Ultrasonic thickness meter

[Blanco]

Just wondering if anyone has experience of these things, are they a worthwhile tool in checking an older chassis? ........... in looking for my next long term purchase, I am concerned to find a really sound chassis, but most sellers don't appreciate big screwdrivers and hammers going to work .

[ejparrott]

In my view, if they don't like you checking the chassis the MoT tester's way, they're probably trying to hide something

[robertspark]

The thing with the thickness testers is you need to get the calibration block too. I'm no expert on the subject but I looked at getting one when I got an ultrasonic flow meter for the job that pays the bills for measuring pipeline thickness

Basically the bit that concerned me about them (and that affects the accuracy of anything ultrasonic) is it works off timing the speed of an ultrasonic pulse bounce. That sounds all well and good but different materials have different ultrasonic propagation rates and it gets even more complex when you have two different materials and it is not a homogeneous material as the propagation rate changes and hence the thickness may change (slightly).

I think they may be a bit on Wikipedia on them that may be of use

[zim]

We use them at work. They're carp on rust. Personally I wouldn't try it on a chassis. What's the thickness of chassis steel - only a few mm when new, may as well just use a tapping stick.

G

[Cynic-al]

We have a few different ones at work for checking plastic thickness over steel and paint / glav etc thickness on steel.

You have to calibrate them and get them perfectly flat to the surface, I can't see them being that much use on a chassis with lumpy flaky bits on both sides?

[gazelle]

I use them on the bottom of narrowboats and dutch steel craft. Even at 10mm it is a real PITA to get readings on the rusty unpainted bottoms.

You need a high frequency one to be able to measure thin plate, something like a Cygnus type machine. If the outer surface is rusted and rough you cannot get a return, and if the inner surface is rusted and rough the signal gets lost. It is worse with the higher frequency probes. Best to use a hammer. You can hear the difference the thinner plate makes.

Cheers

Martin

[simonr]

I've seen an 'Expensive' one that plotted a graph on screen showing the layers (changes in density which reflect some of the ultrasound). This, with a bit of interpretation can indicate the thickness of paint, zinc coating, rust & steel that might make up a component.

However - it looked very expensive!

Si

[gazelle]

I've seen an 'Expensive' one that plotted a graph on screen showing the layers (changes in density which reflect some of the ultrasound). This, with a bit of interpretation can indicate the thickness of paint, zinc coating, rust & steel that might make up a component.

However - it looked very expensive!

Si

I have seen them used by specialist NDT companies. such as these clever chaps in Palma. One of the yacht survey companies on the south coast has one.

Multiples of thousand pounds and needs a lot of expensive training to be able to interpret the results. Even a basic decent spec 3 echo unit that just gives the steel thickness and ignores the paint is around £1400 and the probes are around £500 each! Hammers are about £15 for a 4 or 8 oz ball peen which should be sufficient for testing a Land Rover chassis! When they go through the bit needs replacing! Simples.

[Blanco]

Well, I am glad I asked..... that is why I asked.... thanks everyone, I'll 'stick with the knockin' stick'

[dirtydiesel]

I bought a £90 one for checking roll cage tube thickness and found it to be as accurate to within 0.1mm

Paint thickness seemed to have little effect, but the amount of paint on most cages is negligible really.

[gazelle]

The other thing to note with UT is that the reading you take is for the spot you are measuring only. Just next to it could be significantly thinner. It is good for sampling, and for confirming other methods, but it is easy to miss the problem bits if it is the only method.