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SparkyLB

Jewel Hole Reamed Too Large

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I recently reamed a hole in a train bridge to .229mm.  I purchased a .230mm jewel and attempted to push it to depth.  I find the reamed hole will let the jewel pass through without a trace of friction.  It enters the top and falls from the bottom.  I measured the reamer on my JKA Feintaster and found it to be .2285mm.  I measured the jewel and it was right on the money.

Being quite inexperienced, I'm wondering what I might have done wrong.  Originally the original rubbed-in jewel was badly cracked, and despite my efforts, I could not straighten out the rubbed portion to use the same sized jewel.  I reamed that hole as above. 

Should one ream only until the tool has done its business and then stop?  I think my repeated attempts to get a nice, clean hole resulted in a nice, clean OVERSIZED hole.  I didn't really have any way to measure the hole I reamed other than to measure the reamer. 

Did I simply go a bit too far whilst reaming? 

 

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How big was the original rubbed in jewel? The material there is minimal, generally you'd ream well oversize to get outside the "rub in" area so there's some substance for the friction fit, unless you have a jewel that's just a hair over original. The reamers can go oversized, we're talking 0.01mm friction fit, best to have plug gages to check (I know nobody has them) or go almost all the way and test.

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5 hours ago, SparkyLB said:

Should one ream only until the tool has done its business and then stop?  I think my repeated attempts to get a nice, clean hole resulted in a nice, clean OVERSIZED hole.  I didn't really have any way to measure the hole I reamed other than to measure the reamer. 

If your jewel falls right through, you must have made beautifully reamed oversized hole indeed..  I assume you used a jeweling set to guarantee uprightness? Any tilt while reaming will enlarge the hole, obviously.

It's too late now to say that you better practice first on a piece of brass or on a junk movement :)    You could measure the resulting hole size with a ~2.3x mm rod with a minute taper turned to it, and measure at the point it binds. If you have a lathe, that is. That's how I do it at least, since I don't have a set of pin/plug gauges.

Maybe you can recover by installing the next size up jewel, if you can get one?

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13 minutes ago, oldhippy said:

When using a reamer always take your time and just a few turns and then test.

I assume you're using the seitz tool? I have a picture from the manual showing how you supposedly use the reamer. As already pointed out by oldhippie and my own personal experience do not follow the example shown in the manual. It is so easy to go past the hole size if you're not careful and end up with a  hole that is too big.

If you have a complete seitz set it should have the hole closing punches.

Then worst-case they also make brass bushings that can be inserted in and then you put the jewel into the bushing.

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13 hours ago, teegee said:

If your jewel falls right through, you must have made beautifully reamed oversized hole indeed..  I assume you used a jeweling set to guarantee uprightness? Any tilt while reaming will enlarge the hole, obviously.

It's too late now to say that you better practice first on a piece of brass or on a junk movement :)    You could measure the resulting hole size with a ~2.3x mm rod with a minute taper turned to it, and measure at the point it binds. If you have a lathe, that is. That's how I do it at least, since I don't have a set of pin/plug gauges.

Maybe you can recover by installing the next size up jewel, if you can get one?

    in this kind of work,  you need the proper measuring tool:pulling-hair-out:      vin

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Hi  That was a bit of bad luck but with any reaming or bushing it is prudent to regulary check the fit. Was it a tapered reamer and from which side did you make the cut. With clocks using a tapered reamer I cut from the inside, the Idea being that when you press in the bush its a tight fit due to the slight taper of the hole. In the case of over boring a clock you can fit an oversize bush and re cut carefully or turn down a blind bush to fit the hole and re drill and ream. This method can be used on watches as well but to be accurate you do need a jeweling tool for the job. There have been plenty of suggestions as to what to do for the best so I wish you all the best which ever method you choose.      Cheers

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Nickelsilver, that's exactly what I did.  I removed just enough material to make a hole leaving no evidence of a previously rubbed in jewel.  I don't know the size of the jewel that came out, as it was shattered.  I did use a seitz jeweling kit.  The stump I used did produce perpendicular planes between reamer and bridge.  The hole was by visual accounts, perpendicular and very clean inside.  There were no impediments to the bridge sitting flat on the stump.  It was a tapered reamer.  The shank is a few thou larger than the business end, and the taper ends in a circular, non-cutting portion of the tool that mic's out to .229mm with the JKA tool.  The jewel measured exactly .230, purchased from seitz for this project.  I made the hole while waiting for the jewel to arrive.  Perhaps the first mistake. 

If I had to guess, the original jewel was perhaps .180mm?  As said above, it would have been wise in retrospect to open a bit, check, repeat.  Sneak up on it as it were. 

It was not a 5-sided reamer, I'm not familiar with the names, but the reamer's cut-out was half the diameter of the shank and progresses to immediately below where the tool is dead on .229mm. 

The seitz kit I have doesn't have hole-closing reamers, but the staking set I have, includes stakes to peen/form the rivet (rounded and open, with the business end round like a doughnut) on the balance staff before flattening out the rivet with the flat open hole stake.  I'll use the former to attempt to open close the hole a bit.  I'll see if I can rectify it that way. 

It was a learning experience.  This was an inexpensive orphaned movement.  If I can't close the hole, I think I'll buy another jewel significantly smaller, I do have a lathe, and see if I can turn a shouldered bush and use that. 

I certainly appreciate all the positive feedback as usual. 

Edited by SparkyLB

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On 2/18/2020 at 2:17 AM, vinn3 said:

    in this kind of work,  you need the proper measuring tool:pulling-hair-out:      vin

Do you mean a pin gauge set? Myeah, I've been looking for one, but no luck. I get by with shallow tapers and ad-hoc gauges, which is not as nice indeed..

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10 hours ago, teegee said:

Do you mean a pin gauge set? Myeah, I've been looking for one, but no luck. I get by with shallow tapers and ad-hoc gauges, which is not as nice indeed..

   yes tool catalog.    you can use spade or some times twist drills.   it's nice have a set of those  anyway.  if  you had a lathe;  you could make " go - no go "  gages.   cheers  vin

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