# New project - Materials question



## Reddinr (Jun 10, 2017)

So, I have a new project to support my habit.  Today my driveway gate opener failed again.  It is one that has an acme screw and plastic nut.  The screw rusts every season.  The nut wears due to the rust abrading it.  I made a new plastic nut a couple of years ago and that lasted until today.  I think today's fail was due to the rust and a faulty switch and the screw just turning through the plastic eventually at the end of the stroke.  I  had fun making the delrin nut that had two types of internal threads, a couple of counter-bores etc.  Learned a bit on that project.

My question is about materials.  I'm thinking a stainless steel screw and bronze nut or just clean up the regular steel screw and make a bronze nut.  A some sort of coated screw would be great but don't know where to get that.   It is always wet here and the arm is not well sealed.  

Anyone have material or other suggestions?


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## Bob Korves (Jun 10, 2017)

I guess we need a new forum "gate repair."  

Well, OK, we do have an Acme thread.  Stainless would be a good idea, but will still rust eventually.  Oiling the screw regularly or using some other rust prevention product might help to keep it from rusting.  Clean it up well first.  The nearby salt water bays may also be a big part of your problem.


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## ddickey (Jun 10, 2017)

Or the 300 days of rain per year.


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## Billh50 (Jun 10, 2017)

it might be a bit  expensive, but have you thought of making the screw from bronze? most boats on the sea use bronze for hardware because of the salt in the air.


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## dulltool17 (Jun 10, 2017)

Billh50 said:


> it might be a bit  expensive, but have you thought of making the screw from bronze? most boats on the sea use bronze for hardware because of the salt in the air.



I like bronze for the application as well.  Maybe use with a Delrin nut would give you some reliable service.


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## kd4gij (Jun 10, 2017)

How long is the screw?  Use Teflon for the nut Motor cycle chain lube on the screw a couple times a year.


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## whitmore (Jun 10, 2017)

Reddinr said:


> Today my driveway gate opener failed again.  It is one that has an acme screw and plastic nut.  The screw rusts every season.  The nut wears due to the rust ...
> Anyone have material or other suggestions?



Good marine-environment materials include Delrin, bronze, stainless steel, and titanium.
Stainless is the inexpensive way to go.  McMaster-Carr sells a couple of grades of Acme
threaded stainless rod, so that may be the low-impact option.  They also stock 'protective bellows'
if the screw would benefit from a weather shroud.  

Being a cheapskate, I'd consider grease and bellows with the original screw.


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## Reddinr (Jun 10, 2017)

I'm inland so it is mostly the "rains a lot" problem.  I'll have a look at McMaster.  The screw is about 30" long or so.  It is housed in the metal housing of the gate opener.  I don't want to spend an arm and leg on this as other parts and pieces may break later and the electronics is getting up there in years.  I generally do a tear-down about once every two years, de-rust, clean lube.  Still, the rust persists so I think stainless is a good step.  Is bronze on stainless a good low friction combination?  Otherwise I'll go back to stainless and Delrin.


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## Reddinr (Jun 10, 2017)

Ok.  About $120 for a 3 foot piece of 3/4-6 x 3 Foot, 316 stainless.  1.75" dia x 4" 932 bronze ~$45.   I also saw an SAE 841 powdered bronze hollow bar of the right size (oil impregnated) for about $65.  vs new gate arm is about $300 or so.  If bronze and stainless works well together, I think I will go that direction.  Oil impregnated or not?  Bronze is new to me machining-wise.


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## 4GSR (Jun 10, 2017)

I think 316 is a good choice. For the nut, try to find some 454 Navel bronze, it would hold up much better than 932 bearing bronze IMO.

If all else fails, get you a piece of Incoloy 925 (Inconel 718 is too difficult to machine)  for the screw and a nut made from 454 navel bronze. Of course, the Incoloy 925 would have to be coated with baked on impreglon Teflon coating or some other anti galling coating.

Another option would to take the existing screw and have it electroless nickel coated about .002" deep.  And make a Delrin nut or better yet, mold one from Moglice material.


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## whitmore (Jun 11, 2017)

Reddinr said:


> Ok.  About $120 for a 3 foot piece of 3/4-6 x 3 Foot, 316 stainless.  1.75" dia x 4" 932 bronze ~$45.



Bronze is very strong, and tough... and if Delrin worked until rust worked in, you can use something softer, like brass (McMaster sells brass Acme cylinder nuts, too).    Stainless and copper/bronze/brass
are OK together when wet. 

Waterproof grease, like motorcycle chain lube,won't hurt.   It's messy, of course.  
As a cheapskate, my first cut would be a replacement brass nut and some grease, with
the original screw (unless it's really eroded).


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## 2volts (Jun 11, 2017)

Why not have both parts made out of delrin?


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## JPigg55 (Jun 11, 2017)

How about C954 aluminum bronze. 3' piece of 3/4" solid round bar is $60.23 from Online Metals.
http://www.onlinemetals.com/merchant.cfm?pid=12987&step=4&showunits=inches&id=759&top_cat=0


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## Reddinr (Jun 11, 2017)

I like the price of the aluminum bronze.  I wondered what it takes to work the stuff so I googled around.  It sounds like a tough material to work with, especially for an amateur like myself.  I think I'll try some bronze and grease on the original, cleaned up lead screw.  

When I was looking for machinability of C954, I found a helpful PDF document listing machinability of various metals.  The link is huge so just Google "machinability ratings quaker chemical" and it comes up first.

Decided against Delrin.  Just too soft for the forces seen at the end of the swing of the gate.  I went ahead and ordered bronze 932 bearing stock and 316 stainless and will put some sort of lubrication in there.  I think that will probably do it.   Thank you for all the input.  Will post a pic. if it comes out ok.


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## Nogoingback (Jun 11, 2017)

kd4gij said:


> How long is the screw?  Use Teflon for the nut Motor cycle chain lube on the screw a couple times a year.



There are motorcycle chain lubes that are wax based rather than grease.  Bel Ray makes one: much cleaner than the usual greasy mess.


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## whitmore (Jun 11, 2017)

Reddinr said:


> I found a helpful PDF document listing machinability of various metals.  The link is huge so just Google "machinability ratings quaker chemical" and it comes up first.




That's a great table.   Looking through it, though, there's some gotchas that
really don't show up.   Some better machinists than I have tried to cut
molybdenum, and had to do it without carbide tools (don't know why),
and also couldn't use HSS.   The molybdenum galled badly with anything
other than carbon steel tooling.   It was a long sequence of make-a-few-passes,
sharpen-a-few-tools.

That shop bought a wire EDM later,  the molybdenum project  convinced 'em to
spend the money.


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## Reddinr (Jun 25, 2017)

I got all the parts and tools so I decided to stop typing & watching "This Old Tony" and get something done today.  So far, here it is.  Bronze and stainless are both pretty new to me.  I ended up with 316 acme lead-screw (7/8" actually, not 3/4", glad I measured)  and 932 bronze.  I now dislike bronze.  What a mess.  The part is coming out ok* but I must have spent a half hour cleaning up the perked-coffee-sized bronze particles from everything.  Still finding it everywhere.  The stuff loves to hide in socket-head screws.  

*Pictures:* 
Old rod and stripped-out plastic nut.  Note the brown grease/plastic/rust goo and plastic slivers.
Acme insert holder I had to rig (tack welded, hope it holds).
Test cut on stainless screw.  Cut easier and better than I thought.  I had lots of "work hardening" worry when I started.  I don't know what the insert is.  I got a cheap Chi. insert/holder kit with the lathe and they have been working for me.
Threaded bronze part (fine thread end that attaches to the aluminum arm of the gate opener.)   Need to clean the bronze fur off of threads a bit.

So did is mention that I now dislike bronze?  Ok, stop smiling 4gsr, I should have listened to you on the naval brass.  On a whim, I purchased the acme insert/holder a couple of years ago for very cheap.  It was just luck that it was the right pitch for my gate.  The holder that came with it was just a little too big for the ID of the inside thread so I made a poorly designed smaller holder in the far end of a small boring bar.  My setup worked well in plastic...  I needed to weld the insert this time for the bronze.  Astute HM's will notice I didn't show you the other end of the bronze piece.   *Yes, the insert rotated.   My brain told me that it would rotate and to tack weld it but my impatient side said eh, just try it.   I should be able to save the piece although it will be a little shorter.  No problem though.

The stainless is no problem so far using inserts.  I do have to thread it for the bearing nut.  That may be interesting.  I got some good Mitsubishi inserts off of ebay for that.  When I'm done I'll probably have a "gate opener's worth" of new tooling so all is going as planned so far.  Have to travel for work now so unfortunately I won't be finishing this for a bit.


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