I frequently get chucks and backing plates from a customer in the Glass Blowing business. It seems Glass Blowers often do whatever it takes to get parts put together just to keep the machines running. There are so many bizarre compilations of components, chucks, and backing plates in that business. The Glass Blowing industry prefers to use metric increments in it's parts and accessories but that is not always the case. Each Blower also prefers their own combination of bizarre chucks, Drill Chucks, on face plates, back plates etc. for the repetative parts they specialize in.
My dilemma: HOW TO DETERMINE THE BOLT HOLE RADIUS FROM EXISTING BOLT HOLES?
I make parts to refurbish Glass Blowing Lathes (Typically Litton models). When I have to make a new back plate for instance, I have to match the 3, 4, and sometimes 5 bolt hole pattern already drilled in the chuck / plate. Since the chucks all have thru holes, I cannot use a compass to find the centerline and determine the bolt-hole radius to make a new backplate etc. I have a method that I use where I install screws/ hole pin gages into the threaded holes, and try to create triangle dimensions by measuring the outside of each pin, subtracting half the width of the pin to find center.
This cannot be the optimal method as there are so many variations that affect precision: metric screws, uncommon screw pitches, worn out screws that tilt in the holes when being measured, undersized or varying screws peak to peak. Often times I do not have the ability to contact the user / owner of the parts since I get the parted-out work from my customer. Sometimes I get the original screws so I can determine by pitch if they are metric or Imperial, which helps in determining the closest common radius, other imes I don't get the screws that were originally used to combine the chuck to the back plate or spindle nose. I often resort to screwing taps into the tapped holes to figure out the pitch thread and therefore the screw size.
I have also used a Co-Ax indicator to determine the center of the hole when inserting Hole pin gages. But that only gives me the point of a triangle/ pentagon so I can make a math calculation from there.
Many glass blowers require tight tolerances. In my attempts at figuring out the bolt hole radius, my measurements fall between common metric and Imperial numbers so I don't know which system was used.
Those of you who have experience with glass blowing chucks will know where I am coming from.
I know there is an easy way, but many of my old timer machinist friends that could answer this have passed on in the last few years. I have searched the internet, this and other machinist sites but cannot find the answer.
I have a DRO with 'Bolt Hole pattern' to drill the new holes, but I cannot figure out how to use it in reverse, and it is not in the Accu Rite manual.
Obviously I have no formal machinist training, but I scratch out a living with decent machines and information from books / friends.
Thank you in advance.
My dilemma: HOW TO DETERMINE THE BOLT HOLE RADIUS FROM EXISTING BOLT HOLES?
I make parts to refurbish Glass Blowing Lathes (Typically Litton models). When I have to make a new back plate for instance, I have to match the 3, 4, and sometimes 5 bolt hole pattern already drilled in the chuck / plate. Since the chucks all have thru holes, I cannot use a compass to find the centerline and determine the bolt-hole radius to make a new backplate etc. I have a method that I use where I install screws/ hole pin gages into the threaded holes, and try to create triangle dimensions by measuring the outside of each pin, subtracting half the width of the pin to find center.
This cannot be the optimal method as there are so many variations that affect precision: metric screws, uncommon screw pitches, worn out screws that tilt in the holes when being measured, undersized or varying screws peak to peak. Often times I do not have the ability to contact the user / owner of the parts since I get the parted-out work from my customer. Sometimes I get the original screws so I can determine by pitch if they are metric or Imperial, which helps in determining the closest common radius, other imes I don't get the screws that were originally used to combine the chuck to the back plate or spindle nose. I often resort to screwing taps into the tapped holes to figure out the pitch thread and therefore the screw size.
I have also used a Co-Ax indicator to determine the center of the hole when inserting Hole pin gages. But that only gives me the point of a triangle/ pentagon so I can make a math calculation from there.
Many glass blowers require tight tolerances. In my attempts at figuring out the bolt hole radius, my measurements fall between common metric and Imperial numbers so I don't know which system was used.
Those of you who have experience with glass blowing chucks will know where I am coming from.
I know there is an easy way, but many of my old timer machinist friends that could answer this have passed on in the last few years. I have searched the internet, this and other machinist sites but cannot find the answer.
I have a DRO with 'Bolt Hole pattern' to drill the new holes, but I cannot figure out how to use it in reverse, and it is not in the Accu Rite manual.
Obviously I have no formal machinist training, but I scratch out a living with decent machines and information from books / friends.
Thank you in advance.
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