Two part question

[pi_guy]

This question is more for the automotive machinist or a machinist. But might come in handy for somebody trying to accurately measure.

The question that came up was I need a four inch standard. What would you do and which items are accurately 4 inches?
Try to think of all the items in your shop that are 4 inches and what would you use.

Now the next question is if you had a number of measuring instruments that were a little off what would you do?

It started off trying to get a depth to set a shift fork gauge, using a caliper, depth micrometer and and a depth caliper and a few other items every thing was a couple of thousands difference. Now it possible between the differences in the tools and the operator error that is where the difference is coming from.

If I get any response and interest I will detail my finding my mechanical engineer that I run things by just came back from vacation.
Started to play by putting a few standards by a height gauge.
One thing in question went to a hardened tool steel bar for a straight edge as it was 1 inch high the other straight edge was 1.250 and it did not do math well. But I think the 1 inch straight edge is a few thousands off from one end to other.
So I know I have some issues and things to check.

 

[General Geoff]

Two 1x2x3" gauge blocks stacked? I'm not a machinist but that's what I'd start with since it's what I have available.

I would think a machine shop would have a whole gauge block variety, one of which has a 4" side.

 

[pi_guy]

I do have gauge blocks round and rectangle. At the time the question was tossed at me was not at swiftest moment. But also I do this in the field and do not have everything that I have back in the shop. So that why reaching out for input.

 

[matt_i]

It doesn't matter if your measurement instrument is off if you use it for reference throughout the project and stick to the same dimensional number.

For example, I want to make a press fit in my shop, I use a micrometer, its going to turn out just fine if I can hit the dimensions that I measure with it for the telescoping gage to bore, and then when machining the new part.

Trouble could come if a person walked into the shop and needs a .4145" diameter land machined on a rod for a press fit. I might make it with the same micrometer, but it could be all wrong if we aren't coordinated to the same standard. He might have solid repeatability with his micrometer to .4140" but one or both of ours could be off.

Maybe I'm not answering the question you asked, but as long as the same instrument is used it doesn't matter if they are different vs. other instruments you might have, or even way off from something like a NIST standard.

 

[BDT/NWMN]

I have a set of six micrometers, so I would count on the 4" calibration pin included in the set.

 

[MushCreek]

The only things I can think of would be gauge blocks or a micrometer calibration gauge. Anything else most likely would be off. 1-2-3 blocks may or may not be the actual dimensions.

 

[MShaw]

If you have a lathe or a mill, why not make a rod as close as you can and use that. I can't imagine that one or two thousandths of an inch would affect the item. You can carry that with you and not worry if it gets lost or damaged.

 

[leg17]

The question that came up was I need a four inch standard. What would you do and which items are accurately 4 inches?/QUOTE]

Get a 4.000 mike standard.

 

[leg17]

Now the next question is if you had a number of measuring instruments that were a little off what would you do?

Determine how much they are "off" and factor that in your measurements.

 

[Git]

I have a 2 x 4 x 6 set of gauge blocks that I got from Amazon Warehouse. List price was $228 but I only paid $26 (for two blocks) because the lid on the plastic case was cracked

https://www.amazon.com/gp/product/B00B5HHWD0/?tag=atomicindus08-20

 

[pi_guy]

It doesn't matter if your measurement instrument is off if you use it for reference throughout the project and stick to the same dimensional number.

For example, I want to make a press fit in my shop, I use a micrometer, its going to turn out just fine if I can hit the dimensions that I measure with it for the telescoping gage to bore, and then when machining the new part.

Trouble could come if a person walked into the shop and needs a .4145" diameter land machined on a rod for a press fit. I might make it with the same micrometer, but it could be all wrong if we aren't coordinated to the same standard. He might have solid repeatability with his micrometer to .4140" but one or both of ours could be off.

Maybe I'm not answering the question you asked, but as long as the same instrument is used it doesn't matter if they are different vs. other instruments you might have, or even way off from something like a NIST standard.

I understand the use same instrument to reduce errors and minimize the difference between tools normally it is the procedure I follow.
But I was interested in verifying that the numbers I was generating were right. Which if the box came back I would want to match numbers to see if issues had come up, and also to be used with other g boxes as a reference.
And to be able to exchange information and order parts of proper dimension.
Using a caliper to measure depth is so so accurate as the measuring face and the small base make getting a good position difficult, where the depth gauge has a better base for more rigidity and the measuring rod and face are stiffer.
The the depth mic has a larger face on measuring anvil sits a little different on the measuring flat spot. So there are variation in the tools that I need to consider.

Part of the question is to come up with standards that are common such as the gauge pins .010 to 2.0 in thousands are 2 inches in height, 1,2 and 3 blocks are great have several pairs will toss a set in the traveling kit. But I want to get a set of 2,4, and 6 inch blocks the cheapest I have seen them is 99.
I picked up at machine shop supply a measuring instrument checking gauge but no instructions so planning to get a handle on that. Just texted a ME with this question.

So far this is a list of standards.
1,2 and 3 blocks
pin gauges
gauge blocks rectangle
gauge blocks round
micrometer standards

 

[larry_g]

Now it possible between the differences in the tools and the operator error that is where the difference is coming from.

Look up how to do a gauge R&R study. Basically you have 10 different people measure the same thing with the same tool. Then you measure with different sizes. You can check the repeatably and reliability of the process.

But I think the 1 inch straight edge is a few thousands off from one end to other.
So I know I have some issues and things to check.

Here you have to be careful with the tool you select. Your assuming that a straight edge is also a parallel. Not necessarily, and it doesn't have to be as only the one edge has to flat to a high degree. On the other hand parallels have to be parallel but not necessarily to a particular width dimension. Another thing to remember that resolution and accuracy are not the same.

For those who are recommending 123 blocks, before I would use one as a measuring standard I would have to KNOW that it is ground to a specified tolerance.

For the OP; You say you have to set a shifting fork to 4". What tolerance do you have? Is it 4" +/-.010" or 4" +/- .0001"? Makes a lot of difference in the tool you choose to measure it with.

lg
no neat sig line

 

[Git]

Another option is a 'gauge block set'

I got this one from Amazon Warehouse (it was a little less than half off). You just have to keep your eyes open

https://www.amazon.com/gp/product/B0006J3ML4/?tag=atomicindus08-20

The specs on my 2 4 6 block set work for me
2-4-6 Blocks.
• Parallelism within .0003"
• Dimensional Accuracy: .001"
• Squareness within .0003" per inch.
• Block hardened to 56—60 RC.
• Flatness within .0002" per inch.
• Matched pairs measure 2"x4"x6".

 

[pi_guy]

For the OP; You say you have to set a shifting fork to 4". What tolerance do you have? Is it 4" +/-.010" or 4" +/- .0001"? Makes a lot of difference in the tool you choose to measure it with.

lg
no neat sig line

thanks

Not setting a shift fork, measuring from the end of case to top of pinion bearing.
This number is used to set the jig so it will be represented as the other half of the case. The dimension is a little greater than 4 inches. So you then set the jig by placing shims under dummy pinion to create the same dimension in the case when the unit would be assembled. If you are familiar with VW cases from early 60's you can not see or adjust shift forks when case is assembled.

 

[American Locomotive]

But once again, what's the specified tolerance? If it's 4" +/- .125", you could probably get by with a block of wood kept in a humidor. If it's 4" +/- .0001", well that's a completely different thing.

 

[mudflap]

....

 

[mudflap]

This question is more for the automotive machinist or a machinist. But might come in handy for somebody trying to accurately measure.

The question that came up was I need a four inch standard. What would you do and which items are accurately 4 inches?
Try to think of all the items in your shop that are 4 inches and what would you use.

Now the next question is if you had a number of measuring instruments that were a little off what would you do?

It started off trying to get a depth to set a shift fork gauge, using a caliper, depth micrometer and and a depth caliper and a few other items every thing was a couple of thousands difference. Now it possible between the differences in the tools and the operator error that is where the difference is coming from.

If I get any response and interest I will detail my finding my mechanical engineer that I run things by just came back from vacation.
Started to play by putting a few standards by a height gauge.
One thing in question went to a hardened tool steel bar for a straight edge as it was 1 inch high the other straight edge was 1.250 and it did not do math well. But I think the 1 inch straight edge is a few thousands off from one end to other.
So I know I have some issues and things to check.

The cylinder bore on a Chevy 350 is 4in...i have a few of those sitting around..

 

[pi_guy]

Well been doing some reading and some testing.
Checked the 1,2 3 blocks with a height gauge and gauge blocks and they were close .0001 or two. So tested my depth gauge and it was 4.0004 at 4 inches tested my depth micrometer and it was 4.006 at 4 inches found a big error.
Picked up a testing stand.
Planning to adjust the micrometer and run a test with all my measuring instruments. Adjust or toss what is off. I have 6 pairs of 1,2 3 blocks so I need to mark them and check.
On degree of accuracy I would like to aim for tenths or at least measure in that range but the final output based on machines and the stuff I work on couple thousands is a honest error range.

 

[ttpete]

thanks

Not setting a shift fork, measuring from the end of case to top of pinion bearing.
This number is used to set the jig so it will be represented as the other half of the case. The dimension is a little greater than 4 inches. So you then set the jig by placing shims under dummy pinion to create the same dimension in the case when the unit would be assembled. If you are familiar with VW cases from early 60's you can not see or adjust shift forks when case is assembled.

Do you have the factory tools to set pinion depth? Sounds like you are working with a Hewland gearbox.

 

[pi_guy]

Do you have the factory tools to set pinion depth? Sounds like you are working with a Hewland gearbox.

Yes FT, LG, DG, MK and Staffs and a couple of odd ball ones