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Red lathe woes..or 'The joy of owning a piece of history'

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DavidA:
Pekka,

I see more clearly what you mean now.

Sadly the taper appears to have been messed up by someone trying to machine it in the past.  I'll have another check with the blue before I commit myself to re machining the taper.
Believe me,  if I can get away with a very minimal skimming then that is the route I will take.

Dave.

PekkaNF:
OK. Then you need plan "B" (VT speciality really :D).

I'm interested on this one too, because ofter few projects I'll get back to my pet project and I need to make ER or MT taper there in a spindle.

Luckily you compound looks substantial, it probably has some extra feed as you already tried it.

One daft idea came to my mind: Can you dismantle the top slide from apron and mount that on temporary mount on the gap? If your compound has enough feed you don't need any apron movement and no provision for that.

Gap bed is very useful for model engineer, specially if you have a faceplate. Those removable pieces are always a bit of compromise and I think that they are not that easy to make.

That 8" overhang is hard to work with, even if you make the tool butt end extra large, you still have that nose down tendency because cross slide support is really very far away and narow. You could try to compensate nose dive by mounting a plate with accurate top surface next to spindle like a chisel rest on wood lathe......this time it would be boring bar rest.

Some ideas, hope it is conversational piece.

Pekka

vtsteam:
There will definitely be spring. But with a sharp tool, and in the case of a one-off operation like this, it's usually just a matter of patience while cutting. A few passes per turn of the compound rather than cranking it every pass.

Since you don't want to go too fast and ruin things, a slow cut isn't really a disadvantage. The whole operation isn't going to take a tremendous amount of time. The only thing to avoid is chatter. That's a matter of speed, cutter sharpness, cutter point width, and  point position (should be very slightly above center on an inside cut). Also, be certain your cutter has enougn relief under to avoid rubbing at the narrow end of the bore.

But you'll know how things are going at the start of the first pass. If you get chatter or rubbing, modify whatever is needed and proceed. You will have only taken off a tiny amount of material, anyway.

You could also try all this out on a test piece, if worried. That would set your compound angle ahead of time, and give you practice with everything else.

If you have a fixed steady, put a piece of scrap rod in it, drill out to the narrow diameter, and then practice boring the taper.Maybe you can even use that piece for something afterwards!

DavidA:
Another quirky aspect of this machine.

The base of the top slide is very nicely engraved with degree marks..  But the fiducial line to use with them is on the opposite side of the top slide and hence won't line up.
I can turn the base through 180 degrees to put it on the same side as the mark,  but then I can't see it .

 :doh:

And why a 6 TPI leadscrew ?
That gives an advance of 166.666 Thou per revolution. Try putting that into your dividing head and making a indicator dial.  I could cut marks at 1 thou on the perimeter , but would have to remember that the last gap in the marks would be odd.  Rather like the system used for the quill on the X1L mill.

Dave.

Fergus OMore:
I'm involved with a more important bit of history which people are trying to mend-me,it happens!
This 6tpi screw is - or was quite normal in the olden days  and the surprise is really that it is graduated. People chalked their settings rather than relied on dials. What you have is is a lathe which 'roughed out' and finishing to precision limits was done on a cylindrical grinder.

My own old Clarkson tool and cutter grinder has only one graduation- for an angle. The rest of things is was on jigs or other devices. It was production machinery whilst my little Stent and Quorn  were made with to do- all things for all men.

Regardless of me 'prattling on'. there was no guarantee that it was a 'dead on' 6TPI on your lathe and going into the realms of 'recurring decimals' was a bit over the top. We can have a scientific calculator for a quid from Poundland and a 'Vernier' not quite from Ornans in the Doubs but Lidl or Aldi.  We had to rely on a slate and pencil or Trachtenburg- if you were a posh kid.

Frankly, I would 'do up' your old mangle my older generation did. For a £20 note you could have a rather nice tool and cutter grinder.

Meanwhile, here's nurse!

Norman

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