A Microscope Repair.

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Pete W.:
Hi there, all,

Thank you all for your replies and suggestions.

Andrew, the approach you suggested was the same as the advice from a couple of posters on the Yahoo Microscopy list. While that might be a good approach in a commercial environment or if I were busting to get the microscope working for some urgent observation, I've decided not to go that way, not at first anyway.

Please don't be offended. :beer: :beer: :beer:

The thing is that I want to know if I can master all the processes required to make a complete replacement spindle - I'll never know that unless I try it. Another reason is that I've been carting my Myford around with me for forty-four years now and I can't justify that if I only use it as a drilling machine! :lol: :lol: :lol:

Another reason is that Graham, the now deceased microscopist who gave me the microscope (and lots of other help, advice and assistance) wasn't a 'quick fix' kind of guy and I'd feel shivers down my spine while standing at the lathe if I took an easy way out! :poke: :poke: :poke:

So I say again, please don't feel offended, guys, I'll go for the complete replacement spindle and hope you don't have reason to say 'we told you so' if I make a pig's ear instead!!
:ddb: :ddb: :ddb: :ddb: :ddb: :ddb:

awemawson:
Pete I quite understand where you are coming from, and after all, you still have the possibility of doing it that way if the taper turns out wrong.

Of course if you take the "Conservationist Approach" you have to preserve as much of the original as possible and make a clear distinction between the old and the new. So in your case you must use a contrasting material that obviously isn't original. Not an approach I agree with, where in old buildings you see new oak scarfed into the old, but not dressed to match, and glass monstrosities attached to Grade 1 listed cottages :bugeye:

Pete W.:
Hi there, all,

Andrew, this microscope is venerable but I don't think it's listed! :lol: :lol: :lol:

So my intention is to make a spindle that is a F³ replacement (you know, 'Form, Fit & Function) for the original one. As to material, I already stated it's EN1A. It seems to be free-turning.

I'm not using oak but I have been given four nice pieces of mahogany which I plan to use to make the accessory drawers that fit inside the microscope case to hold the spare objectives and eyepieces.

Today's task has been refinement of my taper test piece. I did attempt to measure the included angle of the original 'stump' using a 'Bevel Box' and standing the 'stump' on a mini surface plate (actually a 3" x 3" sample of granite from a stone merchant's) but it didn't help me much, the degree scale on my top-slide is too coarse and has about a degree of zero error!

So, having made a first attempt two days ago and persevered this afternoon, I achieved this:

My tin of 'Micrometer' engineer's blue has been kidnapped by the shed gremlins so I used a Sharpie, I was quite pleased with that result having arrived at that fit by trial and error. :thumbup: :thumbup: :thumbup:

So, just to test the result, I removed that piece of rod from the chuck and turned a taper on the end of another piece - it fitted too. :thumbup: :thumbup: :thumbup:

My next task is to contrive a tool to turn the run-out groove at the ends of the two lengths of ¼" x 40 tpi ME thread, it needs to be quite narrow. I do have a grooving tool holder that takes TC tips but I only have 2 mm tips, I need more like ½ mm. I was wondering if I could grind up a piece of hack-saw blade but all my old hacksaw blades are bi-metal. Then I saw a slitting saw blade being used for parting on Stuart's thread on here.

So, as I'm in no great hurry, I shall go into cogitate mode for a while. :coffee: :coffee: :coffee:

Pete W.:
Hi there, all,

I've been pottering-on with this project. It's all quite simple stuff compared with most of you other guys' posts but it means that I'm getting some workshop time,
so share my joy!! :thumbup: :thumbup: :thumbup:

The new spindle will have each end turned down to 0.150" diameter and then a section of ¼" x 40 tpi ME thread each side of the tapered section. So I have to machine one end, then remove it from the chuck or collet and turn it round. The initially machined end will be a bit awkward to hold. So, today's task has been to make a fixture to hold the spindle while I perform that second set of operations.

Starting with a short piece of ⅜" EN1A rod, I faced both ends and centre drilled one. Then I through-drilled a pilot hole and opened it up with a #24 drill:

Then I opened about half the length of the hole with a #1 drill (tapping size for ¼" x 40 tpi ME thread according to G.H.Thomas):

I then tapped the enlarged section of the hole ¼" x 40 tpi ME thread, starting with the taper tap held in the tail-stock drill chuck and pulling the vee-belt by hand to turn the job. When I'd got enough thread to locate the tap, I finished the operation with the second and then the plug taps in a hand tap-wrench:

I completed the fixture by turning it round in the collet and cleaning up the drill exit hole with a centre drill.

I've found that my ¼" x 40 tpi ME thread die has a pronounced lead so I don't think it will thread as close to a shoulder as the Cooke, Troughton & Simms original part! I do have a 40 tpi Whitworth form chaser but it's too deep to fit in the Dickson quick-change tool-holder.
So I've had to dig out the original ML7 tool-clamp with its elephant-foot screw - just one snag with that, the shed gremlins have kidnapped the spherical washer!! :bang: :bang: :bang: so finding that is going to be Saturday morning's first job!

I held the work in the collet today, for better concentricity and to minimise overhang, but I found that it's sometimes difficult to get the tool near the work-piece - the three-jaw gets the work-piece within reach of the tooling.

philf:
Pete,

A bit late to suggest something different perhaps but couldn't you make the spindle with the two plain ends and a threaded centre portion. The taper section could be tapped and then be 'loctited' on to the threaded portion. The threads would then be complete right up to the taper.

Phil.

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