Brass lead screw nut or cast iron?

[dabear3428]

I agree it looks like brass in the photo on Amazon. Wear? The softer usually material wears out first. Would you rather the lead screw or the nut wear out first and need to be replaced? I also wondered about oiled (impregnated) bronze, as used for sleeve bearings/bushing. Would this be better than brass?

Likewise, if you had a cast iron vs brass gib against a steel way which surface would you prefer to wear out. Getting a new gib is certainly easier than resurfacing a way. Also, if the gib wears evenly you can just tighten it up... at least for a while.

i'm assuming that the steel lead screw would wear better than the cast iron. i'm planning on building the mount to adapt this to my mx-600A lathe so if the cast iron threads is not a huge drawback i can always mod it latter if and when it becomes an issue.
thanks to all for the input.

 

[B2]

There are different kinds of both cast iron and steel. I have limited experience with cast iron, but what I have says that it is hard and brittle and the hard stuff is difficult to work. Steel is commonly stronger, meaning that it can bend or stretch (tensile strength), but some forms are commonly hardened. I would not even start to make a cast iron lead screw or thread a rod. I would think that the threads would tend to break off after a while. However, I have tapped into the cast iron parts of my mill, and the threads were not all that clean. I have diamond sawed a cast iron sewer pipe off by hand. It was a slow go. Usually, when plumbers need to cut a cast iron pipe off they use a special chain with cutting wheels on it to wrap around the pipe and tighten it until the pipe breaks. When construction guys need to remove an old cast iron tub that is built in they start hitting it with a sledge hammer and it breaks up into pieces. If you tried to do that to a piece of steel it would just dent, not break. Anyway, if you knew what the materials types were you could look up the hardness values. I did a quick google for you about the two: https://www.rapiddirect.com/blog/cast-iron-vs-steel/

Having said all of that we still do not know the answer. One thing about these two items is that the nut is wearing all of the time, while only a portion of the lead screw is in contact with the nut for any given job. If you are always at the same spot on the lead screw then I would expect the steel lead screw threads to wear faster than the nut's threads. On the other hand if the nut were softer then maybe you never see the lead screw wearing. Lubricate a lot and keep it clean. Grit is your enemy. It is like sand paper. You would never wrap sand paper around your threads and think that they were not going to wear. I have used sand paper to hand remove material from my mill's hardened steel ways. It just takes some time, but it works.

 

[Jake M]

i recently purchased a amazon compound slade for my 9X24 mini lathe, this is to replace the aluminum compound that shipped with the lathe. the add clearly showed a brass nut for the lead screw, but what was shipped has the lead screw threaded into the cast iron of the slide and no separate nut. how big of an issue is this?

In context, I think the issue here is about zero. You're not talking about high end stuff here, you're in the price point where long term maintenance will involve replacement of parts, not hand scraping for bearing, and thus, not changing dimensions, so I see no cost to you in having the nut being directly part of the casting instead of separate. And one less point to wiggle... So functionally, no loss. As far as wear rate? No worries at all. EVERY lead screw has backlash, which ALWAYS must be accounted for when dialing dials. More can be annoying, but the mechanics of operation stay just exactly the same, no matter what. The reason you'd really call something like that out is if the screw wore down MORE (everything wears...), if the screw wore down MORE in the most commonly used area, and started messing with dimensions in a way that affected your work. Which it probably won't. But a worn nut... You'd have to wear it right out completely until it no longer retained the screw enough to keep the tool bit where you left it. I see no issue there. And the cast iron will wear well, and not be very non aggressive towards your lead screw. There are different grades of cast iron, which will give different degrees of long term performance, but even in the worst possible case........ I wouldn't sweat it.

i can use as is and later machine a brass nut and rework the slide to fit it.

Wholly unnecessary, but a very good project if you wanted to "make it yours". No down sides to that as long as you get the fits good, but I wouldn't. I don't think you'll see any difference in your work, accuracy, or enjoyment of the lathe.

 

[FOMOGO]

Another option for a nut is Delron. Check on you tube or google it for info. The round stock can be cut in half lengthwise, heated, and the pressed onto the screw for a perfect fit. Requires very little lubrication, and supposedly holds up well. On a mini lathe might last a life time. Will be giving this a try on one of my larger lathes. Mike

 

[RJSakowski]

There are different kinds of both cast iron and steel. I have limited experience with cast iron, but what I have says that it is hard and brittle and the hard stuff is difficult to work. Steel is commonly stronger, meaning that it can bend or stretch (tensile strength), but some forms are commonly hardened. I would not even start to make a cast iron lead screw or thread a rod. I would think that the threads would tend to break off after a while. However, I have tapped into the cast iron parts of my mill, and the threads were not all that clean. I have diamond sawed a cast iron sewer pipe off by hand. It was a slow go. Usually, when plumbers need to cut a cast iron pipe off they use a special chain with cutting wheels on it to wrap around the pipe and tighten it until the pipe breaks. When construction guys need to remove an old cast iron tub that is built in they start hitting it with a sledge hammer and it breaks up into pieces. If you tried to do that to a piece of steel it would just dent, not break. Anyway, if you knew what the materials types were you could look up the hardness values. I did a quick google for you about the two: https://www.rapiddirect.com/blog/cast-iron-vs-steel/

Cast iron is high in carbon. As cast, it is hard and brittle. Cast iron sewer pipe is white cast and it is both hard and brittle. There is no reason to further treat it to do its intended job. Cast iron use to make machinery is either grey cast or nodular iron. It has been heat treated to convert it from white cast to a softer and more ductile metal. As such, it is a totally different animal than white cast. It can be machined and has significantly higher impact strength. Cast iron has been used for more than 1oo years for automotive engine blocks with no undue concern about the strength of threaded holes. There would be no reason to expect a premature failure of a threaded hole for the lead screw in the casting.