Sheet Metal Tolerance

On a cnc punching mechine, 5 mils

For bending, 10 mils each bending (principaly du to sheet thikness)

For sheering, depend on the sheer and on the operator (nesting is better than sheering)

Laser are better that punching on hier gauge and if more detail or lot of hole of different diameter

Dont hesitate if you have other questions I have done a lot of this

Tolerance is relative to size, the smaller the part, the tighter the tolerance.

+/- 1/16" to 1/32" is usually standard on basic fabricated parts. For thick metal, around 1/4", the tolerance goes to around 1/8"

If you need prototypes or low volume parts made, please call or e-mail for a quick quote.

Marcus Stackpoole

(568) 839-7979

stackpoole77@yahoo.com

www.cypressmanufacturing.com

that depends on the thickness, radius of the bend and the type of metal. Use these formulas:

soft copper/soft brass: allowance=(0.55 x thickness) + (0.5 x 3.14 x radius of bend)

aluminum, med-hard copper,med.-hard brass, soft steel:

allowance= (0.64 x thickness) + (0.5 x 3.14 x radius of bend)

bronze, hard copper, cold-rolled steel, and spring steel:

allowance= (0.71 x thickness) + (0.5 x 3.14 x radius of bend)

compliments of my text book "Descriptive Geometry: An Integrated Approach Using AutoCAD", Kevin Standiford, Debrah Standiford.

it seems odd though, are you really an engineer? why would you not know this already? I'm only a sophomore at ITT-Tech and I learned that a month ago.

You should keep your insulting comments to yourself schoolboy! This forum should always encourage even the dumbest of questions so that everyone feels free to ask what they need to know without being insulted.

You will find that you learn 10 times more when you are on the job than you will ever learn in school!

Watch that ego, it will get you in trouble.

The best advice I ever got while coming up in my trade was to never burn bridges.

Insults burn bridges!

Good answer..

I too have been brought down by seemingly "ignorant" coworkers who have turned out to know more than I will ever learn-

Ok, here is my input for sheet metal design and fabricating.

We have a an "old timer" at my workplace with many years of experience in bending and welding. He has a chart based on his experence of the proper bend deductions for materials and thicknesses.

Sheet metal flats come in different lots, and not all lots have the same thickness. Therefore, I have to change my bend deductions (not K-factors!) in SolidWorks based on his first test bend. And sometimes the guys programming the punch-press have to re-program because I had to change the bend deduction. When you make a change to the bend deduction, the overall part dimensions do not change (therefore no ECO required), but the flat pattern dimensions do indeed change.

Also, I will add that 0.090" thick aluminum is the most difficult to work with. Also, I always try to make the thickness in my SolidWorks parts the same as the lot thickness. For example, we have noticed that most, if not all, of the 1/8" thick aluminum is typically running at 0.120 thick. Therefore, all of my SW parts are at this thickness.

You will find out after school that sometimes equations mean very little, and working with an experenced craftsman (or woman), can get parts out the door much faster.

my bad I was thinking bend allowance not tolerance, sorry about that.

Hi Jagan

I own a precision sheetmetal shop, and have 25 years experience in all aspects of the company. The tolerances we can hold without issue are as follows:

Shearing +/-.005
Punching +/- .003
Forming +/- .010 across two bends and +/- .015 across 4 bends ie. hat sections

This is our standard tolerance, but we make exceptions when a closer tolerance is required. BTW... We don't use the standards solidworks has for calculating bend allowances.

Hope this helps.

SRP

That is interesting you don't use SolidWorks default tolerances for bend allowances. Is that because of material type or thickness?? Or do they just not hold up in the real world. I am a design Mech Eng and always looking at improving my designs and drawings.

thanks,

EJ

Here is the bend allowance formula that we use everyday for developing highly accurate blanks for sheetmetal stamping.

Bend Allowance:
(0.01743*rad.)+(0.0078*material thk.)=
(material required per degree of bend)*(degree of bend)= bend allowance

please suggest tolerance lenthwise( upto xx.x mm can give +/- x.x ) how much provide for sheet metal .

maybe this is what you had in mind?

if so gl

.o2

Why are people talking about bend allowance, when the original question was tolerance? I usually use +/- .020 across two bends, knowing that the typical capability is about +/- .010 (makes things easier on everyone). Of course the tolerance depends on the size of the part. Anything over about 60" I start adding more tolerance.