Aluminium as a feed nut

[Ian S CParticipant @iansc]

I was called in to sort out the excessive play in the cross slide lead screw on a ML 7 lathe, it was thought that a new nut would fix it, but on examination , the steel screw was very badly worn, but the nut appeared to be quite good. The lathe had been used in a motor garage, the main thing it was used for was polishing comutators with emery cloth, and the abrasive had become embedded in the soft metal of the nut. I was able to get a nut and lead screw for its original price of $NZ 5 as new old stock.

Ian S C

[Piero FranchiParticipant @pierofranchi37209]

Had a start at making the test sample out of aluminum today,

good job to as it taught me the best sequence of doing it.

 

the original was a bronze type nut, of about 1 & 3/4 inches by 1 & 1/2 by 1 & 1/2

 

if any one can spare a off cut please pm me

Edited By Piero Franchi on 31/12/2017 15:07:22

Edited By Piero Franchi on 31/12/2017 15:07:42

[Perko7Participant @perko7]

The brass lead-screw nut on the cross-slide on my 1927 Ideal lathe gave way about 12 months ago, i made up a new one out of ZA27 alloy supplied by a friend with a home foundry. So far it has not shown any signs of excessive wear. I keep it well-lubricated but other than that it lives in a tunnel full of swarf and other nasties.

[Piero FranchiParticipant @pierofranchi37209]

From what others have said, I am inclined to agree about the environment of this feed nut and aluminum being more prone to ingress in-bedding into it and causing extra wear on the feed screw

ill be looking on flee bay for a bit of aluminum bronze

[SillyOldDufferModerator @sillyoldduffer]

Hi Piero,

You asked earlier 'which is better, brass or bronze'?

The answer depends on what you need. Bronze is 'better' as a material than Brass for this application, but Brass has a long history of being used as well. Both alloys are suitable for bearings, bronze being superior.

Bronze will last longer but it's more expensive and harder to machine. A Brass nut won't last as long, but it will be cheaper and easier to make.

So how long does the replacement have to last? Strikes me that the nut won't work hard in a Tool and Cutter Grinder but it will be exposed to grit. Perhaps you should think of the nut as a consumable item. If it lasts 5 years, you've won, if it only lasts 6 months, think again. I'd be inclined to use Brass, perhaps making a spare while I was at it.

There's a collision of ideas in this department:

1. Do it properly, fix it once, using the best materials. The problem with this approach is the risk of time and money wasting, with chaps proudly producing gold-plated products too late that can't be sold at a profit.
2. Make it 'fit for purpose' using cost-cutting methods in the understanding that all engineering solutions have a limited life. The problem with this approach is the risk of time and money wasting due to the solution being cheap to the point of nastiness, or even a horrible bodge!

Coming to a balance is all part of the fun. In the case of your nut, I suggest:

• Aluminium is cheap and easily machined but almost certainly too soft to last.
• Brass is relatively expensive, very easily machined and 'fit for purpose' for light to moderate use.  It's also easy to source.
• Bronze is most expensive, harder to machine and best for moderate to heavy use. An expensive bronze bearing may demand regular maintenance; it cost so much you have to look after it. Normally Bronze would last longer than Brass but the presence of grit in a grinder might remove that advantage unless you keep it clean.

Really useful if you can tell us later what you did and how it worked out.

Dave

Edited By SillyOldDuffer on 01/01/2018 10:52:59

[Ady1Participant @ady1]

Made an ally feed nut for my drummond leadscrew years ago, also the small backgear cog

Been great so far and I'm a pretty rough user, burned through two bronze nuts in two to three years

I use T6 aluminium

edit: I wouldn't go back to bronze, ally is a doddle to cut and very hard wearing

Edited By Ady1 on 01/01/2018 20:20:33

[Howard LewisParticipant @howardlewis46836]

One scarcely mentioned aspect here, is lubrication.

Camshafts / Big Ends running direct in the parent metal have a pretty much constant supply of lubricant; often pressure fed, which is why they survive under conditions of high rubbing speeds and loads. Leadscrew nuts tend to be lubricated, as and when we think about/remember it, consequently, swarf and abrasives tend not to be flushed out, (even with manual pump systems)

Rubbing speeds on leadscrews and nuts are unlikely to be high, but loads can be fairly high if deep cuts are made.

The one combination to avoid is using the same material for both halves of the bearing/shaft or nut/leadcsrew, because this is likely to lead to galling unless very well lubricated.

I need to practice what I preach and lubricate my machine more frequently!

Howard

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