Flywheel turning hits a problem – 4 jaws to big!
Just had a short session this morning and continued with the flywheel project for the Seal engines being built. However after getting the outside turning round and facing off I was left with 2.6315" diameter (need 2.5" finished size) so was pleased with progress. I don't know what specification the brass is made to but it machines great!
So feeling smug I thought I would rough turn the inside of the cavity (will be the rear of the finished flywheel) and using one of my home made boring bars before reversing the blank and bringing the front to roughly the correct diameter so that finishing cuts could be made all the better when running the lathe at faster speeds than the unbalanced blank would allow. This is when I hit a snag! One that I did not expect or had come across before using the Turner lathe.
The diameter of the cavity when finished, will be 1.75" and when I reversed the jaws, they were too big to go inside the cavity! So my smart thoughts went out the window! I will now have to remove the remaining excess by another method.
I did however resolve a question I had about the small diameter of the valve liners for the Seal. The answer came to me when studying the drawings last night and the reason is the need for the valve spring to sit over the outside of the valve guide. Mystery solved and I will just have to be careful when making them!
When I resume work on the flywheel I will hold the turned part in the 4 jaws as normal. A few photo's below show progress........
- Thank goodness there is more than the 2.5″ diameter required
- Boring the cavity which will be the rear of the finished flywheel
- My 4 jaw chuck proved to big for the cavity in the flywheel!




January 19th, 2010 at 11:41 am
Why can’t you use a 3-jaw to clamp on the inside diameter of the cavity?
January 19th, 2010 at 6:40 pm
I can use a 3 jaw chuck as suggested, but the accuracy difference between 3 and 4 jaws is such that flywheel wobble is easier to create with three jaws, and I want wobble free flywheels!
That’s not to say I won’t use the 3 jaw because the final turning will be made when the flywheels are mounted on a mandrel and turned between centres. I have yet to make my mind up as to the approach to take. Perhaps the first step will be to check the size the 3 jaw will take……
Mike
February 26th, 2010 at 1:54 am
Maybe a hollow aluminium stub mandrel to match the inside diameter (maybe 1/2 to 1 thou’ interference fit), with a shoulder for the faced end, brass in the oven, ally in the freezer, pop together and allow temp’s to equalise. That would leave the outer surface of the flywheel and the shoulder on the mandrel to check with the dti to true in the 4-jaw, then once you’ve finished (*Light* cuts!) either pop ‘em back in the freezer or machine away most of the ally then dunk in strong caustic soda for a few hours? Might mean sacrificing a chunk of scrap ally, though…. It looks like there’s not quite enough depth for an expanding stub mandrel, which was my first thought