Press fit tolerances

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hebertjo

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Apr 28, 2008
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231
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Phoenix, AZ, USA.
I have read a lot of posts on gent/statesman clips not fitting the finial and cracking due to excessive plating on the fittings. So my question is what amount of interferance makes for a good press fit and how much is too much. I took some measurements on a retro kit I am about to assemble so we can have some numbers to talk about. The clip will not slip over the finial on this kit.

Upper tube ID = 0.4620
Final OD = 0.4660
Center ring OD = 0.4645

Lower tube ID = 0.3790
butt cap OD = 0.3830
nib section OD = 0.3825

Thanks,
 
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CaptG

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Jan 3, 2007
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Otsego, Mi, USA.
I have found that the plating does vary in thickness from kit to kit. Plating is not an exact science and will vary batch to batch. I use a dremal to give a quick grind to the inside of the clip ring until it is a nice fit. I also use the dremal to lightly sand the inside of the tubes so the press fit pieces become a snug slip fit, meaning I can squeeze the parts together with my fingers. They are still snug enough that they will not fall out. I apply a bit of 5 minute epoxy on the inside of the tubes to hold the parts together. I have no problems now with an expensive tru-stone, acrylic blank, or exotic hard wood cracking after all the work and polishing is done because one of the pieces was crooked or too tight because plating was thick or brass tube was on the low limits of the size tolerance.
 

johnnycnc

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Feb 27, 2006
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Location
columbus, IN, USA.
I have read a lot of posts on gent/statesman clips not fitting the finial and cracking due to excessive plating on the fittings. So my question is what amount of interferance makes for a good press fit and how much is too much. I took some measurements on a retro kit I am about to assemble so we can have some numbers to talk about. The clip will not slip over the finial on this kit.

Upper tube ID = 0.4620
Final OD = 0.4660
Center ring OD = 0.4645

Lower tube ID = 0.3790
butt cap OD = 0.3830
nib section OD = 0.3825

Thanks,

I have an opinion, so here you go!:biggrin:
You reference Gent/Statesman, but your numbers and the Retro reference are different. The Gent series is larger.
In my opinion, and from my hands on experience, .001-.002 makes a good press fit.
.003 and up constitutes a condition that makes parts hard to press, and damage more likely. .003 might not be so bad in some cases, but more than that is just asking for problems.
I'll question your tube i.d. measurements, though. Calipers are not the tool for this, it has been discussed before, but in short, the flat on the jaws
throws your measurement off a bit on an inside diameter.
My across the board with those tubes, many sets, has been that they are closer (not exactly..) to .464 and .381 i.d's.
Your center ring o.d. may be misleading, the delrin thread sleeve is often the larger part of that assembly.
The clip not going over the fitting you mention is not uncommon,
there was a big discussion over that inside of the last few months.
And it's the hole in the clip, I believe, not the fitting itself, that has the problem.

My 2 cents worth!:)
 

hebertjo

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Apr 28, 2008
Messages
231
Location
Phoenix, AZ, USA.
Thanks for your opinon johnnycnc less then .003 is a lot less then I would have thought!

How do you measure the ID of the tube if not with calipers?

Thanks,
 

fernhills

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Jan 22, 2007
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2,142
Location
Hellertown, PA, USA.
I have done many Gents, so this is what i do . Squeeze the clip ring on first. As soon as it gets past a certain point it snaps right on. If you grind it it will be to loose, and you will need glue to hold it on. When you pay $35.00 for a kit i don`t think you should augment the parts. Carl
 

johnnycnc

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Feb 27, 2006
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Location
columbus, IN, USA.
Thanks for your opinon johnnycnc less then .003 is a lot less then I would have thought!

How do you measure the ID of the tube if not with calipers?

Thanks,

I use pin gages, they are precision ground cylinders in sets, mine at .0005 increments. The diameter tolerance is .0002 (two tenths) for size of each.:)
And the brass tube expands more than we realize, that can cause problems
with cracking and splitting on fussy materials with rigid glue bonds.
 
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