Casting a windmill gear in grey iron

I learned a lot from the various methods used to try and cast this gear.
Obviously the gears could have been cut from blanks, but the fact is that they did cast gears in the old days, and so I like to be able to know how to do that accurately.

The lost PLA that David is using seems to be the best for this application, and my guess is the gears cast using that method could perhaps be used as-is with some cleanup.

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Ed, your photos did not paste into the message you posted. I have had that trouble before.

Denis

 

Well nuts, I copied the URLs from the windmill forum. Ill try and fix them tomorrow.

 

Yup, that’s how I got into trouble by copying and pasting one site to another...

Denis

 

Here you go:

 

Mach - Thank you very much for the assist!

 

It's a safer idea to save you photo locally on your computer and then UPLOAD it here. This way it stays here forever instead of relying on links for eternity.

Nice machinery!

 

Back in thread #380 I showed the linseed oil molds for the gear. Believe it or not today was my first iron pour since then. I had forgotten the plan I originally had in mind and improvised with the molds that I had made. One change was to use a horn gate into the gear half mold in the drag and then using the boss side pattern which protruded from its mold to register them. I used a filter under the offset basin, but it looked like a clean pour. It was still hot when I shot this photo. I'll check it tomorrow see if it is machineable.

 

ESC, That looks very nice!

ESC, if it appears to be machinable let me know and I will send you some postage. Same with you David, if/when you get to it. I do have another of this same model of windmill, that I may rebuild someday.

 

I'll test it tomorrow.

 

Ed, it machined sweet. I got a 28 on the Brinell scale against 46 on the rotors which is expected given the different cooling rates. There was just a bit of eccentricity, so I just faced the end to verify machinebility.

 

Brinell of 28? I expect about 10 on the Rockwell C scale. Shore 28 is in that range. But Brinell (500kg) would be 196. I must be looking this up wrong.
Denis

 

Denis, I don't have a manual for the tester, I just took it as the B scale on the dial. I have some test pieces, and I get a reading that seems to match the numbers on them.
I'll go out and set up the C scale and see what I get.
I used the C scale and got 36.

 

You are talking about a Rockwell C of 36? That is certainly machinable, but is fairly hard for grey iron. Annealed steels are often around 10 on the Rockwell C scale and 4140 PreHard is about 22 to 28. So, a 36 is a moderately hard steel.

When testing my grey iron castings, I commonly get single digit Rc readings using my calibrated Wilson Rockwell hardness tester.

If you knocked it out of the sand when it was still red hot, you might have hardened it (similar to flame hardening). Medium hardness in a gear is not a bad thing. Did you use any FeSi immediately prior to pouring?

Denis

 

Most Rockwell testers use A & B scale. To reference the A scale you have to put in the tungsten carbide or diamond ground point. The B scale is usually a 1/16” 60–62 Rockwell ball bearing for testing hardness is under 30 Rockwell.

The “A” scale using tungsten carbide or diamond is usually good to about 72 to 78 Rockwell. It’s not very favourable below 10-20 Rc.

The “B” scale using 1/16” ball bearing shows is really good results in the 5-30 Rc.

Cast-iron should be kept between 9-20 Rc. on A scale.

Mild steel is most often found at 10-14 Rc.
Annealed 4140 18–25 Rc.
Mill un-annealed 4140 can be 32-40 Rc.

Having knowing reference plates for Rockwell testing helps tune the tester.

Keep in mind you can’t test against the raw surface. You need to grind or machine away before testing. Many materials after poured or Heat treated have a extra hard candy shell. It is a mistake to measure the shell.

Here’s a little video that I put together a few years ago when I was grinding cam bearing seats.

This is my prepping for a treat of A2

 

Hmmm, Annealed 4140 is about 10-15 (13) Rc. See screen shot below.




4140 Prehard is about 28 Rc. It can be hardened to 40 (or more) Rc See screenshot:


A typical axe head would test at Rc 45-50 and a good woodworking chisel 60 or better.

I have tested a lot of grey iron and it should be about 10 or less Rc. I do have reference calibration plates and do periodically check my tester. It has been stable providing consistent results. I use Wilson factory-supplied diamond Rc 120 degree indenters.

I have also tested many batrches of 4140 prehard and annealed steels and hardened steels and can confirm the above observations.


Denis

 

If you’re using 120° Indenters you’re using the A scale (Diamond or tungsten carbide) they start showing false readings below 10-15 Rockwell. Softer materials should to go to the B scale.

I personally only use the A scale.

I have personally hardened 4140 to 60 Rc. And then drawn it back to 52 Rc. It has very similar characteristics to O1.

 

Are you sure that 120 is specific to A scale? Here are the specs for the various indenters: Note that BOTH the A scale and C scale indenters are 120 degrees:


Denis

 

Most scales for Rockwell use A&B for measuring metal hardness. Certified testing plates help calibrate A particular machine. Knowing what scale you’re using with knowen pushpin is absolutely required before distinguishing RC value.

Edit; Dennis, I’m not disputing your findings. Your experiences with 4140 and mine might be totally different.