Reamer hole

[Optimus]

Good day experts
I've decided to make a Jan Ridders flame eater as my first project I had to scale it down some too fit my wee lathe but my question is this. I want the cylinder to end up at 3/4". I have a buddy bringing me in a 3/4" chuck reamer which I will check if its over or under when I get it, what should I turn the bore to before I ream. Right now its at 23/32 should I go a bit more ? Oh & it's aluminum sorry no idea what grade just some scrap blocks from a suspension lift kit I found. From my searching some say leave 1/32 others say 1/64 just curious if it makes much of a difference & is this how you would finish a cylinder bore?
Thx Lee

 

[Brian Rupnow]

Lee--In aluminum, you will be alright at .030" under. Its nice if you can do .020 under, but the closer you get to being just under the reamer size, the closer you get to being just "over" reamer size, which mean a ruined part.---Brian

 

[RManley]

I would be very careful about reaming such a large hole as you are likely to get a pattern down it that looks like a rifle bore, then you will never get rid of it. Why cant you just bore the hole, after all thats what the full size boys do, and make the piston fit. So what if its +/- a thou or two. Boring can produce almost mirror finishes without difficulty, especially in aluminum (aluminium spelt wrongly ).

Rob.

 

[Optimus]

Thanks Brian that makes sense. Rob I didn't think about getting a bad pattern inside with a reamer. Is boring to size the typical way to finish bores & forget the reamer? Sorry probably a dumb question but its my first model & just want to do it the right way.

 

[Hopper]

You could consider boring it a thou or two undersize then finish it off with a brake cylinder hone.

 

[RManley]

I would do what hopper said, although just make sure you clean it afterwards otherwise you'll be honing your cylinder out for ever. I would always bore any important hole as you're in total control then. Make up a plug gauge with a few steps on the end (-3 thou, -1 thou etc) so you know where you are and then bore it carefully with a nice sharp tool with a 20-30 thou radius edge and a bit of top rake. Do not make the mistake of running the lathe too fast, take it nice and slow and you'll produce a perfectly round smooth hole.
Rob.

 

[Optimus]

Awesome thanks very much guys that's what I'll do. Whew! could of made a right mess of that this is a great forum thx

 

[Brian Rupnow]

RManley---I have made about 13 engines and with the exception of two cylinders which were cast iron, all the rest were aluminum. All of the bores were reamed to size with straight flute "chucking" reamers. I have never seen marks similar to what you are talking about. The aluminum I use is 6061. I'm not saying you are wrong. It s just that I have never seen this phenomenon in any of the cylinders i have reamed.

 

[Mainer]

I would probably ream with a spiral flute reamer and possibly lap the bore slightly if the finish needed improving.

 

[RManley]

Hi Brian,

The great things about this hobby is that there are so many ways of doing things and im sure that both methods would work well. I was only suggesting that boring may be a better option as Optimus called his lathe 'wee' making me think of something that may have trouble holding something as large as a 3/4" reamer solidly enough, an assumption on my part.
In the UK we had a company making 5" gauge steam loco kits called Winson. One day a member came into the clubhouse to show us the axle pump that didnt pump any water under pressure. Taking it apart we found that the bore had been reemed to size. The rifling patters made by the reamer was so large that water was getting past the 'o' ring! That put me off reaming anything important. That could be down to worn tools etc. I just dont know.

Usual disclaimer, its what I've seen so it's what I avoid.

Rob.

 

[kvom]

My CNC class made a score of these engines as part of our class project. Even boring on a commercial CNC lathe didn't result in a sufficiently frictionless bore, and all the engines had to be honed to get them to run. We also used graphite powder as lubrication.

I have a 3/4" reamer that I used to ream axle holes for my locomotive. It's a quite hefty tool, and doesn't leave any marks. Run it at half the RPM and twice the speed of drilling, with cutting fluid. Since it's easier to fit the piston to the bore than the reverse, I'd suggest leaving 1/32" and then reaming. If there's a pattern left, bore it out a bit more. Then hone.

[ame]http://www.youtube.com/watch?v=_aU2Xhlp4dc[/ame]