Brass or Bronze for a leadscrew nut?

[Andrew TinsleyParticipant @andrewtinsley63637]

[Andrew TinsleyParticipant @andrewtinsley63637]

The above says it all, the nut being for a steel leadscrew,

Regards,

Andrew.

[MWParticipant @mw27036]

Supposedly you'll get more lifetime out of a bronze one, although i'm not sure how accurate that guess is.

Michael W

[Jeff DaymanParticipant @jeffdayman43397]

bronze (or acetal polymer ) would get my vote, if we're having a poll

(and the nut doesn't have to last 10,000 years…)

[Andrew TinsleyParticipant @andrewtinsley63637]

I seem to remember someone , somewhere, writing that bronze would wear a steel leadscrew, Where as brass nut would wear rather than the leadscrew. Ergo, it is preferable to use brass.

I have no idea if the above is true, hence my query. Obviously it is cheaper to make a new nut than a leadscrew.

Andrew.

[FMESParticipant @fmes]

Posted by Andrew Tinsley on 22/02/2018 15:35:12:

I seem to remember someone , somewhere, writing that bronze would wear a steel leadscrew, Where as brass nut would wear rather than the leadscrew. Ergo, it is preferable to use brass.

I have no idea if the above is true, hence my query. Obviously it is cheaper to make a new nut than a leadscrew.

Andrew.

Thats right Andrew, and I've seen many an example of gudgeon (wrist) pins in small two stroke engines well worn where in contact with the bronze, mainly due to the bronze picking up the fine metallic particles as parts wear and becoming quite abrasive.

BUT, bronze on a leadscrew is preferred as it will wear better as the cyclic operations are considerably less than a small engine, brass will also tend to 'squash up' giving a more sloppy fit over time.

Regards

Lofty

[Mick B1Participant @mickb1]

Posted by Jeff Dayman on 22/02/2018 15:00:13:

bronze (or acetal polymer ) would get my vote, if we're having a poll

(and the nut doesn't have to last 10,000 years…)

You mean like Delrin? I wouldn't've thought that would take the pressure of heavy forming or knurling.

I'd think bronze would be best. In any tribological situation with different hardnesses, the softer material will tend to get gritty particles embedded in it, which will then abrade the harder. But it should happen less with bronze than with brass, and bronze's higher strength will enable it to withstand higher pressures where tools have to be applied forcefully.

[Rick Kirkland 1Participant @rickkirkland1]

Very nice, , , , but what type or grade of Bronze? ? ? . . . . Ohh look, it's Tin Hat and coat on time. . .

[Andrew TinsleyParticipant @andrewtinsley63637]

I have heard that acetyl polymer is good for leadscrew nuts. It has even been suggested as a material for model IC conrods!

I can't believe the latter and would have grave doubts about the former. Can someone explain why it should be good for leadscrew nuts? I have certainly seen it used in the US for this purpose. however I am a doubting Thomas!

Andrew.

[Mick B1Participant @mickb1]

Posted by Andrew Tinsley on 22/02/2018 16:58:53:

I have heard that acetyl polymer is good for leadscrew nuts. It has even been suggested as a material for model IC conrods!

I can't believe the latter and would have grave doubts about the former. Can someone explain why it should be good for leadscrew nuts? I have certainly seen it used in the US for this purpose. however I am a doubting Thomas!

Andrew.

This outfit:-

http://www.thomsonbsa.com/lead-screw-nuts.html

…is proposing acetal for light- and medium load leadscrew applications. I can see it working well with positioning leadscrews for printers, electronic component inserters and suchlike, where there's little load, and that mostly square rather than parallel to the leadscrew CL. I.e., for the accurate transmission of motion rather than force.

Edited By Mick B1 on 22/02/2018 18:07:34

[MWParticipant @mw27036]

Speaking of bronze, people automatically assume that because it's a relatively softer material to machine than cast iron, that therefore it's easier to cast,

Brass and bronze are actually one of the harder ones to get right because of the alloying elements in them, zinc or tin.

Michael W

[FMESParticipant @fmes]

Posted by Rick Kirkland 1 on 22/02/2018 16:57:45:

Very nice, , , , but what type or grade of Bronze? ? ? . . . . Ohh look, it's Tin Hat and coat on time. . .

I only work with Admiralty Standard.

[Mick B1Participant @mickb1]

Phosphor Bronze PB102 machines nicely and wears well.

[Mark RandParticipant @markrand96270]

What's wrong with grey cast iron?

[HopperParticipant @hopper]

I used brass for the replacement half nut on my M-type some years ago. I'm sure it will outlast me.

Original half nuts on Myfords and other lathes including I think South Bend and Craftstman are made from Mazak, an alloy of aluminium, zinc etc and very soft, much softer than brass. I think the aim is to have the halfnuts wear out without wearing the precious leadscrew. A lathe with a worn leadscrew will never screwcut accurately, but one with worn halfnuts will. The halfnuts are meant to be a consumable, like brake pads and clutch plates. Easier and cheaper to replace than leadscrews.

And of course there is bronze and there is bronze. Phosphor bronze, if you read the specs, is recommended for use with hardened steel shafts, so I would hesitate to run it on a non-hardened leadscrew. Leaded bronze, sometimes called gunmetal, is more suitable for use against non-hardened steel.

Cast iron, as suggested in a recent post, would be good too. Cast iron and steel are a good and commonly used combination in bearing/shaft situations and the cast iron contains enough carbon to be "self-lubricating" to some extent and yet is quite hard so resistant to swarf embedding.

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