Profile of a Surface

[kmcmm]

I am relativly new to sheet metal. My question is how do you decide how many points to take when checking the profile of a surface. I have a surface that is about 8 inches across and 12 inches tall. I was thinking of taking 20 to 25 points on the surface in order to dimension the profile. My question is, is that overkill or a good number and how do the rest of you normally decide how many points to take.

[bw_bob]

I decide by knowing the vendor and what kind of workmanship he has. If it's a new vendor and i know it's a critical surface then i would probably use a little overkill. It's up too you, if you know the vendor.

[kmcmm]

It is a part that we stamped in house.

What I was wondering was if any of you had a general rule of thumb you used. Maybe the number of points dependent on the size of the surface.

[bw_bob]

In my opinion with that size i would not consider 20 to 25 points overkill. If its a real critical surface i might use more.

[Jan d.]

I always take the tolerance into account. And for sheet metal, where the welds are, or stiffeners (on the far side) or fixture resting points (these are candidates for high points).

If the surface has very little potential "warp" features, I think 20 to 25 ought to be sufficient. If you see features that may cause high/low spots ("warpers") I would locally check more points to try to catch those defects. Always take some points close to the edges! Typically, there is where you find the most warping.


Jan.

[kmcmm]

Thanks for the advice guys.

[Paul Sarrach]

1 point every 100 mm as a rule. Less than 8 inches, points, one at each end one in the middle. Same for the Trim. If the don't like it, they will tell you to add more. But usally not. What most of the Auto motive want is one point every 100mm thats only for 1 part. Then when its time to do the PPAP, it is cut down to only the GD&T Print call outs. But every now and then you get a ******* engineer who don't know ***, and will want 1 point every 2mm

[mchough1]

You might want to check your customer requirements. I didn't see any application for the part, but for Aerospace componants, many companies like Boeing, Lockheed, Grumman, etc... actually state in their quality requirements the amount of points required per square inch, linear inch, and so on. Better to be safe than????

Mike

[Paul Sarrach]

I always take the tolerance into account. And for sheet metal, where the welds are, or stiffeners (on the far side) or fixture resting points (these are candidates for high points).

If the surface has very little potential "warp" features, I think 20 to 25 ought to be sufficient. If you see features that may cause high/low spots ("warpers") I would locally check more points to try to catch those defects. Always take some points close to the edges! Typically, there is where you find the most warping.


Jan.

Jan is correct about the need for more in area such as welds. But when you run into those the print will reflect, and most likely the project manager or someone will come to you and give you a detailed list of requirments.

I always take one of my surfarc points as an edge point and tolerance the "S" because that is were the feeler will enter, and if you could show a bad part good if you dont.

[kmcmm]

Jan is correct about the need for more in area such as welds. But when you run into those the print will reflect, and most likely the project manager or someone will come to you and give you a detailed list of requirments.

I always take one of my surfarc points as an edge point and tolerance the "S" because that is were the feeler will enter, and if you could show a bad part good if you dont.

No such luck, I don't get a detailed list of requirments and what it a project manager . Here recently all I have gotten are the reports from the exit PPAP's. No print or anything close to one.

[Paul Sarrach]

No such luck, I don't get a detailed list of requirments and what it a project manager . Here recently all I have gotten are the reports from the exit PPAP's. No print or anything close to one.

Well I would at the least check everything that was on the PPAP report

[CMM170]

Your best bet is to use a surface scan. The more hits the better the average.

[Paul Sarrach]

Your best bet is to use a surface scan. The more hits the better the average.

I have to dissagree. In the Stamping world you can always check a part and find something wrong with it. I will find something on the amount of hits and post. Less is more. I am highly intl lean checking. If they want more they will tell you. Yes, you must check every area that is functional, your best bet if you have a gage is check all the areas that the gage checks.

[Jeffrey Lovely]

blue the part up and rub the part against a surface both sides if flat
hit the high and low spots (then decide how many extras are needed )
when asked why and where you took your hits
keep the sample and show them
this is pretty accurate and will keep em satisfied

[rebeldude]

One company we do work for specifies, 1 point for every 50mm, unless there is a change in the form, then to add more