Hi all, Not that I am planning on casting iron ... yet ... but I have been contemplating the "how would you question" all day. A little background, One of my interests is restoring antique farm windmills ... particularly older and rarer specimens. On a current mill I am working on, the pinion gears are worn so bad they are pointy, they have definitely seen better days. The gear should be about 3.7" in diam, width is close to 2", 15 teeth, with a short boss on one end. It would be slick to cast this thing slightly oversize by a couple 10ths (including teeth) and then clean it up on the lathe & mill. What method would you use to cast this gear? Greensand? - Wouldn't the lack of draft be an issue? Lost Foam? - Has anyone ever done lost foam in iron? I know it is done commercially. What would you use in place of the drywall mud? Lost Wax? - Hmm, just thought of this one as I was typing. Is that even feasible? What would you use for the shell? Any other ideas. I'll probably just end up using some cast iron stock (Durabar) and spending a bunch of time on the lathe and mill. But I am interested in all of your input, for the future, as the pinion gears on these old relics are generally worn pretty bad.
Some old gears like that I've seen have draft and were originally sand cast. An alternative is to cast them in bronze or brass. Generally I believe cast iron was used because it is cheaper and the strength of brass or bronze is sufficient. I don't see why drywall mud would not work with iron. I'm getting ready to try it with brass.
I would use lost PLA casting. 3D model the gear, print it, then either use block investment or ceramic shell. Id probably cast it in bronze as well....
I have made pattern for spur gears for greem sand casting in cast iron I cut the pattern with a 2° tapper for gear teeth I hope this helps you Dave
Till the late 1800's most gear where cast and and not machine . In 1970's I saw blevel gears being made and used as cast The pattern was off shelf gears used The be for the 1900's patterns for gears most teeth was hand made, then glue to round circle They gear tooth profile is not same as today tooth. Most time replace a gear be for 1900 you need to make tool cutter. Dave
I'm no engineer or skilled machinist, that said... I don't think a cast gear would work very well at anything but the slowest of speeds. Even moderate deviations in the angles of the teeth (pressure angle) can fairly quickly chew the teeth off a pair of gears. I've seen plenty of cast gears where the teeth have been machined in afterwards, but (aside from die-cast) I can't think of a single one that's been cast with the teeth defined as part of the casting. I think you'd be far better off casting a gear blank and machining the teeth in. Perhaps teeth would come out close enough from a shell, I don't have the experience with it to say.
Back in the 1800's nothing ran fast. If did run fast gears you will earplugs . I am a skilled machinist Spur gears are easy to cut But bevel gears takes at less two cuts and cast gear works great hand drive and low speed Dave
Most steel back geared windmills were produced at or after the turn of the century. Prior to this they were mostly wood bladed (of a couple configurations) and direct stroke (not geared). Most of the gears that I have run across are a 5DP gear, 14.5 PA. Thus my comment about probably just spending some time on the lathe & mill with durabar. Yep, that is why I said "cast a couple 10ths oversize and clean it up on the lathe and mill."
Cast gear have there place for low speed. If need low cost bevel gears it is best way to go for low speed uses You do need to take in shrink when making the pattern. Dave
