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AN509-8R8 screws with sharp edges

F

FinnFlyer

Well Known Member
My RV-4 kit came with some machine screws that have sharp edges which sits nicely in dimpled skins (wing tanks, forward fuselage skin and so on).
Does anyone know what they are called and where to get them?
The last batch of MS24694-S5 (supposedly the replacement for the AN509-8R8 screws specified in the plans) I got from ACS have rounded edges that do not at look nice compared to my original screws.

Finn
 
The AN509/MS24694 screw is 100 degree countersink screw designed to be flush with a countersunk or properly dimpled hole. If that wasn't what you got, then they were mis-labeled. And, that would not be the first time thats happened for sure. There are some other machine screws that are 82 degree I think. WOuldn't be surprised if you got those by mistake.

ms24694.jpg
 
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N804RV said:
The AN509/MS24694 screw is 100 degree countersink screw designed to be flush with a countersunk or properly dimpled hole. If that wasn't what you got, then they were mis-labeled. And, that would not be the first time thats happened for sure. There are some other machine screws that are 82 degree I think. WOuldn't be surprised if you got those by mistake.

ms24694.jpg
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Well, the drawing you attached shows two vertical lines at the head. Wouldn't that indicate a rounded head edge?

When I'm talking about a sharp edge I mean what you see on a countersunk rivet.
 
FinnFlyer said:
Well, the drawing you attached shows two vertical lines at the head. Wouldn't that indicate a rounded head edge?

When I'm talking about a sharp edge I mean what you see on a countersunk rivet.
Click to expand...
I know what you mean and have received various batches of screws over the years that may be slightly different in appearance. It possibly depends on the supplier or maybe even how the machine was set up for that parts run. I always ordered by part number and I don't think there is any more you can do to get different edges other than try ordering from different sources and hope for a randomn sample that is sharper.
 
FinnFlyer said:
Well, the drawing you attached shows two vertical lines at the head. Wouldn't that indicate a rounded head edge?

When I'm talking about a sharp edge I mean what you see on a countersunk rivet.
Click to expand...

I can pull out some tomorrow and take pics if you want. I have some still in the original marked bags from ACS. But, I've used a bunch and the MS24694 and the AN509 are both flush in countersunk or dimpled applications, at least in my experience.
 
N804RV said:
I can pull out some tomorrow and take pics if you want. I have some still in the original marked bags from ACS. But, I've used a bunch and the MS24694 and the AN509 are both flush in countersunk or dimpled applications, at least in my experience.
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Thanks. I think I ordered the wrong ones (MS51959). I'll try ordering MS24694 and see what I get. The ones that get the most use are forward fuselage top skin and spinner screws.
 
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Out of curiosity, with a caliper, "mic" the outside diameter of one with a sharp edge & one with a rounded edge. I wouldn't be surprised to find the "rounded" edge is a bit smaller in diameter. If the screws are "tumbled" after manufacture to "smooth" out the edges, this can be the result -- not saying it is, but tumbling can take the "edge" off ...

YMMV - but different manufacturers had different procedures, all within "spec", but leading to a different (perceived) results.

HFS
 
Looking at the MS24694 specification, the flat edge is shown as a maximum dimension, with no minimum listed. So one batch might have sharp edges and another an obvious flat edge.

Dave
 
HFS said:
Out of curiosity, with a caliper, "mic" the outside diameter of one with a sharp edge & one with a rounded edge. I wouldn't be surprised to find the "rounded" edge is a bit smaller in diameter. If the screws are "tumbled" after manufacture to "smooth" out the edges, this can be the result -- not saying it is, but tumbling can take the "edge" off ...

YMMV - but different manufacturers had different procedures, all within "spec", but leading to a different (perceived) results.

HFS
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You're right. Variation on the 509 / MS24954 sharp vs more rounded is about 4/1000" on the ones I measured. So simply manufacturing tolerances.
But real issue turned out to be my ordering MS51959's (82 Deg) instead of MS24954.
 
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You probably won't see the difference on only .004" diff in diameter. But 82* heads don't "nest" very well in 100* dimples - that's going to be your answer ...

David
 
Do yourself a favor and get any 82 degree head screws OUT of your shop. I can't think of anything on my -7 that used any 82 degree hardware, ONLY 100 degree AN hardware.

If you have some non-AN 82 deg items laying around, someday you will mix them up and use them by mistake, virtually guaranteed.
 
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