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- since 1996 -

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Technical Discussions
David Bunch
David Bunch
23:32 Dec-12-2009
Plastic angle beam wedges out of degree tolerance

Both my AWS and ASME shoes are wearing out of tolerance with respect to appropriate angle. I've tried sanding them with ultrafine sand paper, but I have found this to be a pretty crude method. A co-worker of mine told me about a former UT tech who used to use a milling machine to get his wedges back to their original angle. Has anyone used this method? If so, what kind of milling machine would I need, and what kind of bits?

Thanks
David

    
 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 836

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
836
16:02 Dec-13-2009
Re: Plastic angle beam wedges out of degree tolerance
In Reply to David Bunch at 23:32 Dec-12-2009 (Opening).

Hi David,

Like many others, I did fiddle with plastic shoes to make them fit the profile of the part I was inspecting and technically ther is nothing wrong with what you are trying to accomplish. But, you can only do this so much. One of the reason the shoe is of a certain thickness is to keep the part of your UT signal that you don't want out of your part. I mean the Null Zone.

But if you would like to fiddle with the your shoes, I suggest using a very flat surface, like an A5 CAl Block for example. The next thing you want is to use the finest sand paper you can find. Like a 600 grit do a wet sending with water or a little bit of couplant. The key here is to put equal pressure on the shoe or in the area where you want to mill your shoe and be patient.

I used to work in the aircraft industry and many times we were able to make scratches disappear in a plastic window in this fashion. The higher the grit number, the smooter the shoe will be. Some people also use a compound called plastic polish, but I don't think it would be necessary in you situation.

Good Luck!!!

    
 
 Reply 
 
Phil Herman
Sales, - Manufacture of NDT Reference Standards/Test Blocks
PH Tool Reference Standards, USA, Joined Oct 1999, 79

Phil Herman

Sales, - Manufacture of NDT Reference Standards/Test Blocks
PH Tool Reference Standards,
USA,
Joined Oct 1999
79
22:01 Dec-13-2009
Re: Plastic angle beam wedges out of degree tolerance
In Reply to David Bunch at 23:32 Dec-12-2009 (Opening).

David,
If you have access to a Bridgeport milling machine equipped with a good, square vise, you can hold the shoe securely while making a shallow pass or two with a carbide endmill. Try .004" (0.1mm) per cut until the worn areas clean up. As Michel mentioned, careful sanding on a granite surface plate or other suitable surface will work in a pinch too. If you prefer, PH Tool Reference Standards offers wedge renewal and radius machining too.
Good luck.
Phil Herman

    
 
 Reply 
 
David Bunch
David Bunch
01:57 Dec-14-2009
Re: Plastic angle beam wedges out of degree tolerance
In Reply to Phil Herman at 22:01 Dec-13-2009 .

Thanks for the advice guys! Right now I'm going to have to go the sandpaper route, hopefully that will get me within code compliance on my wedges.

I work for the strangest NDT company in the country. I get absolutely zero funding for the UT program. Believe it or not, I've actually been paying out of pocket for the last 6 months for transducer cables. Nor can I get my company to pay for an ASME basic block. It'll all pay off though once I pass my API QUTE exam. Phil, if I ever get on with a real company, I'll be sure to throw some business your way for your helpful advice.

    
 
 Reply 
 
Roger Duwe
NDT Inspector, API-510, 570, 653
MISTRAS, USA, Joined Jan 2009, 148

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
02:10 Dec-14-2009
Re: Plastic angle beam wedges out of degree tolerance
In Reply to David Bunch at 01:57 Dec-14-2009 .

For folks that don't have access to a milling machine or a surface plate:
Use a piece of glass windowpane for a surface plate
Rough the angle in with 60-80 grit [medium-coarse] sandpaper, checking the angle on an IIW calibration block using thick couplant [to fill in the sanding scratches]
When the angle is correct, then start smoothing out the scratches with the fine [200 grit] sandpaper. "Us poor boys may have poor ways, but they work"

    
 
 Reply 
 

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