Speeds for Machining Cast Iron Parts in Lathe

[Twizseven]

After advice on what sort of speeds people use to machine cast iron parts.  Having just made the Robinson Hot Air engine the main casting is of a reasonable size and necessitated using the 10" 4jaw chuck.  I ran this at my slowest speed which is 54rpm.  Problem I have is the gearbox is very noisy in this gear and does not sound very happy.  The next speed up is I think 85rpm which is quite a bit quieter.  Other speeds are quieter still.  Is this too fast a speed to use.  I appreciate it does depend a little on the size and shape of the casting you are trying to hold.

Smaller parts can always be done on the Super 7

Colin

[Jasonb]

Your biggest issue with that part would have been balance, if you had run at a suitable cutting speed then the lathe may have started to jump about a bit.

As you were using carbide you could have gone a lot faster. I often turn 9 - 10 " flywheel castings the around 300rpm which is towards the fast side as that suits the vari speed machines better. but if you work to 100m/min or 300ft/min that should be OK.

So take those numbers and divide by dia in ft x 3.142 for imperial or diameter in meters x 3.142 for metric.

Which for that 5" flange is 300 / (5/12 x 3.142) = 300/ (.416 x 3.142) = 300 / 1.309 = 229rpm

or 127mm is 100 /(0.127x 3.142) = 100/.399 = 250rpm

[john mills]

hi
i would think you could run faster with carbide tooling i would try see how long your tool lasts .years ago i had to programs old nc machines two lathes the lowest speed was  we  66 rpm on one of them the other i don't have seeds for but it was similar  we machined a lot of cast iron and sg iron lots of crane wheels and sheave wheels not many were less than 10" dia i remember some were more like 20" dia cutting speeds were much higher the speeds
Jasonb suggest should be ok try and see how the tool lasts and your lathe likes running at.the old lathes were a good size and heavenly built and did use coolant.
     John 

[steamer]

Also it depends on the quality of the iron.   If it's got a lot of hard spots, or inclusions, or just a lot of hard scale, can force you to run slower.....if it's got a "skin" make sure your first pass gets underneath it, and you'll need to slow it down as well....carbide tooling works best for that as well.

On the other hand

Durabar?    turns like butter....HSS works great.....

Dave

[Twizseven]

Thanks, Jason, John and Dave,

Will move to higher speeds unless shape, weight, size dictates otherwise.  Need to give my ears a rest.  Or I have to dismantle headstock on the Colchester which does not appeal.

Colin