Stein

iTrader: (46)

Prints and models are done (Thanks, Chad) and the prints have been sent out for quotes. Any feedback on the design?

It would be slightly cheaper to go without lightening holes, but probably not enough to matter. Might be $5.00/set. I calculated the weight savings as 1.15 lbs per side, 2.3 total for the set.

What do you think? Lightening holes or no?

levnubhin

iTrader: (30)

In the intrest of saving time and considering it dosent really save much weight I say NO holes.
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N3v

I want one of these, but for me its extremely important that these things hug the original frame rails as closely as possible to avoid adding any ride height issues.

Stein

iTrader: (46)

Including air gap and material thickness, the bottoms should be about 1/4" lower than the existing rail.

patsmx5

iTrader: (16)

Definitely lightening NO holes. And definitely MORE mounting holes to fasten them so that they actually do something for rigidity. I'd like to see 10 holes to mount them per side vs. 4. I'll drill my own if others think it's not needed, but IMO, it is.

Stein

iTrader: (46)

I see your point. I will lay out the car, hopefully tonight, to see where I can add holes and hit good flat metal and miss anything that will get in the way. The BRG is in the shop and I can pull my 99 in to make sure that there aren't any differences between the NA's and NB's.

levnubhin

iTrader: (30)

Are you saying you do or donot want them.
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patsmx5

iTrader: (16)

I typed the words bassackwards. I do NOT want any lightening holes in them. To me, they would kill the rigidity.

Stein

iTrader: (46)

I knew what you meant Pat. I have been thinking about it and I have updated my quote request to both options, with and without lightening holes. I am now erring on the side of without holes, considering the small reduction in weight and they are bound to be at least a bit less expensive. The estimator is out until Monday, so it will be next week before I see a quote.

BenR

iTrader: (2)

+1

cjernigan

iTrader: (13)

Tomorrow I will measure the weight of a rail with holes and without holes using the solidworks function. Let you know what I find out. These things are so thing though I doubt we'll be saving all that much. The strength of these rails comes from the bent edges not necessarily the material between the bends necessarily. I'll get my friend to run it through Cosmos for a little FEA with and without holes. Who knows without holes might be stiffer.
Get you guys some hard data tomorrow.

curly

iTrader: (25)

if I get a profile and length I'll FEA it up on catia and get a weight within a half hour

and pat, making holes in the rails does not necessarily decrease its rigidity, in fact taking away material can often strengthen an object (although I do not believe that applies to these)

Atlanta93LE

iTrader: (5)

I'm a structural engineer, and now that design issues have come up, I'll pipe up and offer what I can. Holes/no holes is a cost and weight issue only. The difference in rigidity is close to negligible. We're simply not going to be transferring enough load to these rails to notice any slight difference in stiffness between with/without holes. As for the number of mounting holes, 4 per side is likely enough, but Pat's intuition is right that more will stiffen the connection. However, 10 is way overkill; it's diminishing returns real quickly. I assume the current placement is a copy of FM's bolt placement? If there are some good spots to add a couple more bolts, go for it, but don't lose sleep over it. If you're concerned about the absolute ultimate stiffened chassis, I'd look to stitch-welding the seams, especially the sills, etc.

It's not a complex part. There has been great success reported with the FM part, and you're not likely to improve on those any noticeable amount with slight tweaks. We're doing this for a more economical solution to the same issue, no? I'm excited about buying these! Thanks Stein!

Midtenn

iTrader: (15)

I work for a sheetmetal fabrication company. We do a lot of "soft tool" work and from what I've seen from your other post, it could easily be ran that way. I could get a quote together pretty quick if you're interested.

posidon42

iTrader: (4)

+1 Minimize lowering impacts as much as possible. Personally, I would like the holes. Also, if you can punch out the holes first, then bend the part, if you can get the holes to 'flange' toward the outside, you can actually increase the rigidity. But as one of the other structural engineers said, it will be negligible and probably just hold more dirt anyway.

Stein

iTrader: (46)

I looked last night and refined the hole locations a bit and added two per side. They are approximately 8" centers now. Any more than that and I started running into seat mount locations.

So, new design will be 6 bolt holes per side, no lightening holes.

cjernigan

iTrader: (13)

Only a 1.15 lb difference without the lightening holes per rail. Pointless to remove that material for the sake of weight savings, dollar per pound it just doesn't make sense.

elesjuan

iTrader: (11)

I agree, but would go either way with or without holes.

Brian-bbc

iTrader: (3)

i'm down for a set

Atlanta93LE

iTrader: (5)

Any updates?