Question for the machinists out there...

[SUNBURNTsnype]

I had to take a measurement on large propulsion shaft bearing at work the other day, using a depth gauge(starrett brand i believe). theres a little spy hole that drops through the outer bearing cover and has a little well that goes all the way down to the top of the main shaft. the distance from the top machined surface of the bearing cover to the shaft OD is about 6.025" - 6.045". We take this measurement periodically and monitor the bearing wear by the increase in this distance over time(as the bearing that supports the shaft wears, the shaft "drops" down lower and lower, and the distance from the top of the cover to the top of the shaft increases). Anyways, in the past I have just used a 6" standard from an inside micrometer kit and a dial indicator on a bridge(similar to what you would use to fine TDC on an engine with the head removed) to measure the .000 - .050" beyond the 6" standard. However just the other day I found a starret depth gauge with rod lengths that can switched for different lengths. I found a 6" rod and was going to try using the depth gauge to take my measurement until i realized how hard it was for me to try and adjust the rod so it was zeroed.

Which leads me to my question for any machinists out there:

What is the proper or best way to zero a depth gauge and for one with a long rod like i was using, 6", how can i check it to ensure it is accurately adjusted? I tried putting the depth gauge body on top of the 6" standard and held it level against a milling machine deck as a flat surface and tried to adjust the rod, but it was rocking so much i couldnt be sure it was level and would have been several thousandths off. I aslo tried the depth appendage on a vernier. caliper, but i had the same problem with it rocking and flexing. Is there some type of fixture to do this properly? I guess i could make something on the mill.

 

[fishywarren]

Are you trying to verify that your mic is true? A depth mic cal block/checker/master.

What type of equipment are you working on? I read bearing cover and it caught my eye. I'm a steam turbine tech for DR and I hear those two words just about every day. lol

 

[chadman]

It sounds like you are describing a depth mic? Regardless, here are two methods to accurately calibrate it:

1) Purchase a 6" standard that has a through hole that alows you to drop the extension through it until makes contact with a flat surface (preferably a granite surface plate). This will support it 360 degrees around the extension so it will not rock.

2) Use precision gage blocks and build up two 6" stacks. Then you can bridge the gage/depth mics across the two stacks to prevent rocking. Calibrate on a flat surface plate as above.

 

[brucer]

you could also measure a 2-4-6 block to verify the depth micrometer.

 

[CJKaz]

I'm a steam turbine tech for DR and I hear those two words just about every day. lol

Fishywarren: Do you ever work with the guys out of the Horsham PA, shop? Spent many hours there on turbine & compressor overhauls. Good bunch!

 

[SUNBURNTsnype]

Thank you all for the responses and information. Yes, you are all correct, it was a depth mic not a depth gauge, sorry i didnt know the proper nomenclature.

I have never seen a depth mic gauge block/cal block before, but it appears that is what i would need. ill have to order one for work. the depth mic i was using had a threaded area on the end with two lock nuts that adjusted the distance, which was then locked down to the mic body by screwing on the finger knob at the end. When i was attempting to zero it with the standard, everytime i tried to tighten the locknuts together, one would move too much or the other would move, and i could never get closer than about .010-.015" after checking it after putting it together. Im sure there is a simple trick or procedure to set it quickly and easily and reliably instead of finger f****ing it for hours with no results. Can you guys walk me through an easy adjustment procedure.

I am on active duty in the coast guard as a machinery tech and this was a line shaft bearing on one of our 378' cutters. it supports the main shaft (there are 2, 1 for each shaft) between the reduction gear and the stern tube. these are oil lubricated pedestial bearings with internal sump and slinger rings. no pumps or pressure lubrication. these ships are old, they were commisioned in the 60's, and refurbed in the 80's.

 

[chadman]

Here is a small tutorial:
http://www.wisc-online.com/Objects/ViewObject.aspx?ID=MSR2502

 

[larry_g]

One thing you can do to take some of the guess out of the adjustment is to figure out the pitch of the adjusting thread. Without going out to look at what it is I'm going to guess it is probably 40 TPI. So if you have a 40 TPI thread divide the pitch into 1". 1/40= 0.025". So one turn of the nut will move it .025". if you divide .025"/6 flats =.0042". So moving the nut one flat you move it ~.004". So if your out 10-15 thou try turning the nut 3 flats or a half a turn. Use the procedure Chadman linked to above.

lg
no neat sig line

 

[Kevin54]

you could also measure a 2-4-6 block to verify the depth micrometer.

Not always a good idea depending where the blocks come from. At best, 1-2-3 or 2-4-6 blocks are for reference only. I have personally saw blocks that were bought in on the cheap that the sides were no perpendicular to each other or they may bee .002+ undersize. To check a piece of equipment that should be calibrated, you need to have calibrated equipment to check it with. If what you are measuring is very critical, you will really need something that is a known precision piece to check it against. I imagine if you are checking bearing wear, then that constitutes using precision equipment.

Check around your area and see if there isn't a place close to being local, or at the worst case, sending the equipment (depth mics) out to be calibrated, so you know exactly what you have. Or if you are going to be using the 6" stem in the depth mics, buy a 6" gage block that has the hole down thru the center. The block itself will be 1" square, a hole thru the center, and at 1" of bearing surface will give you enough surface for the base of the depth mic to set comfortably flat.

 

[larry_g]

Another thing to consider, you do not need to have an exact 6.0000" standard. What you do need is a standard that is a known length. If it is 5.9950" or 6.0035" it doesn't matter. What matters is that it has been precisely measured and documented. As long as your tool indicates the same number as the standard measures you are good.

lg
no neat sig line

 

[brucer]

Not always a good idea depending where the blocks come from. At best, 1-2-3 or 2-4-6 blocks are for reference only. I have personally saw blocks that were bought in on the cheap that the sides were no perpendicular to each other or they may bee .002+ undersize. To check a piece of equipment that should be calibrated, you need to have calibrated equipment to check it with. If what you are measuring is very critical, you will really need something that is a known precision piece to check it against. I imagine if you are checking bearing wear, then that constitutes using precision equipment.

I've been a toolmaker for 25 yrs. I have never seen or bought a 123 block or 246 block that was out of specification, I work in a shop that is iso compliant. I myself own 4 sets of 246 blocks and 8 pair of 123 blocks, I quit buying the high dollar blocks because the ones from china that I've bought were usually within .0002 and parallel as close as could be measured with micrometers and in the mold industry that close enough, heck cnc mill tables are out more than that..

Anyhow, in his application it doesnt matter if the opposing sides of the block is square or perpendicular all he needs is the 6" sides to be parallel, you take a set of 6" mics and verify the 6" height, then calibrate the depth mic accordingly.. You could do it with a piece of flat 1/2" plate, stone it off to remove burrs and depth mic the 246 block to verify the calibration of the depth mic in relation to the block.

 

[Kevin54]

I've been a toolmaker for 25 yrs. I have never seen or bought a 123 block or 246 block that was out of specification, I work in a shop that is iso compliant. I myself own 4 sets of 246 blocks and 8 pair of 123 blocks, I quit buying the high dollar blocks because the ones from china that I've bought were usually within .0002 and parallel as close as could be measured with micrometers and in the mold industry that close enough, heck cnc mill tables are out more than that..

Anyhow, in his application it doesnt matter if the opposing sides of the block is square or perpendicular all he needs is the 6" sides to be parallel, you take a set of 6" mics and verify the 6" height, then calibrate the depth mic accordingly.. You could do it with a piece of flat 1/2" plate, stone it off to remove burrs and depth mic the 246 block to verify the calibration of the depth mic in relation to the block.

That's true, but for someone that has never used something like that, are you going to buy new, are you going to buy used? IF you know what you are buying that makes a world of difference. WHen I started in Tool and Die I worked with a bunch of old toolmakers. Some of their equipment I wouldn't sell at a flea market. 123 blocks that have been ground undersize, parallel bars that are not parallel and so on. I have never depended on other people equipment unless I know how they take care of their tools, or it has to have a recent Cal. sticker on it. Another for instance, we had a Lead Grinder. He was considered of of the best around. He was selling off a lot of his equipment that he had made himself. Another toolmaker came up to me and showed me a matched set of angle plates he bought for $100. He was bragging about them and I ask him how he knew they were good. He said "Because Bob made them". So? I put both angle plate together face to face and slid a .010 shim in at the bottom of the faces. The Lead Grinder had also at one time reground something or another for every toolmaker in that department which at one time was 40 Toolmakers back in the day.

That's why I say that it takes a known calibrated tool to calibrate a tool. You can grab a block and mic it, no problem if it 5.750" long or 6.000" long, but then you need a calibrated mic to check the block. That is why I said depending on where the blocks come from. Oh, just to let you know, those two angle plates are still being used today to make other tools. Our Metrology department was never set up to test squareness on angle plates.

Not always a good idea depending where the blocks come from.

 

[fishywarren]

Fishywarren: Do you ever work with the guys out of the Horsham PA, shop? Spent many hours there on turbine & compressor overhauls. Good bunch!

No sir I have not worked out side of Texas. Mostly stuck inside all day in the Houston Service Center.

 

[Steinmetz]

I had to take a measurement on large propulsion shaft bearing at work the other day, using a depth gauge(starrett brand i believe). theres a little spy hole that drops through the outer bearing cover and has a little well that goes all the way down to the top of the main shaft. the distance from the top machined surface of the bearing cover to the shaft OD is about 6.025" - 6.045". We take this measurement periodically and monitor the bearing wear by the increase in this distance over time(as the bearing that supports the shaft wears, the shaft "drops" down lower and lower, and the distance from the top of the cover to the top of the shaft increases). Anyways, in the past I have just used a 6" standard from an inside micrometer kit and a dial indicator on a bridge(similar to what you would use to fine TDC on an engine with the head removed) to measure the .000 - .050" beyond the 6" standard. However just the other day I found a starret depth gauge with rod lengths that can switched for different lengths. I found a 6" rod and was going to try using the depth gauge to take my measurement until i realized how hard it was for me to try and adjust the rod so it was zeroed.

Which leads me to my question for any machinists out there:

What is the proper or best way to zero a depth gauge and for one with a long rod like i was using, 6", how can i check it to ensure it is accurately adjusted? I tried putting the depth gauge body on top of the 6" standard and held it level against a milling machine deck as a flat surface and tried to adjust the rod, but it was rocking so much i couldnt be sure it was level and would have been several thousandths off. I aslo tried the depth appendage on a vernier. caliper, but i had the same problem with it rocking and flexing. Is there some type of fixture to do this properly? I guess i could make something on the mill.

Use gage blocks ("jo blocks") on a granite surface plate.