Ski Builders Forum

My camera's on the fritz, so I can't post photos, but my camber mould was routered direct with no need for a template, as it consists solely of arcs - one for the mould itself, a pair for the tip block, and another pair for the tail block.

The mould itself is cut from 18mm MDF (the thickest I can router out direct), laminated. Sheets of MDF are 2440x1220mm. For the camber mould itself, I have a single arc with a chord of 2m and a rise of 3cm (that's a couple of yards and just over an inch in "exact" imperial terms), and I cut them with a total depth of 5cm and 3cm (i.e. one going direct across the chord, and another with a 2cm by 2m rectangle of MDF underneath), 21 "slices" alternating 5cm, 3cm, 5cm, etc for a total mould width of 378mm. I've only used 3cm of camber because I'll be steaming my cores to shape before pressing, so I'm expecting minimal springback. Makes the mould a shitload lighter, too.

I cut with a 6mm router bit.

So, how did I cut it all?

First, consider 2 ribs, one of 5cm, the other of 3cm. These can be cut from a 2m x 86mm (50mm + 30mm + 6mm) rectangle of MDF, putting the curves on the "inside" (i.e. cutting "curve to curve") this leaves a handy pair of tip / tail ribs which can be further shaped. Cutting the rectangles is a piece of cake with a circular saw and a quickly knocked up saw guide. In theory (and in practice, there's plenty of room for "slop"), I could have got 14 such rectangles from a single sheet of MDF, but I only needed 10 and an extra 5cm rib.

So, how to cut those curves? Okay, I lied a *bit* when I said I didn't need a template - I actually needed a very simple routering jig and 8 nails. And a load of space.

A not-terribly well known thing about arcs is that you can draw them without needing a full radius (or even knowing what the radius is) - all you need to know is what we (handily) know already - the length of the chord and the depth of the arc. There's a pretty good explanation here of what I'm doing, it's called the long compass. From this you can guess what I did. No fiddling with templates, just a little setup time and a 2m length of 6mm ply, and you can rip out perfect arcs every time.

I took the same approach to reprofiling the tip / tail ribs.

i got my last one cnc'd for under 200 bucks, i'd rather have that option available again

Even if i got one piece as a cnc'd template, I'd still probably spend half that money on the MDF itself, then hoping and praying that I line each piece up EXACT and to drill the holes exact? If this were still a hobby I'd consider trying to do something by hand

Tufty, Thank You!!!!!!!

I finally understand. I have been trying to figure out how to do tip and tail pieces better. Now I know. Awesome.

knightsofnii wrote:i got my last one cnc'd for under 200 bucks, i'd rather have that option available again ;)

Even if i got one piece as a cnc'd template, I'd still probably spend half that money on the MDF itself, then hoping and praying that I line each piece up EXACT and to drill the holes exact? If this were still a hobby I'd consider trying to do something by hand ;)

I'm not suggesting you're doing anything wrong, especially if you're doing this for money, but the cost difference is flagrant. A sheet of 18mm MDF over here comes to ~ 50 euros if you buy it from a DIY store, and less if you go to a decent wood merchant. Making sure the registration is good is where the nails come in - basically with 4 nails you can make jig up to get the exact same placement every time.

Mind you, less than 200 for a full CNCed mould is bloody good value for money.

yea i'm not sure i'll be seeing those prices again unless i can get my own cnc machine.

I'd love to see some photos of what you're talking about because I'm not followin you too much.

I'd love to also make a couple adjustable molds but i'm just worried about how they'll hold up to pressure repeatedly

knightsofnii wrote:I'd love to see some photos of what you're talking about because I'm not followin you too much.

Some more description follows, with some sketches, as and when I have time:

My Long Compass was made from a rectangle of 6mm ply. Slightly longer than my camber mould's final length and wide enough that I could mount not only the router, but also a length of batten to keep it all stiff. Fnarr. Cut the sheet sorta diagonally to give an offest between the two ends of each cut piece equal to the intended camber depth, join the shortest two ends together, mount the router in the centre. Looks a bit like this:



The sheets of MDF for the camber mould itself were cut as follows:

1 : cut sheet from 2440 to 2000 length
2 : cut sheet into rectangles of 2000 long by 2 x "rib" depth + router bit diameter. In my case I wanted 2 separate rib depths to get a "toothed" mould to be able to slide the tip / tail blocks in, by alternating "high" and "low" ribs in the mould, so my rectangles ended up being (2 x camber height) + base height + bit diameter.

Once that lot's cut, clear some space (about 4.5m wide), and chuck down a sheet of some "disposable" material (OSB in my case) that can have nails banged into it. Centre a rib blank on this sheet, and bang in 4 nails to position it, as follows:

Facing one long side of your blank, bang in 2 nails to hold the far side from sliding away from you. Add another 2 nails to hold it from sliding side to side. These last two nails should be lower than or flush with the blank (i.e. 18mm or less protruding). An alternative is to cut a couple of "L" shaped bits of 18mm MDF to hold the far two corners. I probably should have done this but I was feeling lazy.

Now bang in 2 bigger nails, more or collinear with the far side of the blank, and close enough to the corners for one side of your long compass to fit between then. i.e. pretty close to the corners, but no closer than the diameter of your router bit. These nails should be higher than the blank, as you'll be using them to guide the long compass. With the long compass placed as per the next step, the start of the cut should start where you want it to - move nails towards or away from you to it (making sure you're parallel on either side)

Should look a bit like the following, where the blank is in blue, the "positioning" nails are in red, and the "guide" nails are green. Obviously, make sure you're not gonna hit your positioning nails with your router.



Place the long compass with the router bit to the left of the blank, turn it on, and with a knee pushing the blank gently against the nails, perform a cut from left to right, making sure the long compass is always in contact with its two guiding nails.

You now have an arc-formed rib. Put it to one side. Take the offcut and put it to the other side

Repeat until you've cut all your blanks.

Repeat with the offcuts. If, like me, you're cutting odd-sized ribs, move the guide nails towards you before cutting.

You now have all your rib blanks cut, and you also have a stack of offcuts that make handy tip/tail blanks. If they are too shallow for your tip / tail lift, make up another, smaller, long compass to suit, and reshape one side.

Does that make sense?

Brilliant!

Very clever!

Head Monkey-

is the cnc machine up and running? what's the status? i have some things that i need cnc'd asap.

Sorry for the long delay... I've been quite busy lately and not had much time for snowboard work.

I'm sorry to report that I've decided not to offer any CNC work for hire for the foreseeable future. I've recently changed my day job, and I'm very, very busy with my new work. This is a good thing, though, even though it's kept me from snowboard building. Honestly, shutting down Happy Monkey was a planned prelude to this change. I had thought I might have time to offer the CNC service, but it's apparent to me that won't be the case for quite some time.

I will continue to update my web site and put up more of my experience there, but that will be slower than planned as well.

Thanks,

Mike

I have a cnc router with a 6'x12' table that we are setting up to cut ski cores in small batch orders (ie: singles would be fine) and offering the service to people who want to build there own skis but don't have the time/space/whatever to built and store all the equipment for each step. We would also be interested in cutting tooling/molds as an additional service. Who would be interested in both/one/anything else?