'Gamma SL', new design, hope to press mon, thoughts?
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
SCHÜSS: i've experience the warping a number of times. it is frustrating as you've experienced. sometimes during manufacturing the base material takes on residue stresses which cause subsequent warping when the material is cut, for example lengthwise in half. differences in temperature and also moisture can have an affect. one thing i do to minimize this is 'pre-cut' the material first. for instance, cut the outline of the shape of the ski, leaving about 12-25mm boarder around the true shape. let the material relax and warp (if it does) for a day or so. then do a final cut. this usually works. if not, then you'll end up with a pair of Kananas!
Either way you may get the distortion that Kam is talking about. I used a router on my last ski and will never do that again. I bleieve the heat generated from the cutting blade caused this. It also creates a BIG mess! If you do get some distortion like I did, I used my Wife's Hair dryer to heat the base and got it to "straighten out". While it was straightened out I clamped it and immeadiately attached the edges. This held the base in shape. I do not know about any undue effects this may have had but It seemed to work.
I would precut the base, let it "relax" then final cut taking my sweet time with the knife with many passes to cut the base material.
Good luck
krockaukum
I would precut the base, let it "relax" then final cut taking my sweet time with the knife with many passes to cut the base material.
Good luck
krockaukum
I think I have already post this but lets go for a reminder:
From my point of view and experiences, pre-cut the base is definitely a good way to minimize distorsion, but you can also add a thin layer (0.1 to 0.2mm) of fiberglass directly on the base before cutting it. The fiber glass will then stabilize the base during cutting and edges bonding.
This is also good to protect the base treatement, prior to edge bonding and final assembly.
I'm use to put a thin kevlar layer (60gr/m²) directly on the base. Cutting with a good knife is OK.
Hope this help ...
Kwetsor.
From my point of view and experiences, pre-cut the base is definitely a good way to minimize distorsion, but you can also add a thin layer (0.1 to 0.2mm) of fiberglass directly on the base before cutting it. The fiber glass will then stabilize the base during cutting and edges bonding.
This is also good to protect the base treatement, prior to edge bonding and final assembly.
I'm use to put a thin kevlar layer (60gr/m²) directly on the base. Cutting with a good knife is OK.
Hope this help ...
Kwetsor.
i fixed it! i used the hair dryer idea and straitend it out to our template. worked great.
however i think next time i will cut the base with the 25mm offset and then leave it for a day and cut the true shape again after that.
thanks for the help guys and i hope this helps other people with the same problem in the future.
schuss
however i think next time i will cut the base with the 25mm offset and then leave it for a day and cut the true shape again after that.
thanks for the help guys and i hope this helps other people with the same problem in the future.
schuss
SCHÜSS 2011
here are my experiences and thoughts:
i've cut base material using a number of different methods. for example, cutting lengthwise using a sharp utility knife or pair of scissors i've seen significant distortion as shown:
similarly with a router. one should try this experiment to see if distortion is a problem before cutting the final shape of the ski.
anyway, this suggests to me that it's not necessarily heat related, but more internal stress or similar. somehow during the manufacturing process the material was not given a chance to reach a stable configuration. i wish i was a polymer expert -- i'll ask someone at work for more insight. so after cutting and the material distorts, by applying enough heat the material continues to reconfigure and somehow returns to the right shape... interesting behavior if you ask me.
so what should we do? maybe it's in our best interest for now to pre-cut the material, then heat it with a blow dryer or heat gun to help stabilize it, then cut the final shape.
now that i have a heated press, i suppose i could find some mateial that's prone to distortion, then heat it with the press, let it cool down, and finally cutting it lengthwise to see if the heat helps to stabilize it...
SCHÜSS: what color was the base material that gave you problems?
i've cut base material using a number of different methods. for example, cutting lengthwise using a sharp utility knife or pair of scissors i've seen significant distortion as shown:
similarly with a router. one should try this experiment to see if distortion is a problem before cutting the final shape of the ski.
anyway, this suggests to me that it's not necessarily heat related, but more internal stress or similar. somehow during the manufacturing process the material was not given a chance to reach a stable configuration. i wish i was a polymer expert -- i'll ask someone at work for more insight. so after cutting and the material distorts, by applying enough heat the material continues to reconfigure and somehow returns to the right shape... interesting behavior if you ask me.
so what should we do? maybe it's in our best interest for now to pre-cut the material, then heat it with a blow dryer or heat gun to help stabilize it, then cut the final shape.
now that i have a heated press, i suppose i could find some mateial that's prone to distortion, then heat it with the press, let it cool down, and finally cutting it lengthwise to see if the heat helps to stabilize it...
SCHÜSS: what color was the base material that gave you problems?
It was the black 2001 ptex from snowboard materials . com. But like with out last ski it wasnt an issue at all. And with one of the skis for this project it was fine and the other went spaz and was out by a fair bit!
Using the heated hair dryer worked really well. Oh did i mention it warped with the edges attached!?! also it was sitting on a flat table. hmm.
For next time i think i will:
1. cut out bases with a 20mm perimeter
2. let it sit for at least 24 hours
3. i would only apply the heat from a hair dryer or a press for example if it did warp.. as i am paranoid that applying more heat to it will make it warp more and if its working ok in the first place then why change it?
any way for now problem is solved however it was a massive pain in the ass.
Also kam i agree, knowing what the plastic is actually doing (stretching, expanding etc) after you cut it would be great as we could prevent it!
With the many skis you have made, is it always an issue or just sometimes?
schuss
Using the heated hair dryer worked really well. Oh did i mention it warped with the edges attached!?! also it was sitting on a flat table. hmm.
For next time i think i will:
1. cut out bases with a 20mm perimeter
2. let it sit for at least 24 hours
3. i would only apply the heat from a hair dryer or a press for example if it did warp.. as i am paranoid that applying more heat to it will make it warp more and if its working ok in the first place then why change it?
any way for now problem is solved however it was a massive pain in the ass.
Also kam i agree, knowing what the plastic is actually doing (stretching, expanding etc) after you cut it would be great as we could prevent it!
With the many skis you have made, is it always an issue or just sometimes?
schuss
SCHÜSS 2011
I'm now using a pin router and a vacuum template to cut out my bases. It works very slick, however, I always 'sneak up' on the final cut with 2 or 3 intermediate cuts. Like bigKam indicated, when I, too, initially cut the material in half with scissors or a knife, the material goes a little whacky. I've done a lot of research regarding flame treating methods, and I just don't think that there is any way around having a bit of post-treatment residual internal tension in UHMW that is only 1.6mm thick. The big expensive flame treating machines use water cooled rollers right under the burner stations in an effort to keep the UHMW material as cool as possible during flame treatment. Some of us have seen how the heat from a hair dryer makes the base material squirm... imagine what it does under exposure to a really hot direct flame. So, I really think that internal stress is just something that we have to learn to deal with because I don't think it can be completely eliminated.
When I say that I 'sneak up' on the final cut, I mean that I first cut the 32cm wide raw material down the middle, then clamp it to the template and take a cut that is about 20mm's larger than the final cut. Then, I release the material from the template to let it readjust itself, then re-clamp and and take a cut that's about 10mm's larger than the final cut. Releasing the material from the template between cuts is really important. Sometimes I make a longitudinal center line on the base material before I start the shaping process, then watch the center line after each cut... the center line moves around quite a bit, but less and less with each successive cut. After my final cut, I remark the center line so that I can monitor for warping over time if I don't get around to laying up the ski for awhile. I've really never experienced any warping of the final base after using the 'sneaking up' process. It's a bit time consuming, but if the builder gets creative with quick-change guides/spacer blocks with their particular cutting method, a straight base can be cut out in 3 or 4 minutes. Before I built my pin router, I used interchangeable router guide bushings and they worked really well. With the pin router, I just have little spacer blocks that drop into the router table and function to hold the template away from the cutter the desired distance. The vacuum template is foot actuated, so I just step on the pedal to release pressure, then step on it again to pull the vacuum.
G-man
When I say that I 'sneak up' on the final cut, I mean that I first cut the 32cm wide raw material down the middle, then clamp it to the template and take a cut that is about 20mm's larger than the final cut. Then, I release the material from the template to let it readjust itself, then re-clamp and and take a cut that's about 10mm's larger than the final cut. Releasing the material from the template between cuts is really important. Sometimes I make a longitudinal center line on the base material before I start the shaping process, then watch the center line after each cut... the center line moves around quite a bit, but less and less with each successive cut. After my final cut, I remark the center line so that I can monitor for warping over time if I don't get around to laying up the ski for awhile. I've really never experienced any warping of the final base after using the 'sneaking up' process. It's a bit time consuming, but if the builder gets creative with quick-change guides/spacer blocks with their particular cutting method, a straight base can be cut out in 3 or 4 minutes. Before I built my pin router, I used interchangeable router guide bushings and they worked really well. With the pin router, I just have little spacer blocks that drop into the router table and function to hold the template away from the cutter the desired distance. The vacuum template is foot actuated, so I just step on the pedal to release pressure, then step on it again to pull the vacuum.
G-man
SCHÜSS, I had the same problem with the same material and supplier, and didn’t discover it until after the edges were attached. If I had finished the skis they would have turned left different than right. When I put the bases together and held the tips even the tails were 1-1 ½” apart. Like you I cut out the base several weeks before I attached the edges and I had cut out the bases for the second pair and they warped too. I thought I had a total loss.
When I made the patterns for the skis I made them to the finished size of the ski minus the width of the edges, and found that my first attempt was not straight. If I continued I would have made some Kanana’s… that is if I had the presents of mind to flip the pattern to make the second ski (not likely knowing me). So I started over. Since I have no CNC equipment and am too cheap to pay some one to do it I make the parts by hand. The only way I could figure out how to get my symmetry right was to make two patterns for the same ski. That way I could flip the parts to check. That gave me two patterns for the same ski which I used to clamp the base between and cut out my shape with a Roto zip and a dry wall flush trim bit.
Here is how I saved the base parts.
Line up one base on the pattern with the TFG side up with the centers even and the base flush with the pattern at the center. Don’t worry about the warp yet. Just make sure the centers of the base and the pattern are aligned and the base is flush to the edge of the pattern.
Put the second pattern on top off set so the edges can be glued on and clamp in the center to a table.
Move to one end and line up the base to the bottom pattern and clamp.
Go to the other end line up the base to the pattern and clamp.
Now the base should be lined up and matched to the bottom pattern, and you can spot glue the edges in place on one side. Flip everything around and do the other side. The edges held the base straight until I was able to press the skis several weeks later. I had to pull the edges off of the first set of bases with a putty knife and clean up the CA glue spots.
On my next pair of skis I did what Kam suggests and cut out the parts big, let them relax, cut out the final shape and still did the steps above to be sure that they were straight.
Hafte
When I made the patterns for the skis I made them to the finished size of the ski minus the width of the edges, and found that my first attempt was not straight. If I continued I would have made some Kanana’s… that is if I had the presents of mind to flip the pattern to make the second ski (not likely knowing me). So I started over. Since I have no CNC equipment and am too cheap to pay some one to do it I make the parts by hand. The only way I could figure out how to get my symmetry right was to make two patterns for the same ski. That way I could flip the parts to check. That gave me two patterns for the same ski which I used to clamp the base between and cut out my shape with a Roto zip and a dry wall flush trim bit.
Here is how I saved the base parts.
Line up one base on the pattern with the TFG side up with the centers even and the base flush with the pattern at the center. Don’t worry about the warp yet. Just make sure the centers of the base and the pattern are aligned and the base is flush to the edge of the pattern.
Put the second pattern on top off set so the edges can be glued on and clamp in the center to a table.
Move to one end and line up the base to the bottom pattern and clamp.
Go to the other end line up the base to the pattern and clamp.
Now the base should be lined up and matched to the bottom pattern, and you can spot glue the edges in place on one side. Flip everything around and do the other side. The edges held the base straight until I was able to press the skis several weeks later. I had to pull the edges off of the first set of bases with a putty knife and clean up the CA glue spots.
On my next pair of skis I did what Kam suggests and cut out the parts big, let them relax, cut out the final shape and still did the steps above to be sure that they were straight.
Hafte
On my first pair I had base warpage issues. To make the skis the sape I wanted. I built a lot of alignment blocks into my mold. I then forced the base into the right shape. I ended up putting 3 screws through my whole layup to force them to lay flat. I then ended up with three holes through each ski. Messy, very messy but it worked.
I came up with this solution having done similar things at PMGear. We had terrible trouble with warped base material. Bases that were out of alinment by less than 1" over their lenght I would supper glue into the mold. 175 degrees F and 100psi would force the base flat and true. But they would be a real pain to lay up with the base refusing to lay flat.
I came up with this solution having done similar things at PMGear. We had terrible trouble with warped base material. Bases that were out of alinment by less than 1" over their lenght I would supper glue into the mold. 175 degrees F and 100psi would force the base flat and true. But they would be a real pain to lay up with the base refusing to lay flat.
hafte's post reminded me of something. Most of my templates are made from 1/2" MDF and I've noticed that, over time, all of them have warped at least a little bit. It took a while for me to realize this because the only good way to check for ongoing straightness of a template is with a really accurate straight edge, and an accurate 6 foot long straight edge is kind of difficult to find. My vacuum driven base template is beefed-up with some square steel tubing to help keep it straight.
I finally found an accurate 6 foot straight at Lowe's, but I had to check through the pile to get a couple of the straightest ones. Prior to finding the straight edges, I'm sure that I made a few kananas. They still skied fine, though.
G-man
I finally found an accurate 6 foot straight at Lowe's, but I had to check through the pile to get a couple of the straightest ones. Prior to finding the straight edges, I'm sure that I made a few kananas. They still skied fine, though.
G-man