# Enlarging A Reamed Hole



## FREDROSSE (May 27, 2015)

When building a steam boiler, I had the tubesheets made, which use 1.250 diameter boiler tubes.  The tubesheets came in with the reamed holes exactly 1.250, and I had trouble inserting the boiler tubes, the holes needed to be enlarged by a few thousandths.  My only reamer was 1.250 also, so I put some 0.005 brass shim stock covering only about 1/2 the diameter of the reamer, and ran the reamer thru the 1.250 holes.  Fortunately this worked very well, I was able to enlarge all 96 holes quickly, and then proceed with building the boiler.

Has anyone else made a reamer to cut a slightly larger hole with this method?


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## JimDawson (May 27, 2015)

That is a cool idea, I've never tried it but you can't argue with success!


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## T Bredehoft (May 27, 2015)

One may acquire expansion reamers, turn a screw in the working end and make it bigger.  You've solved your problem, though.


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## ARKnack (May 27, 2015)

I would have thought that the shim stock would have been eaten up when reaming. Good solution.


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## brino (May 27, 2015)

FREDROSSE said:


> My only reamer was 1.250 also, so I put some 0.005 brass shim stock covering only about 1/2 the diameter of the reamer, and ran the reamer thru the 1.250 holes.



Hey FREDROSSE,

Neat on-the-fly technique; I am glad it worked out for you.

To be considered as a go-to technique, could you comment on two points:
What hole size did you end up with? (did it expand by 5 thou?, likely the reamer cut into the shims too...)
Did they remain round?
-brino


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## EmilioG (May 27, 2015)

Cool. Glad it works. May come in handy in a pinch.
What RPM?  Drill press or mill or?
I imagine that the reamer pushed against the shim while cutting, so it must have been slow yes?
How was the shim placed? above the cutting end? below?


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## Ed ke6bnl (May 27, 2015)

do you need to put the tubes int he header and expand them to fit and seal, I have seen that in large boilers at work.


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## f350ca (May 28, 2015)

I've done the same thing a few times, works like a charm.

Greg


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## mike silvia (May 28, 2015)

I've done it a couple times too in a pinch but I used paper


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## Dinosaur Engineer (May 29, 2015)

We used to use matchsticks in the flutes to slightly enlarge reamed holes


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## machinejack (Aug 1, 2015)

Gee I thought I had invented that idea years ago.


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## Line_Bore (Oct 31, 2015)

I've used that trick on smaller holes if I didn't have access to (or time to make) a barrel lap. A cigarette rolling paper works well. 

Sent from my LG-H345 using Tapatalk


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## Vintagengineer (Feb 26, 2019)

This is an old toolmakers trick, very well known in the UK. You can also grind a drill to cut oversize.


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## markba633csi (Feb 26, 2019)

Great idea, I'll have to remember that
Mark


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## Toolmaker51 (Jul 26, 2020)

Shimming a reamer is not unheard of. Brass and soft steel work best, and don't really show mark from reamer. The flutes of a reamer don't so much cut along the length, only the first small portion. Their action is more burnishing of tool marks. They taper away [less] from the tip. 
Normally the shim is cut resembling a iso-triangle. The point, inserted between a pair of flutes holds it in place, the shape allows a gradual increase of diameter without collapsing shim or jamming in hole. Get results by steady feed rate, as the uncovered corner edges produce something like boring.


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