New project - Materials question

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.

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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).

Why not have both parts made out of delrin?

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

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.

kd4gij said:

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

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.

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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.

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.