skis 19/20
I took my latest pair of skis out to the Canadian Rockies for a week long ski trip. My ski partner and I spent 3 days a sled accessible cabin south of Golden BC where we found powder every day. We then headed up into Rogers Pass to ski the Youngs Traverse and 7 steps of Paradise followed that the next day with a long tour up towards Vulture Peak off the Icefields Parkway. The new skis were awesome in the powder, soft enough to keep the tips up and when pressed really popped me out of my turns. Hardpack, not so much but they were not made for that.
Last weekend I pressed my 5th pair of skis. These are a copy of the first pair I made with my friend Oliver in Northern Vermont. I liked that first ski as they were just the right size and flexibility for skiing the tight trees we find in the backcountry up here in the north east. I have not skied them yet but I have high hopes. Here are the details.
Length: 174
Dimensions: 130/106/120
Core: 2.1/11.5/2 mm
Core Material: Ash/Poplar with Cherry side walls
Core length: 146cm this does not include the triangle sections tip and tail
Core weight, 703 g and 689 g
Topsheet: White Oak veneer
Ski1
1.704 grams
Tip rise 59mm
Camber 3mm
Tail rise 19mm
Ski2
1.725 grams
Tip rise 55mm
Camber 2.5 mm
Tail rise 21.5 mm
19oz Fibreglass
5.8oz Carbon fibre 0-90 Plain weave
Epoxy: Entropy CPM/CPS 1.5 cups/.750 cup (Just enough epoxy for this press)
I heated the press mostly from the top keeping the bottom blanket at 40c (according to the PID but it was probably closer to 56c in the vacuum) while the top blanket was set to 80c for the duration of the curing time which was 55 minutes. At that point I turned off the heat and kept the vacuum press running for another 2.5 hours.
I am happy with the tip and tail rise and especially the 2-3mm camber. It was exactly what I was aiming for. The differences in measurements is due to one ski shifting back slightly while I was applying epoxy and getting everything ready for pressing. So I will have to figure out an easy method to prevent this. I am thinking about hot gluing off cut base material at the tip and tail to stop the shift from happening. I also had issues with the edges at the tips and tails, which I think is due to poor bending, something else I am also going to have to work on over the summer.
Photos will be posted when they are back from the shop getting the bases and edges tuned.
Last weekend I pressed my 5th pair of skis. These are a copy of the first pair I made with my friend Oliver in Northern Vermont. I liked that first ski as they were just the right size and flexibility for skiing the tight trees we find in the backcountry up here in the north east. I have not skied them yet but I have high hopes. Here are the details.
Length: 174
Dimensions: 130/106/120
Core: 2.1/11.5/2 mm
Core Material: Ash/Poplar with Cherry side walls
Core length: 146cm this does not include the triangle sections tip and tail
Core weight, 703 g and 689 g
Topsheet: White Oak veneer
Ski1
1.704 grams
Tip rise 59mm
Camber 3mm
Tail rise 19mm
Ski2
1.725 grams
Tip rise 55mm
Camber 2.5 mm
Tail rise 21.5 mm
19oz Fibreglass
5.8oz Carbon fibre 0-90 Plain weave
Epoxy: Entropy CPM/CPS 1.5 cups/.750 cup (Just enough epoxy for this press)
I heated the press mostly from the top keeping the bottom blanket at 40c (according to the PID but it was probably closer to 56c in the vacuum) while the top blanket was set to 80c for the duration of the curing time which was 55 minutes. At that point I turned off the heat and kept the vacuum press running for another 2.5 hours.
I am happy with the tip and tail rise and especially the 2-3mm camber. It was exactly what I was aiming for. The differences in measurements is due to one ski shifting back slightly while I was applying epoxy and getting everything ready for pressing. So I will have to figure out an easy method to prevent this. I am thinking about hot gluing off cut base material at the tip and tail to stop the shift from happening. I also had issues with the edges at the tips and tails, which I think is due to poor bending, something else I am also going to have to work on over the summer.
Photos will be posted when they are back from the shop getting the bases and edges tuned.
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- Posts: 33
- Joined: Tue Jan 28, 2014 1:15 pm
- Location: Greenwater, WA
Re: Round Top skis 19/20
Just use 3m spray adhesive about 10 cm long under the waist of each base and stick it to the metal sheet that sits on top of your wood mold. They’ll pop right off after pressing - use a good mold release. Any adhesive grinds right off in the first pass. I struggled with the same issue!
Re: Round Top skis 19/20
Hmm, that is an excellent suggestion. I think I am using a good release paste but I will definitely try the 3M spray when I start building again. Thanks for commenting.Wvmtnbiker wrote: ↑Wed Oct 04, 2023 11:06 am Just use 3m spray adhesive about 10 cm long under the waist of each base and stick it to the metal sheet that sits on top of your wood mold. They’ll pop right off after pressing - use a good mold release. Any adhesive grinds right off in the first pass. I struggled with the same issue!
Re: Round Top skis 19/20
I have my 8th pair of skis done. This past winter in the North East was tough, the backcountry wasn't in but thanks to some free passes I was able to enjoy 3 days of skiing at Smugglers Notch with my normal backcountry partners. Skiing lifts for the first time in a long time exposed the problems with the first pair of skis I made. That the tips just do not provide any float and the large camber makes smearing turns much harder on teles.
So a redesign was in order. The new pair were designed for area skiing with side country and spring turns on corn snow. I have to say that I think this pair has turned out to be the best pair yet, at least in terms of finish and no obvious flaws. Nothing shifted in the press (more about that later) and even my first attempt at marquetry turned out not horrible.
Details
Length: 178
Dimensions: 124/94/111
Core: 2.3/11.6/2.3 mm
Core Material: Ash/Poplar with White Oak side walls
Core length: 130.5cm this does not include the triangle sections tip and tail
Core weight, 708 g and 692 g
Tip fill: 2.2 mm plastic - fill length is 26.3cm
Tail fill: 2.2 mm plastic - fill length is 21.3cm
Topsheet: Bubinga wood veneer with lightening bolt inlay
Ski1
1841 grams
Tip 60mm
Camber 3mm
Tail 17mm
Ski2
1822 grams
Tip 60mm
Camber 3 mm
Tail 17 mm
**** Boot centre = 52% of running edge of 130.5 which is 67.5cm from the widest part of the tip
19oz Fibreglass
5.8oz Carbon fibre 0-90 Plain weave
Epoxy: Cridel ER100 Resin and EH406 hardener. Used 400g of resin and 100g of hardener (Just enough epoxy for this press) I should have used an extra 100g/25g to be comfortable
I usually use Entropy epoxy but after 6 years the resin has hardened and I wasn't able to liquify it. The backup was the Cridel I had gotten from Ben in Mtl and it seems to have worked although I am sure I made some errors with weighing the hardener. Next time I will pour it into a secondary container instead of trying to get it right from the large container.
To solve the skis shifting in the press I actually crazy glued a small length of edge at the back of the mold so that I always knew where the tails had to be. It really helped as I was applying epoxy the bases were moving around. In the end it worked very well, I was worried that the edge would be permanently attached but I guess the heat released it during the press.
Also new for this pair was the inlay/marquetry. I had two short lengths of Bubinga leftover from the powder skis and figured I could use them for this build if I put in a maple inlay for the boot centre. Then I wondered how hard it would be to add a design hence the lightening bolts. They are not perfect but they do look pretty cool.
Now a question for those that have made it this far in the write up. How can I lighten up these skis? I have thought about making the cores thinner but I don't think that would shave any real weight off the skis. Lighter fibreglass? How would that impact the way the ski handles? I am just starting to investigate this topic but if you want to weigh in I would appreciate it.
So a redesign was in order. The new pair were designed for area skiing with side country and spring turns on corn snow. I have to say that I think this pair has turned out to be the best pair yet, at least in terms of finish and no obvious flaws. Nothing shifted in the press (more about that later) and even my first attempt at marquetry turned out not horrible.
Details
Length: 178
Dimensions: 124/94/111
Core: 2.3/11.6/2.3 mm
Core Material: Ash/Poplar with White Oak side walls
Core length: 130.5cm this does not include the triangle sections tip and tail
Core weight, 708 g and 692 g
Tip fill: 2.2 mm plastic - fill length is 26.3cm
Tail fill: 2.2 mm plastic - fill length is 21.3cm
Topsheet: Bubinga wood veneer with lightening bolt inlay
Ski1
1841 grams
Tip 60mm
Camber 3mm
Tail 17mm
Ski2
1822 grams
Tip 60mm
Camber 3 mm
Tail 17 mm
**** Boot centre = 52% of running edge of 130.5 which is 67.5cm from the widest part of the tip
19oz Fibreglass
5.8oz Carbon fibre 0-90 Plain weave
Epoxy: Cridel ER100 Resin and EH406 hardener. Used 400g of resin and 100g of hardener (Just enough epoxy for this press) I should have used an extra 100g/25g to be comfortable
I usually use Entropy epoxy but after 6 years the resin has hardened and I wasn't able to liquify it. The backup was the Cridel I had gotten from Ben in Mtl and it seems to have worked although I am sure I made some errors with weighing the hardener. Next time I will pour it into a secondary container instead of trying to get it right from the large container.
To solve the skis shifting in the press I actually crazy glued a small length of edge at the back of the mold so that I always knew where the tails had to be. It really helped as I was applying epoxy the bases were moving around. In the end it worked very well, I was worried that the edge would be permanently attached but I guess the heat released it during the press.
Also new for this pair was the inlay/marquetry. I had two short lengths of Bubinga leftover from the powder skis and figured I could use them for this build if I put in a maple inlay for the boot centre. Then I wondered how hard it would be to add a design hence the lightening bolts. They are not perfect but they do look pretty cool.
Now a question for those that have made it this far in the write up. How can I lighten up these skis? I have thought about making the cores thinner but I don't think that would shave any real weight off the skis. Lighter fibreglass? How would that impact the way the ski handles? I am just starting to investigate this topic but if you want to weigh in I would appreciate it.
Re: Round Top skis 19/20
Hi,
some things come to my mind regarding the weight:
some things come to my mind regarding the weight:
- I don't think your skis are heavy regarding their surface area. if you want to use it as touring skis, then yes, they are a bit heavy.
- You could try to add some lighter wood (e.g. paulownia) to your wood mix.
- Poplar soaks liquids quite well. In your layup process, you could wet the glass/carbon separately with just the amount of resin needed. My guess is tht the poplar soaked some of the excess resin
- Your tip and tail fillers are pretty long and plastic is heavier than wood. You could try to make your wood cores a bit longer into tip and tail - that should also increase vibration damping
- You could try to work with more carbon than glass. As carbon is about 2.5 times stronger then glass, you need less to achieve the same stiffness's. However, carbon has a totally different characteristic - glass makes a damp ride, carbon is "snappier" and makes a more agressive ride. For me, pure carbon is too agressive, I use it in combination with flax which adds great dampening to carbon.
Re: Round Top skis 19/20
Hi PMG,pmg wrote: ↑Thu May 09, 2024 8:16 pm Hi,
some things come to my mind regarding the weight:
- I don't think your skis are heavy regarding their surface area. if you want to use it as touring skis, then yes, they are a bit heavy.
- You could try to add some lighter wood (e.g. paulownia) to your wood mix.
- Poplar soaks liquids quite well. In your layup process, you could wet the glass/carbon separately with just the amount of resin needed. My guess is tht the poplar soaked some of the excess resin
- Your tip and tail fillers are pretty long and plastic is heavier than wood. You could try to make your wood cores a bit longer into tip and tail - that should also increase vibration damping
- You could try to work with more carbon than glass. As carbon is about 2.5 times stronger then glass, you need less to achieve the same stiffness's. However, carbon has a totally different characteristic - glass makes a damp ride, carbon is "snappier" and makes a more agressive ride. For me, pure carbon is too agressive, I use it in combination with flax which adds great dampening to carbon.
You raise some excellent points.
- Weight - I think you are correct, for the size of the skis they seem to be about average. These are meant for lift serve and spring tours for turns. As a telemarker I have been dealing with heavy gear for years so the skis are about right ;-)
- lighter wood - It has been suggested that I add paulownia to my cores but trying to find some in the lengths I need around here in Quebec is proving difficult, I think I will have to expand my search to include the north east USA as well. I assume these strips would replace some of the poplar but not all of it
- Epoxy take up - I apply my epoxy with a roller which uses far less epoxy than pouring it on and spreading with a squeegee. This results in minimal squeeze out on the sides but I see what you mean, I will see what I can do for the next pair.
- Tip/tail filler - I was wondering about this. I have not done an early rise ski like this using a ratio of tip length to ski and in the past I had always ended the cores at the widest point. For the next pair I will end the wood side walls at the widest points (tip/tail) but extend the cores well into the tip/tail area and just bring the plastic down the sides as a side wall
- Carbon - while using more of it in my skis would be an interesting experiment I still do most of my skiing in the backcountry so super stiff is not what I am looking for. I am intrigued by the flax, I have been reading about you guys using it for years but I have never seen it for sale in the usual places here in North America. What weight of flax do you use and what weight carbon do you use with it? I have other furniture projects this summer but would like to make another pair of these skis at the end of summer with the changes to see how they compare side to side
Re: Round Top skis 19/20
Hi,
I am always using a single layer of 300g/m² uni flax directly below the top sheet - this is how bcomp (the manufacturer of the flax fabrics I use) recommends it. It really has a great dampening effect like this.
The carbon I am using is differently from ski to ski, but mostly 300g/m³ triax with additional 320g/m² glass for increased torsional stiffness. In future builds, I will do a bit a different carbon setup: only 80g/m² uni and 240-300g/m² biax to further increase torsional stiffness.
With this numbers it is important to mention that I mostly build very sportive on piste skis with less than 85mm underfoot.
I am always using a single layer of 300g/m² uni flax directly below the top sheet - this is how bcomp (the manufacturer of the flax fabrics I use) recommends it. It really has a great dampening effect like this.
The carbon I am using is differently from ski to ski, but mostly 300g/m³ triax with additional 320g/m² glass for increased torsional stiffness. In future builds, I will do a bit a different carbon setup: only 80g/m² uni and 240-300g/m² biax to further increase torsional stiffness.
With this numbers it is important to mention that I mostly build very sportive on piste skis with less than 85mm underfoot.