Swing through gap

Have you ever had that feeling , that the lights have just been switched on ? The problem was, how to get a six dia x 1/8 thick plate into the chuck on my lathe so I could drill bore and face it . The chuck is big enough , external jaws fitted , but the jaws wouldn't swing through the bed gap ,when holding the plate . Bright idea!! drill and tap each jaw 6m/m on the last step , screw in a caphead on each one , now the work is clamped using each caphead to clamp the edge of the plate, works perfect. I am sure someone else will have solved this in a similar way but still , its all part of the fun . I think someone mentioned using glass has a lapping in plate , , I use a small double glazed unit 10 x14 inch much stronger than one sheet of glass and most units are made from toughened glass these days. have fun Stewart

Nice one!! That will be stored away for future use! Good bit of lateral thinking there!

Might be an idea to drill a small hole through the spacer material, otherwise it could become convex/concave depending on the change in air pressure/temperature.

I had a unit, much larger I admit, which showed Newton's rings when it was high pressure and cold enough.

Edited By peak4 on 18/06/2016 22:06:20

You could make a barometer out of it. One description of a glass surface plate came up many years ago in ME, a shallow wooden box filled with tar/pitch, and while it is hot the piece of plate glass is placed on top. Ian S C

Stewart - a very useful suggestion and one that I shall store away, Was this a 3-jaw or 4-Jaw chuck?

Hi Bandersnatch , the chuck is a 3 jaw 6'' Rohm on a Drummond lathe one of the last ones I think , before it went to Myford . Don't forget , the holes need to be drilled PDC otherwise you will have runout of the part you are machining. Stewart

Thanks, Stewart. Yes, that's really what I was getting at for the 3-jaw. I guess centring the chuck on a rotary table would be one way of locating the holes. Or perhaps a simple template - flat bar with two holes, one located over a rod gripped in the chuck, the other hole used as a drill-guide. Thinking out loud.

Not critical for the 4 jaw.

Blue the ends of the jaws, and with a scriber or other pointed item in the toolpost rotate the chuck past the scriber by hand and it will mark the 3 jaws in the same place. Take them out, mark ctr line the other way and drill.

Doing it with soft jaws would save having to drill & tap the harder stepped jaws then again if you had soft jaws you wouldr just machine them to hold the 6" piece of work.

Edited By JasonB on 20/06/2016 08:11:40

Glass as a lapping plate No No No No No. The lapping plate /lap needs to be softer than the item being lapped. Why? because if not you will push the lapping compound into the component and despite your best efforts you will leave some behind, this will cause rapid wear on your components when they are running. If however you are just using the glass as a backing for fine wet and dry that is a good idea.

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Dusty,

Strictly; you are, of course, correct.

There is, however, another thread running at present; discussing 'lapping' [sic] with abrasive paper on a flat surface, so your "however" is probably a safe bet.

MichaelG.

Edited By Michael Gilligan on 20/06/2016 08:52:06

Thanks Michael, yes I saw that after I had posted on this thread. I thought that I would leave well alone on that thread as it appears that it relates to using wet and dry which for the sort of work we do is more that adequate. I must say as an ex-toolmaker I am not a big fan of lapping for most things model engineers do. It does have it's place, but generally not in a model engineers workshop. Now a hone that is a different story.

Hi The glass lapping plate, not thought about using it other than with wetndry paper . ,use it mainly for sharpening wood chisels and the plane blade occasionally . Re finding PCD ,Idid as suggested but used a piece of HSS tool steel held in the tool post and ran the spindle Stewart.

Dusty, hundreads of model compression ignition and glow engines been built by model engineers over the years all with lapped piston/cylinder where a hone would leave far too rough a finish. And what about all those Minnie traction engines with a lapped cylinder for the silicon O ring to run against.

Edited By JasonB on 20/06/2016 10:40:50

Jason, sorry, but I cannot agree re honing. Millions of engines have been produced commercially over the years and I would venture to suggest that they are honed as opposed to lapped, which would be far too time consuming for commercial production. The surface finish is to a certain degree controlled by the coarseness of the grit in the hone and by technique in using the hone. I accept that we all have differing views of how things are done and that in most cases their is no right way, but that is my view. I remember 50 odd years ago having to make a number of checking gauges for The Royal Small Arms factory at Enfield they all needed flat lapping and needed to be identical to within .0001" must have been my penance for some misdemeanour of which I was unaware.

Dusty I thought were were talking about lapping in the home workshop not honing commercial engines.

The fact that MEs have been lapping their pistons into the bore of their aero engines since the 30s or earlier shows that lapping does have its place in the home workshop, Not all have access to honing machines and as no rings are used the method is to lap piston directly to bore.

I'd be intertested to know your method of fitting the piston to the bore with what you have at home?

Sorry to disappoint you Jason but I do not have any sophisticated equipment, nor do I have access to the same. My comments were in response to your assertion that honing would leave far to rough a surface.

Not having an engineering background I thought you may have been able to suggest a better method for hobby engineers like me to make these engines which I have only ever seen others make by lapping, seems not

Jason, I would as I have said, prefer to hone the bore to fit the piston. The figure of eight marks left by the honing have the advantage of retaining oil, albeit microscopically. The only problem would be if a hone were not available due to the small size of the bore, then and only then would I consider lapping. As I said before this is my preferred method, experience has taught me that if something works and gives the desired result then that's fine. Each to their own. The good thing about this forum is we all learn from it, I know that I have despite my background, there are wrong ways of doing things (which are dangerous or make it impossible to perform other operations) but many ways to achieve the desired result. I have no intention of making one of those noisy little beasts anyway, gave tem up in my model aircraft days.

Edited By Dusty on 20/06/2016 19:28:23

Honing in a full sized engine will leave so many marks per inch.

In a model engine it will be the same. Honing doesn't scale.

To scale honing you finish up with lapping.

Simples.