VAP

<center><img src="http://pictureposter.audiworld.com/711/mafdimples.jpg"></center><p>
I refer to them in-house as "MAF dimples." They are inside EVERY MAF I've ever done. The inlet side of the MAF will usually have 2-5 of these while the outlet side usually only has 1-3 of these. They are only discoverable when a MAF housing has been centered in its milling fixture then as the end mill starts to make its way down into the bore on a tapered/spiral plunge of the cutting tool. These are significant little craters running as deep as .030" tho most hover in the .010"-.020" depth range. The ones I'm showing in the pic start as MUCH larger diameter craters than they appear in this pic as these have been reduced in diameter by milling. But I pulled these before the last pass of the cutting tool. So in this pic the dimple depth is closer to .008"/.010" as the last pass cut depth is set to .012" which will completely eliminate the dimples. The dimples are never in the same place in any 2 MAF housings and are not limted to being near the outlet end as pic might have you thinking. They can be anywhere in the middle of the inlet/outlet taper and can be quite close, almost touching/overlapping each other or disassociated and far apart and anywhere/everywhere within the MAF bore. I've never come across a MAF with fewer than 3 dimples or more than 8 and 5-6 dimples scattered randomly about inside per MAF is average.

When cast at the foundry these MAFs not only have these pockets but the inlet ends and outlet end are ALWAYS .060"-.095" off-axis from each other. That is to say the center of the inlet diameter and the center of the outlet diameter are NEVER centered over each other! Once air gets inside an unmodded MAF housing it has to make a turn to get out the other end.

Both these events wreak havoc on volume, velocity and air samplings across the sensor wires in the form of turbulence. The dimples cause air to bounce around all over the place and change directions while the mis-matched inlet/outlet cause a low pressure air column on one side of the MAF and a high pressure colum at the 180* opposite side as air, like any solid, liquid or gas will ALWAYS seek the "easiest" way out, ie; "path of least resistance."

Early on when establishing the ideal inlet/outlet taper angles which vary by more than 40% from each other I also had to establish the shallowest cut that would allow perfect "straight-thru" alignment concentricity between inlet/outlet but also eliminate 100% of the internal dimpling found inside the MAF housing wall surfaces. If I over-bore I lose velocity and if I under-bore flow volume, velocity and smooth air is compromised by the dimples and inlet/outlet not being aligned with each other. The tolerances here leave me about a .0005" window to work in. And 50 millionths by anyone's standards is downright incredible tolerances that would NEVER otherwise be found in ANY MAF housing!

dragon-ryder

abnormalities in the aluminum used, varying casting conditions, etc... I'm sure it wasn't a tightly toleranced part to keep costs down. I have seen the pockets before though there were 3 in the 471 MAF housing that I used to turn this:

<img src="http://img.photobucket.com/albums/v697/anokiernan/Audi%2090/IMG_1805.jpg">

but as far as the TIR, the bore was only .010 off axis. Why not just use a 4-jaw and turn the taper, then you'd know for a fact that you're holding runout tight. VMC's are inherently bad at holding concentricity due to the inertial effects of the moving components. I'm sure you know this but I'm curious as to why you choose not to turn your MAF housings?

VAP

yet machining a single inlet/outlet clamping fixture setup is a snap. Also a 4 jaw can create "divits" and gouges in the inlet where the jaws dig into the aluminum. Additionally I cannot cut the sampling tube by turning the MAF on a lathe. And I would have to do both inlet/outlet tapers individually, by hand via the compound slide on the lathe. Not to mention I would have to reverse the jaws on the lathe to secure the outlet end of the MAF housing in the chuck as it cannot open wide enough to accept the outlet end OD. By doing these on the mill I can clamp the MAF housings FAR more rigidly and securely than a lathe chuck, hold and machine far tighter, more concentric circles than I can set the lathe chuck up to run or hold when trying to smooth over the previously cut sensor "nibs" that remain from cutting it out of the MAF housing with a sawzall (or other). Using the mill I have no extra step (sawing) in sampling tube removal. The end mill cuts the sampling tube out in it's first pass while also blending in the first altered-from-stock taper angles. Using a 4 jaw chuck in the lathe, "every" MAF housing must be set up individually and checked for TIR. In the mill I have a single fixture that does both inlet/outlet clamping and thusly only "one" setup for the entire production run be it 1 or 1,000. The mill then does everything to perfectly align the outlet with the inlet. This way I have 2 MAFs fixtured simultaneously and the program is running inlet task on one MAF then moves over and does the outlet task on the inverted/fixtured MAF beside it. I would "guesstimate" the CNC mill would do these at a rate of 4 or 5:1 over the lathe with greatly enhanced accuracy. Basically the mill allows me to merge the inlet/outlet variances by "averaging" the opposing ends so nothing is done from one side only but rather half &amp; half which keeps the bore more closely centered within the MAF body...which could never be done on a lathe without making eccentric/offset chuck-holding fixtures on an individual basis for EVERY MAF housing turned.

I've attempted both ways but the CNC mill is WAY WAY faster, easier and far far more accurate at internal TIR and concentricity.

dragon-ryder

When I did mine, I clamped on the outer rectangular flange faces with the 4 jaw where the casting is more rigid and bottomed the flange against the jaw faces to square the housing for mounted perpendicularity. Finally I indicated the ID true at the ID position closest to the jaws (within reason) and began turning. As you mentioned, interrupted parting is quite a chore... Certainly not a production method. At any rate, you must have a blast making these parts! Keep up the great work

VAP

same one found in all the "rolling machine shops" in Formula 1. Incredibly rigid with tightest tolerances I've EVER personally seen or used in a lathe regardless of size except perhaps an American Haas Turn 1 CNC/manual lathe.

But a Haas Turn 1 is a 6-8 month from today goal! I'm about $8k short of having the cash to buy it outright tho I started tooling up for it over 2 years ago.

cbkenison

I like these contributions to the forum. Taking any more orders for MAF, HVRS, or SXTB+?

odelay12v

sounds really interesting!

VAP

just finished the SXTB+ run 3 weeks or so ago and probably won't do another this year. HVRS will likely never be done again tho I should never say "never" as it has a way of biting me in the butt.

XTB's are always in-stock at 90-95% completion and can be further modified before shipping to XTB+ specs which will out-flow an SXTB but not an SXTB+

odelay12v

go to any of the local KC audi club meetings or GTG's?
I have gone to quite a few but since we had our kids not been nearly as active..

cbkenison

btw pic not loading