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Persistent issue machining aluminum wheels - white spots / mottling

Rpi

Plastic
Joined
Mar 8, 2020
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 is specifically built to do wheels, and frankly is quite easy to use - digitizing is done with a probe and the default parameters for RPM are based on rim diameter which is inputted into the system for each wheel. All the parameters they know and use are already set up and we have tested with them on the phone - Nome of the parameters we changed have made a difference.
 

Rpi

Plastic
Joined
Mar 8, 2020
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.

Thank you. I've tried a larger nose radius (333 size if that makes sense), which is the size that was recommended to me by another rim shop. I cam understand that some may be inevitable but I can't imagine (and know for a fact) that the severity of what I am getting is normal, nor would I deliver that type of finish om a customer wheel.
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
Thank you. I've tried a larger nose radius (333 size if that makes sense), which is the size that was recommended to me by another rim shop. I cam understand that some may be inevitable but I can't imagine (and know for a fact) that the severity of what I am getting is normal, nor would I deliver that type of finish om a customer wheel.

I'd wonder if an insert with a wiper geometry might not work better, leaving a "precision smear" for the finish. Would be shiny and "machinish", but burnish the surface along with cutting. This should eliminate the show-through of underlying structure.

Regardless, I suspect RPM is lower than ideal, but if that's the way the machine vendor designs it then you're stuck. Perhaps also look into stiffer tool holding, that insert and holder shown in post #8 is a diving board, not supported at the extents of the cutting edge. Maybe try a different holder/shim.
 

atex57

Hot Rolled
Joined
Sep 6, 2006
Location
SW Wisconsin
The machine is specifically built to do wheels, and frankly is quite easy to use - digitizing is done with a probe and the default parameters for RPM are based on rim diameter which is inputted into the system for each wheel. All the parameters they know and use are already set up and we have tested with them on the phone - Nome of the parameters we changed have made a difference.

What I am getting at is, do all the other purchasers of this machine have the same problem or are you the only one?

Someone is getting it right, talk to the ones that do not have this problem and ask THEM for advice. We can only guess here.

Ed.
 
G

Guest

Guest
Constant surface feet is set by G96. I adjusts machine RPM according to diameter to keep SFM consistent regardless of the diameter you are cutting. On a facing operation the RPM will increase the closer it gets to center.
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
This is a brand new machine?

In the Porsche wheel pics looks like the uninterrupted cut is beautiful, but interrupted goes to shit.

There could be something loose or not adjusted right.

I don't feel like 900 RPM is anywhere near fast enough for what you're doing though. 900 RPM will look like shit near the center in aluminum.
 
Joined
Apr 14, 2018
Location
Totalitarian Ruling Capital, EastAsia
I don't feel like 900 RPM is anywhere near fast enough for what you're doing though. 900 RPM will look like shit near the center in aluminum.
I assumed he meant 900 SFM, as it seemed he was a touch in the dark about css.

A version of this is what most everyone uses

Wheel Machines – Femco USA

or at least all six of the wheel companies who supplied us use these. Watched them run, inserts are pcd, looked similar to a knux with a much bigger tnr than a 3 ... but if he really meant 900 rpm, that could be a problem. The Femco's run up to 2500. One pass, dry and fast.

Also, what he is seeing is not that bad (in the better areas, anyhow.) There's a reason lots of wheels are polished, plated, or painted. You tend to get that mottled look even in the best conditions .... still looking for old emails, sorry.
 

CarbideBob

Diamond
Joined
Jan 14, 2007
Location
Flushing/Flint, Michigan
Just a guess from left field but of the original pics #4 is the most inserting to me.
When turning if you load the tool it pushes a poop pile out the lead edge onto the stock and your current "groove" is smeared while you plow.
Hitting it again and it gets a little better. Normally takes 2-4 revs before back to clean cutting depending on the size of the poop pile.
Since cutting is not great you produce the same pattern or weld, build, release somewhere else so it looks like random "dull spots".
Bob
 
G

Guest

Guest
Surface feet per minute is the accumulated distance the tool travels per minute on the circumference it is cutting. So with using constant SFM the rpms would be running 10x faster at the 2" diameter than the 20" diameter.
 

Rpi

Plastic
Joined
Mar 8, 2020
Just a guess from left field but of the original pics #4 is the most inserting to me.
When turning if you load the tool it pushes a poop pile out the lead edge onto the stock and your current "groove" is smeared while you plow.
Hitting it again and it gets a little better. Normally takes 2-4 revs before back to clean cutting depending on the size of the poop pile.
Since cutting is not great you produce the same pattern or weld, build, release somewhere else so it looks like random "dull spots".
Bob

This was one of my theories, but then how would I prevent this? No matter what, since at every turn at a certain spot of the wheel, it will be picking up some poop pile no?
 

B1 SCOTT

Plastic
Joined
Feb 4, 2009
Location
Mississippi
A shop that I drill wheels for just bought an ATRUMP vertical wheel lathe. I will be over there on Monday and will ask if they have been having any issues.
 

Rpi

Plastic
Joined
Mar 8, 2020
Rpi, if you want, PM me your location.
I have a free day next week, and would enjoy helping you troubleshoot this issue, if youre reasonably close.

Cheers.

Hi, PM sent, but I'm in Toronto, Canada.
 

D Nelson

Stainless
Joined
Jan 7, 2015
Location
Missouri Ida
cfcd8d3f2f1cab82179e39adb79e5e59.jpg
okuma wheel lathe 100 horse spindle 2500 rpms


Sent from my iPhone using Tapatalk Pro
 

B1 SCOTT

Plastic
Joined
Feb 4, 2009
Location
Mississippi
I asked the shop I do work for if they have any issues. They said yes. He said more rpm sometimes helps. Also said Mercedes wheels are some of the worst. Wish I could have got some good info to help you out.
 

Rpi

Plastic
Joined
Mar 8, 2020
I asked the shop I do work for if they have any issues. They said yes. He said more rpm sometimes helps. Also said Mercedes wheels are some of the worst. Wish I could have got some good info to help you out.

Thanks for the feedback. Any idea how they deal with it when it does come up for them?
 








 
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