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Discussion Starter #1
New 9" fabricated housing from QP. The bottom flange of were the center section bolt on is out 0.035" in an inch. It's the opposite to a much lesser extent at the top of the housing. Even with a bunch of silicone I'm thinking the studs to mount center section are going to be pointed in many directions.

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Call them tomorrow and ask them what the flatness tolerance is for the flange.

I didn’t check mine from them, but I also didn’t buy the fabricated housing.
 

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Discussion Starter #7
Call them tomorrow and ask them what the flatness tolerance is for the flange.

I didn’t check mine from them, but I also didn’t buy the fabricated housing.
I'm going to email Mike at QP tonight with a couple of pictures. I completely understand that metal moves when welded, but I would think it would be trued up a little bit more afterward. My main concern is being able to fit the carrier over the studs if they are going off in different directions as it's a already a pain when everything is perfect.
 
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Spammer Hammer
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I would think the flatness tolerance would be .010” or less.

You can trig it out. Measure the max diameter of housing stud and subtract that from the min hole diameter of the third member case. That will give you the total positional tolerance for the hole pattern. Being a fixed fastener application, the tolerance would be split between the housing studs and the third member holes. Go conservative and give 2/3 of the tolerance to the third member housing leaving the other 1/3 for the rear end housing. Then sketch out the stud diameter tilted at the .035”. If the stud axis is within that 1/3 tolerance diameter for the full length of the protruding stud, it will go together.
 

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I'm thinking that when you torque that all down it'll be pretty flat.
Mine seemed a little off too. In fact I could not use the gasket I bought with it. I was a bit afraid the third member wouldn’t go on since the gasket didn’t fit. But as they suggested, I put my silicon down and the third member dropped right on down. Torqued it down n zero issues.

Chris
 
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Ideally, that flange should be machined after it's welded. And a bit of extra material on the flange to start with to allow for the machining.
 

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Discussion Starter #12
I'm too burnt out to do math at this point. I started heating the garage up to 65º Saturday morning so I could do the final welding on the housing today and that was a waste of a significant amount of NG. I'm thinking of buying an extra set of axle brackets form Shaun and using the 8" this season. I guess if QP says it's fine and I put the studs in and it the center section won't drop in, it's not fine?
 
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Nope, bite the bullet and send it out to a machine shop to get it machined flat. Otherwise the studs won't be perpendicular to the flange.
 

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I'm too burnt out to do math at this point. I started heating the garage up to 65º Saturday morning so I could do the final welding on the housing today and that was a waste of a significant amount of NG. I'm thinking of buying an extra set of axle brackets form Shaun and using the 8" this season. I guess if QP says it's fine and I put the studs in and it the center section won't drop in, it's not fine?
Thats what I did. It looked like the studs might have been a little off as noted above(as maybe the surface wasn’t exactly flat) and mine dropped right in. Zero issues to date.

Chris
 

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Machining the face of the housing will not straighten the holes.

Is the entire flange out of shape?

If there is only a few areas where the flange has gotten wavy I would use a crescent wrench and a piece of pipe to GENTLY persuade the flange flat. You may have to use two wrenches to keep the "low" or flat places from becoming lower. It won't take much leverage to true up the surface and the wrenches, when adjusted snugly, will not mar the surface of the housing.
 

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New 9" fabricated housing from QP. The bottom flange of were the center section bolt on is out 0.035" in an inch. It's the opposite to a much lesser extent at the top of the housing. Even with a bunch of silicone I'm thinking the studs to mount center section are going to be pointed in many directions.

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Boy, that doesn't seem right to me (and I spoke to Mike just recently about potentially putting one of these in my car). Mike seems like a straight-up guy, and QP seems to know what they are doing, so my guess is that they know about this and might have an explanation. My first action would be to call QP and speak with Mike, find out if this is a common result with these housings, and determine what, if anything, should be done about it. Who knows, maybe it straightens itself up when you bolt in the third member.
 

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.035" in that short of a distance is a significant angle. I can't imagine it is optimal to have the carrier mating to the house on a small area on the inner edge of that mating surface.
 

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I
I'm going to email Mike at QP tonight with a couple of pictures. I completely understand that metal moves when welded, but I would think it would be trued up a little bit more afterward. My main concern is being able to fit the carrier over the studs if they are going off in different directions as it's a already a pain when everything is perfect.

I'm curious, keep us updated.
 

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Nope, bite the bullet and send it out to a machine shop to get it machined flat. Otherwise the studs won't be perpendicular to the flange.
Machining the surface flat will not change the angle of the holes. If the holes were bored perpendicular to the flange, then they are out by the same angle. The only way to straighten the holes (studs) is to bore the holes perpendicular to a flat plane.

To mill it, it may not just be the .035 on the one side. As you move around the housing it could grow by a factor of 10 when you get to the other side of the housing.
 
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