"shouldering" cores for edges

[SHIF]

Alex13, Are you using VDS rubber above the steel edges?

-S

[Alex13]

Yep the base is 1.2mm and the step is 1.33 so that could have been another cause, though my brain tells me that should have lessened the impact rather than accentuated it.

No not using VDS on this board. A strange set of circumstances had me using carbon fibre along the edges by mistake. This may have had an effect on the indents. The next board coming out today will have VDS, will post a pic up in a couple of hours on how it went.

[doughboyshredder]

imo, that's from the difference in base thickness and edge thickness. Essentially a little pocket was there during pressing which allowed more epoxy to get in there creating the issue that you see. I would pick the epoxy out with a sharp instrument and wax that bitch up.

Looks like a good flat base.

[Alex13]

No. 2 came out pretty similar, with teeth marks around the tip and tail as well. I think you're right, it must be the difference between the thickness of the base and the edge step. It makes no difference once ground, just aesthetics.

[Richuk]

If you are lucky those teeth marks won't re-appear when you wax - temperature dependant.

[switzch]

This is a good way to shoulder your edges, just be careful when starting as the tip is vulnerable - two passes each side and you are done. Placed a piece of mdf on top to hold the tips in the correct position on the second pass. One small slice and then another.



Sorry, the photo is a really crappy - but you get the picture. Using the same jig used to make the core. I'm going to remake the jig. Template from Snowcad, smaller radius than ski.





Controlling the width of the cut - clamps are ok. I might end up screwing to the bench in future.

Im not sure I fully understand what is happening here. Few things.. If the core is bottom down on the router table and the template is somehow attached on the top, what exactly guides the core around the router bit?

[Richuk]

The core isn't guided around the router, it's guided over the router bit - only half the bit is available to cut. The mdf is curved, at a slightly greater radius than the core - it just stops any sudden movement when the core is pushed forward and over the cutter and against the mdf.

The length shown in the picture works with the clamps and table, depends on the set up.

[switzch]

@Richuk Yes, that makes sense, thanks. I didnt notice that the template was reversed from a normal core template.

[sir.orange]

i was on the ISPO last week in munich. guess what i saw there on a fischer freeride ski, that was cut into sections to show new bindings. the core had absolutely now recess at all. you could see very clearly that the core was pressed concave into the ski. in the center spot, the gap between base and core was a glass layer of maybe .8mm. following the core towards the edges you coiuld see how it raised up to a much bigger gap. could nt find out what the dark wedge is, but it gave the core a concave shape, definetly...so far to what the "big guys" do..

[vinman]

I'd guess VDS.

[chrismp]

could be pigmented epoxy.

[skidesmond]

could be pigmented epoxy.

I'd say pigmented epoxy too.

Not surprised the core wasn't recessed. It's an extra step in the production of the core. It looks like they notched the side of the core to accept the plastic sidewall however. Something I have contemplated, a "hybrid sidewall" where the plastic sits on top of the edge like below, but above is a wood sidewall. In my case I wanted the plastic there to protect the sidewall while sharpening/setting the edges.

[gketcham]

So back to the original topic.
My first pair of skis turned out concave on the base. That was with p-tex sidewall (UMHDWWHP I always forget the order of letters) and aspen core. Maybe I just didn't press hard enough.
Unheated, 60psi, pretty lousy job with the layup.

Profiling 2nd pair of skis, I cut two straight line pieces of MDF for my profile jig to run my router straight across and shoulder the core edge as well as slightly level one side of my core/sidewall.
It was really tricky to router that line perfectly and get the same depth throughout the whole core (which i mark up to not great tools/ methods). I had the cores secured with carpet tape which holds great but leaves nasty residue.

(OFF TOPIC) What are good ways to get carpet tape residue off my cores? Belt sander just gummed it up.


Sorry for the long post. I would love some input. Sorry I don't have pictures.

[g-ram]

It was recently explained to me by a former engineer from K2 that the shoulder in the core is for more than just for base concavity. He said its essential for maintaining a correct resin/glass ratio. If you dont shoulder then all the pressure is on your edges making that part of the ski resin poor and other areas of the ski resin rich. This can be fixed by the edge rabbit or using a fiberglass spacer cut to fit inside the edge teeth on top of the base. Also, he recommend routering a pocket for the fiberglass mat binding reinforcement on top of the core for a similar reason.

We made a simple jig for our edge rabbit where we temporarily screw the template to the top of the core and it rides on an elevated plywood point fence on the router table. The bottom of the core is lightly trimmed with a straight router bit set to the width/height of the edge teeth. Hopefully this makes sense. I'll try to post pictures next time we have it set up.
Graham

[richie]

I quickly freehand along a pencil line following the skin plan shape a 0.6mm rebate approx 8-10mm "sideways" into my core and after introducing this into my process I noticed immediately when doing the first basegrind that it was more even grind on first passes and less edge high. This honestly takes me only 10 mins per core. I do this after core profiling and if I am getting to the thinnest parts of the tip and tail I stop a bit sooner so I don't blow through. Bit rough but until I get my cnc going this is how it is for me and its been good. The point made about the super high pressure on the edges and glass if the rebate is not causing a dry laminate above the edges makes some sense to me too. One theory I have is that the lack of a rebate in an earlier splitboard I made caused the edge to be hydraulic'd off the base in a place least likely for the edge to come away during pressing, the extra pressure on the edge and glass being squeezed hard led to no resin passing through and a pressure buildup in the resin cavity pushing the edge out.

On a different note I just scored a beauty electric power hacksaw to chop up the steel for my cnc table, progress towards the goal! I'll do a cnc build log on skibuilders too and share my lessons learnt and hopefully my successes and not too many failures......



And my cnc table steel...... 4 of 4m lengths of 125x125x6mm SHS bit overkill but she'll be a well damped and nice and stiff. I'm getting it cnc levelled too before the main linear profile bearing rails go on. Fun project....