Bad day & a pigs ear with a reamer

I am trying to make a Stuart 10V which I started 40 years ago but stopped for various reasons.

I have bored the cylinder with a home made boring bar made from 12mm steel with a 3mm * 12mm round cutting tip set in that I made years ago. That worked OK & I was quite proud of the finish. However, At some dim & distant time in the past I find that I purchased a 3/4 inch expanding reamer & it has never been used /abused until now.

I have had a real hassle using it & with the cylinder in the lathe & thought all I had to do was centre it on the tool post & feed it in with the lathe running at lowest speed ( 30-40RPM) Total disaster. trying to keep the reamer on the centre does not work, It jams in the cylinder. The handle caught in the cross slide & I ended up trying to turn the chuck by hand with the reamer waving in the wind.

I gradually expanded the reamer & really messed up a nice hole . It is now just 3 thou under 3/4 one end about 6 thou the other. & 13 thou under in the middle. I have lines running longitudinally down the bore, not around as one might get if turned. I have taken it out of the chuck & do not really want to re centre unless really necessary.

When you have stopped laughing could someone be kind enough to give me some guidance on how one should use this tool please.Years ago I did the front suspension on my Morgan very successfully several times with a 1 inch reamer & that had a nice cone to form a guide & the reamer slid on a rod. But this one just waves about in the breeze

Edited By Sam Longley 1 on 16/04/2016 17:36:38

Oh = hang on . sitting here in the armchair ==it has occurred to me that just because it has a square top it does not stand to reason that i should have used the tapping handle. Should I have stuck it in the jacobs chuck off the tailstock??

Edited By Sam Longley 1 on 16/04/2016 17:41:03

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.

No, I originally tried to get it in line by centering it on the tailstock fixed centre & feeding the tailstock in gently. The cylinder was still in the 4 jaw chuck having been bored to almost 3/4 inch

Edited By Sam Longley 1 on 16/04/2016 17:52:01

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

Sam

I'm afraid you will have to put it back in the chuck and, if you take your time and do it carefully, you may be able to rescue the cylinder. Continue with the boring exercise until you have a smooth bore - if it ends up a little bit larger than specified you should be OK - just turn the piston to fit. Don't worry I'll bet everyone here has made a boo boo at some time ( or often!) - the important thing is to learn from your mistakes and not repeat them. ( I must admit to repeating a few myself though - but not necessarily confined model engineering!)

Norman

The instructions on Stuart's plan says ream. Are you suggesting that this might not be required?

Sam

I would think about honing the bore to size rather than reaming it.

There is an extremely detailed article showing how to do it here.

http://www.modelenginemaker.com/index.php/topic,1908.0.html

Phil

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

Sam, I have machine reamed thousands of gear blanks made in EN24 with adjustable reamers, but these are of the David brown 2 bladed type, I guess you used the multi-bladed type which are not suitable as stated.

I would re-bore and make the piston to suit as suggested above.

Chris Gunn

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

Sam, I have to say that I agree with Andrew, no need for any sort of fancy finishing as long as the bore is parallel and smooth you need do nothing else. In my opinion adjustable reamers are the devils creation designed to captivate unwary model engineers. Remember a reamer is a sizing tool not a finishing tool, you can get a better finish on a plain drilled hole provided the drill is doctored.

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

Sam

I don't know if you have come across the resource but Harold Hall, a past magazine editor, has a comprehensive site with a strong ME content. Part of that site is devoted to the machining of the Stuart no.10, See HERE . It's well worth a read and should give you some good tips on set-ups etc.

Regards

Norman

Hopper

Thanks

I had another go the next day & it came out really well & only a few thou over the 3/4 inch

I just seem to have had a "non thinking" day for some reason- I had just come back from drilling one of my RC planes into the ground & ended up with a bag of balsa chips. Should have stayed in bed

It would be better to use one of those small hones sold for brake cylinders than a reamer. A nicely bored cylinder is actually good enough for steam purposes, but if you are going to use O rings, the honed finish would probably be easier on the O ring.

John

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