Lapping a small bore

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Dick_Morris
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Re: Lapping a small bore

Post by Dick_Morris »

thin wall brass tube
Brass isn't that good for a bearing surface, and I wouldn't use it for something that would get a lot of use. However, in this application I agree with Bill. It's a good choice and probably a far site better than aluminum.

About 50 years ago John Matlock sold books, tools, model engineering casting sets, and survivalist supplies. He sold a die cast cylinder of about 3/8" or 1/2" bore with the steam ports cast in, but not any other parts or prints. I ran across a couple of them a few days ago. Another project that never quite got off of the ground. :(
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Greg_Lewis
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Re: Lapping a small bore

Post by Greg_Lewis »

Bill Shields wrote: Fri Sep 16, 2022 10:43 pm You could always bore it slightly oversize and slide in a piece of thin wall brass tube with the desired ID.

I have never really liked aluminum in this application.

A bit of loctite and off to the races.. :mrgreen:

That's an interesting idea. As you can see in the photo, there is plenty of meat in the casting for an insert. The plans call for Teflon piston rings, so something like that just might be the answer.
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Bill Shields
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Re: Lapping a small bore

Post by Bill Shields »

Even a blind pig....
Too many things going on to bother listing them.
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Fender
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Re: Lapping a small bore

Post by Fender »

rmac wrote: Fri Sep 16, 2022 6:16 pm
Fender wrote: When you tighten the screw in stages, the rubber washers will gradually expand the copper tube
Really? Does the tube have to be slit lengthwise for this to work?

-- Russell Mac
No, the copper is soft enough to “bulge” from the internal pressure from the rubber washers, without a slit.
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milwiron
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Re: Lapping a small bore

Post by milwiron »

I'd also be very tempted to sleeve it especially if the aluminum is dead soft.
"Measure twice, curse once."
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Greg_Lewis
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Re: Lapping a small bore

Post by Greg_Lewis »

milwiron wrote: Sat Sep 17, 2022 4:27 am I'd also be very tempted to sleeve it especially if the aluminum is dead soft.

I have no idea as to the alloy but it machines very well. It isn't at all sticky like some al.
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Eyeball Engineering — Home of the dull toolbit.
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rmac
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Re: Lapping a small bore

Post by rmac »

Fender wrote: Sat Sep 17, 2022 4:18 am
rmac wrote: Fri Sep 16, 2022 6:16 pm
Fender wrote: When you tighten the screw in stages, the rubber washers will gradually expand the copper tube
Really? Does the tube have to be slit lengthwise for this to work?

-- Russell Mac
No, the copper is soft enough to “bulge” from the internal pressure from the rubber washers, without a slit.
Live and learn! I wouldn't have thought that in a million years. Thanks.

-- Russell Mac
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Greg_Lewis
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Re: Lapping a small bore

Post by Greg_Lewis »

Here's a link to this little PM Research wobbler. It's highly unlikely that mine would ever run on steam; it will probably spend most of its time on the shelf with a few runs on air to entertain the kids (and perhaps the grampa :) ).
https://www.pmmodelengines.com/shop/ste ... -engine-2/
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
theg8nw
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Re: Lapping a small bore

Post by theg8nw »

Burnish it in. A small bearing on the end of a rod is all you need. It works done it many times.

Check this out. https://matmatch.com/learn/process/burnishing
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SteveM
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Re: Lapping a small bore

Post by SteveM »

I picked up an engine like that at a flea market for cheap.

Cylinder was bored very rough.

I also don't like the idea of aluminum, so I was considering sleeving it as well.

Steve
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Greg_Lewis
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Re: Lapping a small bore

Post by Greg_Lewis »

The idea of burnishing is interesting. Being aluminum this shouldn't be too difficult. I don't think this bore has to be super accurate, but smooth is certainly better. As I wrote above, the tool marks are almost invisible, but since I'm just playing with it I'd like to see how much better I can get it. Worst case is that said technique fails and I bore it oversize and sleeve it.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
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Greg_Lewis
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Re: Lapping a small bore

Post by Greg_Lewis »

Hi folks. Here's the end of the story, and some of you will be aghast at what I've done.

Remember that the goal of this was to keep the expense to a minimum. As Jack says, "Go with what you've got." This little toy (though all of what we do are toys) will only run on air and then perhaps not more than a few dozen times.

I found a spiral flute reamer on Ebay for $20, but considering that in some 35 years of, as my sig line says, turning perfectly good metal into bits of useless scrap, I've never needed such a reamer and more than likely will never need one again. So that is set aside.

The steel bearing ball is a great idea, and I found a package of 10 of them on Ebay for about $6 and change. But, again, I'd have to spend six bucks and I'd end up with ten bearing balls that would just sit in my scrap — uh — parts — department until my heirs end up stuck with all the detritus in my shop. And the idea of just tossing them after I'm done with this is heresy.

The idea of burnishing it with a ball bearing is a good one but I was afraid of trying that because the forces I suspect would be required would not be tolerable by my Atlas lathe (a.k.a. The Flexible Flyer).

So I woke up about half past six the other day and while I was lying in bed waiting for the clock to chime seven (I'm retired. I do not get up early.) it dawned on me. If I made up a doohickey sort of like a boring bar, but with a spot on the end that would hold some abrasive paper, I could run that into the bore sort of like a one-legged brake cylinder hone. (You young'uns have probably never seen a brake cylinder hone....)

So below are the pix. The toolmarks from boring all went away and it all worked out fine. The cylinder did end up with a very slight taper, but only .004 (which is only .002 per wall) which is of no consequence in this case. (If it was something Really Important, I think I would have bought the reamer.)
IMG_0423.JPG
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IMG_0427.JPG
IMG_0430.JPG
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
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