Note also: Many (most?) motors have a face with a step. This is useful in that your plate can have a hogged out section that mates with that step such that the motor's XY location gets fixed by that interface and not your bolt pattern. At that point, the bolt holes can be fairly loose since they are for the most part merely pulling the motor tight against the plate and the plate friction and that step interface keep the motor secure. Of course the bolts also keep the motor from rotating on the plate by their being hole-aligned with the motor holes and bolts going thru them.
From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Myles Twete
Sent: Monday, February 7, 2022 10:00 AM
To: electricboats@groups.io
Subject: Re: [electricboats] Bolt hole tolerance when laser cutting 1/2 inch stainless steel
Caveat: I am an engineer, but not mechanical.
Having said that, I've done some mechanical engineering designs and chosen hole sizes on parts during a couple of my contracts.
Realize that these are interfaces.
And sure, with single holes, you might get away with a close or tight tolerance for that each hole.
But even then, the fastener choice matters and perhaps a heavily plated, poorly toleranced or non-standard bolt gets spec'd and won't fit the hole that standard bolts would.
And there's a big difference between single, non-dependent holes vs a constellation of holes as you are defining for mounting the motor to the plate. And for that part of your design, you should consult the motor manufacturer's mechanical drawing for the motor. And if that does not inform as to spacing tolerances for the motor holes, then ask them. For sure, when you are dealing with a constellation of dependent holes, your hole diameters will need to be at least a little bit larger to accommodate the worst case sum of the tolerances of (1) motor hole spacing, (2) your plates matching hole spacing, (3) other factors?
In case this helps….
From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Steven Borg
Sent: Sunday, February 6, 2022 5:37 PM
To: electricboats@groups.io
Subject: [electricboats] Bolt hole tolerance when laser cutting 1/2 inch stainless steel
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
