Wrong dial indicator

Wrong dial indicator

Postby gordo999 [OP] » September 13th 2015, 5:48am

I just noticed I goofed ....again!!!

First, I have a thread going on my differential/rear axle bearing change but I thought this topic merited a fresh thread since it's a technical issue on it's own.

I bought a dial indicator for about $25 bucks and I should have known it was too good a deal not to have a hitch. The first hitch was the it had no holder but I figured I could fab one easy enough.

The indicator is a Peacock PCN-S. What I did not see when I bought it was that the scale is graduated in 1/1000 of a millimetre. I also did not know enough about dial indicators to realize there are different types of actuators.

Here's a link to Peacock indicators. Mine is listed as 'high accuracy', so that's one good thing.

http://www.labtek.net/Peacock-2.htm

When I saw people using dial indicators to check ring gear backlash, the indicators were positioned so that the gear face pressed on the end of the actuator, moving it toward the dial. What I just learned about the PCN-S is that the actuator is mounted on a jewel bearing and the gear needs to move it perpendicular to the dial.

I just built myself a complicated holder using 1/4" rod and it did a good job of holding the actuator against the gear face. When I moved the ring gear relative to the pinion, however, I was barely getting a reading of a few thousands of a millimeter. After reposition it I got a reading of 12/1000 of a millimetre, not nearly in the range I need. There was likely enough lateral play in the actuator to get a reading sideways rather than head on.

Here are some questions:

1)The full range of this indicator is marked as 70/1000 mm. That is only half the range of the scale, however, located at 6 o'clock, and the dial will continue to rotate till it's back to zero, then go beyond.

70/1000 mm is 2.7 thou (0.0027"). If I run it one full revolution that gives me 140/1000 mm which is 5.5 thou. Since my gears teeth on the ring gear are 2 cut, the recommended backlash is 4 thou. The actual range is 0.003" to 0.006".

A reading on the indicator scale of 100, which would be around 9 o'clock on the scale, should be about 4 thou.

Anybody have opinions whether I am right, or out to lunch?

2)About gear marking compound. I was trying to get a tooth pattern before removing the ring gear/carrier. I have heard the 2-cut gears show a different pattern than the older 5-cut gears.

I applied some yellow GM marking compound and turned the ring gear using the pinion yoke. I tried to apply resistance to the ring gear as I turned. I may have put on way to much compound, however, since the markings produced by the pinion gear was indistinct. Also, the pinion transferred a lot back to the ring gear.

What is the correct amount to apply, barely enough to coat the tooth?

3)How do you get that gunk off the pinion gear? Is it safe to leave it overnight?
Original Poster [OP]
gordo999
Firing on 7 Cylinders (L1)
Firing on 7 Cylinders (L1)
Years of Membership: gordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full years
Posts: 747
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Joined: October 2014
Gender: Male
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Van Model Year: 2001
Van Make/Model: GMC Safari
Extra Info: Cargovan 4.3 RWD

Re: Wrong dial indicator

Postby gordo999 [OP] » September 13th 2015, 8:22am

Turns out I don't have a dial indicator, I have a test indicator.

http://www.mahr.com/index.php?print=1&NodeID=14636&ContentID=15627&Overview=1&ActionID=0&view=1&nl=-1&nld=-1&year=-1&Language=DE-CH

Same thing essentially, from what I can gather, but the test indicator seems to be higher precision and has an actuation lever that pivots rather than plunges.
Original Poster [OP]
gordo999
Firing on 7 Cylinders (L1)
Firing on 7 Cylinders (L1)
Years of Membership: gordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full years
Posts: 747
Topics: 71
Images: 5
Joined: October 2014
Gender: Male
Alias (AKA):
Van Model Year: 2001
Van Make/Model: GMC Safari
Extra Info: Cargovan 4.3 RWD

Re: Wrong dial indicator

Postby gordo999 [OP] » September 14th 2015, 7:58am

Tried the indicator today setting it up properly with it's actuator parallel to the gear tooth rather than pointing at it perpendicularly. The dial went around one revolution plus a tad when the ring gear was moved so as to take up slack while holding the pinion gear steady.

I rocked it back and forth several times and one revolution is close enough. That means 140/1000 of a millimeter. You can look up a converter on the net but you can also do it by hand.

There are 25.4 mm in 1 inch. To get a thousandths of an inch, or a thou, divide 1 inch by 1000 to get 0.001". Do the same with the number of millimetres to get the equivalent number of mm. That is 25.4/1000 = 0.0254 mm. That is, 1 thou = 0.0254 mm.

Since my test indicator has graduations of 0.001 mm, I want to know how far it should move to represent 1 thou. Put another way, how many times does 0.001 mm go into 0.0254 mm. The answer is 25.4, so on my indicator 1 thou would be read at 25.4 on the scale.

My indicator scale is set up so it's maximum reading 70/1000 is located at 6 o'clock. Obviously, the meter is intended for use on measurements that go back and forth, like some galvanometers in electronics. That kind of galvanometer has it's needle set at 0 in mid-scale. However, the indicator meter is also set up so it will continue to revolve a full revolution and beyond. I want to use that characteristic but it means re-configuring the scale.

If you view it from 0 to 70 clockwise, the scale reads in 10s as 10, 20, 30....up to 70. But if you read it from 0 counter-clockwise to 70 it reads the same. What I am doing is adding to 70 at 6 o'clock so that it reads, 80, 90, 100....till 140, which corresponds to 0. That is, the meter has turned one revolution clockwise, indicating 140/1000 mm (70 microns + 70 microns).

Note: in metric, a micron is a millionth of a metre. A millimetre is 1/1000 of a metre and my indicator measures 1/1000 of a millimetre per graduation, which is 1/1000000 of a metre, or a micron.

A thou is 25.4 times as large as a micron.

So what's 140 microns in thou? If 25.4 microns is 1 thou, then 140 microns should be 140/25.4 = 5.5 thou. That's within bounds for my 2-cut gear type (2001 Safari) but it's close to the recommended max of 6 thou.

Since half-scale is 70 microns/25.4 thou/micron = 2.76 thou, half scale is nearly my minimum setting for 2-cut gears. Therefore setting my backlash from 8:30 to midnight on the scale should keep me in bounds. Closer to 9 o'clock on the scale would be better.

http://www.convertunits.com/from/thou/to/mm

Rather than mess around with the pinion gear shims I will likely re-install with the same shims using the new bearing and see what backlash I get. Of course, that depends on how close the dimensions of the new bearings coincide with those in there. If i can get the rear pinion bearing off without destroying it, and it's dimensions are the same as the new one, I may experiment by honing out the old bearing.
Original Poster [OP]
gordo999
Firing on 7 Cylinders (L1)
Firing on 7 Cylinders (L1)
Years of Membership: gordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full years
Posts: 747
Topics: 71
Images: 5
Joined: October 2014
Gender: Male
Alias (AKA):
Van Model Year: 2001
Van Make/Model: GMC Safari
Extra Info: Cargovan 4.3 RWD

Re: Wrong dial indicator

Postby gordo999 [OP] » September 14th 2015, 12:21pm

gordo999 wrote:What is the correct amount to apply, barely enough to coat the tooth?

3)How do you get that gunk off the pinion gear? Is it safe to leave it overnight?

Answering my own question...I wiped the gunk out of the teeth with a paper towel, it did not dry out overnight.

If you use too much compound (GM yellow) the pinion gear will pick it up and transfer it back to the ring gear. It can make quite a mess, transferring so much that it's hard to tell which teeth you marked. I ended up putting some goop on the edge of the ring gear to mark the area. If you use your fingers to put drag on the ring gear you have to be careful not to erase your marks.


It likely does that anyway but if you keep it to a very light coating, just enough to coat the gear surface without it forming ridges and lumps, the transfer seems to be minimal. I used a Q-tip.

I have read different articles on how often to rotate the ring gear with the pinion to mark the face. Some say to move the ring gear back and forth across the pinion gear several times but one article hooked the yoke nut up to a drill (maybe it was an impact drill) using a socket and turned it that way.

In my limited experience, running the pinion in one direction many times seems to give a better mark. Also, a lighter coating of marking compound prevents the pinion transferring too much goop back to the ring gear, giving a better mark. At least, if there is too much goop on the ring gear, the pinion tend to obliterate the markings on the ring gear by piling goop over the area where the mark should be.

I ran it so the pinion drove the ring gear clockwise, which seems to allow the pinion gear to hit the drive side of the gear first.
Original Poster [OP]
gordo999
Firing on 7 Cylinders (L1)
Firing on 7 Cylinders (L1)
Years of Membership: gordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full yearsgordo999 has been a member for 6 full years
Posts: 747
Topics: 71
Images: 5
Joined: October 2014
Gender: Male
Alias (AKA):
Van Model Year: 2001
Van Make/Model: GMC Safari
Extra Info: Cargovan 4.3 RWD


 
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