Ski press - perfectly flat surface

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pavelbozak
Posts: 57
Joined: Tue Jun 10, 2014 6:18 am
Location: Europe

Ski press - perfectly flat surface

Post by pavelbozak »

Hi there!

I got some older "U" an "I" beems for free and I decided to built a new ski press from them - more comfortable for loading cassettes (classicaly from side).

I was thinking that irons should be flat and right angled itself but unfortunately it is not true... Even in an ironmongery when I was looking for perfectly straight and right angled profiles, I was told that it is not common to buy and it is very expensive to buy... I don t know, I am not good in these things. For an idea in length of 2.5 m, the beam could be a bit twisted or the right angle is not perfect and that means that I will not get perfectly flat surface of my ski press....

My budget is not huge and I d like to keep my skibuilding relatively "cheap" :D ... so I d like to use my irons that I have for free. Even if I bought regular beems, it wouldn t be better...

My idea is to built iron frame from beams as "flat" as possible and the rest of mistake caused by inaccurated beems try to compensate with some MDF mold filling (that MDF surface could be then routed to compensate inaccurate flatness)

Have anybody some experience with fighting against inaccurate flatness? Would be grateful for any advices.The more brains, the more knowledge :)

I will be more clever after the the frame is completed and "flatness" measured. But I like couting with problems earlier than they happen...
MadRussian
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Joined: Thu Sep 30, 2010 12:32 pm
Location: USA

Post by MadRussian »

U channel not always at 90°.
I beam should be flat and straight.
Anyway I think the most simplest way to fixed the flatness will be when frame is built to put FLAT metal plate on top of bottom frame. thicker the better all depends how much space left underknees of the plate to feel
1/2" to 3/4" should suffice.
I think leveling with mdf will be time-consuming and possibly without any results.
Again metal plate most likely not cheapest but will be much better in the long run if to factor in the cost of materials and time to do it more than one time.

talk to good metal fabricator/welder he will give you some ideas
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
pavelbozak
Posts: 57
Joined: Tue Jun 10, 2014 6:18 am
Location: Europe

Post by pavelbozak »

well, my father has some experience with welding and building iron constructions, so when my parents asked me what I want as a christmas present, I said nothing but I would be grateful if my father helps me with the press frame. :D I am so modest son....

So that is our vision of the ski press (sorry for that uggly drowing, I am really not Picasso...:)

Image

Image

We also got idea with some plate or plates over the bottom beams. In fact there would be free spaces between the beams if there is nothing above it.

I have seen lots of frames in here. In fact many of them are really so massive. But according to our calculations, the setup on the pictures should be strong enough even for 6bar pressure. I am only not sure about the flatness... Hell yeah I am talking about mistake or deviation up to 1 mm per m, but it will consume lots of time and lots of effort to built it, so I would like to built it as precise as possible.
24Dave
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Joined: Mon Oct 03, 2011 2:14 pm

Post by 24Dave »

how about pouring a layer of self-leveling concrete over the top of the bottom I beams. I would put some metal screen of lath down first then float the cement. A good mason would do that for cheap if you have no experience. Your mold would then go on top of that layer of cement.

I would probably want to put all of the I beams on the bottom and all of the U or C beams on the top for consistent flex, if one type was more rigid you might get some concave or convex bases pressing at higher pressures.
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MontuckyMadman
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Post by MontuckyMadman »

A 12mm plate keyhole or side welded is fine + Sufficiently thick mold and al skim it will be flat.
pavelbozak
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Joined: Tue Jun 10, 2014 6:18 am
Location: Europe

Post by pavelbozak »

Thanks for suggestions.

24Dave
PostPosted: Mon Dec 15, 2014 8:27 pm Post subject:


how about pouring a layer of self-leveling concrete over the top of the bottom I beams. I would put some metal screen of lath down first then float the cement. A good mason would do that for cheap if you have no experience. Your mold would then go on top of that layer of cement.

I would probably want to put all of the I beams on the bottom and all of the U or C beams on the top for consistent flex, if one type was more rigid you might get some concave or convex bases pressing at higher pressures.
Yesterday evening I was looking on my cutted irons and i was thinking about the same - putting all I beams as a bottom part of frame and U as top. In fact I beams are cca 0.5 mm higher.

Self nivelating concrete - that will be my last chance, if it is very bad when completed.

In fact originally i was thinking about concrete bottom part of mold few months ago. That would look so massive and peefectly flat but then it would be impossible to move with the press. Maybe one day, if i have my own workshop :D
gav wa
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Location: Perth

Post by gav wa »

When you build your frame lay your I beams on the bottom and check them before you weld them. You might be surprised by how level they are. If you need to twist one end a little, then weld the other end then clamp the other end in place and weld. With a little bit of extra time and care I think you should be able to get quite a nice flat surface to lay a thick piece of MDF over for your press base.
Danielbroski
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Location: Boulder, CO

Post by Danielbroski »

I had the problem where my beams were slightly concave. What I did to help flatten the beams is I bought some Bondo all purpose putty ($25) and spread it on the beams. I then took a piece of angle iron and ran it across the beams to smooth out the putty. Worked super well and was cheep.
24Dave
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Joined: Mon Oct 03, 2011 2:14 pm

Post by 24Dave »

If it goes bad, self leveling cement is applied very thin like 1/8 to 1/2 inch and has a lot of compressive strength.



you just need to make a level box and have a good straight edge
pavelbozak
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Joined: Tue Jun 10, 2014 6:18 am
Location: Europe

Post by pavelbozak »

Thanks for all advices! That self leveling cement looks very cool. Ff it goes too bad, that could be my last rescue :) But maybe it would be better to use thicker layer, or would not?
24Dave
Posts: 124
Joined: Mon Oct 03, 2011 2:14 pm

Post by 24Dave »

I'd make it around 1 to 1.5cm thick. The only problem I could foresee with the thin self-leveling cement would be that if it cracked from flexing, you would want it thick enough to stay in place. It will flex a bit without cracking, but depends on your press stiffness.
pavelbozak
Posts: 57
Joined: Tue Jun 10, 2014 6:18 am
Location: Europe

Post by pavelbozak »

Hi guys!

The press is welded now. The surface is not as perfectly flat as I planned, some I beams twisted a bit, so I am going to try to fix it with self level concreate layer (cca 1.5 cm thick). And there will be 2 layers of 3 mm thick metal plate. I think it should be almost perfectly flat then :) We will see after weekend. I post some pics as soon as it is ready.
mammuth
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Location: somewhere in the alps

Post by mammuth »

forget the 2 layers of 3mm .... way better if you use one thick plate ... warps less under pressure

you could level with epoxy too
Tom
pavelbozak
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Location: Europe

Post by pavelbozak »

The plates will be there only as smooth spacers. Maybe not necessary. But level surface should be ensured from the concreat layer... I hope, we will see :)
mammuth
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Location: somewhere in the alps

Post by mammuth »

Not sure if the concrete will break over time ... there are products with more and less flex... And some of the self levelling products are limited to less then 10mm thickness per application (had some mindf.ck with this when doing my kitchen)

I would try to find a nice 10mm steel plate and mount it

Or just use epoxy (i have seen workshop floors made with epoxy .. supernice and super durable).
Last edited by mammuth on Thu Apr 30, 2015 12:30 pm, edited 3 times in total.
Tom
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