New press - Mongo style !

[Mongo]

As I said in another post (http://www.skibuilders.com/phpBB2/viewt ... 8&start=60)
I have a problem with the frame bending a little bit under pressure, not even that much pressure, just 40 PSI... resulting in skis with convex bases. I measured about 1,5 mm of deflection over the 16" span (width of the press)
The bending might not be the only cause of those convex bases (my mold is not perfect as well) but the fact is it bends !

I was wondering if other skibuilders (mongo ? Gman ?) with this kind of press noticed any deflection.

Thanks !

First off, excellent post and information in the other associated thread. I have really enjoyed reading about the development of you press.

I have never been had any measureable deflection on my press in either the 0 deg or 90 degree direction of my press. That being said, my setup may be slightly different than yours with regard to how force is distributed to the load frame members. I have a 3/4" plywood board below my bottom mold and above my top mold, and both my bottom and top molds are a minimum of 6" thick. My press is also bolted down to a steel 2x2x0.125 cart that has transverse members matched to that of the load frame. I also matched each vertical member on the swing gate individually when I welded it up so any longitudinal and associated torsional flex in the 0 deg direction should be limited.

I ran a physical test on every welded member to qualify it when I was in college and the largest deflection I had measured was 0.004 in the far left hand topside compartment in the longitudinal direction.

From all of the skis I have pressed with it, I have had very flat bases from true bar tests. My $0.02 is that the transverse reinforcement from the cart, and having my CNC for the bottom mold, is giving me good results. I haven't run any numbers, but I would not anticipate a significant base deflection translated up through your bottom mold from a max amplitude of 1.5 mm on a transverse member.

Kepp up the good work, the skis are looking great. If you could post a pic of the base with a true bar on it to show the deflection, that would be very interesting and helpful.

[ben_mtl]

Thanks for those comments Mongo.

As I stated in the other thread I reinforced the press using some 2"x.25" flats that kinda sandwich every transversal members.
I cannot see any deflexion in those parts now when under pressure (I use a ruler on the bottom)

You're right your press is beefier than mine, thanks to your cart. I didn't have acces to a weling machine anymore when the time cam to make the cart... hence the lightweight 2x4 one.
I do have a 5/8" MDF plate under my bottom mold and a 3/4 plywood (cheap so not that smooth) for the top mold.
I'm pretty sure my next improvement is gonna be with the bottom mold, which has really been poorly CNC cut.

My last skis still came out a bit convex but less that the previous ones, that's improvement (except I lost rocker also on those skis, which sucks) !
I'll take pictures of the base tonight before I drop them at the skishop for a base grind.

[ggardner90]

i love to see 80/20 in use i have used it for a lot of projects and it is always awesome. i am thinking about using it for my press but im not totally sure yet i would love it if you could share some specifics on how you built and programmed your cnc router

[kohto]

sexy press

[JoseSnow]

Nice Press!

Did you make any maths on that?? It does not look to strong.

I might be wrong.

Oh and would it be to much to ask what are the dimensions of the inside cavity you used?? Just to make sure I am going in the right direction.

Nice job