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MATERIAL THICKNESS HELP!!

Postby hankim93 » October 3rd, 2017, 6:37 pm


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Hi guys!
I'm currently in progress of a furniture project and I wasn't too sure which thickness of "STEEL" I should use for my head rest.
I was thinking of 1 mm, 1.5 mm or 2 mm. please have a look at my drawings and suggest me any ideas!
I am planning to bend to that curve and screw it on to both part, head rest and the seat.
Also i do want a bit of springiness but not too much! So it doesn't form out of shape.
It's not the best drawing but hopefully you guys can understand my drawings!
Thanks!
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Re: MATERIAL THICKNESS HELP!!

Postby ralphzoontjens » October 4th, 2017, 2:37 am

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Hi,

That means you are adding 1 to 2 pounds of steel to the chair.
You don't need that much just for the head rest. Be aware that steel is very stiff.
My calculations show that with 1mm steel you will have a deflection of just half a mm with decent (500N) loading of the headrest.
In other words, you can make a more lightweight construction!
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Re: MATERIAL THICKNESS HELP!!

Postby iab » October 4th, 2017, 7:30 am


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ralphzoontjens wrote:l you will have a deflection of just half a mm


Is that around the moment arm?

As to thickness. It depends. I'd recommend spring steel otherwise it will hold it'd bend if the headrest is deflected too much. Also, steel is cheap. Buy 0.5, 1.0 and 1.5mm, make them all, determine which is best.

I'd also go with stainless steel.

Do something about the form, your rectangle of steel is not good (and I'm being kind by saying not good). Also consider buying a 3.0 and 6.0mm piece of aluminum and making prototypes.

Quite frankly in a problem like this, drawings and opinions suck. Make prototypes, then decide.

Re: MATERIAL THICKNESS HELP!!

Postby iab » October 4th, 2017, 7:32 am


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And another thing, looks like you are planning to screw that plate into place. What magical screwdriver will clear your design?

Re: MATERIAL THICKNESS HELP!!

Postby ralphzoontjens » October 4th, 2017, 10:26 am

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As a side note, it would make for a nice fiber reinforced plastic or carbon piece.
My conclusion was just based on a simple cantilevered steel beam calculation - I haven't done many of those by the way but what you do learn is that steel is counter-intuitively stiff. So elaborate your design structurally and aesthetically, eliminate the sharp edges, and have a shop make a few spring steel pieces for you, it will not be very costly and see how it turns out.
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Re: MATERIAL THICKNESS HELP!!

Postby AndyMc » October 4th, 2017, 9:25 pm

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iab wrote:
ralphzoontjens wrote:As to thickness. It depends. I'd recommend spring steel otherwise it will hold it'd bend if the headrest is deflected too much. Also, steel is cheap. Buy 0.5, 1.0 and 1.5mm, make them all, determine which is best.

I'd also go with stainless steel.


I agree with both of these points. 301 grade spring steel will keep its shape (to an extent), while regular steels will remain deformed if pushed. Keep in mind that your part will have sharp edges, even when deburred and linished, when using sub 2mm sheet metal.

It's also a very large radius to control with a press break (even using a pipe blade and a huge v block, and would likely need to be rolled instead, before folding the 40mm flanges. This is another issue if you end up using spring steel, as it a can be a challenge to bend in a reliable and controlled manner.

Re: MATERIAL THICKNESS HELP!!

Postby ralphzoontjens » October 5th, 2017, 1:12 am

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You can also roll the edges over with a wire edge for a good finish.

While we are at metal shaping, how about hydroformed aluminum.
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Re: MATERIAL THICKNESS HELP!!

Postby iab » October 5th, 2017, 9:09 am


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AndyMc wrote:It's also a very large radius to control with a press break (even using a pipe blade and a huge v block, and would likely need to be rolled instead, before folding the 40mm flanges. This is another issue if you end up using spring steel, as it a can be a challenge to bend in a reliable and controlled manner.


A pyramid roller for $99 from Harbor Freight should do the job for 2.0mm and lower with only a 120mm width to get that radius. Feeding it twice, both ends, through the roller will even the curve. Then a $99 break press for the flanges.

Re: MATERIAL THICKNESS HELP!!

Postby AndyMc » October 6th, 2017, 6:42 pm

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Rolling that radius at a 2mm thickness isn't a problem, nor is adding the flanges.

When fabricating spring steel you have to push the material a lot further than regular steels to get the desired profile, and can be a challenge to control depending on your press tooling and which direction the material grain runs. Your comment below sums up the solution though, get some materials and test it until you know what works:

iab wrote:Quite frankly in a problem like this, drawings and opinions suck. Make prototypes, then decide.


To the OP, how accurate does your sheet metal need to be, what's your tolerance? I assume this is a 1 off and not for volume production, do you need repeatability? Are you fabricating this yourself or getting a shop to do it?

Either way, if you go with spring steel make sure that it can be cold-worked. I also think you should design a better way to assemble your parts.


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