PM-727m New mill has arrived!

[Sloth2009]

You can use a much larger diameter boring bar in that big of a hole, and will have more success with surface finish and with finishing to the desired size.

I think I will get one from Mesa Tools. American made and reasonably priced.

 

[Bob Korves]

It is not so much that it is American or Chinese. Steel is steel, and it all has essentially the same stiffness, regardless of grade or hardness. If you want stiffer boring bars, you need to go bigger or go to carbide, which has a higher elastic modulus. Bigger is lots cheaper than carbide, and the hole in your pic shows room for a much bigger boring bar. Obviously, that is just the cutting tool I am speaking of. If there is flexibility or play in the machine or the boring head or the setup, it will cause much the same problems.

 

[Sloth2009]

This project will eventually be an offset cam using pieces of steel tubing and a bronze sleeve bearing. The plan is for the cam to actuate a sledge hammer in a homade power hammer design. There are cam hammer designs online which typically use a large ball bearing with an off center shaft or a wooden spiral cam. I decided to design this cam a bit different because I belive it will be more robust and easier to repair and modify than others I have seen. I can also cut the cam “to length” as I see fit.

Today I drilled then bored the solid shaft with an off center hole which will provide 1.25” of total throw. I also drilled and tapped some holes for some 1/4-20 set screws. The 2 1/2” solid shaft slides over a 3/4” keyed shaft which will be eventually driven via a drill motor and some v-belt pulleys.

 

[Sloth2009]

It is not so much that it is American or Chinese. Steel is steel, and it all has essentially the same stiffness, regardless of grade or hardness. If you want stiffer boring bars, you need to go bigger or go to carbide, which has a higher elastic modulus. Bigger is lots cheaper than carbide, and the hole in your pic shows room for a much bigger boring bar. Obviously, that is just the cutting tool I am speaking of. If there is flexibility or play in the machine or the boring head or the setup, it will cause much the same problems.

This is the one I am looking at from Mesa.

 

[Bob Korves]

This is the one I am looking at from Mesa.
View attachment 246486

I am not familiar with that boring bar and do not know the tool shank capacity of the boring head. If it is 3/4", then you would be gaining all you can by increasing the bar diameter, short of cutting down the shank of an even bigger one to fit the boring head. Length is also an issue. Any excess length length sticking out beyond what is needed to go through the bore of the work diminishes rigidity. I often run boring bars to within 1/4" or less of hitting the boring head, QCTP, or whatever is holding the bar. It makes a big difference in cutting ability, lack of chatter, and being able to finish to size without a bunch of spring passes that can easily go oversize.