What's new
What's new

Persistent issue machining aluminum wheels - white spots / mottling

Rpi

Plastic
Joined
Mar 8, 2020
Hi everyone,

New user and brand new to the machining world.

I have a new CNC lathe that is a wheel specific machine – it is made to refinish alloy rims. We are in the rim refinishing business and we only machine alloy wheels. The machine is new, and we and the manufacturer have been trying to resolve this persistent issue for weeks to no avail, so I was hoping someone has perhaps seen this or has a way of dealing with it.

The issue: when cutting the face of the wheel, I am getting a “mottling” effect with white spots all over the face of the wheel at random and a cloudy/hazy finish. I’ve been told this has to do with the aluminum cast used in alloy wheels, and specifically that it has to do with silicon content in wheels and that different manufacturers of wheels may have worse material that causes this – but I’ve now tried countless rims from multiple manufacturers and I get the EXACT same finish. Please see some photos attached. It almost looks like the a camouflage pattern that is stained on the wheel. It cannot be removed by washing, wiping, including with cleaning with any cleaning product, acetone, wax & grease remover, etc. Sanding it down removes its, but then I also remove my machined lines and machined finish that I need to have on the wheel. Polishing looks like has some effect, although hard to tell if it is just hiding it or removing it. I have been able to scuff it with high grit scuff pads to a reasonable degree to remove the marks.

Note: the white spots are definitely more pronounced in the centre of the wheel compared to towards the outside lip of the wheel.

At this point, I have tried experimenting and testing with every variable I can think of under the sun based on many people’s advice, including:
- Changing federate from 2 to 15 and everything in between
- Changing RPM from 350 to 900 and everything in between
- Changing cutting tool heads
- Changing turning inserts (carbide, 331, 332, 333), and PCD (332)
- Changing wheels – I’ve now tried wheels from Audi, Mercedes-Benz, Lexus, Honda, Jaguar. All give me the EXACT same issue.
- Changing approach angle
- Using A9 oil, WD 40 to prevent chips from hitting the cut areas
- Not cleaning the wheels and also cleaning wheels before machining, using each of soap and water, acetone, varsol, wax & grease remover
- Chemically stripping the wheels and not
- Sandblasting and not
- “Seasoning” the turning inserts by cutting 20+ wheels and using brand new inserts

None of the above have made any difference in the finish/effect I get. The wheels feel smooth to the touch and there is no texture to the white spots.

Does anyone have any ideas or has anyone experienced this? Any clues or thoughts would be very much appreciated as I am at my wits end with this issue.

Thank you


EDIT - March 10.

It looks like my long response post is not going to get "moderator approval" anytime soon, so will try writing responses again.

Thank you everyone for trying to help!

Dualkit:
- Sorry, I don't know what surface feet is? Feed rate is constant and controlled by the machine, but as above, I've tried feed rates from 2 - 15.
- Tool nose sizes I've used are 331, 332, 333 (aka 160404, 160408, and 160412)
- The machine does not increase the feedrate as the RPMs turn down. The RPMs do go down as the cutting tool moves from centre of wheel out towards the lip.

Delw:
- What are high sheer inserts please? Looking into it. The inserts I use are for Nonferrous, and I've tried a number of them. Please see some photos of some of the inserts I use attached.
- the manufacturer says no one that has this machine uses coolant and it is not required for wheels - I have tried A9 oil and WD40 though.

D Nelson:
- the fastest the machine is able to turn the wheels is about 900RPM for say a 19" rim
- I have tried diamond inserts as well (PCD)

Macds:
- Have tried oxidized/damaged wheels and also perfectly fine wheels, no difference.
- the pattern does not disappear when there is an uninterrupted cut - it doesn't disappear in any case, no matter what I've tried.
- It is a Lehigh MR2540 machine

EmmanuelGoldstein
- have tried diamond, have tried cutting as fast as machine would allow, and have tried cutting dry, and have tried big nose radius and smaller ones, the chucks that are on the machine are purpose built to hold wheels and are the same ones used by all other rim repair shops using this machine
- re aging - have tried old wheels and new ones (i.e. from a 2017/18 model year car), no difference.
- all the wheels I've done I've bought for practice, so none of these wheels will ever hit the road. Have tried wheels that have been extensively cut, and ones that have not been cut at all - no difference.
- How do I get in touch with big nose Tony?

Thanks!
 

Attachments

  • IMG_20200211_225558.jpg
    IMG_20200211_225558.jpg
    92 KB · Views: 1,116
  • IMG_20200213_175213.jpg
    IMG_20200213_175213.jpg
    93.7 KB · Views: 594
  • IMG_20200304_162550.jpg
    IMG_20200304_162550.jpg
    93.7 KB · Views: 672
  • IMG_20200304_172343.jpg
    IMG_20200304_172343.jpg
    99.2 KB · Views: 736
  • IMG_20200306_121612.jpg
    IMG_20200306_121612.jpg
    91 KB · Views: 509
Last edited:
Are you using constant surface feet? What size tool nose radius? Are you increasing the feedrate while turning down the RPMs?
 
Ive seen that finish on crap alum in 6061 and 7075 more so in 7075. use high sheer inserts made for alum specifically. whats happening your rubbing more than cutting. Ive only seen it on big dias and import alum from the suppliers. also richen your coolant up a tad it helps
 
I see the same effect when working with cast aluminum and striving for a smooth finish.
 
64cb07df08b17f8959d7e8f04d9a6fe5.jpg
this wheel was turned at 2500 rpm with a diamond insert that is the finish off the machine
Don


Sent from my iPhone using Tapatalk Pro
 
Are you tying to remachine oxidized OEM wheels?
Not that it matters, just curious.

The pattern looks very consistant across the face, and between different castings.
Almost looks like the pattern disappears when you have an uninterrupted cut, is this the case?

What kind of machine is this?
I think youre getting harmonics from the cut interruption + not a sharp enough cutting tool.
 
Thank you everyone for the responses.

Response to above questions:
@dualkit
- I'm not sure what surface feet is, sorry. Can you please clarify?
- re tool nose radius, I've tried 331, 332 and 333 (160404, 160408, 160412)
- feedrate doesn't change through cutting process, but RPM does - the machine automatically turns the rpm down as the cutting tool reaches the lip of the rim (machine cuts from center of the rim out). So if 18" wheels start at 760rpm when the cutter is in the centre of the wheel, by the time the cutter works its way to the lip, it would be spinning at about 600rpm. Machine is automatically programmed to do this. I can do a manual override to keep it at constant rpm, but it doesn't make a difference.

@delw
- what is a high sheer insert please? I'll look it up but I've tried a number of inserts based on other peoples recommendations
- the inserts I use are for nonferrous, attached are a few pics of the types of inserts we use - have tried rounder nose and pointier nose, carbide and diamond, all yield the exact same results
- manufacturer says none of their clients use coolant and suggests against it, so we don't use coolant. They do sometimes suggest using A9 oil, which I've tried.


@D Nelson
- I have tried diamond (PCD) insert, no difference - do you mean a SCD or MCD insert?
- the maximum rpm the machine allows me turn say a 19" wheel is 900rpm - many other rim repair shops use this same machine, this US brand is a bit of a pioneer in the industry

@macds
- we are machining oem rims, some may be damaged or oxidized, but many of the others have not been
- the pattern does not disappear with uninterrupted cut - the only appreciable difference in the severity is it is more severe closer to the centre of the wheel rather than towards the lip
- below link is the machine:
Lehigh CNC Rim Lathe MR-2540, MR-2940
 

Attachments

  • IMG_20200309_232303_01.jpg
    IMG_20200309_232303_01.jpg
    85 KB · Views: 216
  • IMG_20200214_154513_01.jpg
    IMG_20200214_154513_01.jpg
    93.3 KB · Views: 241
Been a few years since I was into this but doubt it's changed much ... we made molds for cast wheels, the material is similar to 356, it's done in low-vacuum counter-cast machines (material goes down alongside the mold, then comes up from the center of the wheel then spreads outwards), almost eveyone was using diamond tools, taking one cut dry and fast. The most common lathe was from Femco, Cincinnati built nicer ones but they cost more and the wheel industry is very price-sensitive.

Fast, dry, diamond, big nose radius, lots of rake, proper work holding (special chucks). That one photo looks terrible, like a pointy tool ?

If you are willing to pay to solve the problem, big-nose Tony in Los Angeles has his shit together.
 
Been a few years since I was into this but doubt it's changed much ... we made molds for cast wheels, the material is similar to 356, it's done in low-vacuum counter-cast machines (material goes down alongside the mold, then comes up from the center of the wheel then spreads outwards), almost eveyone was using diamond tools, taking one cut dry and fast. The most common lathe was from Femco, Cincinnati built nicer ones but they cost more and the wheel industry is very price-sensitive.

Fast, dry, diamond, big nose radius, lots of rake, proper work holding (special chucks). That one photo looks terrible, like a pointy tool ?


I've tried responding to all above comments, says mods have to approve so will wait for that to happen, but have done dry, diamond and big nose radius, no difference.
 
Im going with poor material bad heat treat? Or oxidation changing the structure. ive ran into this on turbo compressor housings. different manufacturers machine completely different. Used diamond, ground high rake aluminum inserts, high speed steel and that works extremely well. Every imported casting i can tell as soon as the cutter hits it they seem to get a good finish but when i take it out of the box to machine for different compressor wheel it can cut like shit. Good luck hope you figure it out.


Sent from my iPhone using Tapatalk
 
... have done dry, diamond and big nose radius, no difference.
That's what everybody does, and your samples are from all over the map, so .... structural changes due to aging ? Mag wheels are totally unsafe after a period of time, aluminum similar ?

That one photo tho, really bad. Looks like it is scraping chunks out instead of cutting.

If you take much off, I'd worry about getting too thin in the corner between the bottom of the bead and the outside .... have you fea'd a thinned-down wheel ?

Big-nose Tony is still an option. He's been in that biz for decades.
 
Based especially on photo #2, it looks to me like your finish is "too good," in that it lets you see the underlying crystalline grain structure in the metal. I see that kind of finish when turning extruded 6061-T6, 2024-T4, and 7075-T6 with a sharp high-positive carbide insert. It does not necessarily mean there is something wrong with the material. I suppose a post-turning polishing treatment might hide the grain structure to some extent.
 
It looks like my long response post is not going to get "moderator approval" anytime soon, so will try writing responses again.

Thank you everyone for trying to help!

Dualkit:
- Sorry, I don't know what surface feet is? Feed rate is constant and controlled by the machine, but as above, I've tried feed rates from 2 - 15.
- Tool nose sizes I've used are 331, 332, 333 (aka 160404, 160408, and 160412)
- The machine does not increase the feedrate as the RPMs turn down. The RPMs do go down as the cutting tool moves from centre of wheel out towards the lip.

Delw:
- What are high sheer inserts please? Looking into it. The inserts I use are for Nonferrous, and I've tried a number of them. Please see some photos of some of the inserts I use attached.
- the manufacturer says no one that has this machine uses coolant and it is not required for wheels - I have tried A9 oil and WD40 though.

D Nelson:
- the fastest the machine is able to turn the wheels is about 900RPM for say a 19" rim
- I have tried diamond inserts as well (PCD)

Macds:
- Have tried oxidized/damaged wheels and also perfectly fine wheels, no difference.
- the pattern does not disappear when there is an uninterrupted cut - it doesn't disappear in any case, no matter what I've tried.
- It is a Lehigh MR2540 machine

EmmanuelGoldstein
- have tried diamond, have tried cutting as fast as machine would allow, and have tried cutting dry, and have tried big nose radius and smaller ones, the chucks that are on the machine are purpose built to hold wheels and are the same ones used by all other rim repair shops using this machine
- re aging - have tried old wheels and new ones (i.e. from a 2017/18 model year car), no difference.
- all the wheels I've done I've bought for practice, so none of these wheels will ever hit the road. Have tried wheels that have been extensively cut, and ones that have not been cut at all - no difference.
- How do I get in touch with big nose Tony?

Thanks!
 

Attachments

  • IMG_20200309_232303_01.jpg
    IMG_20200309_232303_01.jpg
    85 KB · Views: 95
  • IMG_20200214_154513_01.jpg
    IMG_20200214_154513_01.jpg
    93.3 KB · Views: 84
Based especially on photo #2, it looks to me like your finish is "too good," in that it lets you see the underlying crystalline grain structure in the metal. I see that kind of finish when turning extruded 6061-T6, 2024-T4, and 7075-T6 with a sharp high-positive carbide insert. It does not necessarily mean there is something wrong with the material. I suppose a post-turning polishing treatment might hide the grain structure to some extent.

My reply posts are not getting posted for some reason. Edited original post. Thanks!
 
I have tried diamond (PCD) insert, no difference - do you mean a SCD or MCD insert?

The diamond inserts that are a solid stone will leave what looks like a polished surface.
Lens makers use them.
 
It looks like my long response post is not going to get "moderator approval" anytime soon, so will try writing responses again.

Thank you everyone for trying to help!

Dualkit:
- Sorry, I don't know what surface feet is? Feed rate is constant and controlled by the machine, but as above, I've tried feed rates from 2 - 15.
- Tool nose sizes I've used are 331, 332, 333 (aka 160404, 160408, and 160412)
- The machine does not increase the feedrate as the RPMs turn down. The RPMs do go down as the cutting tool moves from centre of wheel out towards the lip.

Delw:
- What are high sheer inserts please? Looking into it. The inserts I use are for Nonferrous, and I've tried a number of them. Please see some photos of some of the inserts I use attached.
- the manufacturer says no one that has this machine uses coolant and it is not required for wheels - I have tried A9 oil and WD40 though.

D Nelson:
- the fastest the machine is able to turn the wheels is about 900RPM for say a 19" rim
- I have tried diamond inserts as well (PCD)

Macds:
- Have tried oxidized/damaged wheels and also perfectly fine wheels, no difference.
- the pattern does not disappear when there is an uninterrupted cut - it doesn't disappear in any case, no matter what I've tried.
- It is a Lehigh MR2540 machine

EmmanuelGoldstein
- have tried diamond, have tried cutting as fast as machine would allow, and have tried cutting dry, and have tried big nose radius and smaller ones, the chucks that are on the machine are purpose built to hold wheels and are the same ones used by all other rim repair shops using this machine
- re aging - have tried old wheels and new ones (i.e. from a 2017/18 model year car), no difference.
- all the wheels I've done I've bought for practice, so none of these wheels will ever hit the road. Have tried wheels that have been extensively cut, and ones that have not been cut at all - no difference.
- How do I get in touch with big nose Tony?

Thanks!

you should read up on surface footage if you're gonna be doing a lot of machining/programming, especially lathes. its a critical parameter that you have to work with.

essentially its how fast the tool 'travels' over the surface of the part. being that this is a lathe part and SFM is a result of a constantly varying radius (at least in this application, where you're machining from larger to smaller diameter), the effective 'speed' of the cutter over the surface of the part is going to change/decrease as you get closer to the center, untill it reaches 0 at dead center. now that you hopefully understand that, if you use constant rpm, your insert load will increase as you get closer to the center which will throw off your machining finish quality, and could potentially wear/break your insert.

i would change to constant SFM instead of constant rpm and see if that makes any difference first.
 
The machine was built to turn wheels.

The mfg should know how to set it up and parameters to run it.

What did they say?

They ARE in that business.

Ed.
 
The machine was built to turn wheels.

The mfg should know how to set it up and parameters to run it.

What did they say?

They ARE in that business.
Femco is not much help, they are just going to tell him what everyone else does -

Diamond inserts, large tool nose radius, dry, high surface speeds. Obviously a light cut, and sounds like the normal wheel chuck.

Looks like the grain structure of the casting, to an extent that's normal, which is why we polished, but the feed lines look like the nose radius is too small.

Have to drag out an old hard disk with ancient mails but will try to find Tony's info for you. I think you will be stuck with a certain amount of grain showing no matter what, tho. It's a casting.
 
I have tried diamond (PCD) insert, no difference - do you mean a SCD or MCD insert?

The diamond inserts that are a solid stone will leave what looks like a polished surface.
Lens makers use them.


I have ordered some single crystal diamond inserts to try, but I think its way overkill as they are 4x the price of PCD and 20x price of carbide and I can't imagine everyone else in the rim repair world is using those.

Interestingly, I did a set of Porsche wheels today and noticed that the bottom part if each spoke doesn't have the issue or have it as pronounced in case that gives anyone any clues. So the part of the rim that the cutter first hits on each turn doesn't have the issue or as much of it, but as it continues the issue shows up.
 

Attachments

  • IMG_20200310_192349.jpg
    IMG_20200310_192349.jpg
    89.7 KB · Views: 309
  • IMG_20200310_190613.jpg
    IMG_20200310_190613.jpg
    92.5 KB · Views: 346








 
Back
Top