am i understanding this? you secured the ream via the toolpost? the only way to do it properly is to center the job on a face plate (assuming this is how it was held when it was bored) and secure the expanding reamer in a chuck in the tailstock. Ive never done anything other than bore a bore so to speak, never reamed one.

Wrong tool and wrong application I'm afraid. Ajustable reamers are intended for use by hand to open up holes on things like steering trunnions, usually for repair. They are not intended for machine use to accurately size a hole and leave a good finish.

I agree with 'fizzy', I mostly bore bores and leave it at that. If I do use a chucking reamer in the lathe I always use it in the tailstock.

Andrew

Exactly. If nothing else, at the time the drawings were done I doubt many modellers had a 3/4" machine reamer to hand.

I wouldn't bother reaming or honing, plain boring will be fine. It's a steam engine, it doesn't require super accurate size and surface finish. If the size is a bit off you can make the piston to suit; which is probably what you'd be doing even if the bore was reamed.

The only caveat is if the lathe doesn't bore parallel to within a few thou; then an altermative finish method may be required.

Andrew

Hello Sam,

I'd rebore the casting, but use the stoutest boring bar you've got with a nice round faced cutting edge, take out a couple thou at a time until you reach almost finished bore size, then don't alter anything, go up and down the bore on the same topslide setting several times using the self act and you'll have a nicely finished bore, It's not too important if it's up or down a couple of thou, it's more important it's parallel.

Best of luck,

Bob Youldon

YOu can use an adjustable reamer in the lathe, and if used properly will give a precision sized hole with a lovely smooth finish.

Bore the hole nice and clean to just a few thou under the desired finish size, say 3 to 5 thou under.

Then adjust the reamer blades so the taper first part of the blades will go in the hole an inch or two but not all the way. Check the blades with a micrometer to make sure the tailstock end of the reamer is set slightly undersize.

Hold the reamer in the tailstock chuck, or by tap-wrench and tailstock centre.

Rotate the lathe chuck by hand, not under power, and guide the reamer in as it goes. A crank handle is handy for this. Or you can cheat and use the chuck key VERY CAREFULLY to rotate the chuck. But it might be better to instead lock the headstock spindle via the backgear and use the tap wrench on the end of the reamer to rotate the reamer while pushing it inwards with the tailstock centre.

Never rotate the chuck in the reverse direction. It messes up the reamer blade edges.

Keep feeding the reamer in until the parallel section of the blades, the last half or third or so passes right into the hole. (Therefore you need big enough space behind the job for the reamer to pass into, either large hollow spindle or spacing between job and chuck etc.)

Rotating the chuck in the same direction by hand, pull the reamer out.

Measure the hole size, and the blades on the reamer and adjust the reamer just a "nudge" to take a small cut then repeat the above process until your hole reaches the desired size.

If you have to go oversize to clean up the dodgy hole, do so and just make the piston oversized to suit the bore.

Edited By Hopper on 17/04/2016 11:57:38

Just remember that those three legged sprung hones will not correct an oval or tapered bore, they will put a finish on it for you but they always follow the original shape of the hole.

If you want to correct dimensional errors you need to use a professional type of hone such as a Delapena, most people will not have access to one of those so the next best thing is to make yourself a simple lapping tool.

As you will have guessed I am not a big fan of those cheap hones, and there are still people giving out incorrect information about what they can do.

Once your bore is round and parallel, by all means give it a quick lick with the hone just to add an oil retaining surface finish.

Phil