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How thick and how precise for the model?

Question asked by Dwight Livingston on May 3, 2012
Latest reply on May 4, 2012 by Kenneth Barrentine

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What thickness and precision do you all use for sheet metal models? What are the ramiifications?

We design in millimeters and use sheet metal gauges currently common in the US. For our sheet metal models, it is my preference to model a sheet metal thickness to the nearest tenth of a millimeter for the thicker gauges, to the hundreth for thinner stuff. I keep the model thickness inside the thickness tolerance. I might try to hit on the low side, since most sheet metal runs light.

I prefer to do this to keep the part dimensions easy. You can't always design on one side of the sheet - many times the thickness gets into the part dimensions.

Others in our department prefer to use the 3-place inch value shown in the charts and convert that to millimeters, no matter how many decimal places produces. Still others, more middle-of-the-road, prefer a millimeter value to two places as shown in some gauge charts.

Thanks

Dwight

Anna Wood May 3, 2012 11:23 PM

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Whatever you decide we, as a manufacture, will deal with. We re-model most every customer part anyways. The thickness is not so much as issue as all the other rounding errors most everyone models with.

i.e, .125 in the SolidWorks part model will be shown on the detailed slddrw as .13, etc. We will also model to take advantage of MMC conditions, etc. There is cut mis-matches to be considered for in progressively stamped parts. Plus many other manufacturing considerations that we may tweak a manufacturing model for to meet the customer requirements.

We inspect to the dimensions on the drawings. We re-model to the dimensions on the drawing (no rounding errors, lots of trailing zeros) with whatever thickness of material we will be getting. We rarely work with stock gage material and get most everything from the mill at +/-.002-.003 thick, so have a bit of an advantage over folks that use stock gage thickness materials when working to close tolerances.

The only time the thickness can become an issue is if you need close tolerances and you are mixing dimensions to the sides of material and have not built in enough tolerance to accomadate. Be aware of that and leave adequate tolerance and it will typically not be an issue.

FWIW, my perspective on things.....

Anna

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Anna Wood May 3, 2012 11:23 PM

FWIW, my perspective on things.....

Anna

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Dwight Livingston @ Anna Wood on May 4, 2012 8:33 AM

Anna

Thanks for your reply and your perspective as a manufacturer. I suspect most all our fabricators also remodel our parts.

"We re-model to the dimensions on the drawing (no rounding errors, lots of trailing zeros) . . . "

On the design end of things, I also like to see models exactly on nominal and check for trailing zeros.

Dwight

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Kenneth Barrentine @ Dwight Livingston on May 4, 2012 12:04 PM

imho remodeling is defeatist.

the vendors in my area use the model and in fact insist on having it.

they use the folded version of the model, not the bogus flat-pattern SolidWorks produces.

their CAM software is far superior when applying K-Fac, BA and BD.

not to mention they are better at applying bend relief's and corner treatments.

unless you're using tolerances of +/- .005" ...

001" - .003" variance in modeled thickness isn't going to make a lot of difference in the grand scheme of a completed part.

typically sheetmetal dimensions are assumed to be measured outside, unless otherwise specified.

and if greater than or less than 90 degrees the dimension is to apex (virtual sharp).

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Ryerson Gauges.xls32.5 KB

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Bernie Daraz May 4, 2012 8:28 AM

Dwight,

I agree with Anna, we frequently have to remodel items submitted for manufacture. Your post indicates a willingness for cooperation as well as compromise too. For one, I applaud you. Your cooperation will result in reduced costs and better delivery timeframes. May I suggest that in your quest for cooperation you consider the following:

Model to the surfaces and edges you need control over of course with respect to the tolerances required. In other words don't model to the outside of your material when the inside dimension needs to be controlled. SolidWorks will allow you or us to alter the material thickness at build time, that will insure you get what you need and will allow us to avoid inaccurate assumptions.

In the case of radii when important, model with respect to tangency as we may have to adjust the radius within the limits of tolerance. Of course dimension your drawing to the same surfaces or points if you want to insure production meets with your requirements.

I'm sure others here will add other important considerations.

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Dwight Livingston @ Bernie Daraz on May 4, 2012 8:44 AM

Bernie

Thanks for your reply.

Bernie Daraz wrote:

Model to the surfaces and edges you need control over of course with respect to the tolerances required. In other words don't model to the outside of your material when the inside dimension needs to be controlled. SolidWorks will allow you or us to alter the material thickness at build time, that will insure you get what you need and will allow us to avoid inaccurate assumptions.

I had not thought of that. It would certainyl save you a lot work if you have to tweak the thickness.

In the case of radii when important, model with respect to tangency as we may have to adjust the radius within the limits of tolerance. Of course dimension your drawing to the same surfaces or points if you want to insure production meets with your requirements.

I am sometimes tempted to model at a maximum bend radius, which can better show what I can get away with. I think, though, that the communication works better with everything at nominal.

Thanks

Dwight

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Bernie Daraz @ Dwight Livingston on May 4, 2012 8:56 AM

Dwight,

I believe I understand when you say you model at maximum bend radius, most fabricators would like to bend with standard practices applied. That could be using standard tooling that might be .008 or .030 radius, you may want to ask. In the case with bends over 90 degrees that minimum might be starting at a tooling radius of .026 or more depending on the material thickness. The actual radius will be a result of the tooling and material thickness as well as the process used to create the bend.

The same results would not be expected of tooled or progressive bending and job shop press brake bending. You may have to adjust your expectations (read dimensions and tolerances) if you're prototyping versus your desired production runs if you use different processes.

For instance on drawings, bend reliefs widths and depths were only dimensioned when we required them to perform as part of the component requirements. Otherwise they were left up to the fabricator to suit the process used.

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6 Replies

Anna Wood May 3, 2012 11:23 PM
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Correct Answer
Whatever you decide we, as a manufacture, will deal with. We re-model most every customer part anyways. The thickness is not so much as issue as all the other rounding errors most everyone models with.

i.e, .125 in the SolidWorks part model will be shown on the detailed slddrw as .13, etc. We will also model to take advantage of MMC conditions, etc. There is cut mis-matches to be considered for in progressively stamped parts. Plus many other manufacturing considerations that we may tweak a manufacturing model for to meet the customer requirements.

We inspect to the dimensions on the drawings. We re-model to the dimensions on the drawing (no rounding errors, lots of trailing zeros) with whatever thickness of material we will be getting. We rarely work with stock gage material and get most everything from the mill at +/-.002-.003 thick, so have a bit of an advantage over folks that use stock gage thickness materials when working to close tolerances.

The only time the thickness can become an issue is if you need close tolerances and you are mixing dimensions to the sides of material and have not built in enough tolerance to accomadate. Be aware of that and leave adequate tolerance and it will typically not be an issue.

FWIW, my perspective on things.....

Anna
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- Dwight Livingston @ Anna Wood on May 4, 2012 8:33 AM
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  Correct Answer
  Anna
  
  Thanks for your reply and your perspective as a manufacturer. I suspect most all our fabricators also remodel our parts.
  
  "We re-model to the dimensions on the drawing (no rounding errors, lots of trailing zeros) . . . "
  
  On the design end of things, I also like to see models exactly on nominal and check for trailing zeros.
  
  Dwight
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  - Kenneth Barrentine @ Dwight Livingston on May 4, 2012 12:04 PM
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    Correct Answer
    imho remodeling is defeatist.
    the vendors in my area use the model and in fact insist on having it.
    
    they use the folded version of the model, not the bogus flat-pattern SolidWorks produces.
    their CAM software is far superior when applying K-Fac, BA and BD.
    not to mention they are better at applying bend relief's and corner treatments.
    
    unless you're using tolerances of +/- .005" ...
    001" - .003" variance in modeled thickness isn't going to make a lot of difference in the grand scheme of a completed part.
    
    typically sheetmetal dimensions are assumed to be measured outside, unless otherwise specified.
    and if greater than or less than 90 degrees the dimension is to apex (virtual sharp).
    Attachments
    Ryerson Gauges.xls32.5 KB
    Like • Show 0 Likes0
    Actions
Bernie Daraz May 4, 2012 8:28 AM
Mark Correct
Correct Answer
Dwight,

I agree with Anna, we frequently have to remodel items submitted for manufacture. Your post indicates a willingness for cooperation as well as compromise too. For one, I applaud you. Your cooperation will result in reduced costs and better delivery timeframes. May I suggest that in your quest for cooperation you consider the following:

Model to the surfaces and edges you need control over of course with respect to the tolerances required. In other words don't model to the outside of your material when the inside dimension needs to be controlled. SolidWorks will allow you or us to alter the material thickness at build time, that will insure you get what you need and will allow us to avoid inaccurate assumptions.

In the case of radii when important, model with respect to tangency as we may have to adjust the radius within the limits of tolerance. Of course dimension your drawing to the same surfaces or points if you want to insure production meets with your requirements.

I'm sure others here will add other important considerations.
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- Dwight Livingston @ Bernie Daraz on May 4, 2012 8:44 AM
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  Bernie
  
  Thanks for your reply.
  
  Bernie Daraz wrote:
  
  Model to the surfaces and edges you need control over of course with respect to the tolerances required. In other words don't model to the outside of your material when the inside dimension needs to be controlled. SolidWorks will allow you or us to alter the material thickness at build time, that will insure you get what you need and will allow us to avoid inaccurate assumptions.
  I had not thought of that. It would certainyl save you a lot work if you have to tweak the thickness.
  In the case of radii when important, model with respect to tangency as we may have to adjust the radius within the limits of tolerance. Of course dimension your drawing to the same surfaces or points if you want to insure production meets with your requirements.
  
  I am sometimes tempted to model at a maximum bend radius, which can better show what I can get away with. I think, though, that the communication works better with everything at nominal.
  
  Thanks
  
  Dwight
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  - Bernie Daraz @ Dwight Livingston on May 4, 2012 8:56 AM
    Mark Correct
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    Dwight,
    
    I believe I understand when you say you model at maximum bend radius, most fabricators would like to bend with standard practices applied. That could be using standard tooling that might be .008 or .030 radius, you may want to ask. In the case with bends over 90 degrees that minimum might be starting at a tooling radius of .026 or more depending on the material thickness. The actual radius will be a result of the tooling and material thickness as well as the process used to create the bend.
    
    The same results would not be expected of tooled or progressive bending and job shop press brake bending. You may have to adjust your expectations (read dimensions and tolerances) if you're prototyping versus your desired production runs if you use different processes.
    
    For instance on drawings, bend reliefs widths and depths were only dimensioned when we required them to perform as part of the component requirements. Otherwise they were left up to the fabricator to suit the process used.
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