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Gunsmithing
dial indicator help
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<blockquote data-quote="Trickymissfit" data-source="post: 495203" data-attributes="member: 25383"><p>surface plates and strait edges come in three ranges Lab Grade, Inspection Grade, and Tool Room Grade. The Government regulates all of them even if they don't own it. Most folks do surface plates to Inspection Grade (about .000050" per foot), and they pay for it in the end. Once you get it good enough to be an Inspection Grade plate it usually is only two or three more passes to make it a Lab Grade. A Lab Grade plate will last much longer than the others (longer usable life span). It actually takes three plates to cut a Lab Grade plate (you master off three plates). These are known as "masters", and are never ever used for anything but mastering another plate. I kept mine locked up in sealed boxes. A Master Plate will often be in the single digit range. So why the .000025" spec? Take a strait line on a surface plate and multiply it out to five feet long. Now you can have an error of .000125" in the total length. A good six foot by nine foot table will usually be under .0002" in the lines running from corner to corner. The one I used to master off of had about .0001" error in it's lines. But nobody ever used that piece of granit but me.</p><p> </p><p>We cut granit with scraped in cast iron plates. These are very flat, and come in all sorts of sizes. The actual cutting material is diamond dust in several grades. I loved doing this, and the funny thing was that everybody thought I was killing myself! I really wasn't working all that hard. </p><p> </p><p>Your gauging equipment must have a fraction of error in it when compaired to the parts being measured on it. If your working with in a thousandth of an inch, then you need to be thinking around two and a half tenths max. The better the job you do, the easier it is for the guy using the piece of equipment, and the faster and better he works. A Devlieg jig mill has a max compound error of .00025" in all it travel. A SIP Diaoptic is about two thirds of that. I used to check a rotary table that had a max error of two tenths of an arc second in it's moves. How you fixed it I never knew because it always checked out within specs. You just have to learn to work close, and some folks never get there</p><p>gary</p></blockquote><p></p>
[QUOTE="Trickymissfit, post: 495203, member: 25383"] surface plates and strait edges come in three ranges Lab Grade, Inspection Grade, and Tool Room Grade. The Government regulates all of them even if they don't own it. Most folks do surface plates to Inspection Grade (about .000050" per foot), and they pay for it in the end. Once you get it good enough to be an Inspection Grade plate it usually is only two or three more passes to make it a Lab Grade. A Lab Grade plate will last much longer than the others (longer usable life span). It actually takes three plates to cut a Lab Grade plate (you master off three plates). These are known as "masters", and are never ever used for anything but mastering another plate. I kept mine locked up in sealed boxes. A Master Plate will often be in the single digit range. So why the .000025" spec? Take a strait line on a surface plate and multiply it out to five feet long. Now you can have an error of .000125" in the total length. A good six foot by nine foot table will usually be under .0002" in the lines running from corner to corner. The one I used to master off of had about .0001" error in it's lines. But nobody ever used that piece of granit but me. We cut granit with scraped in cast iron plates. These are very flat, and come in all sorts of sizes. The actual cutting material is diamond dust in several grades. I loved doing this, and the funny thing was that everybody thought I was killing myself! I really wasn't working all that hard. Your gauging equipment must have a fraction of error in it when compaired to the parts being measured on it. If your working with in a thousandth of an inch, then you need to be thinking around two and a half tenths max. The better the job you do, the easier it is for the guy using the piece of equipment, and the faster and better he works. A Devlieg jig mill has a max compound error of .00025" in all it travel. A SIP Diaoptic is about two thirds of that. I used to check a rotary table that had a max error of two tenths of an arc second in it's moves. How you fixed it I never knew because it always checked out within specs. You just have to learn to work close, and some folks never get there gary [/QUOTE]
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