Adjustable Molds?

[melvs]

How have you guys found to best make the molds adjustable to different sizes without remaking any parts? Is there a way?

Getting much close to having this project getting to construction. The press frame is going to be made this weekend (I hope) and then it's onto the molds.

[littleKam]

i'm sure others have a much better method for an adjustable mold but here's a simple method:

1. first make just the camber portion with no tips or tails.
2. make the tip and tail molds separately. these tip and tail portions simply sit on top of the mold and are held in place using any of following methods: double-sided tape, bolts, nails, etc. i found that the strength of attachment doesn't need to be that strong. the force from your bladder will actually hold it place.
3. put a smooth, relatively thick piece of material (i.e. HDPE) covering the entire mold to make the transition from the tip/tail to the camber section smooth.



hope this helps.

note this mold is only adjustable for the ski length and tip/tail curvatures only. it doesn't allow you to adjust the camber, which would be difficult to design if you intend to use a pneumatic press.

[*ARMADA*]

thats pretty much what i did

[melvs]

I can get a lot of different thicknesses of HDPE. Would something like .025 be thick enough, or are you talking 1/8-1/4 of an inch?

[kelvin]

you might want something a little thicker so it smoothes out the transition and any bumps in your ribs. For our molds, we have a couple of sheets of 1/8" melamine or hardboard (cheap at Home depot) with a 1/8" sheet of hdpe on top.

[melvs]

Why is MDF used? what is it about it that makes it the material to use over anything else?

I'm guessing it is because it doesn't compress or change under the pressure that a press puts on it, but couldn't you just make it out of some plain wood? Just looking for some info. for when I talk with the carpenter(s) who is(are) gonna help me make the molds.

[kelvin]

We use mdf because it is:
1. relatively cheap (~$35 for 4'x8')
2. easy to machine
3. stable and very flat
4. strong in compression

the bad thing about mdf is it creates a lot of fine toxic dust. Wear a respirator when cutting. It also weighs a ton.

you could use plywood, but cheap plywood is not always flat and has voids, more expensive plywood is more expensive. Real wood will have movement due to wood grain.

-kelvin

[melvs]

as alwys, thanks a ton for the info. I picked up (hopefully) the final load of i-beams tonight, and will start building the frame this weekend. I can do one of two things. I have enough i-beams to make a 2 8" wide sections of press with the top and bottom having no space between, OR I can have one 16-20 inch press with no spacing between the beams (16") or small spacing between the beams (>16"). What would you reconmend? is 8" enough to use for a mold?

[AndrewT]

If you make the adjustable bottom mold would you still need to make a different top mold?

[fastfoot]

If you make the adjustable bottom mold would you still need to make a different top mold?

No. We made an adjustabel top mold. We used a 2x4 in every other space from every other end and a tip block in every space. I know it doesn't make sense so I will take a pic Monday and post it.

[j-steezy763]

i would like to see those pics.

[danishstock]

I also used the "every other" mold method. Pics available here. [/url]http://picasaweb.google.com/danishstock ... 628450[url]

Since the photo, I have added a threaded rod through the whole assembly with several holes at different positions in the tip pieces so they can be moved forward or back in 1 inch increments. The nuts are counter-bored as to not rip the vac bag.

Good luck,

Eric

[Greg]

Well, I am in the process of putting together a fully adjustable mold for vacuum pressing.

Once I get it together (a few months) I will post some pictures. But, just as a teaser, if it works out, I should be able to make everything from XC skis (with huge amounts of camber) to rockered skis with regular camber underfoot and big rockered sections fore and aft... I am also hoping to be able to use it to do the stringers for a wooden surfboard... but that will happen sometime in the summer (if ever)... here is a teaser pic I posted earlier

And, for the nay sayers... Just remember your basic physics that says that with a vacuum press, the only counter force is the ski core.

http://luleaut.facebook.com/photo.php?p ... d=10226372

[flamingo]

Hi Folks,

Hope it's ok to revisit this old thread. I'm in the process of designing and building an adjustable mold similar to the one littleKam sketched out above.

My question for those of you who have done this before:
Did you design the bottoms of your tip and tail molds to be flat, and run along the curved surface of the camber mold? Did this result in the tip and tail molds rocking back and forth slightly? I guess you could eliminate this problem by curving the bottom of the tip and tail molds to match the camber... but then you could only use that one camber unless you rebuilt everything.

Am I overthinking this? Will putting a flat surface on a curved surface with such a large radius not matter with the precision we're talking about?

Thanks for any advice. I've been reading this forum for a long time, and have been blown away by the amount of useful information on here.

[vinman]

I compromise a bit. I leave my tip and tail mold flat but I tend to flatten out my camber molds towards the tip and tail. i.e. if I'm building a 4mm camber mold I begin bring everything closer to flat toward where my tip and tail molds will sit. I find they sit nicely no matter what though. If something with more camber looks like it is going to rock a little I shim under the tip/tail mold with some left over base material. The biggest thing I find with this type of mold is to make sure the tip/tail mold matches perfectly with the height of running length board, or else you'll get a funky base hump/ depression. gain base material Or tip spacer works well for this type of shim.