Practical practices.

[RollingCamel]

We are going to manufacture the chassis on Sunday, however while preparing the chassis to be cut and bended, i wonder about the practical practices that i should talk into consideration.

For example, nearly all the meeting tubes meet at a point however this may make tube notching much harder than if i offset a tube a bit. I'd really appreciate your take on such topic.

[Adambomb]

Naturally that is how you'd want to do it...but in practice coping tubes manually (with a bench grinder) this way takes an army of about 5 newbies about a week to do.

There are some tricks however, I know Solidworks will create the notching pattern for you, then you can un-wrap the pattern to a flat profile, print it 1:1 scale and glue it on the end of the tube and grind to the lines (obviously make sure you have some sort of alignment mark for the two ends so they're not rotated relative to each other). Even better, find a company that can use a laser-cutter to notch them (WORKS AMAZING...although this is the sort of thing you want to budget at least an extra month or so for).

If you are super pressed for time, however, and not terribly concerned about strength (i.e. you're using over-sized tubes) it may well be worth it to make the compromise of offsetting them to get the job done faster.

When it comes to racing, there are certainly times this quote applies:
"A good plan, violently executed now, is better than a perfect plan next week." -General George S. Patton, Jr.

[RollingCamel]

I already made the cut list by solidworks however in some parts i may get thicknesses near to zero.

[Hector]

Lining up the tubes to one node is in your best interests. You'll end up with a stronger, stiffer frame that way. Coping with all tubes aimed may be a little more difficult, but not so much that you'll be unable to do it. Make sure to pay careful attention to which tubes get welded on first - sometimes you can simplify manufacturing by rearranging the order in which you attach the tubes.

The paper-wrap method has worked OK in our experience. To those who have a good eye and can cope well, it slows them down a bit. To those like me who are coping-challenged, it helps speed things up.

As Adam mentioned, if you're pressed for time go ahead and offset them. An imperfect frame (and car) that is finished on time is a million times more useful than a perfect, unfinished frame when race time approaches. Unless you've got insane workers and project management skills, you'll always be a day late on a dollar short on these project. FSAE - do it quick, do it cheap.

[Jersey Tom]

You'll have to submit a SEF for zero-thickness tubes.

[RollingCamel]

Originally posted by Jersey Tom:
You'll have to submit a SEF for zero-thickness tubes.

Duh...i don't find myself laughing.

What i meant is that some edges could get very sharp especially with tubes of same outside diameter when you trim.
Another thing with solidworks when trimming the bulkhead supports at the front bulkhead the tubes don't get trimmed properly, it leaves a tip intruding into the bulkhead.

[fixitmattman]

A halfway decent tube notcher will make your life easier. You can start with an e-bay one at first, but you'll eventually want to move up to somethign of some measurable quality. Recommend the compound cuts on a mill if possible. Good design for manufacture really speeds up fab. Seen a lot of the mythical 8 tube nodes, you just can't easily or quickly fabricate that crap with the resources most teams have. After that manufacturing reviews became mandatory, hahaha.

As for the sharp edges, that's what grinders are for. You'll need to be preparing the edges of nearly all your tubes for proper weld penetration anyways, this goes hand in hand.

[RollingCamel]

Unfortunately, We aren't going to weld the chassis ourselves we are going to a fertilizers manufacturing company which will do our machining and welding. However, they are not good in machining.

I got them the drawings and the cuts however they they said that they'll do the notching using their "experience". Will be there with them supervising the work. Other thing they don't have good bending abilities so we'll improvise something.

[Adambomb]

+1 on supervising. We get plenty of "agricultural types" here. They're the hardest workers, most practically smart, and overall best guys in the shop, [B}once you convince them that +/- 10 mm is not an acceptable tolerance when building race cars.[/B] We lose a few of them that way, they get tired of us scrapping their junk parts and switch over to baja http://fsae.com/groupee_common/emoticons/icon_wink.gif.

I'm a little scared about the lack of bending capabilities...trying to "ghetto rig" something will VERY LIKELY result in kinked or flattened tubes. Especially with welded-seam tubes (also, should go without saying, but just to make sure...seam always goes in the lowest stress point...the center radius of the bend...I only say this because our HPV team didn't heed that advice and kinked their roll hoop. They just put some Bondo on it and painted it over it and called it good though http://fsae.com/groupee_common/emoticons/icon_eek.gif ). At a bare minimum I'd pack them full of sand to prevent kinking.

[RollingCamel]

The main and front hoop are from seamless tubes. They should bend the tubes tomorrow and strangely they don't want us there.

Ah well we have many tube to spare...

[Test Driver]

Be careful. Practicing best practices now can lead to OCD like behavior even when doing this for LeMons cars.

Check out the six tube node on the lower left hand. All at the center of the bend and welded in-car!

http://www.flickr.com/photos/1...t-72157604525683685/ (http://www.flickr.com/photos/10090957@N05/2544042796/in/set-72157604525683685/)

Cheers

[Adambomb]

Originally posted by Test Driver:
Be careful. Practicing best practices now can lead to OCD like behavior even when doing this for LeMons cars.
Cheers

+1

It can make the difference between a car that is well-developed and reliable and one that makes its first run the day before and breaks at competition, albeit with "more perfect" design.

[RollingCamel]

They have done the major cross-sections. The bends are good but there is an error margin which they say around 5mm... could be taken up by the brackets.

They tig welded the cross-sections but will use oxyacetylene in other parts. If we disagree on something they tell us that they well get our stuff in good quality and we shouldn't care about the procedures.

However, i want to take your advice on something. I could reduce the weight at the front part, it is quite heavily fortified and i realized how stupid i was today.

Picture will follow.

[RollingCamel]

Original design:

http://i3.photobucket.com/albums/y89/AK-47-RaM/chassisbuilding.jpg

Alternative:

http://i3.photobucket.com/albums/y89/AK-47-RaM/chassis.jpg

[RollingCamel]

One point there should be a minimum of 3 straight tubes to the front bulkhead. Any excess triangulations could be of different tube sizing?

The the supports meant by the SEF is the 3 tubes plus any other triangulations.

[Adambomb]

You would think that, but we've had trouble with it in the past. In '06 we had an extra triangulating member that was thin wall, and they almost made us cut it out before we could pass tech. Personally that seems asinine, I really can't understand why that would be a problem (and if it was, why simply cutting out a triangulating member would actually be beneficial). There's one thing I really like about FSAE: unlike many other places, they're usually concerned more about the intent of the rule than the letter of the rule, but this seemed to be an exception.