Re: [electricboats] Bolt hole tolerance when laser cutting 1/2 inch stainless steel

Thank you once again, Dan, for your excellent and thoughtful advice!

:-)

Steve

---- On Sun, 06 Feb 2022 18:30:08 -0800 Dan Pfeiffer <dan@pfeiffer.net> wrote ----

It's a bit easier to make a hole bigger than to make it smaller. 

I had some issues with this.  I tend to try to fit the 3/8 bolts in 3/8 holes and I ended up enlarging them, usually by one size (64th) to get the assembly manageable.  But I was working in aluminum and enlarging a hole is easier than steel.   But it's manageable.  I would consider going for the tight fit clearance and getting a couple reamers in 64th steps (or smaller) to adjust holes as needed. 

These are available in .005 increments:
https://www.amazon.com/Drill-America-Qualtech-High-Speed-32/dp/B00FXJB57U/ref=sr_1_3?crid=3TX7OA7QZMKMR&keywords=17%2F32%2Breamer&qid=1644200365&s=industrial&sprefix=17%2F32%2Breamer%2Cindustrial%2C83&sr=1-3&th=1


I also designed my mounting plate so the lateral positioning of the components didn't need to be too precise.  1/32 would be more than fine for tolerance.  Probably even 1/16.  But it was very important that the motor shaft and output shaft (prop shaft) be parallel and stay that way (no flexing).  If not the belt will walk off the pulleys or there will be excessive belt wear. 


Dan Pfeiffer

On 2022-02-06 8:36 pm, Steven Borg wrote:

Progress continues on the 55' electric motor conversion.

Next question: When laser cutting my 1/2" stainless steel plate for the motor mount (or other parts), what hole tolerance should I consider?

I get different answers when I look online: Clearance Hole Chart (amesweb.info) 
suggests that for a 1/2" bolt a 'close' fit I should be between .531 and .538, and 'loose' fit .609 and .625 with 'normal' fit in between.

But other sites are more prescriptive, telling me that I should use .5156 for a tight fit and .5312 for a loose fit. (basically 1/64" clearance for tight, and 1/32" clearance for loose. Clearance Hole Size for Bolts and Screws (Imperial) - The Engineer's Bible (engineersbible.com)

And, I've heard people say just always add 1/16" to nearly every size bolt hole. 

Given SendCutSend and everyone else seems to have a tolerance of +/- .005", I'm struggling to understand what kind of fit I should go for.  I'd hate to have a motor plate whose 4 support holes were just far enough off to not be able to mount the motor... :-O

Hoping there are a few folks who've been through this before!

:-)
Steve