Racer Al
Stainless
- Joined
- Feb 20, 2006
- Location
- Oakland, California, USA
Hello everyone;
One of my clients is doing a short run production of an RC motorcycle, and he needs some bronze bushings. All of the dimensions are metric. He hasn't provided any tolerances.
We've agreed that SAE 660 is adequate for the task.
I've looked over Machinery's Handbook and can't locate anything on how to specify tolerance for such a bushing. I assume there is a ratio of tolerance to diameter -- " X-thousandths per D-inch of diameter". Is there a "rule of thumb" for this?
His drawing shows a 7mm (.2756") bushing running on a 6.98mm shaft. That's about .0007", which seems tight to me. In fact, it seems impossible to assemble.
So, regarding reamers: there don't seem to be many metric sizes, and certainly no over/nominal/under sizing groups like the imperial sizes. Should I just use a "close enuf for gubmint wurk" imperial reamer?
How are fits specified in the metric system? Are they always done to the outsize surface? In plain English (pardon the measuring system pun
) does metric system design always make the hole a nice even number, then make the shaft smaller for the running fit?
That seems good design practice because it's far easier to adjust the outside that to hit some obscure number on the inside.
One of my clients is doing a short run production of an RC motorcycle, and he needs some bronze bushings. All of the dimensions are metric. He hasn't provided any tolerances.
We've agreed that SAE 660 is adequate for the task.
I've looked over Machinery's Handbook and can't locate anything on how to specify tolerance for such a bushing. I assume there is a ratio of tolerance to diameter -- " X-thousandths per D-inch of diameter". Is there a "rule of thumb" for this?
His drawing shows a 7mm (.2756") bushing running on a 6.98mm shaft. That's about .0007", which seems tight to me. In fact, it seems impossible to assemble.
So, regarding reamers: there don't seem to be many metric sizes, and certainly no over/nominal/under sizing groups like the imperial sizes. Should I just use a "close enuf for gubmint wurk" imperial reamer?
How are fits specified in the metric system? Are they always done to the outsize surface? In plain English (pardon the measuring system pun
That seems good design practice because it's far easier to adjust the outside that to hit some obscure number on the inside.