Sourcing gunmetal for leadscrew nuts.

Anyone know of a source please. I have tried several of the usual suppliers without any luck.

Andrew.

Most places call it leaded bronze grade LG2 or SAE 660. But it is bezt to make halfnuts from plain brass as it wears the leadscrew less.

Edited By Hopper on 30/03/2020 21:20:24

I bought some of this when I made some:

**LINK**

Thanks Hopper and Old Mart. Now I am confused, I was under the impression that gunmetal and bronze were somewhat different in alloy composition. I also thought that it was phospher bronze that could wear the leadscrew excessively and that gunmetal in fact was much better!

My very worn nut isn't brass because of its more reddish tinge I assumed it was either bronze or gunmetal. Anyone know for definite about the relative merits of brass, bronze, phospher bronze and gunmetal for leadscrew applications? Whatever material my nut is, it has certainly worn badly in both the axial and radial dimensions, the leadscrew shows no appreciable wear.

Thanks,

Andrew.

Bronze is an alloy of copper and tin, whereas Brass is an alloy of copper and zinc.

Gunmetal is an alloy of all three - mostly Copper and Tin but with a touch of Zinc too.

The properties vary according to the mix of materials. If you use Brass as Hopper suggests it might wear a bit faster but it will also be cheaper than bronze generally - so why not make two brass nuts whilst you are set-up to do so and not worry about both of them wearing out...your lathe may have seen a lot of use to get to the stage it is at....

Regards,

IanT

PS the main drawback of brass (at least from my point of view) is that the zinc can be leached out if used directly in boiler construction, which then weakens it - hence the use of bronze (e.g. no zinc to leach) for any brazed-in boiler parts...which is not a problem with leadscrews. Might not be as tough but will you use the lathe so much it's an issue?   

Edited By IanT on 30/03/2020 23:42:39

Phosphor bronze is harder again and is recommended only for with hardened shafts. LG2 is the recommended bronze for general bearing use on non-hardened shafts.

Havent seen gunmetal advertised in years. When was the last time guns were made from yellow metal? LG2 bronze seems to be the modern equivalent. It contains tin, lead, zinc, nickel and iron if it is made to full spec -- but probably varies depending on manufacturer.

Brass halfnuts, like Myfords cheapo Mazak ones are sacrificial like brake pads and clutch plates: they wear faster and save wear on the more important and expensive mating component. Unless you use your lathe all day every day, brass will outlast you.

But if you want bronze go with LG2.

Edited By Hopper on 31/03/2020 02:48:35

Edited By Hopper on 31/03/2020 02:49:58

Edited By Hopper on 31/03/2020 03:01:03

LG2 = Leaded Gunmetal

Yes but commonly referred to these days by most suppliers as LG2 Bronze, rightly or wrongly.

Edited By Hopper on 31/03/2020 09:13:57

Have you thought of just casting your new nut in white metal around the leadscrew? I think there has been a Model Engineer article about how to do this . It was many years ago, perhaps someone can find it.

I would think it's easier to screwcut a lump of commonly available brass or bronze in the lathe. It's a basic job and no need for a furnace, crucible etc. (Or sneaking in to use the kitchen stove and a stainless saucepan while 'er indoors is out shopping.) . Plus, probably harder to buy white metal than gun metal these days. Kind of a lost art that stuff is.

I reckon white metal might be a bit soft and allow chips of swarf to embed and score the leadscrew in the long run too.

There are several (even many?) different ‘white’ metals. I have two lumps of either about ten or twenty kg each but I’m not sure of the grade. Some have more lead (and less tin) while others have considerably higher tin content. Other metals may be included for other enhancements.

I suspect mine is of lower tin content, but should still be good enough to re-metal vintage tractor con rods (mine typically only run at up to 1200rpm).

LOL so much for it being hard to obtain then! You've got the market cornered.

(You havent been rushing out buying it up like toilet paper have your? )

Edited By Hopper on 31/03/2020 09:36:22

Many varieties of white metal / babbit. As ever getting the right one is essential for best performance. Which may be tricky these days. Not only the getting but also the specifications.

My wartime built Pratt & Whitney Model B 12 x 30 is said to have white metal half nuts. Obviously worn but still of decently functional standard despite having clearly been subject to pretty hard use over the years. Leadscrew has most of the wear

Advantage of bronze, gunmetal et al is that, for our level of use, pretty much anything will do.

Clive

I have used white metal often in a preserved railway context and I know the differences between grades! Compared to a simple turning and thread cutting exercise, it really isn't worth considering in my opinion.

The nut in question is off the downfeed of my Royal shaper. It isn't brass and has worn very badly. I appreciate that 50 thou backlash is neither here nor there in such a context. I am replacing the nut, purely because the backlash irritates me!

From what has been said, I might as well make a couple out of brass and be done with it! Much to my surprise I already have a 7/16" X 10tpi Acme tap in my collection, so all I need is a lump of brass.

Thanks everyone for the help and suggestions.

Andrew.

I've purchased some SAE660 (LG2) from Macc Models Ebay store in the past. It may be cheaper to buy from their web site but postage might have to be factored in. They also supply very thick walled tube which may offer a good starting point for a plain bearing if the dimensions are favorable.

Macc Models SAE660 bronze.

Some info about SAE660 from another web site.

Ed.

Edited By Ed Duffner on 31/03/2020 11:56:54

You didnt say it was a shaper downfeed screw and nut. Subject to shaper impact forces. Much more than a lathe leadscrew. Consider using the LG2 for more tensile strength and toughness.

Hello Hopper,

I did describe the application in another earlier post, but only got one reply, so I didn't bother to repeat all that again! I shall take your advice and use the LG2. Is that material the one that machines like mild steel? I know some of the bronze / gunmetal family can be a swine to work with.

Thanks,

Andrew.

It would help if we knew the size of the leadscrew. I bought the hollow stock as it saved waste and was cheaper, being sold by weight. Any of the bronzes or brass will do for non industrial use, keeping the leadscrew clean and well lubricated is the key to long life. I use spray chain grease on leadscrews and nuts, it gets in all the surfaces and can be applied easily.

.

Was this the one, Andrew ? ... **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=154383

Doesn’t look like you waited very long ... or am I missing some of the history ?

MichaelG.

Hello Old Mart,

As I said above the size is 7/16" x 10tpi . This means that none of the MaccModel or Metal 4U cast SAE660 rod with hole is going to work, as the cast in holes are all too big.

Thanks,

Andrew.