Low(er) Priced Ultrasonic Thickness Gauge

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nm9stheham

nm9stheham

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I wanted to get one of these for measuring cylinder wall thickness, but the price on the 'shop' grade ones is over $1k. So took a chance on a 'chinesum' one. Found one on Amazon for $180 shipped. Model is TM8812.

Got it here and it seem to work OK. First measured some non-vented brake rotors where could measure the thickness exactly with calipers, and the ultrasonic gauge read within .001-.002", when averaging a few readings. The resolution is only .004" so finer individual readings can't be had with this unit.

With that done, I measured 2 blocks and it seems to read as it should. Without another sonic gauge available to compare it against, the calibration versus a flat rotor is the best I can do to check this unit's accuracy. You hold the probe so that the line in the middle of the probe's face is vertical in the cylinder bore (i.e., parallel to the bore axis). I stayed about 3/4" from the top of the bore and at least 1-1/4" or more more from the bottom of the bores, to stay away from the areas where the casting thickens.

The probe with this has a flat surface, so to make it conform better to the curved cylinder wall, a fine file was used to slowly take material off of each side of the probe head. Do this so that the head is slightly convex across the face, with the vertical line in the middle (where the sonic waves are launched). I made sure to not touch the vertical line with the file. (You can kinda see how the probe surface is convex in the pix of this higher priced gauge and probes: PR-82 Sonic Tester Racing)

Instructions are not the best as expected. Learned that:
  • Calibrate on the disc on the side of the unit only with the unit set for steel
  • Use white lithium grease for best coupling to the cylinder bores; other greases may work. Oil is OK too. Spit works in a pinch LOL
  • This unit can be set for different materials with presets; use preset 'cd10' for cast iron
  • Or, it can be set by sonic velocity of the material with a 'VEL' button
  • The display update speed is slower than commercial units claim to be
  • The resolution is only about .004", but IMHO the casting surface irregularities on the water jacket side are that much or more.
  • Readings were pretty repeatable. When I went back to re-check a few spots, I could only go by the prior 'grease spot' to determine location, and I'd expect cylinder walls to vary a few thousandths if not in the exact same spot, simply due to the casting irregularities.
If I manage to do a dozen blocks with this, then that works out to $15 per block, so that seems pretty decent for an amateur home shop. It was easy to see which sides of each cylinder wall were thick and thin.
 
I bought one off Ebay a year ago and it came with a 10mm probe and was too big diam to do cyls, works great on flat stuff and the outside of pipes. I ended up getting a 8 mm probe and that seems to work, still a good deal and I have used it a lot for different things.
 
How much do machine shops charge? Heck you could start doing it for ppl local for 30 bucks and pay it off really quick.
 
I don't know the shop cost DF75, but that IS an idea. Of course, much/most of the value in this whole process is to know what is too thin...

I got this to see how much could be bored out a 1968 273 block. Interestingly, it had much more consistent wall thicknesses than a later 360 block. Maybe the 360 block was a 'Monday' casting LOL. Too bad it was not here for the 225 and 340...

brian6pac said:
I bought one off Ebay a year ago and it came with a 10mm probe and was too big diam to do cyls, works great on flat stuff and the outside of pipes. I ended up getting a 8 mm probe and that seems to work, still a good deal and I have used it a lot for different things.
Click to expand...
This one has '8.0' on the back of the probe head, so maybe that means 8 mm but it measures 10 mm across the fact of the probe. I filed it as described to make it couple up better.
 
I also filed it to fit a 4.0" bore but the the reading was off after that, It must have changed the frequency or something. So that's when I got the 8mm probe.
 
For a quick and cheap calibration just buy a cheap starret or mitiyoto 1/4x3" block. Heck I think I have something that would work for you. PM me your address and next week I'll send it to you. Free. I have lots of engineering goodies.
 
My unit came with a 5mm calibration block built in.
 
Peter Bates said:
For a quick and cheap calibration just buy a cheap starret or mitiyoto 1/4x3" block. Heck I think I have something that would work for you. PM me your address and next week I'll send it to you. Free. I have lots of engineering goodies.
Click to expand...
That's very much appreciated! Engineering goodies are great to have. But like on brian6pac's unit, this sonic gauge comes with a disc of calibrated thickness built into the side of the case.

And I checked this gauge against a brake rotor because it is cast iron, and I wanted to make sure I knew how to set the gauge up for the different material velocity. The sonic velocity through cast iron is about 20% lower than steel so you have to be sure to set it up right, or the results will be waaay off.
 
nm9stheham said:
That's very much appreciated! Engineering goodies are great to have. But like on brian6pac's unit, this sonic gauge comes with a disc of calibrated thickness built into the side of the case.

And I checked this gauge against a brake rotor because it is cast iron, and I wanted to make sure I knew how to set the gauge up for the different material velocity. The sonic velocity through cast iron is about 20% lower than steel so you have to be sure to set it up right, or the results will be waaay off.
Click to expand...
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How's it going with your tester?
 
nm9stheham said:
That's very much appreciated! Engineering goodies are great to have. But like on brian6pac's unit, this sonic gauge comes with a disc of calibrated thickness built into the side of the case.

And I checked this gauge against a brake rotor because it is cast iron, and I wanted to make sure I knew how to set the gauge up for the different material velocity. The sonic velocity through cast iron is about 20% lower than steel so you have to be sure to set it up right, or the results will be waaay off.
Click to expand...
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I'll try again.
How you making out with your new tester?
 
I'm not sure how his worked out but mine works great, I used it on head ports and cyl walls very handy tool.
 
I had ordered the UM6500 and the 6mm probe. The probe showed up but not the meter. Got my money refunded and just ordered the TM8812. Should have it in a week or two. Thanks guys !
 
604B1duster said:
I had ordered the UM6500 and the 6mm probe. The probe showed up but not the meter. Got my money refunded and just ordered the TM8812. Should have it in a week or two. Thanks guys !
Click to expand...
I think it would always be best to calibrate with a similar thickness and definitely the same material that was being checked. The master calibration piece should also have the same profile. For example, if you were investigating cylinder bore thickness, your master should be a piece of cylinder bore, similar curvature with a known thickness.
 
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