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BOXFORD IMPERIAL DIAL

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GRIFFIN:
When I recently took delivery of my imperial long bed Boxford AUD MKII, I was very slightly disappointed by the fact that it had metric dials fited. I was told by the previous owner that it had originally been a school lathe and they had probably fitted them  post metrication. I couldn't help thinking that this was a little silly as the machine had an imperial thread cutting gearbox but decided to change them for imperial ones anyway.

I found someone selling them on ebay for £50 each but they were out of stock, so I decided to have a go at making my own. After all, how difficult can it be to scribe 100 equally spaced marks round the circumference of a piece of metal when all you have is a rotary table on a milling machine?
 :lol:

I decided to use aluminium, mainly because it would be easier to knurl, scribe and number punch than steel and it doesn't need to be particularly hard wearing. After going to my local Metal Supermarket and picking up a suitably sized off-cut of 50mm round bar for £12, I cut a lump off in the horizontal band saw and popped it in the 3 jaw chuck to start work.

I was pleased with my new Boxford and it was a good job to learn on. I roughed it out first, leaving  some excess metal to allow for errors and finishing to remove any marks made during production. I started the centre hole off with a drill then fitted my boring head into the tailstock to make a precision fit. The next thing was the knurl for which I used a single straight one with the leading edge slightly away from the work piece in order to minimise pressure. At this point I discovered why I shouldn't have lubed the back gears, Etc. quite so much, as the belt started to slip. :palm: After liberal wiping of the T lock drive belt with isopropyl alcohol, the slipping stopped and I carried on. Next  turned down the main diameter to raise the knurl above the main body, again allowing an extra few thou for errors in marking the graduations.

Next step was to scribe the increments, which I did using a scriber in the drill chuck of my mill drill and an er32 collet mounted in the 2 morse taper on my rotary table. The ten thou markings were easy as they were 36 degrees apart, I then moved round another 18 degrees and added the five thou marks every 36 degrees. At this point I was glad I left the diameter bigger than needed, as I messed up and got the spacing wrong, so had to remove metal and start again. :doh: Second try was perfect as was the addition of the smaller one thou marks which were 3.6 degrees apart. I followed this up by stamping the 2mm numbers round the dial which were not very good, so I was almost happy when I realised I'd done them upside down :bang: I then machined a recess in which to add the numbers the right way round and this was the result.

awemawson:
 :thumbup: It came out well in the end  :bow:

John Rudd:
Nice job Griff, shows how a little effort and perseverance can make a bad job into a good job and less scrap pieces......

Of late, I've had three attempts at getting something right.... :Doh: Maybe I should take up knitting....? :lol:

DavidA:
Griffin,

Have you checked, with a dial guage, exactly how far each item moves for one complete turn of the dial ?

It may be a metric imperial gearbox, but is it an imperial lead screw ?

same goes for the cross slide.

Dave.

GRIFFIN:
It's an imperial machine with an imperial gearbox David. the only metric things are the dials. One revolution of the imperial dial is 100 thou or a tenth of an inch that ads up to 2.54 mm, the metric dial says it moves 2.5 mm per revolution, which is 4 hundredths of a mm out per revolution. This was probably quite acceptable in a school environment. Having said that, I will check all screws and gears before I trust it enough to cut any threads.

Cheers, Griff.

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