Help me decide which of these to set CPI

L

littleb28

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Hi,

In order to set the CPI I need an accurate known length, right? Problem is, I don't have many of those kinds of accurate tools (like calipers) or objects (like gage blocks). I have a mitutoyo 1 inch micrometer, a harbor freight 6 inch digital caliper, harbor freight parallels which seem to be manufactured to inch increments (I could for example use the 6 inch distance on them), and various small drill bits and end mills. Alternatively, I can just use the screw pitch on the table, but it's a 30 year old harbor freight micro mill, so that accuracy may also be off. What is my best option for getting an accurate CPI measurement? My best guess is milling a block less than 1 inch and then measuring its exact size with the micrometer.
 
Greetings,
Welcome to H-M.

I think that having a piece of known length or know diameter to high precision is fundamental.
I found the linked new 8" standard for about $21, all in.

The next issue is, you didn't mention that you have a Dial Test Indicator (DTI). What method are you intending to use to determine when you have traversed the table from one end of a known length to the other?

www.ebay.com

MICROMETER STANDARD "MITUTOYO" 8.0" | eBay

MICROMETER STANDARD "MITUTOYO" 8.0" like new.
www.ebay.com
 
Thanks, that looks like something I can use.

I was going to use either an edge finder on both sides of the piece, or an end mill and a piece of paper that I slide in between. Do you think that method works? I also have a littlemachineshop dial indicator, but I can't picture how I would use it.
 
Have you looked at the information on Yuri's site? his calibration process is pretty clearly explained.

Do you have the budget available to buy a decent DTI?

DRO Scale Calibration

Blog dedicated to DIY digital readout TouchDRO and other hobby machining and engineering subjects.
www.yuriystoys.com www.yuriystoys.com
 
Actually I skipped the specific section where it mentions the DTI because it's under the 1-2-3 block heading which I hadn't planned on buying, but I see now how to use the DTI for this. Do you think the littlemachineshop DTI isn't good enough?
 
littleb28 said:
Thanks, that looks like something I can use.

I was going to use either an edge finder on both sides of the piece, or an end mill and a piece of paper that I slide in between. Do you think that method works? I also have a littlemachineshop dial indicator, but I can't picture how I would use it.
Click to expand...

Those methods are better than nothing. Without having micrometers to measure greater than 1", the DRO will have to be your reference, until you acquire more tools.
 
littleb28 said:
Actually I skipped the specific section where it mentions the DTI because it's under the 1-2-3 block heading which I hadn't planned on buying, but I see now how to use the DTI for this. Do you think the littlemachineshop DTI isn't good enough?
Click to expand...
Good enough is a very tricky issue and the answer is based on many personal criteria.
I recommend that you start a new thread asking "What is the best DTI within my budget?"
I'm not the best source for that because I like Swiss made DTIs. If you've got a few hundred $$ to spend in a Swiss made DTI and some accessories, I can advise.
 
Why not use your hand wheels to calibrate the DRO? If you had success with them before adding a DRO then you should assume that are for for purpose and accurate enough for you? Zero the DRO and hand wheel at one side of the travel then move across using the hand wheels to a nice round figure (say 24 inches). Now compare what the dro says cz the handwheels (which should be exactly on 24 inches). As long as the distance is long the minor error in your hand wheel reading will be averaged out.

Sent from my SM-S908E using Tapatalk
 
littleb28 said:
Hi,

In order to set the CPI I need an accurate known length, right? Problem is, I don't have many of those kinds of accurate tools (like calipers) or objects (like gage blocks). I have a mitutoyo 1 inch micrometer, a harbor freight 6 inch digital caliper, harbor freight parallels which seem to be manufactured to inch increments (I could for example use the 6 inch distance on them), and various small drill bits and end mills. Alternatively, I can just use the screw pitch on the table, but it's a 30 year old harbor freight micro mill, so that accuracy may also be off. What is my best option for getting an accurate CPI measurement? My best guess is milling a block less than 1 inch and then measuring its exact size with the micrometer.
Click to expand...
I used this video to set mine.
It would be best to usr the tools mentioned, look on Amazon for the 1-2-3 blocks and a cheap indicator. I think you'd have less than $100 in a economy set.

Touch DRO calibration video
 
Thanks for the help everybody. I think I'll just start with using the handwheels, then when I get a gage block set or something like that I'll recalibrate it with my current dial indicator, then when I upgrade my dial indicator I'll recalibrate it again.

edit: or I'll get 1-2-3 blocks
 
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