Very slightly enlarging a hole?

Z

zondar

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Hello Forum Members,

I need to plan for a way to very slightly enlarge a hole. By very slightly I mean about 0.0001 at a time.

I'm trying to create a tight sliding fit part in brass on a 0.25" steel rod (nominal). The rod is reasonably well-dimensioned after a lot of hand work, but not perfect.

I have tried reamers in 0.250 and 0.251. The 0.25 is slightly too tight (it binds), and 0.251 is slightly too loose (it slides smoothly but rocks ever so slightly). I could buy yet more reamers, though I'd rather not if there are other options that are more generally useful.

What tool (a hone maybe, assuming one would fit?) or other method can evenly expand a hole very slightly?

Thank you.
 
Why not fit the rod to the hole ? Sounds easier than the opposite to me . But , you can get a burnishing tool . Matter of fact , I have one but for doing 1/4" rod and not a hole .
 
I take a piece of wood about that size, and put lapping compound on it, and run it in a drill.
Or you can use very fine diamond paste.
For that little bit, I am betting that even metal polish will work.
you can run it in the drill or by hand, or a hand drill. if you get the wood too far undersized, wet it a little at a time.
 
mmcmdl said:
Why not fit the rod to the hole ? Sounds easier than the opposite to me . But , you can get a burnishing tool . Matter of fact , I have one but for doing 1/4" rod and not a hole .
Click to expand...

The rod is 36" long. Yes, I could try to take off material a little at a time, starting from one end, and fitting the brass part as I go. The brass part doesn't have to slide down the whole length, even, maybe just the first 12-18".

Looking around, I see there are "precise-fit lap" tools available, which are expandable and intended to use with lapping paste. There are also "lapping sticks" available - pre-made wooden dowels - per the suggestion above. These look like solutions too.

I should carefully map out the rod's diameter across it to see how much deviation there is. That might be the deciding factor in which way to go.

Many thanks.
 
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Lapping is probably what you need to do as Woodchucker mentioned above.
You can take a wooden stick and attach a piece of fine abrasive paper then twirl it in the hole either by hand or power (drill)
Use some oil to get a smoother finish
Check fit frequently
-M
 
@zondar

My guess is that you should be asking how to lap the rod so it is round and consistent diameter for the length required.

You say the rod is nominally 1/4" diameter but I didn't see how long the hole is (length of engagement)?
 
Yes, I was thinking that I should map the diameter of the rod across its length, as if it's uneven, any hole would be too large or small at some point along it.

After a quick look, it's typically about 0.2506" diameter, with deviation from that of about -0.0001 to +0.0002.

With the brass I have on hand, the hole would be about 7/8" long.
 
Lapping may not be the best idea for a soft metal such as brass, as the abrasive is liable to embed in the brass, causing future wear to the rod.
 
benmychree said:
Lapping may not be the best idea for a soft metal such as brass, as the abrasive is liable to embed in the brass, causing future wear to the rod.
Click to expand...
I see there are special "soft" lapping compounds that purportedly do not embed particles in soft metals.
 
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