Holes in aluminium pulley - Jet 1015

[RickSmith2020]

Hi all. I’ve just noticed both pulleys on my lathe have lots of holes in them. Does anyone know if this is a casting issue or is something eating away at them? I’ve had the lathe apart 3 or 4 times and never noticed them before. They’re about the size of woodworm holes. Is there some kind of super woodworm that can eat through aluminium?
Thanks in advance

 

[lurker]

Mutant Woodworm!

My guess is casting bubbles

 

[RickSmith2020]

Maybe the holes were filled with something and it’s just all fallen out. I’m very meticulous with my equipment, I’m sure I would’ve noticed them before. Thanks lurker

 

[dannyr]

best guess agree with lurker casting porosity -- a few holes shows less than brilliant cast, but shouldn't affect use -- these could have had a polymer filler in them when you bought it or more likely just been smeared over by the machining of the grooves in this aluminium or zinc alloy now revealed by wear and heating.

the one other possibility would be holes from a balancing process but that'd be a very strange place to put them

 

[RickSmith2020]

best guess agree with lurker casting porosity -- a few holes shows less than brilliant cast, but shouldn't affect use -- these could have had a polymer filler in them when you bought it or more likely just been smeared over by the machining of the grooves in this aluminium or zinc alloy now revealed by wear and heating.

the one other possibility would be holes from a balancing process but that'd be a very strange place to put them

I’m leaning towards the idea of them being filled. That machining smear theory sounds plausible too. I guess we’ll never know.
Thanks for your reply

 

[Br5d]

For balancing maybe??

 

[RickSmith2020]

The holes go all around both wheels so I wouldn’t imagine they’re for balancing, although it’s a little odd that every hole is in the grooves, with no defects on the ridges. Mystery!

 

[dannyr]

Porosity in a reasonable casting may be like an aero bar chocolate ie deeper, with a reasonable surface layer - so cutting the grooves has 'found' this.

I worked with foundries on porosity (we had an (expensive) solution) - more of it than designers thought. I remember work on big BMW engine block castings a few years ago in Bavaria - the BMW designers assured us there could be no significant porosity from their foundry - long story short, there was plenty of deep porosity (just like yours) and they had to use the solution.

 

[RickSmith2020]

Porosity in a reasonable casting may be like an aero bar chocolate ie deeper, with a reasonable surface layer - so cutting the grooves has 'found' this.

I worked with foundries on porosity (we had an (expensive) solution) - more of it than designers thought. I remember work on big BMW engine block castings a few years ago in Bavaria - the BMW designers assured us there could be no significant porosity from their foundry - long story short, there was plenty of deep porosity (just like yours) and they had to use the solution.

That makes sense. Thanks for your reply!
I’ve just noticed some metallic looking bits in the grooves of the micro v belt. So I think the conclusion is that they’re casting bubbles which were filled with some kind of metallic filler. Thanks everyone!

 

[RickSmith2020]

Also, we’ve had a couple of frosty nights recently, and my workshop is not insulated. So perhaps the expansion and contraction caused by the temperature change loosened the fillings.
Belt cleared out of all metallic bits and lathe now running much quieter.

 

[minilathe22]

I wonder if the metal turning to form the grooves pushed swarf into the holes, and only recently through the belt wearing on it, did they appear.

 

[RickSmith2020]

Swarf! I was trying to think of that word. That’s certainly a possibility, although I mainly just use the second fastest setting, so wear wouldn’t be the culprit across all the settings.