P.M. Research #5 Steam Engine

[GreenTwin]

Nice perseverence.
Sometimes one has to get a bit creative to make things happen.
Makes me think that a pre-machining annealing session may be a good idea for some kit gray iron castings.
Looking good so far; nice work !
P.S. - Nice lighting on the photos; I always seem to get dark shadows and such in my shop photos.
.

 

[Sarah]

What are you using to drive your small taps? Joe Pie has several videos where he uses a tiny, shop-made driver--it is just a knurled disk of aluminum about 1 inch in diameter. There is just a set screw to retain the tap. He has different different drivers for different size taps.

They are safer to use than most drivers as the small diameter makes it difficult to put too much torque on the tap.

FWIW.

Craig

Hi Craig,

Thank you for your suggestion and I will look at his videos. The tap driver I use is the one in the photograph below. I use the knurled section at the bottom most of the time and the T section when it gets harder. I can be a bit clumsy sometimes and I think with that, the tap being in the blunt side and the harder material proved too much for the poor tap! One of the skills I need to work on

 

[Sarah]

Nice perseverence.
Sometimes one has to get a bit creative to make things happen.
Makes me think that a pre-machining annealing session may be a good idea for some kit gray iron castings.
Looking good so far; nice work !
P.S. - Nice lighting on the photos; I always seem to get dark shadows and such in my shop photos.
.

Thank you for your comments . I have my eye on another P.M. Research casting kit so I'll have to do some research on annealing. I have a couple of led panel lights over my bench which makes it a nice working area. I do need to put some good lighting over my machines, especially the milling machine.

 

[GreenTwin]

I have seen some use a torch to heat a gray iron casting, to anneal it, and a buddy of mine uses an electric kiln to do the same.
I will check with my buddy to see what temperature he uses to anneal his gray iron.
If I were going to anneal gray iron, I think I would use a kiln for a more even and consistent temperature control.
.

 

[Jasonb]

If you have an open fire of wood burner put it in there for the evening and then leave to cool SLOWLY over night in the ashes. Failing that a bucket(metal) or large metal tin with a few holes for air punched in the bottom will do. Us ecoal or a good sack of wood putting the castings into the fire once a good hot bed has built up and continue feeding the fire then leave covered to cool overnight. A torch can work for small areas or small section projecting parts of a casting but doing the lot is easier.

You need to get it to red hot which is in the region of 870-900 deg C.

Another option when using small taps is to put the tap wrench onto the round part of the shank, if things get tight the wrench will slip before the tap breaks.

 

[GreenTwin]

I leave my gray iron castings in the sand overnight, and let them cool as slow as possible (as Jason mentions about slow cooling of iron).
Using the correct amount of ferrosilicon during the casting process is also important to avoid the chill spots.
Chilled iron has the same characteristics as tool steel, but luckily it can be avoided if you pay attention when castings parts.

I know of one foundry person who uses the correct amount of ferrosilicon, but still uses a post-casting annealing process, just to be sure there are no chilled spots.
The type of scrap iron that is melted can also affect the casting machinability.
I have heard that using ductile iron scrap may cause hard spots in the castings, but I suspect it is more of a section of the casting cooling too fast, and not allowing the graphite to be distributed in the casting.
.

 

[Steamchick]

I use 4-jaw pin chucks to hold sub-1/8in diameter taps. The body of the pin chuck is then twiddle between first finger and thumb and you can be very delicate when tapping, with a lot of feel. It doesn't need brute torque for small taps, but a lot of control so you DO NOT BEND the tap, which will snap at the first hint of bending. T-type taps are very hard to control without bending the tap.
K2

 

[Sarah]

Thank you gents for your comments regarding annealing the castings. I have a friend with a wood burning stove which I can use. When I do the next castings I'll have to volunteer to clear the ashes out next morning Out of interest how would I be able to measure the temperature the stove gets to? Would it just be the castings getting red hot?

 

[GreenTwin]

My buddy did not respond about how he anneals his gray iron castings, so I will have to resort to consulting "The Book", page 179 (index attached).
The Holy Grail of castironism, so to speak.
Be back shortly.
.

Edit:
Annealing generally reduces the grade level of gray iron one level, ie: if starting with Class 40 gray iron, it will be slightly less strong Class 30 gray iron after the annealing process. Not a problem for model engine castings in my opinion.

There are three typical gray iron annealing processes:
1. Low-temperature (ferritizing) annealing.
2. Medium-temperature (full) annealing.
3. High-temperature (graphitizing) annealing.

Low temperature annealing is between 1,300 F and 1,400 F, at 1 hour per inch of section.
Medium temperature annealing is between 1,450 F and 1,650 F.
High-temperature annealing is between 1,650 F and 1,759 F.

Once a piece of cast iron has been heated, it should be cooled slowly.
Slow cooling is also important for stress relief.

Apparently the medium and high temperature annealing are used when the iron is of higher alloy content, and does not respond to the low-temperature annealing process.
I would suggest starting with the low-temperature annealing process, and try that method first, to see if it improves machinability significantly.

If you don't have a kiln with electronic temperature controls, then I guess you could try the charcoal method that JasonB mentions.

I have heard that if you use a torch of some type to heat a gray iron casting, then it should be heated somewhere between "medium red" and "red", per the attached cast iron color chart (not an exact method, but would probably be accurate enough).
The torch method (depending on exactly what type of torch is used, and how concentrated the flame is) is a good method for annealing just a small area of an overall casting, such as the bosses you were trying to drill.
I guess if I were annealing, I would just anneal the entire piece, just in case there were other hard spots somewhere else in the casting.

And as I mentioned, use slow cooling regardless of which method is used.
.

 

[Tug40]

On my #5 standard/frame I had the top & bottom & bore for the crosshead finished when I realized i couldn’t drill the valve slide boss’s or mill the crank bearing base, they were so hard.
I next put the frame in my wife’s wood fired pizza oven, it’ll get over 500deg, let it set overnight, still no joy. Prob not hot enough, although the Pizza was very good.
I called PM for some guidance, & they sent me a new frame free of charge, said do the chilled parts first, in case they have to send me yet another frame.
The replacement frame they sent machined fine.
They stand behind their kits.
To be fair, Stuart has also replaced a chilled part, good folks also.
I have a PMR #1 & #6 kits on the shelf, I don’t foresee any problems with them as long as I live long enough to finish them ;-)

 

[Jasonb]

Yes a bright red is what you want I just do it by eye. The thicker the material the longer it needs to sit at that temp so the whole thing gets hot enough. For the science the process is "graphitizing annealing" this converts the hard carbides which have formed into Pearlite and Graphite

I have done very small items (the usual to suffer) with a large propane torch but to do a whole part like that would use a lot of gas and you will be there for a long time and then left with finding a way to allow it to cool slowly.

The thing to do is when you first get the castings is to run an old file over the likely areas that tend to chill. Typically corners, small protruding bits and anything thin such as valve chest covers. If the file skids off without making an impression then those areas are likely chilled so cook them before doing any other work as you may get a bit of scale on any already machined surfaces and even the possibility of some movement as the process also relieves any stresses in the casting.

This maker of casting sets had a reputation for hard/chilled parts and a couple of areas showed that with the file so I just did the lot. It was the tops of the two bearing pedestalls that were affected as I would have expected as they are thin and stand proud of the main volume of metal so cool faster. You can also see the change in colour after wire brushing the casting to remove ash/scale. The valve chest being about 5mm thick also showed signs of being hard in the corners but machined fine after treatment