I have a set of BBS Motorsport 3 piece with what I have been told are magnesium centers.

What precautions need to be taken when machining the centers?

The rears are 16 x 10 et 2 with a 2" thick hub. I would like to machine 10 - 20 mm off the hub to change the offset.

Thanks

Eddie

might be safer to just buy new inners and outers from BBS motorsport in GA.

I have their number if you want it.

No idea how magnesium machines, I know it is very brital.

Isn't magnesium the stuff that's fun to watch burn... and almost impossible to put out?

Reducing that thickness sounds like a bad idea to me. Magnesium is light but requires more material than ...say aluminum...to achieve a given strength. I'm assuming the wheel designer (& BBS makes good stuff) did his homework and called for that thickness for that reason.

The centers for the front wheels are idential except for the thickness of the hub. The front hub is only 25mm thick.

Essentially, the rear wheels have built in spacers. The early Porsche 930s came stock with 23mm spacers.

I have 70mm rear studs and they're not long enough!

Thanks

Eddie

i've never machined mag., my biggest concern would be that the surface is machined as well as the stock surface so that the wheel does not wobble or vibrate.

as long as you don't remove any more material than the fronts, you should be fine, make sure you have the "hubcentric" feature done as well (i guess for the rear of a 914, no use, but if you plan on putting these on a 911)

well there you go! get 100mm studs!!!

Andy

I my lathe had a bigger capacity, I might try it myself. I remember something about using special cutting/cooling oil with magnesium ... kerosine based?

My lathe only has a 8" capacity. It should be a fairly easy job with the correct tools.


Thanks

Eddie

I know that the engine cases prior to the 3.0 liter SC engine are magnesium. How are they machined?


Thanks

Eddie

so is the 901 case.

Check closely where where the bolts attach the rim. you say the hub is 2inches thick and you want to
remove 20mm. On a hub that thick my guess is the mounting holes are offset or recessed into the hub. If you remove that much material make sure it is not paper thin where the bolts end up fastening. Hope u understand what I am trying to say...

Right,

The bottom of the lug hole has a radiused bowl to mate with the lug nuts. If you cut that away, the wheel will become a nice coffee table base

Ask here:
Practicalmachinist.com

Best home-based metalworking site on the net IMHO.

Sean

Great site.
On my favs list now.

Shop porn!!

Paul

From: http://www.magnesium-elektron.com/about-ma...nesium.asp?ID=4

"When machining magnesium, carbide tools are generally preferred when long production runs are expected. Magnesium conducts heat quickly away from the tool tip, so as long as the tool remains sharp, machining magnesium is an inherently fast process. Magnesium is normally machined dry. If coolants are necessary, then a light mineral oil should be used, rather than a water based lubricant. After machining magnesium using a water based lubricant, the storage of the resultant swarf is more difficult, due to the risk of reaction between the swarf and the water.


Magnesium components are almost impossible to ignite through the machining process, as magnesium must be heated to its melting point before it will burn. Magnesium swarf can be ignited, but the fast machining process should produce large chips which reduce this risk, as will good housekeeping practices. Cleaning machines regularly and correct storage of the resultant swarf are important aspects of machining magnesium.. "


DR Thanks for the tip on lug hole radius. since I have more than 50mm of stud protruding from the brake rotor hub and I can't get 10 turns on my lug nuts, I don't think the lug holes are radiused very deep.

I'll get some pics and measurements tonight.

I already voted so I can go the the Elliott Bay Motorsports Club Meeting and suck down a few while talking about fast cars!

Thanks

Eddie

Anyone have a BIG metal lathe or milling machine that needs to be exercised?

Eddie ,
I talked to wife ,I can't make the meeting, I can machine your wheels, Machine back side or Deepen lug holes. This weekend would be good to get er done.
Jeff

Jeff,

Nice to hear from you. Sorry about the late reply to your email. I don't look at the roadfly email box very often. You missed a great day at Bremerton saturday. It would have been a great day to get your 914/6 on the track. Next spring for sure!

If I remove about 20mm from the rear I should be able to maintain adequate clearance both inner and outer and be able to run 265/45/16 rubber on the rear. Might be overkill and ruin the balance, but currently the car tends to be biased towards oversteer even with a 2 psi tire pressure differential. I can always get 1 inch narrower outter rim halves and get 10mm studs.

I'm currently running 16 x 9 et2 245/45/16 on the rear with about 10mm- fender clearance and about 45mm+ frame clearance.

The 16 x 10 BBS wheels have 5.125" backspace (Overall wheel width of 10.875" calculates to et-16 ... pulled OUT 16mm).

Again, nice to hear from you.

Eddie

What is the feel rate on mag?. Two Flute end mill? Chip load? RPM?

Yup, Beginer Machinist.
Pat

I machine Mag all the time…Type 1 cases are made from it.

I don’t use carbide as it tends to chatter, use a sharp tool bit and on cases I use about 400-500rpm. It cuts easy.

For fire safety, as long as the tool is not burning the work (it may smoke a bit as you cut ..that's normal) your OK and a big box of baking soda on hand would put out a fire.

I’ve set Mag on fire, pretty intense, but I’ve never caught it on fire from machining it.

Just be careful when you sand Mag with sandpaper.Please don't smoke or get near a flame