Brian builds Atkinson Engine

[Brian Rupnow]

I bought some grey cast iron today from Barrie Welding here in town. They weren't sure about the "pearlitic" but they said that this cast iron material is what local engine rebuilders make cylinder liners from, and small custom cylinders. It is very fine grained with no voids, cuts extremely well, and is self lubricating. I bought a 5" length of 2 1/2" dia. and a 3" length of 1 1/2" dia. for ten dollars total. The material I bought comes in round bars of varying diameters.----Brian

 

[Brian Rupnow]

I've just chucked the 1.5" diameter peice of cast up in my 10 x 18 lathe and experimented with a few cuts. Yes, it definitly is DIRTY. Lots of black, nasty powder off it. Can someone advise me as to speeds and feeds with this stuff, and should I be using HSS or carbide tooling? My lathe has 3 "hi speeds", namely 550 rpm., 970 rpm., and 1620 rpm. When turning mild steel with HSS I generally take my roughing cuts at 550 rpm and finish cuts at 970 rpm. I only use the 1620 for finishing cuts on aluminum. All of the stock I generally work with ranges between 1/4" up to 1.5" diameter. I can't take more than a .010 deep cut with my machine. (Thats .020" on the diameter) in mild steel or my lathe shudders and wants to levitate. Does this cast iron have a hard outer "skin" that must be broken through? The HSS tools I currently have ground have no top-rake, as it doesn't seem necessary in aluminum or brass, and it seems to work fairly well turning mild steel. Should I grind an HSS tool with top-rake to turn this material? What kind of finish can I expect to get with turning only----no emery cloth after the fact. Lots of questions I know, but any help would be appreciated, as I haven't worked with this material before. I am not too concerned about the finish on the cylinder, as I plan on reaming the final bore and I can emery cloth the outer diameter to a good finish if I have to , but I do want to be able to turn a really good and accuratly sized finish on the piston when I get to it.

 

[swilliams]

A few answers Brian (not necessarily text book)

The cast bar shouldn't have a hard outer skin. You'll be ok turning it using HSS with no rake but you probably want less RPM, especially for the large diameter. Cast iron is soft and easy to turn, it's easy to get a good finish on. It will probably make your HSS tool go blunt more quickly than steel, especially if the speed is high. Mess aside the stuff is easy to work with, get stuck in, you'll be fine. Don't be shy about resharpening your tool.

Steve

 

[Captain Jerry]

Brian

I'll offer my 2 cents but I'm sure you will get more valuable information. Your lathe is bigger than mine and probably more rigid. I use brazed carbide tools and moderate high speed with up to .040 DOC for rough sizing. CI has very little flex and stands up to the cut better with no digging in if the cutter height is right. There is much less springback than with more flexible material. Second pass removes almost nothing. For finish cuts, you can go to higher speeds and slow feeds with a DOC of .001 or less. For finish cuts a radius on the tool tip is important. Even on good grade CI like DURABAR, the outer skin is tougher (slightly). Cuts of .010 might not be enough to get it.

I like to use brazed carbide with no top rake. BUT FIRST! I hone a very sharp edge on the tool with a small diamond disk. A fine carbide edge may be subject to chipping but I have almost no problem when turning good quality cast iron. It might be worse if using scrap or reclaimed stock. Interrupted cuts with carbide are more likely to chip but the tools are cheaper than HSS ( I can buy them for less than a dollar each and all I have to do is hone the edge, not grind to shape.

One problem that I found when I first experimented with CI is that since it is cut dry, you cannot baby the feed. Carbide can take the heat, HSS not so much.

Jerry

 

[Brian Rupnow]

Okay, guys and dolls---Its math time. I checked it out on the internet, and for grey cast iron the pundits recomend a rough turning surface speed of 24 metres per minute and a finishing surface speed of 41 meters per minute. Lets work with the roughing cuts first. 24 meters x 1000 divided by 25.4 divided by 12 gets you to 78.7 feet per minute surface speed. My material is 1.5" diameter, so 1.5 times 3.14 divided by 12 equals 0.392 feet around the circumferance of my material. My closest lathe setting to get where I want to be is 210 rpm. So---210 x 0.392 equals 82.32 feet per minute surface speed. (I had been trying to work with 550 and/or 920 rpm). To move on ahead to the finishing cuts, 41 is roughly 1.71 times faster than the 24 meters per minute, and since this math is linear, the rpm of the lathe should be 1.71 times faster than the roughing cut speed, so 1.71 x 210 equals 359 rpm. Also, 1.71 x 78.7 SF/M=135 surface feet per minute. My lathe has a 350 rpm setting, so that will get me a finishing surface speed in feet per minute of 350 x 1.5 x 3.14 divided by 12 equals 137.4 surface feet per minute, which is "pretty close" to the theoretical 135 surface feet per minute. I'm still not real sure on the HSS versus carbide tooling, but I will probably hog away the majority of the diameter with brazed carbide tooling and then switch to HSS with a fairly large nose radius for the finish cuts. Here is a link to the speeds and feed chart I used.
http://www.roymech.co.uk/Useful_Tables/Manufacturing/Turning.html

 

[ShedBoy]

I don't know what fpm I had going but I was running 325rpm on 25.4mm diameter and was having no issues cutting with a .047 wide HSS tool. Plunging making fins for a poppin. Finish will always look grainy I think (someone may know more than me) straight off the tool. Using carbide to clean the outside I was running 585rpm no problems. Yes it is horrible dirty stuff, I vacuum alot while the machine is feeding. I lapped the bore after drilling to a mirror finish with wet and dry on a stick, then copper pipe in bore with diamond paste all hand held lapping.

Brock

 

[Captain Jerry]

From that chart, it shows cutting speeds for carbide to be about 3 times faster than HSS and when the radius gets down to 7/8" for the piston it looks like about 600 RPM for rough and 1700 RPM for finish with carbide.

Jerry

 

[steamer]

Your feeds and speeds compute correctly. Jerry's comment on Carbide is also about correct.

Make sure your lathe has the power and rigidity to take the cut at speed with carbide and all is good...otherwise you make chip the tool.

Cool looking build.....i'll be watching!



Dave

 

[Brian Rupnow]

This is the finish I'm getting with a brazed carbide at 350 RPM (which is about 137 feet per minute surface speed.)

 

[kvom]

I plugged numbers into G-wizard and got the following for a .10" DOC:

Carbide tooling: 1217 RPM, 478 SFM, .007 IPR, 1.9 HP
HSS: 204 RPM, SFM 80, .015 IPR, .69 HP

If I force RPM to 550, then with HSS: 216 SFM, .015 IPR, 1.87 HP

 

[Jasonb]

I doubt Brians small machine will get anywhere near 0.1" DOC more like 0.02"

Myself I never bother working out speeds just suck it and see.

J

 

[AlanHaisley]

Brian,

Okay, guys and dolls---Its math time. I checked it out on the internet, and for grey cast iron the pundits recomend a rough turning surface speed of 24 metres per minute and a finishing surface speed of 41 meters per minute. Lets work with the

Remember that most tooling speed charts are designed to maximize production and minimize tool wear at the same time. So long as you don't go too fast and burn a tool, I'd look for finish quality and accuracy more than anything.

Alan

 

[t.l.a.r. eng]

Just a thought after studying the photo, try switching to HSS tooling. Grey iron usually cuts like butter with sharp tooling.

 

[Brian Rupnow]

What does DOC mean? To me it has always signified "Double Overhead Cam"?????

 

[Jasonb]

Depth of Cut.

And DOHC is Double overhead cam

J

 

[Brian Rupnow]

Thanks Jason--Now another question. My carbide tools are very pointed. I do have a green wheel for grinding carbide. Would it be reasonable to grind a radius on one of my carbide tool to expect a better finish?

 

[Jasonb]

I don't use the brazed carbide tools much now but when I did I did not put a radius on them, same when I use HSS just very little back clearance much like the one in your photo.

If you are having finish problems then swap the carbide for a similar shaped HSS tool.

J

 

[Brian Rupnow]

I tried grinding a rounded nose on a carbide to see what would happen, but really there was no improvement over the finish achieved with a sharp carbide---just a bit more chatter. My best finish results so far are with a carbide at .005 depth of cut and 350 rpm. With a newly sharpened HSS which has a slightly rounded tip (about0.030 rad) the finish is about the same at 350 rpm. If I want to, with the carbide I can take a .010 depth of cut and it really makes the dust fly but leaves a rougher finish.

 

[NickG]

Hi Brian, I use an HSS tool the same as I would use for brass, slightly rounded tip as you say and small top rake of a couple of degrees. If 350 rpm is your slowest speed you're right using that, would probably be better even slower.

Nick

 

[Brian Rupnow]

As promised, here is the initial machining of the cyllinder. Since my chuck wouldn't open far enough to grip the 2.5" diameter peice of cast iron, I put the reverse jaws in to hold it. Of course this doesn't hold it by very much, only about 3/8", I used my dial indicator and tapped the free end around untill it was running true, then drilled the end with a center drill so I could support the outboard end with my live center. My chinese lathe has an extremely wide saddle, so that always creates some problems in getting the tool to cover the full length of what you are machining---Thats why the topslide is setting at the angle it is. The cutting tool is setting "backwards" in the pictures because I wanted to "face" as much of the end of the material as I could reach. The turning was all done at 350 rpm with a brazed carbide. I found that a .010 DOC was about optimum for my machine. Why did I buy 2.5" diameter material when the cylinder is only 50mm (1.97") diameter?---Because that was a "short end" left over at my steel supplier, so I got it cheap!!! Right now I don't know what my next move will be. Probably I should bore and ream the center hole before I attempt to cut the fins on the outside of the cylinder---However, with so much material stuck out past the jaws, and such a small grip on the material, I may try to set up my steady rest (which I have never yet used) on the cantilevered end before doing any drilling.