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| A Microscope Repair. |
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| Pete W.:
Hi there, all, again, After the catastrophe of the second attempt, I retired to lick my wounds (figuratively speaking) and to ponder a 'better way'. This afternoon, I was ready for the third attempt! I chucked and centred a fresh piece of material and reduced most of its length to a diameter of 0.350". I then machined a groove sufficiently far in from the outer end of the bar for the threaded section plus the spigot. I used the mini-thin grooving tool and cut to a root diameter a few thou less than the core diameter of a 1/4" x 40 tpi ME thread. I then reduced a section of its outer end to 0.250" diameter, temporarily removed the tail-stock centre and used a tailstock die-holder to thread that outer section, resulting in this: I used a different die from the one I used for my first attempt. What I replied to Steve back then about 'all my dies' was plainly wrong - this one cut a good thread and I was able to run a nut right up to the shoulder, like this: I restored the tail-stock centre support and turned the tapered section, like this: When it was close to size, I tried the polariser unit on the taper and took VERY careful and light cuts. I stopped when the top surface of the polariser unit lug was as nearly flush with the top of the taper as I could see by eye. Then I used the mini-thin grooving tool again to define the 'back end' of the tapered section, like this: The next operation was to turn down the section of the job between the base of the taper and the chuck to, again, 0.250", with this result: I then further reduced a section of the job immediately in front of the chuck to a diameter of 0.150". This was looking ahead to having to cut off the job and reverse it in the lathe to allow access for the 1/4" x 40 tpi die to thread the section behind the base of the taper. I'll then support that short section of spigot on a drilled brass bar-end in the tail-stock chuck. But that comes later! Here's what it looks like: The final operation in today's session was another application of the mini-thin grooving tool to define the length of the threaded section above the taper, like so: Looking ahead, the next operation will be to turn off the surplus thread at the current tail-stock end and reduce the diameter to 0.150" to form the spigot at that end. Then to cut off the job at the narrow neck at the chuck end, reverse the job in the lathe and use the tail-stock die-holder to thread the section next to the wide end of the taper, then mini-groove to define the desired length of that thread, then reduce the surplus thread at that end to the spigot diameter, i.e. 0.150". All of that promises to present some centring challenges!! Watch this space!! :nrocks: :nrocks: :nrocks: :nrocks: :nrocks: :nrocks: |
| vtsteam:
That looks pretty! :beer: Fingers crossed.......! |
| Pete W.:
Third attempt continued: At the end of my last post I outlined the next operations and today's workshop session more or less followed that sequence. First of all I removed the surplus thread and finished the spigot to final diameter on the end nearest the tail-stock (i.e. next to the narrow end of the taper). I left a bit of thread because the tail-stock centre limited how close to the end I could go. Here's a photo: Next, I removed the job from the lathe and removed excess material from each end, using a junior hacksaw. I then trimmed the spigot to length and reversed the job in the lathe using the fixture shown in my first post in this thread. I supported the short spigot in a piece of drilled brass bar, held in the tail-stock chuck, like this: I then realised that I was getting ahead of myself,and swapped the tail-stock chuck for the tail-stock die-holder and cut the thread, like this: You can see that, as with the other end, this die cut a clean thread right up to the shoulder. I ran a couple of nuts onto the thread to verify. Next, I used the mini-thin grooving tool to define the required length of the thread and removed the excess thread, finishing at the desired spigot diameter, 0.150". For careful light cuts, the mini-thin grooving tool also works well as a right-hand knife tool. I then defined the required length of the spigot. Here's a photo: I then removed the job from the lathe and cut off the excess length from the spigot, using the junior hacksaw. The torque applied during the latest turning operations had tightened the job in the thread of the fixture and I had quite a tussle to remove it! The only part I dared to hold in the bench vise (with fibre jaws) was the spigot but it wouldn't grip. Eventually, I gripped the spigot in the tail-stock chuck and the fixture in another chuck and was able to separate job from fixture. I returned the job to the lathe and used a Swiss file to break the sharp edges and then used the junior hacksaw to start a screwdriver slot in the end of the longer spigot, finishing the slot with a Swiss file. That produced this: I think (and hope!) that this concludes the lathework. The next step is a trial assembly of the spindle, its mounting bracket and all the optical components that swing on the spindle. I can already see that I've cut the lower threaded section and the lower spigot a bit shorter than ideal but hopefully they'll be good enough. |
| Pete W.:
:update: :update: :update: :update: :update: :update: I decided that one isn't good enough! I went out to the workshop this afternoon to clean down the lathe and, sort of 'on autopilot', found myself machining another! :palm: :palm: :palm: |
| awemawson:
Well shelf spares are always handy ! I'm terrible in that if I acquire a useful 'thing' particularly if it contains electronics, I grab any spares that crop up and box and store them. Almost guarantees that they'll never be needed. Example #1 : I have a complete set of electronics, electrics and servos for my Diesinker EDM rescued from one being scrapped. Example #2 : pretty much a re-run of the above for my Wire EDM |
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