Strange Bar Bell Weight Material

[MozamPete]

I brought a new three jaw chuck the other day, primarily as the one that came with my lathe didn't have the reverse jaws but also it is about a half inch bigger which is useful for an upcoming 'production run' of about 300 pieces I have planned.

So now I need to make a new backing plate which I think is within my capabilities. My initial idea was to use what I assumed was a cast iron bar bell weight I had as there is no metal supplier locally where you can get anything other than mild steel. But it is not cutting nicely so now I'm wondering what material it is.

When it does cut I get the typical fine dusty shavings I would expect from cast iron but it is very hard to get it to cut and when I use a carbide insert tool (with a brand new insert) I'm actually getting sparks off it (not something I have seen before)

Any ideas as to what the material is or what I'm doing wrong?

 

[kd4gij]

What is the diameter of it and what rpm are you running?

 

[brino]

Any sand inclusions in the casting?
-brino

 

[Andre]

Might be hard spots in the iron. I would try slowing things down and take deep cuts, to get down under the hard spots and lift them out as opposed to cutting them in half.

 

[MozamPete]

What is the diameter of it and what rpm are you running?

About 6.5" diameter and 240 rpm (which is the slowest my lathe will go without putting it in back gear)

Doing the calc I see that is way to fast so I put in the backgear and brought it down to 40 rpm which should give me the 20m/min surface speed I see quote for cast iron. Boy that seems slow.

Cuts a bit better, no sparks now, but it is still struggling. If I try to take big cuts I don't have the torque and the work stalls even in backgear so 20 thou is about the max possible. Maybe I'm just asking too much from my little Myford ML7.

 

[janvanruth]

stop right there
think about the trouble you wil have in threading the stuff.....
bar bell weights are notoriuos for beeing cast from whatever mr.Lee can melt in his crucible and are mostly not really machinable.

 

[4GSR]

Put it in back gear! That'll let get more torque built up for a heavier cut. Use high feed rate on cast iron at first. If using insert tooling, use a insert that is flat on top or at negative rake. Go with a C-2 grade of carbide.

 

[joshua43214]

Don't do this....
Please

Those things are made from random stuff that look like steel and what ever is too slow to run away from the scrapper.
The metal is just heated until is sort of melted, and just dumped in with minimal degassing and probably no other treatment or testing. Not only will they have large voids, they will also have random inclusion of anything from sand to dead cats.

This is not the kind of material you want supporting a heavy piece of material and chuck rotating and speed...

 

[Wreck™Wreck]

CI can be extremely hard as cast, this is especially common with products that are finished as cast with no post process machining required beyond snagging as would often be the case with a weight. The only considerations would be castability and cost, it was never intended to be turned or milled after casting.

 

[ogberi]

I'll bet dollars to donuts it's chilled white cast iron. I tried turning a 5 lb hand weight, and found carbide would barely touch it. HSS tools, the workpiece simply ground the cutting edge right off. I thought it might be a hard skin, so I used an angle grinder to grind off about 1/4", and tried to drill it. Ruined a good HSS drill bit instantly. I believe those weights are cast from the skimmed off crunk, brute-force melted and poured hotter than the hinges of hell before it freezes mid-pour. Machining weights seems to be a crap shoot, some machine well, others are suitable only for doorstops. Sounds like you have a new doorstop.