New project - Materials question

[Reddinr]

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?

 

[Bob Korves]

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.

 

[ddickey]

Or the 300 days of rain per year.

 

[Billh50]

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.

 

[dulltool17]

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.

 

[kd4gij]

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

 

[whitmore]

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.

 

[Reddinr]

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.

 

[Reddinr]

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.

 

[4GSR]

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.