# Turning cast iron, carbide or HSS preferred?



## Aaron_W (Apr 26, 2019)

I need to turn a couple of cast iron lathe chuck backplates. All I have at the moment is a set of 1/2" carbide insert bits. I do have some 3/8" HSS blanks I can grind. 

I've actually never used carbide tools, other than boring bars. Also my first time turning cast iron. I gave a test cut on the cast iron and am not impressed with the finish, but there are a million variables other than the carbide that could be to blame.

If HSS is generally preferred anyway, then it is worth putting this aside for a day and grinding some tools. If carbide works better, then I'll spend a little more time getting things adjusted right.

Plates are for 6" chucks on a 10x24 lathe. This is the first real project with this lathe since getting it set up.  


I can see why people don't seem fond of working with cast iron, it is like standing in front of a sand blaster.


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## 4ssss (Apr 26, 2019)

The carbide will hold up a lot better


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## jbobb1 (Apr 26, 2019)

When taking finish cuts, un-coated carbide seemed to give a better finish for me.


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## mikey (Apr 26, 2019)

I would use carbide, too.


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## Aaron_W (Apr 26, 2019)

Ok, it looks unanimous, I'll keep at it with the carbide.


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## benmychree (Apr 26, 2019)

If one does not like to be sand blasted by chips, you can use a paint or chip brush to stop the stream and just let them fall into the chip pan; same goes for bronze chips.  Unlike some, I like machining cast iron.  A sharp tool with a small radius should give a good finish with a fine feed.


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## darkzero (Apr 26, 2019)

CI is really abrasive & killer on HSS. It can be done though if you don't need to machine a lot of it & not in a rush. I don't mind machining cast iron, it machines nicely with no cutting oil needed but the mess & clean up sucks!


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## stupoty (Apr 26, 2019)

I use almost exclusively HSS tools on my lathe, for cast Iron I use the brazed carbide type tools, they hold up pritty well to it's abrasive nature.

Stu


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## mikey (Apr 26, 2019)

Aaron, you can use carbide inserts or brazed carbide. Even HSS will work but won't last as long. If you go with carbide, try turning the tool and use the edge right behind the nose radius on your finish passes - makes a really nice finish.


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## Titanium Knurler (Apr 26, 2019)

Aaron, I just turned down a Shar’s D1-4 back plate for their set-tru-style ER-40 collet chuck the other day. This was my first time turning down a back plate and working with cast iron so I contacted Seco and asked for their recommendations. They recommended their CP500 carbide insert for cast iron, especially if there are interrupted cuts(screw holes) to contend with.  I turned down the OD, face and adapter boss OD. Here are their recommendations and some photos:











Hope that helps


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## mikey (Apr 27, 2019)

I would suggest you cover EVERYTHING that isn't actually involved in the cut, and cover anything close by, too. I promise you will be glad you did.


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## Aaron_W (Apr 27, 2019)

No screw holes to deal with, I have to add those myself, a chance to use my transfer screws.

I know very little of carbide, but what I have came with the lathe, a set of 1/2" holders made by H.B. Rouse. They have silver grey triangular inserts maybe 3/8" along each side. I don't know if these are good or cheap, but they say made in U.S.A. so guessing at the least they are not bottom of the barrel ebay specials.

On the surface finish, it seems I was just being too timid and taking too light of a cut. I cranked it up and by taking 2-3x deeper cuts I'm getting a nice shiny finish.


I've been able to spend very little time in the shop the past 8 or 9 months, but it is starting to come back to me.


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## Aaron_W (Apr 27, 2019)

mikey said:


> I would suggest you cover EVERYTHING that isn't actually involved in the cut, and cover anything close by, too. I promise you will be glad you did.




Too late, but I have a shop vac. The chips are like grains of sand, not the dust I've heard about so they don't seem to travel all that far.


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## ch2co (Apr 27, 2019)

I’ve found that there is cast iron and then there is cast iron. Often completely different beasts. Carbide preferred.


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## MarkM (Apr 27, 2019)

On uninterupted cuts I ll use brazed c2 carbide.  There are times though I like hss with high cobalt  just for the fact if I lose the edge I can just go over to the grinder and touch it up rather than eat up an insert.   I usually start with the high speed for economics.
I d suggest to wipe down the oil and cover your ways and whatever you can.  I use foil to cover and tape a section to the crosslide to overlap the ways.  I actually don t mind cast,  but it can be quite mysterious with imperfections.


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## Tozguy (Apr 27, 2019)

As Mark I use C2 brazed carbide for cast iron. C5 or C6 grade carbide does not seem to be as shock resistant.
Aaron, the shop vac idea is what I use as well. It might have helped to wet the c.i. with kerosene or furnace oil to keep dust down.
Those triangular inserts should work, is that what you used?


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## stupoty (Apr 27, 2019)

mikey said:


> I would suggest you cover EVERYTHING that isn't actually involved in the cut, and cover anything close by, too. I promise you will be glad you did.



I sometimes ware a dust mask when turning cast iron, when I don't my nose blows are a very cast iron graphite colour 

Stu


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## stupoty (Apr 27, 2019)

Aaron_W said:


> On the surface finish, it seems I was just being too timid and taking too light of a cut. I cranked it up and by taking 2-3x deeper cuts I'm getting a nice shiny finish.



If you need to take small cuts you can crank up the feed rate, cast iron likes a lot of feed from my experience.

Stu


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## Titanium Knurler (Apr 27, 2019)

stupoty said:


> I sometimes ware a dust mask when turning cast iron, when I don't my nose blows are a very cast iron graphite colour
> 
> Stu



Maybe more than I wanted to know


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## stupoty (Apr 27, 2019)

Titanium Knurler said:


> Maybe more than I wanted to know



I was trying to be subtle but I couldn't think of a way , very sorry 

I think it's an under rated thing to be careful of with cast iron, their is a lot of silicon in it and I under stand in the olden days when people did a lot of cast iron and before extraction was common (as were dust masks  ) that water was often used insted of cutting fluid to keep dust down.

Stu


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## MarkM (Apr 27, 2019)

You know stupoty I am going to start wearing a mask from now on.  Thanks!


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## Titanium Knurler (Apr 27, 2019)

Stu, was just kidding, of course.  It is a serious topic but just struck me as humorous for some reason.  Mike


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## Cooter Brown (Apr 27, 2019)

Grey cast will make HSS scream super load but Ductile iron cuts very nicely with HSS..... Grey cast makes powdered chips and Ductile iron makes curly  chips that look like 12L14 chips....


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## darkzero (Apr 27, 2019)

stupoty said:


> I sometimes ware a dust mask when turning cast iron, when I don't my nose blows are a very cast iron graphite colour
> 
> Stu



I was making 2 chuck back plates the last time I machined CI & didn't wear a mask. When I went to wash my hands & face my nostrils were black. My dinner also tasted very irony that night for some reason.


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## Cooter Brown (Apr 27, 2019)

Here are some pictures from when I cut a back plate for a lathe chuck that was made out of grey cast.... I had to use carbide to cut this type of cast iron, I tried HSS and it made the loadest screeching sound I have ever heard so loud that I started to lose control of my hands lol....
It made a massive pile of powder...


I chucked my 6" 3 Jaw in an 8" 4 Jaw to turn down the back plate OD to match the chuck.....


This is a South bend Heavy 10 with a 3' bed....


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