Keeping your skis symmetrical is, not quite but, almost impossible.
I make a pattern out of thin hard board. This gets sanded and shaped until its as close to perfect as it can be.
Then I pick 1 side edge and mark it (so I can remember which one I liked the best)
This gets screwed to a piece of 1/2'" MDF tip, tail, and center.
I trace it with the router then flip the pattern over, screw it using the same screw holes and trace it with the router again.
This should give you a fairly symmetrical template.
Now mark 1 side #1, the other #2.
Bend edges to side #1 and mark them #1
Bend edges for side #2.
Now when I cut my base I cut side #1 glue on edges #1 and put in the mold.
Flip the template over cut base #2 glue on edges #2 and this goes in the mold.
This way even if I get a bit of a banana ski the bananas are symmetrical.
Lots of typing to explain what I think is a pretty simple solution.
Hope this makes sense!
sam
Cutting base material - ptex
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
My method to achieve almost perfectly symmetrical skis is to make my P-tex templates perfectly symmetrical and keep the P-tex material attached to both sides of the template during edge attachment, and up until the ski building session.
First I create a master template from ¼” MDF and only shape one side of the ski, keeping the material about 25cm wide to prevent short-term warping. Then I use this master to cut both sides of my p-tex template using the exact same curve for both sides, similar to Sammer's method. Then I attach both edges simultaneously to one ski base and then the other, keeping the process symmetrical.
My P-tex templates are made from a sandwich of MDF and hardboard with fiberglass and epoxy in between. There is very little chance that these will warp over time. I’ve measured their straightness using my seven foot true bar (2" x 2" x 1/8” wall aluminum square tubing) and found my templates and resultant skis are symmetrical within the accuracy of my digital calipers.
-S
First I create a master template from ¼” MDF and only shape one side of the ski, keeping the material about 25cm wide to prevent short-term warping. Then I use this master to cut both sides of my p-tex template using the exact same curve for both sides, similar to Sammer's method. Then I attach both edges simultaneously to one ski base and then the other, keeping the process symmetrical.
My P-tex templates are made from a sandwich of MDF and hardboard with fiberglass and epoxy in between. There is very little chance that these will warp over time. I’ve measured their straightness using my seven foot true bar (2" x 2" x 1/8” wall aluminum square tubing) and found my templates and resultant skis are symmetrical within the accuracy of my digital calipers.
-S
This is a possible option:
The uhmwpe is screwed to the blank and the desired pattern is cut using a bearing flush trim bit. Putting a paper template on top of the blank and screwing the strip on top will work and retain a good level of accuracy. Little or no finishing is required, although a much longer piece of PE would be better. If not PE, then a strip of soft wood. Flip like Sammer and SHIF suggest.
To get the tips right, you can do something like this - just do it over and around the tips with the paper template beneath:
viewtopic.php?t=2405&postdays=0&postorder=asc&start=45
Laser cutting the template is also a good and cheap alternative - I have found it be to be cheaper than CNC. I had an issue with the bearing on the cutter creating a groove in the template over time, so it eliminates this problem too:
viewtopic.php?t=3126
3mm mild steel
If you have the time, making a pre-mold for appling the edge might help with the base warp - the second revision was made using the PE strip (scroll down the tread). Holding the ptex in place using perm peel double sided tape may help with any residual problems.
Hope some of this helps - I have a tendency to over complicate!
The uhmwpe is screwed to the blank and the desired pattern is cut using a bearing flush trim bit. Putting a paper template on top of the blank and screwing the strip on top will work and retain a good level of accuracy. Little or no finishing is required, although a much longer piece of PE would be better. If not PE, then a strip of soft wood. Flip like Sammer and SHIF suggest.
To get the tips right, you can do something like this - just do it over and around the tips with the paper template beneath:
viewtopic.php?t=2405&postdays=0&postorder=asc&start=45
Laser cutting the template is also a good and cheap alternative - I have found it be to be cheaper than CNC. I had an issue with the bearing on the cutter creating a groove in the template over time, so it eliminates this problem too:
viewtopic.php?t=3126
3mm mild steel
If you have the time, making a pre-mold for appling the edge might help with the base warp - the second revision was made using the PE strip (scroll down the tread). Holding the ptex in place using perm peel double sided tape may help with any residual problems.
Hope some of this helps - I have a tendency to over complicate!
I think sammers method would work best for me but it might have to wait until the next round of building as I already have my MDF templates made. I usually have a paper temples printed out in full length and them use spray adhesive to stick it to the MDF. I then rough cut it with the jig saw and shape it with a sander down to the line on the paper.
I think making the single sided hardboard pre-template and the cutting the MDF with that seem like it would be very good.
Guess for this pair I'll just have to measure better.
I think making the single sided hardboard pre-template and the cutting the MDF with that seem like it would be very good.
Guess for this pair I'll just have to measure better.
Fighting gravity on a daily basis
www.Whiteroomcustomskis.com
www.Whiteroomcustomskis.com
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skidesmond
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Vinman- Getting the template symmetrical is only part of the problem, even if you have a CNC template. I'm going for CNC from now on just to alleviate 1 headache. But I made my last template in the same manner as you did and everyone else. It takes patience.
Also make sure the edges fit along the p-tex w/o any stress. Otherwise the edges can pull the p-tex out of shape. I had 2 bases symmetrical, attached the edges. The next day when I went to press the middle was about 2 mm off but only on 1 ski. I tore of the edges, re-shaped the metal edges and re-attached. They were fine after that.
Also make sure the edges fit along the p-tex w/o any stress. Otherwise the edges can pull the p-tex out of shape. I had 2 bases symmetrical, attached the edges. The next day when I went to press the middle was about 2 mm off but only on 1 ski. I tore of the edges, re-shaped the metal edges and re-attached. They were fine after that.
Last edited by skidesmond on Fri Aug 19, 2011 3:04 am, edited 1 time in total.
Yes I think edge tension might have been an issue for me also. On my nephews ski the base is nearly perfect and then after putting the edges on it was way out of shape. I've done exactly what you did. I peeled the edges off, cleaned up the CA glue leftovers, rebent the edges to fit better and I'll re-edge the bases tomorrow. Hopefully this will take care this pair at least.
Fighting gravity on a daily basis
www.Whiteroomcustomskis.com
www.Whiteroomcustomskis.com
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MontuckyMadman
- Posts: 2395
- Joined: Fri Jun 20, 2008 9:41 pm
I cnc my base on a drag knife cutter and clamp it to the cnced template immediately.
this last round I had some warping. Worse than I have seen. I attached the edges to a cnced template like shif mentioned but one ski was wayyy askew, like several cm off in the tip.
I was unsure what to do but as I drove around with the skis clamped in alignment on the template in my car in the heat, when I took them off after they cooled they were back aligned again.
there was still some warpage so I made a simple cassette system on my AL sheet.
I laid the template down and hot glued thin pieces of wood that were the same thickness as the base with edge to my AL sheet.
So when I dropped the edged base on there it straightened the base into true.
Very easy and basic and is reusable for any ski you have an accurate template for.
this last round I had some warping. Worse than I have seen. I attached the edges to a cnced template like shif mentioned but one ski was wayyy askew, like several cm off in the tip.
I was unsure what to do but as I drove around with the skis clamped in alignment on the template in my car in the heat, when I took them off after they cooled they were back aligned again.
there was still some warpage so I made a simple cassette system on my AL sheet.
I laid the template down and hot glued thin pieces of wood that were the same thickness as the base with edge to my AL sheet.
So when I dropped the edged base on there it straightened the base into true.
Very easy and basic and is reusable for any ski you have an accurate template for.
sammer wrote: I'm still a tang on top guy.
I was able to re-edge the base I previously thought I screwed up and it now fits the core nicely with room to spare. Thanks for the help guys.
Fighting gravity on a daily basis
www.Whiteroomcustomskis.com
www.Whiteroomcustomskis.com
I think what skammy does is the way to go. You cut the base on the template and keep it in place with vacuum while you put the edges on. This is like on3p and I think moment also.
I have a vacuum hold down template, but then shift the cut base to an identical island template for edging. I never noticed any issue til the last pair. It was a nice day so I worked outside. The base was purple and heated in the sun. I cut the base out then moved it to the edging station which was in the shade. The base was about 4mm too short and a bit bent so it didn't line up with the edging template. Thought I'd stuffed it. But, then I moved the edging template back into the sun and like magic it expanded back to correct length and shape. I edged it and hopefully they will be ok. Looked ok once superglue was dry and I undid the clamps to stick it down to the cassette. I'm a little worried what happened after I took the edged base out of the sun (shrink again), but I left it clamped inside while any contraction would have occurred. Then again once it goes in the press it heats up again so really how much control do I have without a real cassette?
I think I learned the lesson that you should try and do base cutting and edging in as controlled a temperature as you can, regardless of how nice a day it is outside!
I have a vacuum hold down template, but then shift the cut base to an identical island template for edging. I never noticed any issue til the last pair. It was a nice day so I worked outside. The base was purple and heated in the sun. I cut the base out then moved it to the edging station which was in the shade. The base was about 4mm too short and a bit bent so it didn't line up with the edging template. Thought I'd stuffed it. But, then I moved the edging template back into the sun and like magic it expanded back to correct length and shape. I edged it and hopefully they will be ok. Looked ok once superglue was dry and I undid the clamps to stick it down to the cassette. I'm a little worried what happened after I took the edged base out of the sun (shrink again), but I left it clamped inside while any contraction would have occurred. Then again once it goes in the press it heats up again so really how much control do I have without a real cassette?
I think I learned the lesson that you should try and do base cutting and edging in as controlled a temperature as you can, regardless of how nice a day it is outside!
Don't wait up, I'm off to kill Summer....
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East Mountain Woodworking
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- Joined: Mon Nov 07, 2011 8:44 am
I'd take a picture but I don't have my stuff at home..