# The Bronze-Loaded Acme Nut Experiment - Part 1



## graham-xrf (Mar 10, 2021)

*Part1* because this is not yet a bronze loaded ACME nut for a compound leadscrew. It is a humble M12 bolt pressed into being a test dry run. This is part of my messing with the compound weld repair, trying to fix up what I can before putting it together again. This also ended up as a bit of a picture show.

My notion is driven by the anecdotes and advertisements for stuff like *Turcite*, *Rulon*, *Metal Loaded PTFE* etc. Metal powder loaded plastic. If the plastic is tough, like Delrin (Nylon), that's good, but requires the metal be in the mix when the nylon is chemically made. Other plastics that are melt-able have a better chance, but I decided to experiment with J-B Weld 3960 PSI "MarineWeld", loaded up with brass er.. bronze powder. Maybe I have the wrong grade powder, but one has to start somewhere. I tried to load up 16g of powder into 4g of epoxy mix. I gave the old bolt the car polish "Turtle Wax original" treatment, and helped it along with some leftover vacuum chamber grease, as release agent. This lets you know that old can of car polish had been in the dusty corner for at least 2 decades. It still seems to polish car!

A re-purposed soft drinks cordial plastic bottle top provided the mold. The powder is hyper-fine, and hard to control. It "pours", and can get everywhere. Being copper + tin, it is very toxic, the dust not to be breathed. Working on this stuff with the safety glasses, and the 3M mask makes one look like auditioning for "Alien" or "The Fly"!



	

		
			
		

		
	
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Getting the powder mixed in on a sacrificial bit of old card was a bit fraught. It made me think that it would not end up "liquid enough". I think I got more than 80% of the bronze into it, and I kept thinking I maybe needed coarser bronze instead of 230 mesh, but in the end, it went into the mold, and took on that "wet" looking surface. 4 to 6 hours to set. 16 hours to cure hard. I left it to the following day.



	

		
			
		

		
	
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Way-hey! I made a plastic nut! It did not look very "bronzy" to me, but then, not the dark grey of J-B Weld either. The question was, would it come off the bolt?
The answer is "Yes". The initial stickiness is broken with a little shove by spanner, then one can turn with the fingers. It was a little "stiff", in places, and "bumpy", which turned out to be that I had casually "flattened off the sharp tops" of the threads with a file. Inevitably, not equal everywhere, and sometimes not so round, this was a mistake!



	

		
			
		

		
	
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The threads inside are a perfect zero backlash copy of the bolt. The plastic nut actually goes onto unsullied M12 bolts quite easily, using fingers, with a slight "firmness". If you catch the light at just the best angle, you can see the bronzy glint speckles in the threads. I am thinking I should have tried harder to get more bronze into the goop, or maybe have a coarser grade of bronze. I also think that there are perfectly good adjustable anti-backlash nut designs that can happen in all metal, but of course, this way is cheap and easy enough to get up a few nuts as needed. Getting a version integrated onto something that would mount into a South Bend compound, or cross-slide requires more, not yet figured out.




So OK - a little experiment. Right here, hardball chip-making folk with the perfume of burning coolant all around should try not to laugh (too much)!


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## Nogoingback (Mar 10, 2021)

Good thinking!


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## graham-xrf (Mar 10, 2021)

A little update. One can "shave" the plastic with a scalpel. It's tough!
What is under there is as in the picture.




It's pretty much all metal-looking, except I did not make the internal threads with a turning operation, and they could just as easily be ACME 10TPI on a 3/8" screw. Is this what we want?

It makes me think that a "quick 'n dirty" fix might be to drill out the old Acme nut, and use it as a mold with the screw set into the hole.

Even quicker and dirtier, is not to bother drilling it out. Just make a "repair" by putting release agent only on the leadscrew, and letting the bronze epoxy take up the backlash.

Then there is the fastest, and "disgustingly filthiest". Not bothering with the release agent on the leadscrew, by leaving all the old oil and grease on it, and only cleaning the nut with brake cleaner/alcohol/IPA and rough up a little to help adhesion. It will fit right back into the lathe as is! 

[Edit: Nah - last notion is doomed. Can't get the leadscrew up the old nut while keeping it clean.]


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## RJSakowski (Mar 10, 2021)

@graham-xrf , Nylon and Delrin are two different plastics.  Delrin is a trade name for acetal or polyoxymethylene and nylon is a common name for polyamide.  A touch with a soldering iron will make the difference very apparent.  IMO, Delrin is a superior plastic to Nylon in mechanical properties. 

Both plastics are thermoplastics and can be melted.Nylon melts at a higher temperature than acetal; approx. 250ºC vs. 170ºC.  The operating temperature range is fairly small as both will start to decompose at higher temperatures.  A small solder pot with temperature control might suffice.

Matweb is a good source of information about materials.


			Metal, Plastic, and Ceramic Search Index


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## mickri (Mar 10, 2021)

You may not need the bronze filler.  Epoxy thickened with cabo sil has been used on boats for decades to make threaded holes for bolts.  West System has info in their books and probably on their website on how to do this.  A paste of epoxy and carbon fiber would be just as strong as steel.  Easier to use too.  Saturate the carbon fiber with epoxy and wrap it as tight as you can around the bolt.

You also shouldn't need to let the epoxy fully cure before removing the bolt.  It just has to go off.  After 4 or 5 hours the epoxy will still be slightly flexible but won't lose its shape when you remove the bolt.  Fully cured epoxy will be formed to any irregularities in the bolt and you may not be able to remove the bolt.


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## MrWhoopee (Mar 10, 2021)

I like it. 

First, a question. Was it brass or bronze powder? You used both terms and they are different. Bronze is the preferred material for lead-screw nuts.

Second, a correction. Delrin is acetal not nylon.

Third, the characteristics that make Turcite and Rulon suitable replacements for bronze are the self-lubricating, wear-resistant nature of PTFE (Teflon) and the rigidity produced by the added fillers.  Rulon is PTFE based while Turcite is acetal with PTFE added.






						Rulon® Fluoropolymers
					

Rulon fluoropolymer PTFE seals offer a range of fluoropolymer blends that can be used in engineering critical parts to provides wear and friction control.




					www.seals.saint-gobain.com
				












						Turcite® |  Aetna Plastics
					

Turcite® is an internally lubricated, acetal-based material (with properties similar to those of Delrin AF) designed for applications with demanding wear and friction requirements. Turcite® creates...



					www.aetnaplastics.com
				




Machinists can be nit-picky bastards.

I still like your thinking.


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## graham-xrf (Mar 10, 2021)

RJSakowski said:


> @graham-xrf , Nylon and Delrin are two different plastics.  Delrin is a trade name for acetal or polyoxymethylene and nylon is a common name for polyamide.  A touch with a soldering iron will make the difference very apparent.  IMO, Delrin is a superior plastic to Nylon in mechanical properties.
> 
> Both plastics are thermoplastics and can be melted.Nylon melts at a higher temperature than acetal; approx. 250ºC vs. 170ºC.  The operating temperature range is fairly small as both will start to decompose at higher temperatures.  A small solder pot with temperature control might suffice.
> 
> ...


Thanks RJ.
So - I could get a lump of Delrin, and melt it, and so have a way of stirring in bronze powder. Of course, many folk turn up new leadscrew nuts straight out of Delrin. It's apparently quite good without any metal loading, and perhaps turning or tapping an Acme thread in is less hassle than melting and casting.

Acknowledgements to @mickri . I never knew that about boat repair.I could make a carbon fibre/epoxy insert, and glue it into a drilled out nut, or even start over with the nut cylinder, make the Acme insert, and then turn it down to drop into the lathe mounting. That last part has to be done without using the compound, and if it is a cross-slide nut you need, then you need another lathe


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## mickri (Mar 10, 2021)

I would cast the epoxy in the nut.  Don't even need to drill out the nut.  It would be better if the inside is all messed up.  This would give the epoxy more surface area and irregularities to bond to.  You could do it with everything in place on the lathe.  Perfect alignment.  Goober up the lead screw with epoxy and slip the nut into place.  Let it cure for 4 to 5 hours and remove it.  Clean up the excess epoxy before it fully cures.  Easier that way.

You want your epoxy mixture to be the consistency of peanut butter or even a little thicker.


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## graham-xrf (Mar 10, 2021)

MrWhoopee said:


> I like it.
> 
> First, a question. Was it brass or bronze powder? You used both terms and they are different. Bronze is the preferred material for lead-screw nuts.
> 
> ...


This is OK. The pictures are thumbnails, but only 1280 x 1024, so not too much mileage on the full size when zoomed, but you can see the powder is definitely bronze. One can get all sorts of proportion bronze, e.g. the marine version is very different from the kind they use to make statues, but I just used the only "bronze powder" I could find on eBay that was not some kind of cosmetic plastic flakes.

This one is 88.98% copper, 10.90% tin, 0.05% lead, 0.032% phosphorus and 0.012% iron - trace amounts.
I have seen advertisements for metal loaded plastic bearings used in industry.
My version has some less than laudable motivations. Keeping the main focus on the pending weld onto cast iron adventure, I was trying for a "quick ,n dirty" that would fix the sloppy leadscrew without needing the lathe itself to get to turning an internal Acme. It was a short-cut without any pretensions to making a very fine Acme nut project.

Ta for the links to Turcite and Rulon


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## RJSakowski (Mar 10, 2021)

I assumed your exercise was ti provide an alternative to cutting an Acme thread.  Some people don't have the capaqbility of single point cutting an Acme thread and Acme taps rend to be pricey.

There was a You Tube video on casting a lead screw nut some time ago.  I don't recall what plastic was used though.  Delrin has a certain amount of "give" to it which could be undesirable.  I would think that a bronze filled Delrin would be better in that respect.


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## graham-xrf (Mar 10, 2021)

mickri said:


> I would cast the epoxy in the nut.  Don't even need to drill out the nut.  It would be better if the inside is all messed up.  This would give the epoxy more surface area and irregularities to bond to.  You could do it with everything in place on the lathe.  Perfect alignment.  Goober up the lead screw with epoxy and slip the nut into place.  Let it cure for 4 to 5 hours and remove it.  Clean up the excess epoxy before it fully cures.  Easier that way.


This is good!
To be clear, you mean to put release agent on the screw before goober up with epoxy, then screw it into the (clean) nut which has already got it's share of plastic. Then assemble the whole thing into the compound, gib and all, and wait..?


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## graham-xrf (Mar 10, 2021)

RJSakowski said:


> I assumed your exercise was ti provide an alternative to cutting an Acme thread.  Some people don't have the capaqbility of single point cutting an Acme thread and Acme taps rend to be pricey.
> 
> There was a You Tube video on casting a lead screw nut some time ago.  I don't recall what plastic was used though.  Delrin has a certain amount of "give" to it which could be undesirable.  I would think that a bronze filled Delrin would be better in that respect.


Yes indeed! I am considering metal loaded melted Delrin. For me, the avoiding of cutting an internal Acme was about the "Catch-22" that the lathe to do the cutting was already knobbled by the compound being missing/worked on, and that SB-9A is in tiny pieces, and ex-workshop has no power anyway. Without going to the obvious pun, I am already somewhat screwed!

I think the video you mean is on post #30 of the thread --> HERE
The video is a bit yuk for purist machinists, but..
To save folk trawling the whole thread, the YouTube link is here -->


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## Superburban (Mar 10, 2021)

Very cool, gives me lots of ideas. A couple of thoughts, A slightly flexible epoxy (if there is such a thing), might be better for lead screws, as I bet most that are at the point of looking for a nut, are also worn, and most likely in the center, and not as much the ends. A softer compound may flex enough to not get tight at the ends, and still give good fit in the center.
Don't know what order you mixed the components, but I would mix the brass powder with one part of the epoxy, then mix in the second part.

Now I will be thinking about all the different two part plastics/ epoxies, and other compounds, and wondering what would give the best results.


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## graham-xrf (Mar 10, 2021)

Superburban said:


> Very cool, gives me lots of ideas. A couple of thoughts, A slightly flexible epoxy (if there is such a thing), might be better for lead screws, as I bet most that are at the point of looking for a nut, are also worn, and most likely in the center, and not as much the ends. A softer compound may flex enough to not get tight at the ends, and still give good fit in the center.
> Don't know what order you mixed the components, but I would mix the brass powder with one part of the epoxy, then mix in the second part.
> 
> Now I will be thinking about all the different two part plastics/ epoxies, and other compounds, and wondering what would give the best results.


Nope - I did it the stupid way! I had to move real fast to get the metal in, which is why I spilled about 5% to 10% of the powder, and it complicated the clean-up. There is pretty much no flexibility in the test nut. I am considering @RJSakowski 's suggestion of melting the more flexible plastic. The notion of a carbon fibre wrap, held together with plastic. is a valid reinforcing for the thermoplastics, and the various other you may be considering.

The dissimilar metal bronze-to-steel in oil is a very good, long-lived bearing interface. PTFE, I think, needs to be a florethylene with additives, so not to "cold flow" under pressure, but for us, is unsuitable because it is not a thermoplastic. If loaded up with metal, that has to happen when the plastic is made.

I take it you mean to mix the powder with the epoxy, then add the hardener, though I suppose it would still work if the powder went into the hardener first.


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## MrWhoopee (Mar 10, 2021)

I haven't heard of anyone doing it, but making a "hot nut" using Delrin AF (PTFE filled acetal) might be the hot ticket, so to speak.


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## homebrewed (Mar 10, 2021)

I note that you've seen descriptions of reflow-forming acetal around a piece of Acme-threaded rod.  Are you avoiding that approach in the quest to incorporate bronze powder into your cast nut?


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## graham-xrf (Mar 10, 2021)

MrWhoopee said:


> I haven't heard of anyone doing it, but making a "hot nut" using Delrin AF (PTFE filled acetal) might be the hot ticket, so to speak.


I am already looking to order in some Delrin and thinking on how to do the "hot nut pour" fix. It's as cheeky a fix as they come. It can hardly hurt to include some metal powder.

Please clarify "Delrin AF". Is that a grade? Now searching on "Delrin AF".


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## mickri (Mar 10, 2021)

No plastic in the nut.  The nut would have to be buggered up enough to slip over the lead screw.   If you screw the nut on you may not get a good coating of epoxy everywhere.

Anything that you don't want the epoxy to stick has to be covered with mold release wax.  Any hard wax will work.  Some people even claim that shoe polish works.  I use Maguires mold release wax.  There are two schools of thought on mixing the filler and resin.  One school is mix your epoxy like Superburan said.  Mix the filler and the resin first.  Then add the hardner.   The other school is to mix the resin and hardner first then add the filler.  I have done it both ways and never noticed any difference in the end result.  The most important thing is to make sure that you have everything mixed very good.  You will have plenty of time to goober up the lead screw with epoxy.  Don't skimp on the mixing.  Goober up the lead screw and slip the nut into place.  It doesn't hurt to wrap everything with siranwrap (sp?) to keep any epoxy from oozing out.  And assemble everything together.

If you are concerned about wear in the lead screw do the molding at a non worn part of the lead screw.  In my experience epoxy doesn't flex when fully cured.  It will be hard.

I don't know if this will work with JB Weld.  I buy my epoxy by the gallon from US Composites in Florida.  I use it a lot on my boats.  I use their 3:1 mix.  3 parts resin to 1 part hardner.  It is better to mix more than you need.  For the size we are talking about I would mix 3 tspn of resin to 1 tspn hardner.  You will have at least 15 to 20 minutes to get everything goobered up and in placed before the epoxy starts to go off after you are done mixing.

Sounds like you are getting several options to explore.


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## graham-xrf (Mar 10, 2021)

homebrewed said:


> I note that you've seen descriptions of reflow-forming acetal around a piece of Acme-threaded rod.  Are you avoiding that approach in the quest to incorporate bronze powder into your cast nut?


It's only that the re-forming as seen in the video then ends up with something that requires a turning operation to finish it into something that will fit into the lathe. This time, the lathe is knobbled by not having it's nut. I would go for hot plastic without additive, but I thought that might wear out too quickly.


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## MrWhoopee (Mar 10, 2021)

graham-xrf said:


> I am already looking to order in some Delrin and thinking on how to do the "hot nut pour" fix. It's as cheeky a fix as they come. It can hardly hurt to include some metal powder.
> 
> Please clarify "Delrin AF". Is that a grade? Now searching on "Delrin AF".


*Delrin*® *AF* Blend is a unique thermoplastic material for use in moving parts in which low friction and long wear life are important. It is a combination of PTFE fibers uniformly dispersed in *Delrin*® acetal resin. ... Bearings made of *Delrin*® *AF* Blend can operate at higher speeds while exhibiting reduced wear.


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## benmychree (Mar 10, 2021)

Just how much backlash does your compound have?  Backlash in a lathe compound is normally not much of an issue, since they do not get much use, compared to a cross slid nut, and that nut is generally a big issue until it is in the order of perhaps 1/4 turn, when it makes jobs such as threading a bit clumsy.


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## benmychree (Mar 10, 2021)

"Being copper + tin, it is very toxic, the dust not to be breathed. Working on this stuff with the safety glasses, and the 3M mask makes one look like auditioning for "Alien" or "The Fly"!
Neither copper, nor tin (especially tin) are particularly toxic, but perhaps we should not breathe the dust, which may injure the lungs.


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## graham-xrf (Mar 10, 2021)

benmychree said:


> "Being copper + tin, it is very toxic, the dust not to be breathed. Working on this stuff with the safety glasses, and the 3M mask makes one look like auditioning for "Alien" or "The Fly"!
> Neither copper, nor tin (especially tin) are particularly toxic, but perhaps we should not breathe the dust, which may injure the lungs.


Hmm - I have read that the copper content in brass is so toxic that bacteria can only survive on it for a minute or two, a perhaps unintentional benefit to those brass pole swing door handles. As to tin, my chemistry high school teacher told us that stannous anything is poisonous. The same teacher mentioned that nearly all metals except gold, platinum, and, in small quantities, some iron are bad for you. When the metals are locked into compounds, then most become safer - with exceptions.

The bronze safety mention was because of the warnings on the label about using an approved respirator. I think it is because of it being such fine dust. Clearly our bronze statues are not a danger to us!


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## matthewsx (Mar 10, 2021)

MrWhoopee said:


> I haven't heard of anyone doing it, but making a "hot nut" using Delrin AF (PTFE filled acetal) might be the hot ticket, so to speak.


I have done it and it does work. Delrin is fine without additives.


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## benmychree (Mar 10, 2021)

graham-xrf said:


> Hmm - I have read that the copper content in brass is so toxic that bacteria can only survive on it for a minute or two, a perhaps unintentional benefit to those brass pole swing door handles. As to tin, my chemistry high school teacher told us that stannous anything is poisonous. The same teacher mentioned that nearly all metals except gold, platinum, and, in small quantities, some iron are bad for you. When the metals are locked into compounds, then most become safer - with exceptions. The bronze safety mention was because of the warnings on the label about using an approved respirator. I think it is because of it being such fine dust. Clearly our bronze statues are not a danger to us!





graham-xrf said:


> Hmm - I have read that the copper content in brass is so toxic that bacteria can only survive on it for a minute or two, a perhaps unintentional benefit to those brass pole swing door handles. As to tin, my chemistry high school teacher told us that stannous anything is poisonous. The same teacher mentioned that nearly all metals except gold, platinum, and, in small quantities, some iron are bad for you. When the metals are locked into compounds, then most become safer - with exceptions. The bronze safety mention was because of the warnings on the label about using an approved respirator. I think it is because of it being such fine dust. Clearly our bronze statues are not a danger to us!


But, we are talking metallic tin here, used to line cooking vessels, tin cans, etc, not stannous compounds, same for copper, in the metallic form not toxic, but in compounds, notably so.


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## DAT510 (Mar 10, 2021)

Overall and interesting concept.  I like the out of box thinking.

You mentioned you can't used your lathes to make a new nut or I get the impression you would try to single point a new one? 

What about purchasing a new blank ACME 3/8 -10 tpi nut and machining it to fit?  Looks like you're in the UK.  Is there a supplier like McMaster Carr?









						McMaster-Carr
					

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.




					www.mcmaster.com
				




But if it's more about the journey.... I get it!


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## graham-xrf (Mar 10, 2021)

benmychree said:


> But, we are talking metallic tin here, used to line cooking vessels, tin cans, etc, not stannous compounds, same for copper, in the metallic form not toxic, but in compounds, notably so.


As I understand it, the plating on the inside of a tin can is to stop it rusting through. The inside of the can also has a very thin film of plastic to stop acidic and sugar compounds taking on the tin.

Years ago, I disposed of all aluminium cooking pots, pans, etc. It did not escape my notice what happens to the inside of the pot below, compared to above the level of the cooking fluids. The old cast iron pots are the harmless ones. Stainless steel is OK for cooking. The chromium stays in the pot. The thing about metals is something I have had all my life, taught from as far back as I can remember - except for the thing about aluminium, which I may have picked up from a science magazine.

It may be a wild tale, but the aluminium ingestion from dissolved into solution, or ingested via oxides is reportedly associated with Alzheimer's I think the hard evidence is inconclusive, but the lady of the house says she does not care to spend years allowing an irreversible process until we find out for sure. This is like the smoking and cancer thing. The statistics were there, but the direct mechanism was not known.

Some info from 2020 --> LINK
I am sure you can find articles to the contrary!


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## graham-xrf (Mar 10, 2021)

DAT510 said:


> Overall and interesting concept.  I like the out of box thinking.
> 
> You mentioned you can't used your lathes to make a new nut or I get the impression you would try to single point a new one?
> 
> ...


No -  it's much worse than that!
Earlier today I had to pay Customs & VAT bill £24.53 ($34.34 USD equivalent) which turned out to be a VAT fraction of £13.53 ($18.94) on _part of_ a package that arrived from Europe last December. The remaining £11.00 ($15.40) is a flat charge known as a "disbursement", which is added on if the goods exceeded £135, causing the shipper (DHL) to have to deal with VAT being collected at the point of import, rather than at the point of sale. Complicated it is, and I can attest that I would not wish having to make enquries involving DHL even on their ememies!

It was an eBay purchase, supposedly inclusive of VAT. The items in the pack were DRO glass linear scales. One item was charged, the others ignored. Presumably it was the one that tripped the limit.

So how about a lathe nut - I had a look. 
	

		
			
		

		
	



At today's exchange rate, that comes to *$75.20 !! *What's with the £35.17 (*$48.88)* to post a little harmless thing that weighs 32.3g (1.14oz) ?
As I mentioned in the other thread I am wary of imports from firms that do not have the route set up. McMaster Carr is not one of them.
Would you pay $75 bucks for a lathe nut you can make?

I do happen to be temporarily  in a situation where I can't use a lathe to fix another, nor use a lathe to fix itself, nor make any kind of machine rotate except something that uses batteries! I suppose it is why I am engaged in "unusual" approaches to repairs, and thinking "why am I always the one so getting to be doing all this desperate sh** er stuff"?


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## graham-xrf (Mar 10, 2021)

benmychree said:


> Just how much backlash does your compound have?  Backlash in a lathe compound is normally not much of an issue, since they do not get much use, compared to a cross slid nut, and that nut is generally a big issue until it is in the order of perhaps 1/4 turn, when it makes jobs such as threading a bit clumsy.


It was gross! I thought 0.025" was too much.
Explained (a bit off topic) in -->This thread which has a short video of it, and pictures.


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## RJSakowski (Mar 10, 2021)

USPS First Class package not exceeding 8 oz. to the UK is $16.25 for 2021.  Not exce3eding 2 lbs., it is $26.  Past that, it is looking like Flat Rate boxes may be less expensive.

Shipping to the UK from the US sucks.  My wife is sending a piece of birthday cake to her twin in a week and it looks like bought the cake from M&S and had it delivered cheaper.

When ordering something from the States, I would recommend checking all the options for shipping.  The vendor in your post above is probably quoting for a small flat rate box ($40.85) and adding in a charge for pickup.





						Retail Postage Price Calculator Mail Services
					






					postcalc.usps.com
				




BTW, I can't help you with your VAT and customs. Sorry!


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## projectnut (Mar 11, 2021)

"Would you pay $75 bucks for a lathe nut you can make?"

The key words here are "you can make".  Is the quality of what you intend to make anywhere near the quality of a new nut, and will it last and perform nearly as long.  As painful as it might be sometimes spending the money is the better alternative.

I was in a similar situation about 10 years ago with my Seneca Falls Star #20 lathe.  In this case there was a sudden clunk and the cross slide refused to move.  Upon disassembly I found the acme nut had been "repaired" on more than one occasion and was to the point it was time to be replaced.  Unfortunately it was a 7/16-10 left hand thread.  The once Acme threaded rod looked more like a 60* thread and it too needed replacement.

With a non functional cross slide and a nut and rod worn to the point repair would have been futile my best option was to replace them.  The 7/16-10 left hand threads were "proprietary" to these machines and about the only way to acquire them was to have them made.  I checked several local shops and came back with prohibitive prices.  In the end I purchased a precision 3/8-10 acme platform nut that had to be modified to fit the machine, and a length of precision 3/8-10 left hand acme rod.

At the time the prices again seemed outrageous, but at least they were less expensive than having the original combination made.  At that time the cost for both was around $140.00 including shipping.  10 years later the pain of the cost has long subsided, and the machine still runs fine and makes accurate parts.  In retrospect I'm glad I spent the money at that time.. Looking online today I can't find either part at the vendors I searched when the machine needed service.


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## graham-xrf (Mar 11, 2021)

projectnut said:


> The key words here are "you can make".  Is the quality of what you intend to make anywhere near the quality of a new nut, and will it last and perform nearly as long.  As painful as it might be sometimes spending the money is the better alternative.


There must be times when something I make for myself ends up less than the bought-in item, but I strain to try and think of them.
Pretty near everything I make well exceeds the specification of the piece it is replacing.
Often, the thing I make is a re-design, or has extra stuff which I take the opportunity to include.
Sometimes what I make is all about function, so I can end up with something that has excellent performance, even if having to live with a less than fashionably beautiful finish.


> projectnut said:
> 
> 
> > With a non functional cross slide and a nut and rod worn to the point repair would have been futile my best option was to replace them.  The 7/16-10 left hand threads were "proprietary" to these machines and about the only way to acquire them was to have them made.  I checked several local shops and came back with prohibitive prices.  In the end I purchased a precision 3/8-10 acme platform nut that had to be modified to fit the machine, and a length of precision 3/8-10 left hand acme rod.


I completely get it about your lathe. You pretty much had no options left, especially if you had no "second" machine to contrive a fix. Even I have never threaded a internal ACME thread before, nothing would stop me trying, short of no resource at all, which is (almost) my current situation. I even got the 29° ACME thread gauge, and started making the HSS tool. Now - I resort to "molding" a nut. In performance, it is pretty much guaranteed to work perfectly. I will allow, the final finish is not likely to be "store bought", but then, it's not the final nut I will put there.

The "final nut" should I feel inclined to make it, will have delivered me the skill to turn up ACME nuts anytime, and again, it is very likely to be a class 3B nut with an anti-backlash feature, and nothing like the overpriced stuff I have seen so far.


> projectnut said:
> 
> 
> > At the time the prices again seemed outrageous, but at least they were less expensive than having the original combination made.  At that time the cost for both was around $140.00 including shipping.  10 years later the pain of the cost has long subsided, and the machine still runs fine and makes accurate parts.  In retrospect I'm glad I spent the money at that time.. Looking online today I can't find either part at the vendors I searched when the machine needed service.


I have again to think about what expensive I spent on ever, whether I felt happy now that the money was well spent. I have trouble with that! There is very little that I thought was pretty much perfect, or felt like great value, and it is usually only minutes before I stumble on it's weak points.  I still have the best car I ever owned, and I am still critical of things about it


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## graham-xrf (Mar 11, 2021)

OK - Bridges have been burned! The nut is now cut and modified. Until it gets some bronze, it can never be a nut again!

This entire scheme is constrained by the fact that the only way the nut cylinder, with all it's works can ever be put in place is to go down the 5/8" hole The plan here is to cut so wide, the screw is able to just drop in, with some little gap around the sides that will fill with bronze-epoxy, yet the tangs reach far enough to ensure good adhesion and load support to the larger thickness that will mold below.

I removed all the thread from the sides, but left a remnant at the main mounting to ensure good axial load bonding. When in place, the top of the cylinder was about 3.8mm below the flush surface of the slide, so there is scope to raise the cylinder about 2 to3mm, to have a substantial amount of epoxy-bronze on that side.

The Acme screw, when in place, leaves only 1.5mm clear from the compound casting. I plan to mold with a 0.3mm plastic sheet spacer under there, to maximize the strength of the other end of the nut, with it only just a tiny bit clear of of rubbing on the casting.





The metal cuts leaving a black (carbon?) powdery residue. Metal sawdust! It's cast iron!  Perhaps a bit short of the tough impact-resistant stuff that we call semi-steel, that they make lathe beds out of. I would have thought that rubbing on hard steel, with enough oil between, this stuff would last well, if not quite like a spindle, but I could be wrong. I can see why folk make replacement nuts entirely out of bronze. It may be possible that during WW2 and through to 1950's, non ferrous metals were expensive and in short supply.

Various (funny) mold constructions have been attempted, but I will post again when I have something.
There is a definite feeling of "OK - you've done it now! You've got waaaaay to far to turn back"!
This happens when you take a hacksaw and file and start carving on your machine!


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## mickri (Mar 11, 2021)

My attitude is if it is already broken I can't hurt it by trying to fix it.   Go for it and tell us how it comes out.


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## graham-xrf (Mar 11, 2021)

mickri said:


> My attitude is if it is already broken I can't hurt it by trying to fix it.   Go for it and tell us how it comes out.


I have been taking pictures at any significant stages on the way. I think I will stay with my first guess of 4:1 bronze/epoxy mix. I filed some on the molded first test sample, and rubbed the sides on some abrasive paper. Then I re-used a small piece of 2000 grit that I fished from the waste bin, and it even seemed to take on a bit of a shine. It has cured as hard as plastics will now. I can still shave bits off it with a scalpel, but only just.
You can kind of see how much metal is in it at the surface. It does not conduct electricity.




I do need to do more stuff on the XRF electronics. It has to share time with this lathe repair, and other works at my place that will end up with a new shop outbuilding.


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## jwmelvin (Mar 12, 2021)

I’m loving this journey of yours and agree that the result you are headed for is top notch.


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## graham-xrf (Mar 12, 2021)

*Lubrication Questions*
We reach a technical question about lubrication, which might be stuff for another thread, but for now, I put it here.

Normally a Acme screw is not an exact volume fit to the nut. The axial forces are taken on the 14.5° angled sloping sides of the thread, and there is a little space between the crests of the screw, and the diameter of the internal thread in the nut. There is also a little space between the core diameter of the screw, and the tops of the internal thread in the nut.

If the replacement nut were all plastic self-lubricating, like the *Delrin® AF*  suggested by @MrWhoopee, acetal mix with PTFE, or any other of the smooth sliding plastics, then maybe we don't care. This time, the plastic in there is a "hard" epoxy with bronze with zero excess space. It will effectively remove all oil off the screw as it moves. The epoxy is a plastic, not like metal, though it has the bronze in there, which will not easily wear the steel unless acting like a lap, with grime dust for abrasive.

1. Should one "drill out" or file the tops of the internal nut threads to leave about 0.001 gap?
2. Should one tape over the tops of the Acme screw before molding, to make a tape thickness gap for oil?
3. Should one resort to grease, or graphite, or silicones dry lube?
4. The renovation manual mentions assemble with "Type C" oil (what is that)?

The nut is "upside down" in use, and there is no hole above to deliver oil anyway. Once put together, all view of the compound screw disappears. It remains inaccessible for lube. That may not matter. It's closed off to everything, not easy to get dirty, and supposedly, does not move much, which is a logic hard to reconcile with the nut wear folks show us. OK, I accept it is often decades of it.

Not to misunderstand, even if the nut just "works" for the while between times I take it apart , and I may have tried some novel lubrication, that's OK. I would be going after more important stuff, but here I am open to suggestions. My "first shot" is going to be a zero free volume casting.


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## Tim9 (Mar 12, 2021)

MrWhoopee said:


> I haven't heard of anyone doing it, but making a "hot nut" using Delrin AF (PTFE filled acetal) might be the hot ticket, so to speak.


There was a blog about that and even a YouTube video ( I think) of where the guy used a torch...or candle to blacken up the screw with carbon. The carbon was the release agent. He then warmed the lead screw to about 300 degrees and pressed screw into a nut spit in half. The original bronze nut had some pieces of delrin which when the halves were clamped together....delrin oozed out.

I am totally simplifying the above. This guy went on with the above experiment and tried many different approaches. Im pretty sure it was on CNZ zone website. Others replicated and refined. It was widely discussed...tweaked...and modified. But...for the most part. It appeared to work pretty damned good in my opinion.


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## mickri (Mar 12, 2021)

The paste wax on the threads will leave a tiny gap.  You could try anti seize.  It doesn't take much space for lubricant.  A thousandth or two would be sufficient.


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## graham-xrf (Mar 14, 2021)

OK - I have made some progress, so now it is time to finish this phase, and start Part 2 as another, but related thread. I have no idea how this is going to work out. So much of it has amounted to "one throw straight", all-in, and the distinct possibility I will have to start over.

@mickri : From what I see of the threads made using the test run 12mm bolt, there is not as much as a thousandth gap. It reproduces even the smallest lines and marks, and the tiny print and production symbols on the inside of the plastic cap.

I made a silly mistake, dreaming up various possible molds, until I remembered the fumbles it took to get it all apart. Here is one of the ill-fated ideas..



	

		
			
		

		
	
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There is so very little room under, between the screw and the compound casting. The piece of 0.3mm milk bottle polythene would allow maximum nut strength, but of course, there is no way to put the slide and compound together without everything to do with the nut going down the 5/8" hole first. I needed something circular, the same diameter as the nut cylinder. Also, I had to get length of it just right.



	

		
			
		

		
	
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 I tried a brief experiment with heat-shrink. It would have been possible this way, but I did not like it. I considered the way it was shaping to be poor, and I wanted far more deliberate control.  These pictures were taken just before I did the deed, and cut the nut up in irrevocable fashion.



	

		
			
		

		
	
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So we come to the "water pipe nut mold". Blue 20mm polythene water piping. The inside diameter was too small to fit straight over the nut cylinder. It could be "forced" if the nut was heated in boiling water, but it was a struggle to work with. What happened next was not without a bit of drama. That will be explained in Part 2, which will be posted as soon as I get some pictures off the phone, and re-sized.

Here is the idea..   
	

		
			
		

		
	



The nut cylinder fit to the slide is always somewhat below flush-fitting. The fit itself isn't great, but maybe that is by design - who knows. However this turns out, you will know that I mangled a (somewhat) working compound nut on a totally speculative unproven procedure that only has "it should work - maybe" going for it!


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