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PostPosted: March 6, 2014, 6:15 pm 
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Nice build guy. Might you have drawings for that spiffy pedal mounting arrangement?

Your front axles scared the hell out of me. Are you going to do something with the rears? They are also known to be less than adequate.


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PostPosted: March 7, 2014, 12:21 am 
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a.moore wrote:
During my last visit at the welding store I picked up a can of dye penetrant and developer to check everything before putting it back together. I think its safe to say the car only scored a 50% on this test....


Educate me. How should I be interpreting the pretty pink pictures?

Thanks, Bill

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PostPosted: March 7, 2014, 12:54 am 
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Its a shot of the dye penetrant NDT. The pink line is the crack in the front spindle, but the rough casting has also picked up the dye. The Spridget kingpins are notorious for cracking in this spot. Though for some reason the shop i used to work at never checked them.


Last edited by cs3tcr on March 7, 2014, 12:58 pm, edited 1 time in total.

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PostPosted: March 7, 2014, 11:14 am 
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cs3tcr wrote:
Its a shot of the dye penetrant NDT. The pink line is the crack in the front spindle, but the rough casting has also picked up the dye. The Spridget kingpins are notorious for cracking in this spot. Though for some reason, at the shop i used to work at never checked them.


This is an educational moment for me. I've not heard of NDT before and I'll Google it to get a little smarter. But, I'm immediately wondering if it can be used on welded joints to help understand how well the weld bead is mixing with the base metal? I'm approaching the time when I'll be doing some critical welds and any reasonable thing I can do to increase confidence in them would be nice.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

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PostPosted: March 7, 2014, 10:51 pm 
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Yo, Andrew-
In that picture a page or so back, there were these two HS series SU carbs on the manifold. It looks as though the tops of the float chambers are attached so that one float hinge point is facing the front of the car and one is facing the rear. I'd suggest you rotate the one that hinges at the front so that it's 180 from that orientation, like the other carb.

What happens is, during acceleration/deceleration the fuel in the chamber is pushed to one side/end or the other and can raise or lower the float and starve the carb for fuel. If the hinges are to the rear of the car, when the car accelerates the fuel sloshes to the rear and the floats are lower, letting fuel flow freely, as it needs to under acceleration. Conversely, under braking the fuel sloshes to the front of the chamber and tends to close up the fuel flow. If you're braking, chances are that's OK.

I had one top on one of my SUs turned 'sideways' so that the carb starved for fuel in right hand turns. It would stumble on corner exit after a long right-hander. Took FOREVER to figger that'n out! Actually, it took my friend Bill pointing it out to me...

OK, nits picked now... The build looks really good, Andrew! I'm looking forward to seeing more!
:cheers:

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PostPosted: March 11, 2014, 10:05 am 
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Codeman - That is a bummer to hear since they are Summit brand. What torque were you using? Do you think anti-seize would have helped?


Vroom - I sort of just winged the pedals (too lazy to go through the whole process of making fancy drawings). I did make a model to make sure the actual master cylinders would fit but it won't really be useful to anyone else. I traced the stock pedals on to sheet metal and went from there. FWIW the pedals are all 0.040" mild steel and most of the box is 0.063" except for the bottom/back - that is 0.040"

I'm still debating what (if anything) to do with the rears. My understanding is that the axle shaft is typically what breaks so while it will be a DNF all four wheels will remain attached. Additionally there is light surface rust on the areas I'd want to check so I don't know if I could even get a good reading; removing the rust would probably fill any crack.


cs3tcr wrote:
Its a shot of the dye penetrant NDT. The pink line is the crack in the front spindle, but the rough casting has also picked up the dye. The Spridget kingpins are notorious for cracking in this spot. Though for some reason the shop i used to work at never checked them.


To add a little to this, the dye penetrant is a two part kit (dye and developer). You spray the red dye on the area to be inspected and let it sit for awhile (the directions say 5-25 minutes - the longer the soak the greater chance it will penetrate a crack). After that you thoroughly clean the area with solvent to remove all of the dye (wear gloves). Next you spray on the white developer and let it sit (again 5-25 minutes). If all is well the developer will remain white. If you see pink it means dye was left behind and you need to investigate.

If you are not extremely careful about removing the dye it is possible for small amounts to remain in tight corners and you'll get false indications. I was extremely careful the second time I did the axle and both crack indications were in the same areas.


Lonnie-S wrote:
But, I'm immediately wondering if it can be used on welded joints to help understand how well the weld bead is mixing with the base metal?


I can't see it showing you much as the dye shows surface breaking cracks. Anything below the surface will not be visible. I would think that x-ray would be the only way to actually do it and even then I'm not familiar enough with the process to be able to say what you could actually see. In the industry I work in we used high, medium, and low frequency eddy current inspections since we're primarily dealing with aluminum; in those cases the defect causes the field to change and the machine picks it up but you can't see much more than the blip on the screen.


JD - I was waiting for something to notice! The tab on one of the floats was broken off so when the lid is not on the chamber everything can flap down and the jet falls out. I just threw the lids on to keep dust out and figured I'd deal with it once I start putting things back together. Great story though - it makes sense now.

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PostPosted: March 11, 2014, 10:16 am 
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Lonnie-S wrote:
cs3tcr wrote:
Its a shot of the dye penetrant NDT. The pink line is the crack in the front spindle, but the rough casting has also picked up the dye. The Spridget kingpins are notorious for cracking in this spot. Though for some reason, at the shop i used to work at never checked them.


This is an educational moment for me. I've not heard of NDT before and I'll Google it to get a little smarter. But, I'm immediately wondering if it can be used on welded joints to help understand how well the weld bead is mixing with the base metal? I'm approaching the time when I'll be doing some critical welds and any reasonable thing I can do to increase confidence in them would be nice.

Cheers,


Lonnie haven't you already done a truckload of weld-and-cut test pieces to verify your welding? further, the dye pentrant would only show you cracks AFTER you'd bashed on the test welds with a hammer, and created some cracks.

BTW, to clarify, NDT is simply an acronym for "non-destructive testing".

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PostPosted: March 11, 2014, 6:56 pm 
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Always
So what does the right hand upright look like? It seems really weird to me that just one side would have a cracking problem. What could it be, the awesome torque put out by that massive Sprite engine?

And I have to say I am really envious how much work you seem to be getting done in what looks like a single bay garage.


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PostPosted: March 11, 2014, 8:34 pm 
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The crack at the root of the spindle is probably a fatigue crack. Even presuming that both spindles started and spent their life on the same car, there is considerable statistical variation in fatigue life on nominally identical parts. The variations in time to crack initiation may be genuinely random, a result of one spindle suffering damage (scoring for example), or simply a result of variations in machining as I don't imagine Spridgets were built in the days of NC manufacturing.

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PostPosted: March 11, 2014, 11:18 pm 
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robbovius wrote:
Lonnie haven't you already done a truckload of weld-and-cut test pieces to verify your welding? further, the dye pentrant would only show you cracks AFTER you'd bashed on the test welds with a hammer, and created some cracks.

BTW, to clarify, NDT is simply an acronym for "non-destructive testing".


Yes, I did a sh*tload. But, that was on simple tubing and plate where I had material to burn (no pun intended). On my suspension, it will be all new types of materials, and expensive pieces too, so I won't be able to practice like before.

Thanks for the NDT clarification too.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 12, 2014, 6:58 am 
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Lonnie-S wrote:
robbovius wrote:
Lonnie haven't you already done a truckload of weld-and-cut test pieces to verify your welding? further, the dye pentrant would only show you cracks AFTER you'd bashed on the test welds with a hammer, and created some cracks.

BTW, to clarify, NDT is simply an acronym for "non-destructive testing".


Yes, I did a sh*tload. But, that was on simple tubing and plate where I had material to burn (no pun intended). On my suspension, it will be all new types of materials, and expensive pieces too, so I won't be able to practice like before.

Thanks for the NDT clarification too.

Cheers,


Not to hijack this neat build thread, but your control arms are still going to be mild steel right? maybe just round tubing as opposed to square, and thicker wall sections? lets take this discussion over to your build thread...

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PostPosted: March 12, 2014, 12:25 pm 
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vroom wrote:
So what does the right hand upright look like? It seems really weird to me that just one side would have a cracking problem. What could it be, the awesome torque put out by that massive Sprite engine?

And I have to say I am really envious how much work you seem to be getting done in what looks like a single bay garage.


I didn't bother taking any pictures since there was nothing exciting. After I wiped away the dye and sprayed on the developer everything remained white (BTW the crack was on the right side - the left side was the one that passed).

When I designed front axles for FSAE cars, I did hand calculations and checked it with FEA. Interestingly enough what creates the most stress is cornering due to the radius of the tire acting as a large moment arm. For bump loads the moment arm is very small so the resulting bending stress is low. For braking the axle just reacts the load exerted by the caliper.

Don't get too envious BTW - my house originally had a one car garage then a previous owner added a two garage directly off of it. The old one car garage is now my work shop. I can get a small (fun sized) car in there by putting it on HF furniture dollies, turning it 90 degrees, and rolling it in. The rest of the stuff (including the Locost) is in the main part of the garage. The basement is also right off of the workshop so I have plenty of space to keep tools out of the way.


Warren Nethercote wrote:
The crack at the root of the spindle is probably a fatigue crack. Even presuming that both spindles started and spent their life on the same car, there is considerable statistical variation in fatigue life on nominally identical parts. The variations in time to crack initiation may be genuinely random, a result of one spindle suffering damage (scoring for example), or simply a result of variations in machining as I don't imagine Spridgets were built in the days of NC manufacturing.


That is pretty much my line of thought and I'd agree with this 100%. Even just a slight difference in surface finish can have a large effect on fatigue life. The fact that the axle was turned from a casting doesn't help much either.

From what I've read it seems that cracking normally does not occur for cars driven "normally". As soon as you throw on sticky tires and start taking corners at 10/10ths, you stress the axles more and enter the area of a finite fatigue life.

The next interesting question would be how many more stress cycles until the axle totally separates?

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PostPosted: March 12, 2014, 12:39 pm 
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Not sure how many cycles it will take, but I can tell you it's no fun when the spindle lets go. A brake line doesn't have enough tensile strength to keep the wheel assembly attached to the car and the axle remains grab nicely into asphalt.

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PostPosted: March 12, 2014, 6:51 pm 
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What I really wondered is why they sell the improved left spindle only. Having thought about this it occurs to me that most "racing" cars do a majority right turns (clockwise tracks) so the typical fatigue failure would happen on that side. How your parts got switched I couldn't guess but most old British sports cars have some serious history.


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PostPosted: March 12, 2014, 7:42 pm 
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Spridget Mania has both sides. I think one just may not be advertised as well.

What do you mean by switched? I'm not following.

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