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