Stuart castings

[Rudy from Norway]

I have bought my first casting kit, a Stuart 10V. I have seen noumerous builds on TouTube and they are all saying the quality is good. My kit on the other hand, is not. Poorly filled molds, lots of glazing, poor accuracy. All castings are more or less bad. I have got a new cylider and have just posted a mail asking for a new soleplate.
Is this a common problem with Stuart?

 

[Charles Lamont]

Is this a new kit from Stuart, or bought elsewhere?

 

[Rudy from Norway]

Yes, bought it directly from Stuart in february.

 

[Blogwitch]

I have been telling people about this for a few years now.

You take pot luck on whether you get a set of castings that can be made into a working and cosmetically correct engine or not.

Bad quality, twisted and the usual one of undersized castings being sent.

Their flashy site seems to show a very well run organisation, but over the last few years, it has gone downhill since it has changed hands a couple of times from the original very good supplier, who gained a very good reputation for the quality of their work to what you get now.

BTW, the answer you will most probably get back if you query them that the castings are the wrong size (usually too small) is that 'you are a model engineer and you should be able to sort out the problem yourself'. How can you sort it out when there in no metal to affix a screw into?

John

 

[Mechanicboy]

Is it a machined kit you ordered from Stuart?

I had ordered the machined Stuart D10 and the surfaces was turned, milled, drilled and treated for bolt. Never been finished with grinding or honing direct from Stuart. Then i reworked with grinding/honing to a perfect fit +created 2 new pistons and 2 crosshead.

 

[Rudy from Norway]

This might be the machined kits gets the better parts. Obviously they will discover bad castings them selves when working on them.

 

[Blogwitch]

You might be quite correct Rudy, they have the advantage that they can pick and chose which castings they use.

I have an unused very complete (piston rings, gears and governor) ST #9, but I have no idea how old it is. If it was from the original suppliers, then I am sure things will fit together nicely, otherwise every casting will need to be critically measured up before trying to machine the parts, just to make sure it will make a decent model.
If more people did this before starting, and getting the bad castings replaced under warranty, then that would force ST to look at their quality control, which, by the looks of it, isn't very good at this time.

John

 

[Rudy from Norway]

Now they offered me a new part, as I expected.
I love the design of the Stuart models and kind of hope they survive. However, that depends on the future quality control.
You konow, when I run my brand new Lathe and milingmachine and using such machines for the first time, I was very disapointed when endmills started to growl and the whole machine was begging me to stop. Not a god start...
So Stuart, thanks for now.

 

[fcheslop]

I found that the pcd for the cylinder studs on the later casting cause break out on the trunk guide flange, I reduced the pcd and all was well
Luckily it was noticed before machining had started in ernest again a reduction or maybe using an old casting as a pattern
cheers

 

[Mechanicboy]

You konow, when I run my brand new Lathe and milingmachine and using such machines for the first time, I was very disapointed when endmills started to growl and the whole machine was begging me to stop. Not a god start...
So Stuart, thanks for now.

What in fact this does is to form a very hard skin on the surface of your casting, maybe only a few thou’ thick, and it is this surface that causes most problems to engineers.

High speed steel cutting tools tend to get bluntened very quickly owing to the hardness of the skin, so what most engineers do is to start off with a well used tool and force it under the skin and literally rip it off. Once you are through the skin of the cast iron, then lighter cuts with a sharper tool will keep its edge longer.

Carbide tipped tools tend to work better with cast iron, but need that first layer taking off with a high speed steel tool first, otherwise you carbide tips may well shatter - depends mainly on the hardness of the cast iron surface.

Another problem associated with machining cast iron on a lathe or mill is the speed of the cut.

Cast iron needs a very slow speed to cut it properly – too high and there will be sparks everywhere and your tools will need re-sharpening very quickly. As a general rule of thumb, to get a smoother finish on cast iron, you tend to need a rounder edge to your cutting tool.

If you feel you need to have a good surface finish on your cast iron parts, as usually they tend to be a bit rough after machining, then using a very fine emery cloth to smooth it down is the best option.

 

[Blogwitch]

Rudy, as Jens has pointed out, if castings are cooled down too quickly they get chilled areas on them that are a very hard skin, and almost impossible to get through.

In an attempt to get rid of this chilled area, if you have a wood burner or open fire, then you can put the castings into it as you are shutting down for the night, this heats up the castings and allows them to cool really slowly, 99% of the time, this will soften the chilled area.

Another way is a tub full of dry sand, place the castings into a deep hollow inside the sand and heat up to bright red, once there, cover over with the hot sand that is in the tub and cover over with a lid to retain the heat, as before, leave to cool overnight.

This picture of the faceplate off my lathe shows a very good example of chilling in a casting.

Whenever you come to use a faceplate, it should always be checked for runout, and if it is more than 0.001" out, then the face should be skimmed all the way across.
I am lucky in that I have fairly large machinery, so I just mounted up a tungsten cutter and sent it on a 20 minute journey across the face.

As you can see, there are two different grain structures shown, one on the outer rim and on the hub, the other between both of those. The outer rim and hub are thicker than the middle bit with the slots, so cooled down slower giving a much finer and softer grain, the bit between them was only thin, so cooled down rather fast and so had a much coarser and harder grain structure, this was the part that was chilled.

John