Hello Everyone,
I recently joined the Cove and am benefiting from it already!
I had a question, hopefully a simple one to start out with. I needed some information about tolerances and stacked tolerances involved in cutting smaller sheets from bigger sheets. Eg. need 20" x 25" from a 48" x 144" sheet. The tolerance on the final product is set, but what is the extent of inspection needed and required for all the intermediate cuts that lead to the final product? Is there any set method or formulas to find the required tolerances so that the final product is within the set limits? Any input is appreciated!

Regards.

Hello Everyone,
I recently joined the Cove and am benefiting from it already!
I had a question, hopefully a simple one to start out with. I needed some information about tolerances and stacked tolerances involved in cutting smaller sheets from bigger sheets. Eg. need 20" x 25" from a 48" x 144" sheet. The tolerance on the final product is set, but what is the extent of inspection needed and required for all the intermediate cuts that lead to the final product? Is there any set method or formulas to find the required tolerances so that the final product is within the set limits? Any input is appreciated!

Regards.
Welcome to the Cove, MM. :agree1:

Tolerances must take into consideration the capability of the cutting process. There's a big difference between what can be held when using tin snips and the precision of laser cutting. The end-use tolerance will (or should) determine the method of cutting to be used. If your end-use tolerance is, for example, +/- .010", cutting by hand isn't going to work, and shearing might work, depending on other factors.

As far as the necessary extent of inspection is concerned, it's no different than for any other process.

What is the material being cut?

Welcome to The Cove, MetalManiac! :bigwave:

Tolerances are set for final product but how you get there is an internal concern.

The amount of waste you'd have in cutting smaller sheets would probably depend on things like the kind of edge you need. Is there a requirement for no rolling, tearing, break marks (showing where the material is actually broken at about halfway through the thickness when shearing) allowed?

The degree to which this matters, and the amount of material that needs to be removed to arrive at the final dimension--and how that needs to happen, i.e. grinding, is to be considered.

If your edges need a lot of treatment because of roll, ragged edge or whatnot, then the shear's blade settings and edge can be looked at because you're right to want to reduce that amount of waste and what needs to be done to fix the edges.

If there is residual stress in the material from being cut, then that is also factored in as above as the need to get rid of the compromised portion demands. I never worked with sheetmetal that presented this kind of challenge.

If none of that is a concern, then I do not see why to care about tolerances when cutting a large piece in to smaller ones. It's all about making the most sellable product with the material we have to work with.

Thanks Jim & Marc,
We are using a sqaure shear for now, but hopefully someday will get to a laser cutter. It is an old beater machine but can still hold tolerances pretty good.

We are working with aluminum.

For now, I am setting some measurements and tolerances to collect some data in order to come up with some acceptable numbers that we can be sure that we can achieve. Currently we have no system in place and I am working from the very bottom to set up a quality system. I am trying as much as possible not to do an over-kill by documenting and collecting all possible data which might not be of use to me for any analysis.

As my earlier example, we have a ±.020" tolerance on a 20" x 25", but to get to that size from a 48" x 144", I will have to get each corresponding cut measured and maintained to the right tolerance. It might be a stretch in the start, but I am hoping that with this study we can be sure of the consistency and capabilities of our machine.

Thanks Jim & Marc,
We are using a sqaure shear for now, but hopefully someday will get to a laser cutter. It is an old beater machine but can still hold tolerances pretty good.

We are working with aluminum.

For now, I am setting some measurements and tolerances to collect some data in order to come up with some acceptable numbers that we can be sure that we can achieve. Currently we have no system in place and I am working from the very bottom to set up a quality system. I am trying as much as possible not to do an over-kill by documenting and collecting all possible data which might not be of use to me for any analysis.

As my earlier example, we have a ±.020" tolerance on a 20" x 25", but to get to that size from a 48" x 144", I will have to get each corresponding cut measured and maintained to the right tolerance. It might be a stretch in the start, but I am hoping that with this study we can be sure of the consistency and capabilities of our machine.

Well, you're certainly approaching from the right direction. Collect the data, analyze it, and the results will help you decide what you can do and what you can't (or shouldn't). In the meantime, inspection should be done to the extent made necessary by your uncertainty.