Basic reaming mistake

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seal killer
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Basic reaming mistake

Post by seal killer »

All--

I'm building another small stationary steam engine. I need a reamed hole for a 0.125" piston wrist pin. It doesn't have to be reamed . . . but why not do it anyway?

So I mounted a #31 wire drill (0.120" dia.) and drilled the through-hole. Then I mounted a 0.125" reamer. All went well.

That is until I pulled out my plug gages and checked the diameter: 0.134". Huh. What had I done wrong. I looked at the reamer and it was indeed a 0.125" tool that came from McMaster-Carr. It must have been the drill bit. I must have stuck a larger one in the hole marked #31 at some time, since one box of bits got dumped and I had to reinsert a bunch of wire drill bits. I mic'd the bit. Right on the money.

I couldn't figure it out.

Then I could. When I said "mounted" what I actually did was put the bit and then the reamer in my 1/2" keyless chuck. No good!

As a test, I mounted the #31 drill bit in a collet and remade the hole a little farther down the line on the piece of 5/8" 1018 round stock I am using for the piston. Being somewhat anal (by now), I checked the hole size with a plug gage. 01.20"+ would just fit. Then I reamed it with the 0.125" reamer from McMaster-Carr. A 0.125"+ plug gage just fit but a 0.126"- wouldn't fit.

I've built several of these engines before and didn't experience the problem. Luck. I'll remember that collets are the key.

--Bill
ps I don't ream a lot of holes. But I think I will investigate floating reamers.
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Bill Shields
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Re: Basic reaming mistake

Post by Bill Shields »

Welcome to the world of accurately reamed holes.

It's a bigger problem in a lathe tailstock
Too many things going on to bother listing them.
jcfx
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Re: Basic reaming mistake

Post by jcfx »

Just curious, is it a particular kind of collet that you were using to hold
the #31 drill or were you relying the grip range of the collet to hold the drill bit ?
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seal killer
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Re: Basic reaming mistake

Post by seal killer »

jcfx--

I used this 1/8" R8 collet.
r8.jpg
--Bill
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jcfx
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Re: Basic reaming mistake

Post by jcfx »

Ah-Ha ! grip range, thanks.
Conrad_R_Hoffman
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Re: Basic reaming mistake

Post by Conrad_R_Hoffman »

I'm confused, not an unusual occurrence. I drill and ream using nothing but chucks all the time and never have a problem. Have you checked the runout of your chuck? Reamers are long for a reason. They can deflect a bit to follow the hold, rather than try to redefine the center. Don't chuck them up near the flutes.
Conrad

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Harold_V
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Re: Basic reaming mistake

Post by Harold_V »

Conrad_R_Hoffman wrote: Wed Nov 30, 2022 2:48 pm Don't chuck them up near the flutes.
Yep!
I had started a post on this subject but didn't complete it. Maybe I should have.

Even with a lousy chuck, acceptable results can usually be achieved by gripping the reamer by only the last ¼" or so. That allows the reamer to seek center effortlessly. The long slender shank helps with alignment, so the reamer has less of a tendency to behave as a boring bar.

The same concept applies to the use of a center drill, especially when used in a lathe. By gripping the center drill by a short portion of the shank, assuming the operator allows a reasonable amount of time for the center drill to find center before applying enough pressure to start drilling, the tip of small center drills (#1 or smaller) won't be broken. I often just hand tighten the (keyed) chuck when using a small center drill so there's little resistance to the drill seeking center.

H
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seal killer
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Re: Basic reaming mistake

Post by seal killer »

Conrad and Harold--

Mistake #2: I had a choke hold on that reamer. All of the shank was stuck up in the collet. Thank you for the guidance.

When I reamed holes for the earlier engines, I probably gripped the shank more like it should be held.

--Bill
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