Boring

Problem with a tailstock is the play in the quill both radially and rock on the locating pin affecting rigidity.

You would be as well on something this big to fabricate a 1-1/2" diameter bar up and screw an inset to the end of it after having sawn, or milled 1/2 the diameter away at the end. Clamp end will have to be designed around your machine.

-- Regards,

John Stevenson Nottingham, England.

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Try a fly cutter supported in both headstock and tailstock, while the work is clamped onto the topslide. I have never tried it but read about the technique in a book. Let me know if you need more details and I will look it up.

Cliff Coggin Kent UK

You don't give any clues as to what size your lathe is. I've just done a 9" long x 2" bore propellor shaft bearing. I had a big old boring bar about 1 1/4" dia, tack welded it onto a home made (mild steel) Dickson toolholder. The bed on my big lathe is quite badly worn near the chuck, this doesn't usually cause me much grief but in this case, a long boring bar with the saddle working over the fairly sharp transition between worn bed & unworn, the bar was exaggerating that transition & causing a substantial taper in the bore. My answer in that sort of situation is to run a David Brown floating adjustable reamer through after boring. Even at that length I got a pretty good result, though it's pretty much the limit before the weight of reamer + extensions causes it to sag below centreline at the inner end of the bore & therefore cut oversize. I could in this case have done the bearing in shorter sections, bored & reamed individually before pressing into place, but I had to clean out the bore in the cast iron housing in one go before fitting any new bearings so decided to use the same setup to do the bronze bush in one piece. A DB reamer for 100mm has at least a 4MT shank, maybe 5MT, so no use at that size on a small lathe.

Cheers Tim

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Thanks for the advice, for the moment I think I will go and find a larger boring bar for the moment, fortunally the accuracy of the bore does not have to be to high for this task.

Stephen.

In message , Cliff Coggin writes

Was this the 'classic' method recommended by the likes of 'LBSC'? Its claimed advantage being that ensured a good standard of parallelism in model steam locomotive cylinders?

I have no idea, but it makes sense to support the boring bar at both ends for extra rigidity. I read about it in Sparey's "The Amateur's Lathe" where the illustration is of a model loco cylinder.

Cliff.

I have made boring bars, especially for one off jobs. either drill a hole through the largest bit of stuff you can fit in the hole and use a set strew to keep a HSS bit in place (yes square bit in a round hole) or even weld on a piece of HSS to a lump of mild steel. Geoff