Ski Builders Forum

I'm vacuum bagging my first pair -- can hear the pump running in the basement as I type....anyhow, was wondering if I can trim them as soon as I'm done pressing, or whether it's better to wait a day or two to make sure curing is complete and any warping or relaxation less likely. I'm pressing both skis at the same time as a single unit (2 bases on one double-wide core etc.). The room is at 80-85 F and they'll have been in the press for 38 hours (more than QCM recommended, but figured it couldn't hurt...).

Scott

Hey Scott
Jury is divided on this issue.
Conventional wisdom is to let them sit for a while (up to a week), but others on here have trimmed them pretty soon after pressing and encouraged people to do this (sometimes I think they just want to see the finished skis posted up )
Anyway if you have the time to let them sit for a few days then I would suggest you do it.
In a lot of the professional production outfits they seem to have racks where they let them sit for a while at least.

I'd say the longer the better.
Unless you can get some heat into them it could take a week or so at room temp for the chains to fully develop.
At least this is my belief, someone please correct me if I'm wrong.

sam

Thanks Falls. Got the time, just impatient to show them off!.... I'm curious, though, how waiting could be detrimental.

Took the skis out of the press this morning and, before trimming etc., would give myself a B+, I think. Made one bonehead mistake....there were a couple splits in the veneer I'm using for a top-sheet and I covered them over with packing tape just to keep them from spreading. Unfortunately, I didn't think things completely through and make sure that the taped side was up when it went in to the press...consequently, the tape didn't allow the epoxy to soak into the veneer in a couple spots which are now a much lighter color than the rest of the top.

Also, I have a few air bubbles under the bases, though not where I would have expected. The bubbles (and it's consistent for both bases) are around the center of the skis, both lengthwise and widthwise. I was expecting any bubbles to be along the edges and more likely at the tip or tail. Is this common? And why? Which leads me to another question: has anyone used an inverted mould, with the top-sheet against the mould surface and the base(s) on top? In a vacuum bag, at least, seems like you'd get better pressure across the base, and be better able to roll out air bubbles.

Scott

Give the top sheet a light sanding. Then apply a few coats of exterior polyurethane. This will take care of the light areas. What did you use for a top sheet?

according to the qcm q and a the epoxy is 99% cured after it hardens and can take 7 more days for the"chains" to fully develop.

Does it matter for your homemade skis with air bubbles and imperfections I don't think so but its up to you to decide.

I know nothing of air bubbles and vacuum bagging but it sounds bad.

As far as inverting your layup the mold is what gives your base the flatness.
Are your air bubbles between your base and 1st layer of glass?

I use vacuum. Once its all bagged and under full vacuum I use a j-roller to roll out the air.
Starting at the middle and working toward the tip and tail pushing the excess epoxy right up onto and over the tip mold.

sam

The top-sheet is a quilted maple veneer and, yeah, I was hoping that when I sand and polyurethane the light areas will disappear. Think I should "paint" them with some epoxy beforehand?

The air bubbles under the base look like they're between the base and glass. Given that they're not on the edges, I think (hope) they're just aesthetic imperfections. And I only used clear p-tex this time to better inspect how things went this first time through.

Could my air bubble issue have anything to do with the shouldering discussion that's going on? I don't see how the added thickness of the edge tabs could cause a convex bottom...wouldn't the flat surface of the mould cause the bottom to be flat, whether the core was shouldered or not? (thanks Sammer for pointing out the problem with an inverted mould -- should have seen that...) Instead, it seems to me that the edge tabs would "lift" the core away from the base and that the rigidity of the core would result in less pressure between the edges than on the edges. The difference in pressure would also vary from greatest in the center of the ski to least at the tip and tail, because of the difference in the core thickness/rigidity. This would be consistent with the location of my air bubbles which are inside of the edges and around the center of the ski (lengthwise). I was continuously pulling 25-27" Hg during the pressing, btw.

Scott

I really want to comment on this one, but since I've been lucky so far, no bubbles, with all my tests and finals. I only have one advise and that is to wet, wet wet the fiber with epoxy.
And also, let them sit for a week (MM said it in a previous reply and it goes for all epoxys(regular)) before cutting them out. It will not solve the bubble issue, but they will cure.

Hi Scott,

I understand what you are saying, but I'm left wondering whether un-shouldered edges can generally resist the forces involved and produce the result you outline or whether they just get compressed? In a vacuum press you may well be correct, but at 60 psi ... I shoulder the edges.

There is a tread in here with lots of arrows pointing up and down, illustrating the forces involved - I think it's in someone's journal.

I'd wait and monitor how your skis stiffen over time. I bounce mind on their tails - gently. To start with they are really soft and and vibrate accordingly. After a couple of days they stabilize and start to feel solid by comparison - I'm using a bit of heat, so it may take longer with yours, but that's when I have cut. I'm still very careful not of compress the ski at this stage. After a week, they bounce and feel solid and I don't mind giving them to the ski tech then. Sorry, this isn't very scientific, but it does at least allow you to get a feel for where you are up too and then you can judge as you build more.

Looking forward to a few photo

agiocochook wrote:The top-sheet is a quilted maple veneer and, yeah, I was hoping that when I sand and polyurethane the light areas will disappear. Think I should "paint" them with some epoxy beforehand?

You could use epoxy first but it's not necessary. The poly will even the tones out. Make sure it's oil based poly and not water based. I haven't found an exterior water based poly yet but just thought I'd mention it. Water based poly won't give the warm tone that a oil based poly does.

I used quilt maple veneer on a pair of skis also. The grain pattern really popped after a few coats. Post some pics.

Another possible culprit could be the pins I used to keep everything in place....I thought I cut them short enough (but not too short such that they would leave dimples on the top), but maybe.... Their locations also coorespond with where the bubbles are and if they were even a hair too long, they would have limited the compression around them.

Fortunately, I'm out of town for two weeks so letting the skis sit for a bit before trimming won't tax my patience quite so much....

Once trimmed I'll try to post some pics. Really appreciate all the feedback -- Thanks!

Scott