Need Help With Project

[morrik27]

A 1000 x 750 shelf whit is to carry 40kg, constructed from 18mm chipboard with a 35 x 35 with white wood edging will sage 68mm. I you are happy with your shelf sagging this amount then fine.

If the shelf is 12mm chipboard then the sag will be 116mm

I didn’t see chipboard so I used OSB it as the same strength as chipboard.

If you used joinery grade timber with a 18mm plywood shelf then the sag would be 46mm.

To have no sag or very little then the self supports will need to be 120 x 25

BTW if you want to check my calculations then all you need to do is visit this site.

I Must be doing something wrong, i get 15.67 mm total sag using the dimensions stated, and a point load of 40kgs?!?!? thats using 12mm OSB(min stiff), floating, and no stiffner.

35x35 on it's own gives 2.15 mm?!?

Also? 120x25?? are you sure? two of those side by side is nearly a floor joist!!!


If you have the wood already, and you've got enough.... instead if putting in the 'green' uprights, double up the stiles, and make them 70x35.

You could make the frame as previously discussed, cut the stiffners to length, then glue'n'screw them straight to the side (might want to plane them smooth first, glue'em clamp, 'n' screw together....You could [probably] stand on that!!!

put a couple strips along the front to stiffen the shelf..

 

[morrik27]

Double check the weight, or consider using something bigger. I quite often use lengths of 3X2 CLS, and plane it down and square it off, only 59p p/m. Although sometimes they can be a bit ropy.

Harsh yes but it makes you think. Every one was going on about M & T joints etc but know look at the timber section size and the weight it is expected to carry.

Why are you encouraging the OP to use a timber that is not at all suitable for the job? CLS Stud work timber not joinery grade timber.

M/T joints in 1 1/4 sqr PAR, is no problem.

You'e right CLS is not 'joinery grade' but to be fair, neither is chipboard or OSB

however, from a cookoo's point of view it is strong, and could be planned down and finished nicely.

and at no point did i say 'you should', 'thats a bad idea' etc, mearly what i would do.

If however you see it as telling somebody to do the WRONG thing, you may want to reconsider your advise on using edging beads on 135 corners?

 

[morrik27]

just been playing on the sagulator, and found this in the notes section...

"7. This calculator can also be used to measure beam deflection. Because beams are typically positioned on edge, use "thickness" to represent beam depth and "depth" to represent the thickness of the beam. The shelf span parameter represents the beam span"

If you look at the diagram at the top, all calculations assume just a shelf, and the strip attached to the front. better to use it to calculate the deflection of the frame itself, in which case you get a deflection of 1.05 mm (assuming a point load, - less if spread across).
Since there will be two, front and back, the total load will be spread across the two giving even less!

the chipboard can then be placed over the top and screwed down - if you've enough double it up for two sheets.

I'm curious now - what's this actually for? (probably should have ask before now, but hey hoo!)

 

[HawkEye244]

I think you've become a bit to fixated by 40kgs.The frame will be supporting ABOUT 40kgs. Not the shelf. And it will not be 40kgs that is a rough estimated maximum. I'm keen on using the same size timber throughout.



If I was to do this :-





with two more 35x35 rails would that be in keeping with what you suggest?

 

[HawkEye244]

You could make the frame as previously discussed, cut the stiffners to length, then glue'n'screw them straight to the side (might want to plane them smooth first, glue'em clamp, 'n' screw together....You could [probably] stand on that!!!

put a couple strips along the front to stiffen the shelf..

I don't understand this. Could you use illustrations ?

 

[morrik27]

Untitled

• morrik27
• 22 Aug 2008
• 1

Hope this explains what i tried to say, just make sure the faces to be glued are smooth, put a line of glue down one, and slide the two together to get a bit of suction then line it up and clamp/screw the two together.

no need to cut anything fancy as the glue/screws will hold and the shelf will be sitting on the tops.

your cross pieces will be fine. Would recommend that the centre one running front to back is 'stopped' (ie not all the way across, as the picture you did), that way you won't see the end grain under the shelf and you'll never know it was there.

hope this helps.

When all said and done, the key to making it strong is to keep the joints for the frame tight, put it together dry (no glue) see how it feels, if you think you need to 'beef it up', put in the extra uprights, do the same....and so on.

if you go all out and still find it's not strong enough, you coud go with the suggestion of floor joists

 

[HawkEye244]

Ok now I understand.I've already assembled the top rail like this :-




I wasn't very certain about connecting the rails to the stiles so I've made the rails seperately and was planning on attaching the stiles with pocket hole joints. This way if I ever wanted to dismantle the carcass I would unscrew and take off the stiles and that would be it.


I'm certain about the shelf part now. Almost. That last question on the picture is the only thing I'm unsure of

 

[morrik27]

you could make the framework of the shelf, less the side pieces. screw down the chipboard top then fix it all to the side pieces which are morticed into the stiles.