.png)
Tweet
In another thread there was talk about sine bars, sine plates and I suggested making a sine magnetic table and promised some photos. This is a setup from my workplace and it has been built in-house from a standard manual magnetic chuck. Brownie points if you make an electromagnet version.
Here is an overall photo of the setup. The conversion we did lifted the chuck 11 mm off of the original table, so nothing noticeable. In the same go I put screw holes and machined a piece of angle iron for the back fence so that it is easy to setup parts straight and especially when the table is tilted so they don't drop.
This a photo from the left hand side of the chuck from the back. It shows the two hinge components and the back stop iron that can be lifted above table surface.
The hinge piece that is connected to the table actually encapsulates the whole corner of the chuck on 3 faces and has two M6 bolts on every face. On the outboard side is a 20 mm diameter hinge pin with a lubrication groove cut in it and a small grease nipple drilled to the end of this hinge pin. The whole thing is made from one piece. Yes, it is not an easy thing to make, but we turned the hinge pin diameter first, then made a jig for the CNC mill so that the pin could be grabbed tightly and then milled it. The inside corner was removed completely to not interfere with the chucks corner.
The "feet" were simple milling jobs with one M6 screw to tighten the clamp around the hinge pin.
The back side corners of the chuck were milled perpendicular to the bottom of the chuck, as the chucks outer surface was left as cast.
In this photo the front of the chuck is shown. In the middle of the chuck a wide flat was milled and four M6 holes drilled & tapped. Not deep, but deep enough. To these was then attached the seen block of steel. It's only purpose in life is to bring the flat face of the chuck under it, so that a round hardend roll can be tightened against it and the chuck bottom surfaces. We used a piece of 11 mm ejector pin that we had drilled for four 5.5 mm holes to put M5 screws through to the steel block. The weight of the table ensures the pin sits against the bottom.
Later on that steel blocks upper surface was trued with the grinding wheel to have an additional flat for reference and weird setups.
And by now the sharp ones have noticed that this is not a sine table as per se, but sort of. There is two different sized rolls (20 mm hinge pins and 11 mm roll in the front) and they are at different heights. So how on earth do you use it? Well, you just have to take these known dimensions in to account when calculating.
But, as we are a tool & die shop and usually see a fistful of different angles on the jobs, we first had just a short expanding list of gauge block heights for different angles, but I then did a calcsheet on LibreOffice that lists all the angles in increments of 0.1 degrees from 0 to 45 degrees and printed that on paper, together with the formula for calculating any angle wanted. This has been in use for a few years and not had the need for calculating a new angle yet.
The formula in the picture says "Mittapala = sin(kulma - 5,7071) * 181.0072 + 18", which in english is "gauge block = sin(angle - blahblah)...".
When the table sits so that the bottom is flat, the 5,7071 is the angle from hinge pin center to the front roll center. The 18 is the height difference. The 181.0072 mm is the distance between the hinge pin and the front roll centers. So in short sin(5,7071) = 18 / 181.0072.
The hinge pin and front roll distance is easy to measure on a surface plate. Measure the vertical and horizontal distances separately using the chucks bottom as a reference and then calculate the hypotenuse using Pythagoras.
Whole lot of work to make it low and useful, but so much joy in using it, makes things very easy.
Here is an overall photo of the setup. The conversion we did lifted the chuck 11 mm off of the original table, so nothing noticeable. In the same go I put screw holes and machined a piece of angle iron for the back fence so that it is easy to setup parts straight and especially when the table is tilted so they don't drop.
This a photo from the left hand side of the chuck from the back. It shows the two hinge components and the back stop iron that can be lifted above table surface.
The hinge piece that is connected to the table actually encapsulates the whole corner of the chuck on 3 faces and has two M6 bolts on every face. On the outboard side is a 20 mm diameter hinge pin with a lubrication groove cut in it and a small grease nipple drilled to the end of this hinge pin. The whole thing is made from one piece. Yes, it is not an easy thing to make, but we turned the hinge pin diameter first, then made a jig for the CNC mill so that the pin could be grabbed tightly and then milled it. The inside corner was removed completely to not interfere with the chucks corner.
The "feet" were simple milling jobs with one M6 screw to tighten the clamp around the hinge pin.
The back side corners of the chuck were milled perpendicular to the bottom of the chuck, as the chucks outer surface was left as cast.
In this photo the front of the chuck is shown. In the middle of the chuck a wide flat was milled and four M6 holes drilled & tapped. Not deep, but deep enough. To these was then attached the seen block of steel. It's only purpose in life is to bring the flat face of the chuck under it, so that a round hardend roll can be tightened against it and the chuck bottom surfaces. We used a piece of 11 mm ejector pin that we had drilled for four 5.5 mm holes to put M5 screws through to the steel block. The weight of the table ensures the pin sits against the bottom.
Later on that steel blocks upper surface was trued with the grinding wheel to have an additional flat for reference and weird setups.
And by now the sharp ones have noticed that this is not a sine table as per se, but sort of. There is two different sized rolls (20 mm hinge pins and 11 mm roll in the front) and they are at different heights. So how on earth do you use it? Well, you just have to take these known dimensions in to account when calculating.
But, as we are a tool & die shop and usually see a fistful of different angles on the jobs, we first had just a short expanding list of gauge block heights for different angles, but I then did a calcsheet on LibreOffice that lists all the angles in increments of 0.1 degrees from 0 to 45 degrees and printed that on paper, together with the formula for calculating any angle wanted. This has been in use for a few years and not had the need for calculating a new angle yet.
The formula in the picture says "Mittapala = sin(kulma - 5,7071) * 181.0072 + 18", which in english is "gauge block = sin(angle - blahblah)...".
When the table sits so that the bottom is flat, the 5,7071 is the angle from hinge pin center to the front roll center. The 18 is the height difference. The 181.0072 mm is the distance between the hinge pin and the front roll centers. So in short sin(5,7071) = 18 / 181.0072.
The hinge pin and front roll distance is easy to measure on a surface plate. Measure the vertical and horizontal distances separately using the chucks bottom as a reference and then calculate the hypotenuse using Pythagoras.
Whole lot of work to make it low and useful, but so much joy in using it, makes things very easy.
The low center height of those hinges and them being inline with the back side of the table means that the table doesn't move in a huge arc and eat up all the Y axis motion of the machine when grinding some larger angle.
Comment