Need an advice. Press consrtuction.

For discussions related to designing and making ski/snowboard-building equipment, such as presses, core profilers, edge benders, etc.

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MadRussian
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Location: USA

Post by MadRussian »

motoman wrote:Mongo style is not that complicated. I think I can perform this work. But the only thing that disturbs me is bolts. Somewhere I have seen that under high pressure they can be deformed as they work on shear.
But in general this is good and cheep variant.
back in the days of USSR a couple bottles of vodka could get any size of I-beam in any length if you know the right people.

here in US East Coast in surplus yard you can pick up appropriate sizes I-beams enough for ski press probably somewhere between $600-$800 in Ukraine it should be somewhere in the range of $100

Mongo style people build and rebuild numerous times iirc. 80 psi you mentioned is an enormous amount of pressure could make this type of press looks like "byblik"

ydachi
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
Richuk
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Post by Richuk »

MM, I think you mean previous evolution of mongo press have been poorly built. Unlike this one:

viewtopic.php?t=2141&postdays=0&postorder=asc&start=30

80 psi??? Somewhere between 40-60psi
MadRussian
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Post by MadRussian »

MM or MR?

maybe ... I no longer follow evolution of press designs.

Main point .... we all build from what available at the best price.
most frustrating parts of the project for me is rebuilding stuff over and over again in my case it wasn't the press it was router profiler

I didn't know what field OP in but in Ukraine it shouldn't be a problem find big structural I-beams or H- beams for dirt cheap

to OP If you can find I-beams above 50 lb/lf don't bother with it calculations of deflection ....of my press I never checked deflection lol don't need to :)
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
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chrismp
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Post by chrismp »

My press is built from metal I found in the scrap yard. Cost me about 100 EUR including the bolts, was quick and easy to assemble, and required very little welding skills (no structural welds in there).

Before I built this press I went back and forth between the scrap yard and my computer a few times to draft some iterations of the press depending on the available stock. I tested all those designs up to 100 psi with Scan&Solve in Rhino and the one I finally built showed very little deflection.

The bolts are 20mm thick V2A stainless steel bolts which have a better shear strength than regular grade 8 bolts.

We usually press at 60psi but have used it at 80psi a few times as well when pressing skis with titanal. Works flawlessly.
Richuk
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Post by Richuk »

Chrismp,

Congratulations on the teaching job.

Are your drawings something you would be willing to share? I wouldn't mind a copy myself )

MR ... my hand eye co-ordinal fails me at times.
casmat
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Joined: Wed Nov 06, 2013 3:26 am

Post by casmat »

Hi all and please excuse me for the intrusion but I did not want to open another post..soon I'll make one
talking about presses, I'll make anoversized press soon (one for all boards/skis) using 300mm high x 150mm base I beam, 3 for the top and 3 for the bottom,average weight 500 kg..

and I was wondering about different types of constructions, looking for the 'stronger'
especially between ''motoman'' construction (I think the most used) and bigkam construction
http://www.skibuilders.com/phpBB2/viewt ... sc&start=0

the advantages of the second method I think are about saving iron/weight/money..and gaining internal space
because when in the first method we have two I beams trasversally at the end that shut everything (meaning we are loosing the space as the widht of the 2 bases of the beams. so the entire leght of the press must be longer)
in the second method we have shorter I beams and at the same time we can use the mold untill the real end of the press..
don't know if I explained well
thanks
mat

ps
motoman..awesome graphics man!!
casmat
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Joined: Wed Nov 06, 2013 3:26 am

Post by casmat »

thinking back.. loading the mold or just the laminate would not be possible from the front because of the external 'pillars', but only from the short side..
but confirming the question about the solidity of the 2 constructions..
peace 8)

ps..afetr modelling in rhino I understood something..

so, as above, (talking about second press) the lenght of the top/bottom beams must be the same lenght of the first to have the right space to load the stuff.
this because using I beam trasversally (example with 150mm base) or using
C beams (maybe 140x60mm) is the same in terms of used space..in the second press we only have 2 'hole' in the short side of the press.

so..the last (and the first) question is..
which is stronger between those constructions?
both sealed with bolts

sorry poems ahahahahhahaha
:oops:
motoman
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Post by motoman »

casmat wrote:
so..the last (and the first) question is..
which is stronger between those constructions?
both sealed with bolts

sorry poems ahahahahhahaha
:oops:
If the question is about bolts, then in first type press bolts work on tension an the second one they receive shear stress. at least 8 grade bolts are good enough to withstand all the loads. For shear stress it is better to use higher grades.
mammuth
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Post by mammuth »

Except press fitting bolts normal bolts are not designed for shear!!! For shear the bolts should clamp the two surfaces well (they should also be not painted and not too smoth) so the surfaces create the friction against shear. For this you need 10.9 or better....
Tom
chrislandy
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Post by chrislandy »

mammuth wrote:Except press fitting bolts normal bolts are not designed for shear!!! For shear the bolts should clamp the two surfaces well (they should also be not painted and not too smoth) so the surfaces create the friction against shear. For this you need 10.9 or better....
Not quite true, a bolted connection in shear has the following failure modes, (probably a couple more as well)
1) direct shear of the face of the bolt
2) necking of the bolt
3) bearing failure of the plate
4) bearing failure of the bolt
5) Block shear of the plate/beam flange/web
6) local buckling failure of the plate
7) prying action from plate deflection

None rely directly on the "tightness" of the bolt, in fact as the clamping force increases the other strength properties decrease. Grade 8.8 bolts are perfectly suitable for 99% of application, 10.9 and 12.9 are not typically used in structural work. You would typically use a 2mm oversize clearance hole i.e. if you use a M16 bolt, drill an 18mm hole, M20 = 22mm hole etc

There are however connections which utilise plate friction which use special Gr10.9 (and higher) bolts called High Strength Friction Grip (HSFG) bolts and also Tension Control Bolts (TCB's) these are designed to utilise the clamping force and offset the loss of bolt capacity against friction between the plates to increase the shear capacity of the connection.

The friction connection relies on correct preparation of the mating surfaces and the correct torque applied to the bolt. There is a British Standard and a Euronorm for the correct surface preparation

TCB's also do not induce any torque or twist into the bolt stem or plate as the tool holds the nut end of the bolt and snaps off when the correct nut torque has been achieved. TCB's are great but you need a special tool to install them (you can hire them in the UK by the day)

HSFG bolts typically have a special load indicating washer which have nodules on the washer that compress when you tighten the nut, but you need to use a feeler guage to check the gap is correct

Hope that helps :)
mammuth
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Post by mammuth »

Basically, i tried to say that in one sentence ;)

Theres a nice paper from wuerth about this. Just have the german version, maybe theres an english version too.
Tom
chrislandy
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Post by chrislandy »

:)

Or just design it to British and European structural design codes EN1993-1-8 (with all relevant 1990, 1991 and other 1993 codes - gawd I hate Eurocodes!)or BS 5950-1-2000

Even if you're European or American the older British Standard BS5950 is great for bolted connection design (plastic design methods) whereas you can go back even further to BS449 and design using a permissible stress elastic design method. You can do it all by hand in a matter of minutes rather than messing around trying to FE model it. OK it's not going to be to the nth trim down but hey, I'd rather it overdesigned by a bolt size or bolt number rather than on the nose and potentially pop!

I love BS-5950, no messing, apply the load factors to the Dead and Imposed loads to get the Ultimate load, use the steel strength, bolt Ultimate (plastic) stress and Serviceability (elastic) stress. Then it's just basic number crunching/engineering to check if it works or not
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