P.M. Research #5 Steam Engine

[Sarah]

My next project is the P.M. Research #5 Steam Engine. The picture below is the #5 from the P.M. Research website. It has a mixture of cast material, including aluminium, brass and iron. First impresions are very good, the cast parts look excellent and the drawings very clear and precise. A lot of the smaller cast pieces are all joined together on a Sprue, this should make it easier to hold whilst machining. A lot of the specified threads are UNC, I will buy a set of 2-56 taps as there are a lot of 2-56 screws included in the kit. For the other threads I will use the BA taps and dies I already have.

The first bit to be tackled was the cast aluminium, or as it's an American product cast aluminum, Base The casting is very good with just a little filing to remove the sprue bit. The base and top were lightly sanded against some abrasive paper on a sheet of glass. This removed a few odd lumps and gave a nice flat surface to work from. The tapping drill size was 1.85mm for the four 2-56 internal threads in the top of the casting. I used the nearest I had at 1.8mm, even though it was smaller than specified it was very easy to run the tap through. I might try a smaller drill bit size next time.

Next will be the Standard and a chance to use my nice new Faceplate

 

[trlvn]

The tapping drill size was 1.85mm for the four 2-56 internal threads in the top of the casting. I used the nearest I had at 1.8mm, even though it was smaller than specified it was very easy to run the tap through. I might try a smaller drill bit size next time.

The reference I use says a 1.75mm drill gives 74% thread penetration. A #50 drill (0.070 inches or 1.778mm) gives 69% thread penetration. Using a 1.85mm would give a very low penetration IMHO.

Craig
(From "Handyman in Your Pocket" by Young & Glover, 2008.)

 

[Sarah]

The reference I use says a 1.75mm drill gives 74% thread penetration. A #50 drill (0.070 inches or 1.778mm) gives 69% thread penetration. Using a 1.85mm would give a very low penetration IMHO.

Craig
(From "Handyman in Your Pocket" by Young & Glover, 2008.)

Thanks Craig, you are correct about the thread, it was very shallow.

The book that I have been using is:

Screwcutting (Crowood Metalworking Guides) by Marcus Bowman (Author)​

That book has been really useful. I have since checked other sources and they specified a #50 or 1.8mm drill bit. When I assemble it all on completion I might use slightly longer 2-56 screws and nuts to be sure. I have ordered some #50 drill bits for the rest of my project

 

[Sarah]

The Standard was tackled next.

The top and bottom of the Standard were uneven, so I took some time to file the top until it was nice and flat. I also checked it stood up vertically with an engineers square.

I needed a way of holding the Standard and I discovered that there is a shelf like form at the bottom of the crosshead guide. A T-nut, wrapped in aluminium sheet, fitted against the shelf perfectly. I could then attach the Standard to a nice flat sheet of aluminum, which can be fixed to a faceplate or mill table.

 

[Sarah]

With the Standard fixed to the aluminium plate, and appearing reasonably flat and level, it was machined in my milling machine. The aluminium plate was placed on two steel parallels in my milling vice and tapped down on top of the parallels. This gave me a nice base to machine from, but it was the top of the Standard which would be my reference for other machining.

 

[Sarah]

The Standard was fixed to my shiny new Faceplate by clamping onto the lower bearing hub each side. My guesstimation with getting a flat base with the engineers square can't have been too bad. The Standard only needed a thin strip of aluminum, from a drinks can, to get the top of the Standard nice and centered with a DTI. The top of the Standard was machined to the drawing, including 2 1/2" into the top of the Standard. To finish the machining a reamer was used to finish off the crosshead guide inside.

 

[Sarah]

The upper bearing hubs were maching together initially, this made it a lot easier to hold and align for machining.