Machining connecting rods.

[cubman]

I need to machine two connecting rods from brass/ bronze castings. One for 1/2 scale IHC Tom Thumb and one for a full scale Tom Thumb. Need some ideas on how to accurately slit the large end. I plan to drill tap size holes for the bolts first. Not sure if sawing through with a band saw and facing off the surfaces is the best way. How do you guys that have done this a lot do it? These castings are scarce so I'm paranoid about messing up. Thanks, Larry

 

[gbritnell]

I machine the faces and end first leaving maybe .005 for a recut if necessary. I then put the tapped hole and relief hole in for the bolts, if that's the way it's made. Some rods have just a clearance hole and they use a through bolt with a double nut on one end. If the rod has enough stock for bandsawing then that's what I do next. Now I put the cap in the vise and mill the mating face to size, the same with the rod. The parts are then bolted together and the cleanup cut is made. Now you can put the crank pin hole in.
gbritnell

 

[cubman]

Gbritnell, Thank you very much. I thought that would be the way to do it but wanted to check with someone with more experience. This is my first engine from castings. I just bought the Tom Thumb over the Internet and the seller didn't tell me it had a cracked and brazed up rod. Luckily I found a fellow with a rod casting.

 

[John Rudd]

Not sure of your location, but in the next issue of ModelEngineer's Workshop, there's to be an article on making conrods......If you can wait that long... ;D

 

[HPME]

Cubman,
If your 1/2 scale Tom Thumb castings are the ones made by Midwest Model Engineering, replacement castings should be available. I haven't talked to Don for some time, and don't know if he is planning to produce more casting kits but I'm sure he has some castings left. I did the drawings for this kit so if you have any questions let me know. If anyone is interested in a set of these castings let me know and I will talk to Don and see what we can do. My Avatar was built from Don's castings.
Daryl

 

[cubman]

Daryl, Thanks for the response. I talked to Don a few days ago. I got a fuel tank and fan parts from him. He said he had some parts left. Didn't know if he would get more cast. Was having trouble finding a foundry. I mentioned the Amish Cattail foundry in PA. I sure hope he does. It's a great engine casting kit and your dwgs are superb. Larry

 

[cubman]

Hi John, Thanks. Nice looking AT6. I had one close to 50 yrs ago. Loved it but couldn't afford to fly it much. Sure rattled the countryside opened up with the prop in low pitch. Larry