Interference Between Lock Mainspring and Barrel

[bluenoser]

I have run into a minor problem with my current build and could use some advice.  There is minor interference between the forward part of the upper leg of the mainspring and the barrel.  I know this is a fairly common issue, but it is the first occurrence for me and I would like to choose the best solution.

The barrel is a swamped Rice VA pattern and the lock is a Chambers colonial Virginia.  The interference extends along about 1" of the the forward end of the upper leg and I believe it includes the bend.  I could either grind off about 1/32" to 1/16" along the upper edge of the spring at a 45 degree angle or I could cut a shallow groove in the barrel.  I have a milling machine, so grooving the barrel would not be a problem.  I think grinding the spring is the way to go, but would like to know what more experienced builders would do.  Although the upper edge of the spring is already somewhat beveled, the area of the bend has been left square edged.  The square edged portion would likely also have to be ground back.
Recommendations?

[heinz]

I would remove metal from the top leaf of the mainspring.  This will have almost zero impab=ct on the performance of the spring.
You will like that lock.  I used one on an early-styled iron mounted rifle. Fairly quick and it sparks like a house fire.  SHoots well even in the rain.

[smart dog]

Hi,
I would grind the spring. The springs on those locks are stronger than they need to be.  I would preserve the nice shape but thin the spring enough to fit keeping the bend nice and square and filing bevels.  By thinning the bend you probably will have to clean up the lower leaf a bit as well as grinding the upper. 

dave

[D. Taylor Sapergia]

I agree with Dave (SD).  Stay away from the bend by filing bevels along the edge of the spring, and a 45 degree angle is appropriate since that is also the angle of the barrel where the contact is happening.  So start your filing just ahead of the bend and use a cylindrical file like a rat tailed file to start the filing.  As Dave has said, you should likely also do the bottom leaf just to ensure that the leaves are balanced.  This filing will have very little impact on the spring's power or performance.  Don't cut into your barrel.

[bluenoser]

Thanks folks - modifying the spring it is.
It only took a few file strokes - probably less than 1/64" - to gain a little clearance.  I did have to extend the bevel all the way to the end of the bend on the upper side.  I don't believe I removed enough material to justify removing material from the lower arm to balance the spring.
Taylor, I thought you might have been drinking your bath water when you suggested using a file  .  I fully expected the spring to be too hard to file and would not have tried filing if you had not made the suggestion.
All is good now.
Thanks again folks

[Bob Roller]

One suggestion about a round file.A cylindrical chain saw file has a finer cut than the rat tail file and is easier to start such a cut with. I beveled all my springs full length on the upper and lower limbs and had no trouble and see nothing dangerous to the spring doing it.
Bob Roller

[Birddog6]

I've had occasion to do this a couple of times. It is a peeve I have with most locks today. If the bolster
1/16" thicker on most locks nobody would have this issue. That being said, filing the mainspring is necessary
at times. When doing so, I always make sure my filing of the spring goes in parallel with the spring. So I would
file it to where I need it, then I would use wet/dry  auto body paper & polish it, while making the polishing
strokes on the spring in parallel with the length.  I've never had one I have worked on in this manner break
later on.  I want to eliminate any cross cut lines or scores cut on the spring. I have always felt leaving a
score or line that was like scribing glass & initiating a weak point. So I always polish the lines out.  Possibly
an waste of time or overkill, but each finds their own lil things they do when building.   

[bluenoser]

The old adage " an ounce of prevention is worth a pound of cure" would seem to apply here.  Finishing up lengthwise MIGHT not gain anything, but it CERTAINLY won't do any harm.  I will purty up the bevel when I strip the lock for polishing and will finish up with lengthwise strokes on wet/dry paper.  I don't believe cross-grain scratches are ever a good thing when it comes to springs.

[Bob Roller]

If there are tool marks ACROSS a mainspring then the possibility of a built in fracture line is there.
There is to much work in making a V shaped spring to gamble with the losing it.
Bob Roller