Wedg1e
They call me Mr. Bodge-angles
- Messages
- 7,735
- Location
- Teesside, England
Following on from John the Doubleboost and his lathe gears, I dragged my dividing head out and drew up a spreadsheet that allows me to work out what hole circles could be used to produce x number of divisions. That led onto a calculator that shows how many degrees, minutes and seconds you need to dial in on a rotary table to produce each hole circle... and after all that mental effort it was only right that I put the thing to work!
My div head (above) only has one hole plate with it, albeit double-sided, so I thought I'd knock up another with a further range of hole circles to extend / fill in some gaps. Now the calculator kept telling me I needed x degrees, y minutes and z seconds and this is where the fun starts because my rotary table is only scaled down to one minute of arc, however I thought I could interpolate the half-minute intervals so I looked for hole circles where the seconds figure was either 0 or around 30 - this includes 51 and 53 holes (31 and 32 seconds respectively). Any error will be divided by 40 in the worm so even 20 seconds of arc could be rounded to the nearest half a minute, I imagine
This is 264 degrees, 52 mins, 30 secs as near as I can make it...
Now I needed some material. Several years ago I did an installation job in a fabrication shop down near Peterborough and as we were packing up I cheekily asked if I could have a few offcuts of plate from the aluminium scrap skip. It was after hours and the guy who was waiting to lock up was the only staff member left so he said he was going to see Jimmy Riddle and would be back in 5 minutes...
A few slices of 6 and 12mm plate duly fell into the back of the van and have been slowly whittled away over the years. As luck would have it I found two 8" diameter circles of 6mm; the div head plates are 6" so I guesstimated the centre of one, drilled a 10mm hole through it, put a bolt and nut through and chucked it on the Boxie. I used the parting tool to core it out rather than turn down from the OD, then as it cooled down I heaved the 12" rotary table onto the Perrin and centred the quill on it (the Perrin has a screw-on centre for its quill).
Centring the disc on the table was a bit of a pain but I did it eventually using a DTI on the outer rim (which was obviously round, having just come off the lathe) and cranking the rotary table like a loon.
Next I fitted the boring head and opened the 10mm bolt hole out to 30.2mm to suit the div head's boss.
I tried to find some sort of on-line calculator that could add degrees, minutes and seconds and there are a few, but they're only any use for adding two numbers and won't produce a column of figures. Dusting off my trusty old Casio calculator I found it has the ability to switch between deg/min/sec and the decimal equivalents, so adding up in decimal and switching the display gave me a list of values for the rotary table... just had to do it 8 times for each of the hole circles that I could fit on.
Armed with the magic numbers I switched the Perrin's boring head for a drill chuck, slotted in a 3mm drill, zeroed against the top of the disc and set the depth stop for 2.5mm. Now it was time to drill holes!
I would have taken some photos but by the time I thought about it, I'd already drilled half the plate and then I found the camera battery was flat. By the time it charged up I was as near as damn finished.
I did my level best to determine the PCD of the three holes used to secure the plate to the div head but in the end I chickened out and just marked through the old plate
Now it was time to fit the plate. Slide on, screws in, fit the sector arms, fit the crank and... wait a minute, the crank's detent pin won't engage the plate! WTF? Ah..... the original plate is 8.8mm thick. The new one is 6mm, the spring-loaded detent bottoms out before it reaches the pate. Doh!
So I had to make a 2.8mm thick spacer to fit behind the plate, but with that done it only bl**dy works!
Just need to stamp or engrave the number of holes for each circle now. And find something to make that needs 57 divisions
My div head (above) only has one hole plate with it, albeit double-sided, so I thought I'd knock up another with a further range of hole circles to extend / fill in some gaps. Now the calculator kept telling me I needed x degrees, y minutes and z seconds and this is where the fun starts because my rotary table is only scaled down to one minute of arc, however I thought I could interpolate the half-minute intervals so I looked for hole circles where the seconds figure was either 0 or around 30 - this includes 51 and 53 holes (31 and 32 seconds respectively). Any error will be divided by 40 in the worm so even 20 seconds of arc could be rounded to the nearest half a minute, I imagine
This is 264 degrees, 52 mins, 30 secs as near as I can make it...
Now I needed some material. Several years ago I did an installation job in a fabrication shop down near Peterborough and as we were packing up I cheekily asked if I could have a few offcuts of plate from the aluminium scrap skip. It was after hours and the guy who was waiting to lock up was the only staff member left so he said he was going to see Jimmy Riddle and would be back in 5 minutes...
A few slices of 6 and 12mm plate duly fell into the back of the van and have been slowly whittled away over the years. As luck would have it I found two 8" diameter circles of 6mm; the div head plates are 6" so I guesstimated the centre of one, drilled a 10mm hole through it, put a bolt and nut through and chucked it on the Boxie. I used the parting tool to core it out rather than turn down from the OD, then as it cooled down I heaved the 12" rotary table onto the Perrin and centred the quill on it (the Perrin has a screw-on centre for its quill).
Centring the disc on the table was a bit of a pain but I did it eventually using a DTI on the outer rim (which was obviously round, having just come off the lathe) and cranking the rotary table like a loon.
Next I fitted the boring head and opened the 10mm bolt hole out to 30.2mm to suit the div head's boss.
I tried to find some sort of on-line calculator that could add degrees, minutes and seconds and there are a few, but they're only any use for adding two numbers and won't produce a column of figures. Dusting off my trusty old Casio calculator I found it has the ability to switch between deg/min/sec and the decimal equivalents, so adding up in decimal and switching the display gave me a list of values for the rotary table... just had to do it 8 times for each of the hole circles that I could fit on.
Armed with the magic numbers I switched the Perrin's boring head for a drill chuck, slotted in a 3mm drill, zeroed against the top of the disc and set the depth stop for 2.5mm. Now it was time to drill holes!
I would have taken some photos but by the time I thought about it, I'd already drilled half the plate and then I found the camera battery was flat. By the time it charged up I was as near as damn finished.
I did my level best to determine the PCD of the three holes used to secure the plate to the div head but in the end I chickened out and just marked through the old plate
Now it was time to fit the plate. Slide on, screws in, fit the sector arms, fit the crank and... wait a minute, the crank's detent pin won't engage the plate! WTF? Ah..... the original plate is 8.8mm thick. The new one is 6mm, the spring-loaded detent bottoms out before it reaches the pate. Doh!
So I had to make a 2.8mm thick spacer to fit behind the plate, but with that done it only bl**dy works!
Just need to stamp or engrave the number of holes for each circle now. And find something to make that needs 57 divisions
