NGH GF38 Prop Washer

[Andy J]

Need to make a 7mm thick washer to take up the play between a wooden prop and a Jen 32mm spinner from JE.  Am I better off making this from steel or an alternative metal.

[Engine Doctor]

Steel is the best option then heat treat it hard then temper to dark blue . You can taper off the face to save a few grams . There are some older big engines that use alloy prop washers but if you do you need a hard springy alloy. 

[Andy J]

Thanks ED, will get some steel on order.  Will need to ask more questions about the heat treatment required when I complete the lathe work.

[Engine Doctor]

A decent piece of steel will probably be ok as is but if you want to heat treat then this how .

Finish to required finish on lathe .

Hang on a piece of wire and heat with a blow lamp to a bright red then quench quickly in water. This will harden it /

Now clean up to bright again with fine wet and dry or a mop to the finish you require .

Hang on wire again and heat gently with a blow lamp . Have a container of oil handy , engine oil will do.

Watch the colour it will start going a  light straw and begin to darken you are looking at a dark purple colour . As soon as it approaches the dark purple drop it in the oil .

This will give it a rust resistant surface and temper it to withstand distortion .

If you over cook it just start again 

Hope his helps

[Robert Cracknell]

The washer will only harden and temper if it is carbon steel (080M40) or equivalent. Ordinary mild steel will still go through the process and will still exhibit the colour changes but will not change its properties.

HTH

[Solly]

Why use metal? Last time I had to do this I used a cut-down hub from a damaged beech prop. Paxolin is also OK as long as you roughen both sides to provide some grip.

[Andy J]

What I have purchased is supposedly bright mild steel.

[Robert Cracknell]

Andy, 

 

Bright mild steel will be perfectly OK for your washer. The process for hardening and tempering as described is what is used for making hand tools such as cold chisels and punches etc.. 

The washers that you buy from any hardware store are just punched out of mild steel sheet and are perfectly serviceable for a myriad of uses up to and including structural steelwork.

If you machine your washer you will end up with a precision item that will be perfectly suited for the use you want to put it too.

[Andy J]

Well received the metal today and it does not machine well as never done any turning of steel before.

 

Problem 1 was that my self centring chuck was not big enough to hold a 40mm bar so had to resort to my 4 jaw chuck.

 

Problem 2 was trying to centre the work using only a Mk1 eyeball. Luckily I managed get it fairly accurate and was able to face off the front and turn the bar down a few 1/1000ths to get it back to a true diameter.

 

Drilling out the centre went ok but chamfering the front edge to blend into the spinner left a jagged cut so it will have to be repeated at some point.

 

Then took the work piece off the lathe just to satisfy myself that the centre hole of the washer was going to slide over the engine shaft which it did and it also allowed me to establish how thick the final washer needs to be.

 

Problem 3 was then getting the job re-aligned in the 4 jaw. This proved to be very difficult so gave up at this point and will return to the job another day.  Thinking if I turn down a scrap bar to the same diameter as the washer clearance hole perhaps I can then use the bar held in the tail stock to at least get the work piece near to the required alignment.

[Outrunner]

Andy you need a DTI or clock to get the workpiece really true in a four jaw chuck. You could try the old fashioned way with a scribing block but it's much more accurate and quicker with a clock.

[Andy J]

Will my concept of a short length of bar sliding into the machined washer hole not work as don't currently have a method of holding my clock gauge.

[Engine Doctor]

Very heath robinson but will get it to a  sort of starting point. 

[Andy J]

Well after an extended attempt trying to get the work piece true using a supporting copper dowel in the tail stock think I need to rethink my approach.

 

Certainly reducing the speed to 400 divided by the stock diameter in inches improved the cutting surface finish but when trying to part off the work piece the bar stock keeps coming lose or jamming and stalling the drive.

 

In short, lack of lathe working knowledge is preventing progress so will need to seek help from a friend who has a far larger lathe and a lot more experience.

[Mr Fro]

2 hours ago, Andy J said:

Well after an extended attempt trying to get the work piece true using a supporting copper dowel in the tail stock think I need to rethink my approach.

 

Certainly reducing the speed to 400 divided by the stock diameter in inches improved the cutting surface finish but when trying to part off the work piece the bar stock keeps coming lose or jamming and stalling the drive.

 

In short, lack of lathe working knowledge is preventing progress so will need to seek help from a friend who has a far larger lathe and a lot more experience.

Hey Andy,

 

What lathe and tooling are you using?

[Andy J]

Nothing special, think I paid about £18 for a boxed set of carbide cutters.

Edited April 13, 2023 by Andy J

[Mr Fro]

2 hours ago, Andy J said:

Nothing special, think I paid about £18 for a boxed set of carbide cutters.

They probably won't be helping matters!

 

With small cuts & low speeds, HSS tooling is generally preferable.