threw your name in there cause i know you've done a fair number of blocks. in response to the block thread i decided to dust of my UT mic and start playing with it.

was looking for some general input from people's experience.

some time ago i took a couple pieces of block (they may be from different blocks don't remember) and machined one to .123" and the other to .230". i didn't have a surface grinder at the time so i just milled them but they're close enough (i am going to grind them now).

when i set the velocity on one i find that it's off by 3-5 thousandths on the other. while i don't like this (like it's really gonna matter) i'm not surprised because they may be different compositions plus i'm calibrating a radius probe on a flat surface which i question the wisdom of. i rock the probe to get the minimum reading then use that.

a friend of mine that owns a machine shop has a UT mic and the standards it came with are pieces of cylinder so the radius isn't an issue. without a complete circumference piece of a cylinder off the top of my head i can't think of any way to get a radiused piece of uniform thickness to calibrate the velocity

another thought is about the couplant in the past i have used the couplant that came with the mic but found it must have some water or other corrosive properties.

where i used to work there was a ton of NDT going on and iirc sometimes they just used different forms of grease (white grease i believe)

i tried some lithium grease tonight and it seemed to work fine, i'd rather use this to prevent any corrosion

looking at the sheets i've seen over the years it seems most people take 12 readings in each hole which seems a little tedious. the mic i have (and i would think most do) has a scan feature where you can start at one end and drag the probe to the other it will then display the minimum thickness measured. i'm not 100% certain of the scan rate but iirc one thing i read said it pulsed at 200HZ but i don't know if it reads every pulse.

i kinda like the idea of scanning each quarter of the hole as opposed to taking three different readings

only concern i have is wear on the transducer but don't think that would be a major issue using grease and only enough pressure to maintain coupling

thoughts/comments?

thanks, i have seen them

while rifling through the case i found a note that i had written velocity numbers on and given the paper i know it came from my machinist friend so i must have gotten the numbers from his mic (i think it came from Goodson)

the velocities on the note are as follows

Nickle chevy .17585

SBC-BBC .19055

BOP/AMC/GM V6 .18732

Ford .18510

there were no velocities for chrysler (but i did write chrysler under nickle chevy) but the number i'm finding closest while calibrating this particular mic for chrysler is .19330

it's been so long since i wrote the note i'm not sure if the nickle chevy velocity was intended to be used for chrysler as well but what i'm finding is considerably different

now i don't know if these velocities are mic specific (they may well be) and what i found with this mic is you can't set a specific exact velocity it changes in increments of .00153 which equates to a .001" change in the reading

bump,

anyone else want to weight in on this?

1: You will not wear out a transducer in your lifetime. 2: We all like "exact" numbers, but sonic checking cylinder walls to within .005 (due to calibration frequency) is not going to make or break any decisions on usage. 3: I use atf as a coupler with my T-Mike.

Would you like a curved piece of cylinder wall for testing? I have a few

thanks Tom those are pretty much my thoughts as well. do you ever scan the bore or just do individual shots? i can't help but think scanning is better the only exception being it won't tell you at what height the thinnest spot is.

Dustin that's just gross

the problem is unless it's a complete circumference of bore i have no way to machine it to a uniform thickness. if i had a full piece i could turn it on the lathe. i'm probably over thinking this as far as calibration i'm just not crazy about calibrating the probe on a flat piece but in reality you have to calibrate the probe to the mic first and the only way to do that is with the flat disc that's mounted to the mic anyhow

Yep, you're definitely over thinking this

Carry on!

order a cheap cast iron cyl sleeve

no Dan i have both a radius probe and a flat one. my (stupidly anal) concern was calibrating the radius probe on a flat surface. like i said in reality the probe must first be calibrated to the mic using the flat disc standard on the bottom anyhow. then once the probe is calibrated to the mic you calibrate it to a standard preferably of the composition of what you're working with. in this case i have a couple pieces of chrysler block that i milled to within .001" flat. truthfully i've been able to hold the total observed error to less than .005" and closer to .003" so with regards to wall thickness i admit i'm just being stupid. in all honesty i don't think it's an issue i think i'm just OCD