What is the best press to make for the least $?
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What is the best press to make for the least $?
Im going between making a vacuum press, or a pnumatic press, and I cant decide. For one, Im lost @ how the vacuum set up works, although i think it may work well for my next skis because they are going to have some special features. Pnumatic presses are strong, but they seem a little sketchy. If someone that uses a vacuum press or pnumatic could send me a pm or just reply, I'd be very greatful.
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I use a vacuum press myself - I think davide's threads have some of the simplest photos of vacuum pressing. All you need is plastic sheet, tape, Masonite and a vacuum pump, an old fridge motor works fine.
The next simplest is a fabric pneumatic press - quite a few here are going down this route - have a look at plywoods threads for info
Have a good look through the skibuilding journals there is some good ideas in there.
I used to work with a clamshell opening pneumatic press with top and bottom heat - it was fast it was strong, but really hard to change from one ski shape to another - it also made screwing things up much quicker - hence I now use vacuum and slow set resin
The next simplest is a fabric pneumatic press - quite a few here are going down this route - have a look at plywoods threads for info
Have a good look through the skibuilding journals there is some good ideas in there.
I used to work with a clamshell opening pneumatic press with top and bottom heat - it was fast it was strong, but really hard to change from one ski shape to another - it also made screwing things up much quicker - hence I now use vacuum and slow set resin
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thefreshpimpofbigair
- Posts: 47
- Joined: Sat Jan 17, 2009 6:55 am
- Location: CB, CO
Vac bagging is simple, easy and probably the way to go for yer first few. Bagging however dose use alot of expendable materials... if you live in the boonies and have to order everything it can be frustrating. That said I made a pair of skis and a snowboard with the vac and bothe came out good. Pre bending the cores with steam was needed to ensure that the vac could suck it all the way. Just finished (95% more or less) a pneumatic press but have not pressed on it yet. It was much more expensive and complicated to set up, but should allow me more flexability with shape changes.
See my vac ste up and new press at: www.flickr.com/photos/rfa2009
Good luck
R
See my vac ste up and new press at: www.flickr.com/photos/rfa2009
Good luck
R
SEMPER LIBERTAS
Yea, I've been taking lots of inspiration from you guys on here. You can check the progress at (URL I can't post yet)
I just spent all evening trying to figure out the strength of MontuckyMadman's Cordura, which you're planning to use? I've come to believe it's about 500lb per 4 in of width of the 1000D cordura.
Have you done the math for your press? According to my calculations an 8' long press with a single layer of Cordura will be able to handle 20,000lb of force. A single hose 8" wide flat inflated to 45psi along 7' of press would come to 30,240 lb of force. A double layer of Cordura (Which Montucky might be making? I'm not sure.) would give 40,000lb strength, which would be enough for me.
But if you're running two hoses for your snowboards...
Two hoses 8" wide inflated to 45psi along 6' of press is 51840lb of force. You'd need at least a triple layer of Cordura according to those figures.
DISCLAIMER: I'm not 100% on any of these calculations. Some might argue that all my forces from the hoses should be doubled since the hose is pushing both up and down. I hope not. My stats for Cordura might not be right either. I got them from (URL I can't post)
that says "Grab Tensile strength - 528 x 472 lb"
and from (URL I can't post yet)
which says that Grab Tensile stregth is usually tested on a 4" wide test strip.
I just spent all evening trying to figure out the strength of MontuckyMadman's Cordura, which you're planning to use? I've come to believe it's about 500lb per 4 in of width of the 1000D cordura.
Have you done the math for your press? According to my calculations an 8' long press with a single layer of Cordura will be able to handle 20,000lb of force. A single hose 8" wide flat inflated to 45psi along 7' of press would come to 30,240 lb of force. A double layer of Cordura (Which Montucky might be making? I'm not sure.) would give 40,000lb strength, which would be enough for me.
But if you're running two hoses for your snowboards...
Two hoses 8" wide inflated to 45psi along 6' of press is 51840lb of force. You'd need at least a triple layer of Cordura according to those figures.
DISCLAIMER: I'm not 100% on any of these calculations. Some might argue that all my forces from the hoses should be doubled since the hose is pushing both up and down. I hope not. My stats for Cordura might not be right either. I got them from (URL I can't post)
that says "Grab Tensile strength - 528 x 472 lb"
and from (URL I can't post yet)
which says that Grab Tensile stregth is usually tested on a 4" wide test strip.
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knightsofnii
- Posts: 1148
- Joined: Tue Jan 08, 2008 6:02 am
- Location: NJ USA
- Contact:
nate, I am not sure how you are getting 20,000 lbs for the single layer of 1000 cordura. Can you explain a little more? I am coming up with 12,000 if I use 96"/4" x 500 lbs = 12,000 lbs. What am I missing? I am very curious about this as well as we are using a double layered cordura bag from Montucky.
Just to let everyone know have used the double layer cordura to build 4 pairs of skis now and we have pressed up to 50psi (on the last 2 pairs). No signs of weakness (knock on wood) and we plan to build a couple more this year. The dual layer bags hold at least (8" wide x 84" long x 50psi) 33,600 lbs. Maybe some sort of homemade grab tensile strength test would be worth doing. Somebody at an engineering school could set something like this up on one of those tensile strength testers I would guess. Montucky might send some samples if somebody volunteered to run this test.
Montucky always wants me to try and blow them up, but I am worried I will damage the molds or something else when they finally rip. I do wonder how much of a factor of safety we have using these bags. I know some of the steel presses can hold 200 psi before they will break or start to deform (huge Ibeams).
Just to let everyone know have used the double layer cordura to build 4 pairs of skis now and we have pressed up to 50psi (on the last 2 pairs). No signs of weakness (knock on wood) and we plan to build a couple more this year. The dual layer bags hold at least (8" wide x 84" long x 50psi) 33,600 lbs. Maybe some sort of homemade grab tensile strength test would be worth doing. Somebody at an engineering school could set something like this up on one of those tensile strength testers I would guess. Montucky might send some samples if somebody volunteered to run this test.
Montucky always wants me to try and blow them up, but I am worried I will damage the molds or something else when they finally rip. I do wonder how much of a factor of safety we have using these bags. I know some of the steel presses can hold 200 psi before they will break or start to deform (huge Ibeams).
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MontuckyMadman
- Posts: 2395
- Joined: Fri Jun 20, 2008 9:41 pm
awesome yeah calculate that crap. All I know is I snapped my flat pine top mold lengthwise a bit over 50 psi. It was crappy and flat so it torqued it in half.
The bands are double layered and overlapped at the seams and box stitched.
I would think the seams would give before the raw uninterrupted weave, especially because sewing puts holes in the fabric.
I will send material for strength testing but it has allot more to do with application.
If you can build a mold structure that can handle 70psi I bet the fabric would be fine.
The bands are double layered and overlapped at the seams and box stitched.
I would think the seams would give before the raw uninterrupted weave, especially because sewing puts holes in the fabric.
I will send material for strength testing but it has allot more to do with application.
If you can build a mold structure that can handle 70psi I bet the fabric would be fine.
I'm figuring based on the hose that I ordered, which is 6" diameter, so lays flat at 9", and inflates to maybe 8" of contact? Just estimates since I don't have the hose in my hands yet.knightsofnii wrote:are you talking 2 hoses 8" wide each? or total 8" width?
Consider that as the hose inflates, its contact patch is reduced.
I really dont know how to estimate it, other than with some kind of pressure sensing gages.
So my previous post had figures for 1 8" hose and 2 8" hose (total 16 in).
Well, I did 90" (I have a 6" brace in the middle of my press that won't have fabric over it) x 2 (for each side of the press) / 4" x 500lb. I don't know if I'm allowed to multiply by two like that. I hope so since with your number even a double layer would be rather risky.nate, I am not sure how you are getting 20,000 lbs for the single layer of 1000 cordura. Can you explain a little more? I am coming up with 12,000 if I use 96"/4" x 500 lbs = 12,000 lbs. What am I missing? I am very curious about this as well as we are using a double layered cordura bag from Montucky. .
Here's the URLs for the cordura figures I used.
http://www.rockywoods.com/Fabrics-Hardw ... lon-Fabric
http://www.uni.edu/tapp/pdf%20files/Ten ... t-Grab.pdf
Here's my press
http://mytonskis.blogspot.com/
http://www.rockywoods.com/Fabrics-Hardw ... lon-Fabric
http://www.uni.edu/tapp/pdf%20files/Ten ... t-Grab.pdf
Here's my press
http://mytonskis.blogspot.com/
Great. This is very helpful. I think for my next few pairs im gonna go for the vacuum press. The versitility of the press will allow me to try some new stuff. I guess all i need to do now is get the pump. Where should I look to get that? Do I just go to a second hand store and buy a fridge to rip out the pump? Also what size of fridge should I be looking for? Bigger is better i guess, so I'll start looking. Ill post after I get it all set up. Thanks
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pradellach
- Posts: 2
- Joined: Fri Oct 23, 2009 8:37 am
Hi, I've been looking at this site for quite a while now but never posted before so... Hi
I've researched the manner of calculating the forces that cordura 1000d can widthstand but to no avail. I dont think that the grab tensile test gives us good results. If you go to page 9 of this power point (address 1) you can see that the jaws dont cover the width of the material. So compared to our application I think the results of these test are alot lower that what the actual tensile strength of the material is... I think the right test would be the wide-width tensile test (ASTM D4595), but I haven't found any results of this test on cordura. Finally, if you read both description of the two test on this pdf (address 2) they stated that the grab test ''As an index it provides an accepted guide to the
strength of products but can not be used in design.''. So anyway I think if you double the fabric you should be ok.
I've researched the manner of calculating the forces that cordura 1000d can widthstand but to no avail. I dont think that the grab tensile test gives us good results. If you go to page 9 of this power point (address 1) you can see that the jaws dont cover the width of the material. So compared to our application I think the results of these test are alot lower that what the actual tensile strength of the material is... I think the right test would be the wide-width tensile test (ASTM D4595), but I haven't found any results of this test on cordura. Finally, if you read both description of the two test on this pdf (address 2) they stated that the grab test ''As an index it provides an accepted guide to the
strength of products but can not be used in design.''. So anyway I think if you double the fabric you should be ok.
Last edited by pradellach on Thu Oct 29, 2009 5:24 pm, edited 1 time in total.