Delrin bushing shaft clearance

Got a small job for a visiting cruising boat stuck here for a while due to the lock down. Freebie, I like helping out visiting cruiser types.

Anyway the bushings in the windvane steering gear are shot.

Shaft diameter 1.125".

Hole size 1.625" which is the OD of the old bushing. Can't measure the ID as it's flogged out.

All shafts & housings stainless steel if it matters.

These things get wet regularly as they're exposed to the elements but are NOT below the water line so not permanently wet.

Existing bushings had zero provision for lubrication and therefore didn't get any. Is it worth fitting grease zerks?

Needs to be a good running fit so normally I'd shoot for maybe 0.002" to 0.004" oversize on the shaft. But Delrin in this environment, dunno. For my own boat I used Vesconite everywhere like this.

Advice on machining tolerances invited.

PDW

I think i would make it .002" oversized it will wear open. The ID will shrink when its pressed in its housing so consider the wall thickness along with the OD.

Delrin self lubricates.

Edit: .002" gap .004" total difference.

at that tolerance level there should be no problems. but make one, let it sit overnight and check it. might depend on the delrin grade you use.

Dupont has all the information you need. Read the design guides. Module 1 is general engineering polymers and discusses bearings in chapter 7. Module III is Delrin specifically.

Add the grease fittings.Won't hurt the Delrin.SS might not be to bad but on steel any rust and the oxide will imbed in the Delrin and wear the steel.I used to make Delrin bushings for Vettes and Vipers and fitted at .001" after pressing in the housing.I used tgp 1045 for axles and tried SS also.I ended up making them greasable,keeps the moisture out and makes them even more slippery.

I got the old bushings out & measured their OD. Not the same which was interesting - they look the same to the Mk 1 eyeball. So got the bore gauges out, also holes not round. Basically they're as-cast, 0.75mm egg-shaped.

ATM the casting is on the Kearns S type HBM so I can bore everything round and parallel in one setup. Then I'll get back to making the bushings. No way I'm trying to make something decent starting from an egg-shaped hole.

Probably aim for a light tap fit then a final skim cut on the bushing ID to 0.004" oversize. Plus grease nipples. It's a freebie but if I'm going to do it, I'm going to do it as best I can.

PDW

Plastics in the wet absorb water and swell. Some more than others. It is very hard to predict. In marine use, loose is good and tight is bad. You should use a .0015 press fit and a .005" running clearance. They will swell in use. You just don't know how much. Greese is good.