Dovetail Slot Trouble

[JCurtiss]

I filed what I thought was a perfect, first-time dovetail.

I filed the base flat and parallel with the top flat on the barrel. I used my home-made triangle file with one side smooth to cut the 45-degree mortises at the ends of the slot.  

I used a brass punch and gently tapped in the rear sight.

Perfect; so I drank a Guinness in celebration of a job well done, or so I thought.

As you can see in the last picture below, there is a gap between the base of the slot and the bottom of the sight.  It seems that when filling the 60-degree mortises, the corners were not as sharp as the should be.  In fact, instead of a corner I ended up with a small fillet.  So the sight tended to ride up to center of the fillet when I installed it, leaving a gap between it and the base of the barrel.    

So how do I correct this problem next time? Perhaps slightly round the edges of the sight in an effort to match the fillets in the dovetail?  Or,...?

Thanks,

Jason







   

[David R. Pennington]

I would take a brass drift and knock the sight down in the middle to fill the gap then do the same on top of the barrel to tighten the dovetails up if needed.
Grind the safe side on your file till you get sharp corners. Take a little off the sharp corners of the sight to match your dovetail.

[David Rase]

Curtiss,
You pretty much answered your own question.  You will always end up with a slight radius in the corners of the dovetails.  To compensate for this you must break the edges of the dovetails on the sight base.  Also, as Dave R stated, file a safe side on your triangular file.  I do  mine on my belt sander.  The last one I saved took about a day to do.  I would sand a bit until the file got warm to the touch and then go about my business in the shop for a while.  I would then come back and hit the file again with the sander, let it sit, you get the idea.  You need to continue sanding until you get as sharp an edge as possible on the edges of BOTH safe corner sedges.

If everything is filed FLAT and you experience a gap, it is normally because the sight bowed.  This bowing is usually caused from the sight being too tight due to not breaking the corners on the sight base.

David

[JCurtiss]

David and David,

Thank you for the advice. 

This first gun is certainly going to have its fair share of rookie mistakes. 

Best,

Jason

[gunmaker]

I use a chisel, flat on bottom and 45 deg. top a few hits with a small hammer cuts a good dovetail without the rounded corners.
 Practice on scrap and go for it....Tom

[D. Taylor Sapergia]

Jason:  your dovetail isn't too bad, especially for your first.  Take the advice given above, and grind the safe side of the triangular file until the edges are sharp, with no roundness at all.  Your dovetail is almost perfect on the left side of the barrel, and has dips in the corners on the right side.  Filing FLAT is something that requires concentrated attention.  I use a felt pen to make the angled flats on both sides black, and mark the depth of the rectangular cut with a Vernier's calipers; on a rear sight like yours, .030".  Then when I'm sawing and filing out the metal, I am careful not to lose that scribed line.  Breaking the edges of the sights male dovetail, and or using a graver to cut a sharp inside corner, is necessary before you try to drive your sight into the dovetail.

Keep practicing...you'll do fine.

[Tim Crosby]

 FWIW; the slot looks a little deep to me, maybe file the site base thinner. Also I wait until all the shaping is done before the sights go on, saves hands and tools. Even with the sights out the corners of the Dovetails can do some damage.

  Tim C. 

[Mark Elliott]

Personally,  I think you did as well as most of us do most of the time.   You just needed to punch the sight down and then the barrel along the edges of the dovetail. 

 I only file the dovetail with my sight base file until the sight starts to go in the slot.  Then I use a specially ground cold chisel to lift the edges of the dovetail slot.  I slide the sight in the now very loose slot and proceed to punch down the edges of the dovetail and alternately the center of the sight to get everything flat in the slot and nice and tight.   
 

[Frank]

Personally,  I think you did as well as most of us do most of the time.   You just needed to punch the sight down and then the barrel along the edges of the dovetail. 

 I only file the dovetail with my sight base file until the sight starts to go in the slot.  Then I use a specially ground cold chisel to lift the edges of the dovetail slot.  I slide the sight in the now very loose slot and proceed to punch down the edges of the dovetail and alternately the center of the sight to get everything flat in the slot and nice and tight.   
 

Mark, Can you show us the grind on that cold chisel? I seem to have much of the same problems as Jason.

[smylee grouch]

A few years ago a friend called me one evening to ask about the gap under his rear sight. He cut it deep enough so you could see some light under it in the dovetail. He brought it in and we took the sight out and tinned the bottom of the sight with soft solder, tapped it back in and no light could be seen.  I think the above advice would be a better fix but the solder filled up the hole and was a fast fix and not really unsightly, no pun intended.

[Pete G.]

If you intend to brown the barrel that slight gap will all but disappear.

[David Rase]

Personally,  I think you did as well as most of us do most of the time.   You just needed to punch the sight down and then the barrel along the edges of the dovetail. 

 I only file the dovetail with my sight base file until the sight starts to go in the slot.  Then I use a specially ground cold chisel to lift the edges of the dovetail slot.  I slide the sight in the now very loose slot and proceed to punch down the edges of the dovetail and alternately the center of the sight to get everything flat in the slot and nice and tight.   
 

Mark, Can you show us the grind on that cold chisel? I seem to have much of the same problems as Jason.

I have a 5/16" cape chisel that I ground a 60 degree angle on for upsetting dovetails as Mark described.  A cape chisel is used for keyways in the machinist's trade.  Here is a link for those of you unfamiliar with the term cape chisel.   http://www.armstrongtools.com/striking-and-struck/punches-and-chisels/armstrong-70-397-cape-chisel-5-16-x-1-2-x-6-1-4.html  I like the feel of a cape chisel better than a cold chisel.
David

[JCurtiss]

Thank you for all the tips and recommendations guys. 

I think I over invested in a particular outcome that I simply will not be able to realize on my first rifle. But on the next one I should be able to avoid the mistakes made on the first; the end result should be a first-rate product.

[Mark Elliott]

Here is a photo of the tip of my dovetail raising chisel.   It is ground to slightly raise the side of the dovetails from 45 degrees.    The long flat sits in the bottom of the dovetail slot. 

[Mark Elliott]

Thank you for all the tips and recommendations guys. 

I think I over invested in a particular outcome that I simply will not be able to realize on my first rifle. But on the next one I should be able to avoid the mistakes made on the first; the end result should be a first-rate product.

I hate to tell you this, but it is going to take a lot more than one rifle and there will still be lots of little mistakes.   There is on even the best of rifles if you look close enough.   It reminds me of a funny story I wish I could repeat, but the well known maker in question is sensitive about such things.   Just be aware that such imperfections happen to the very best of us.   We just get better at covering them up.

[sqrldog]

Well said Mark.

[D. Taylor Sapergia]

Oh yeah!!

[hudson]

I am thinking clean up the corners of the dovetail. Now looking at the sight I would set it on a solid flat surface and using a tool ground to fit one of the cross groves in the sight try to upset an hopefully lengthen it, probably should do this first. Finley clean up the sight with file and sand paper. By the way do we mean.30 degrees not 45?

[Cory Joe Stewart]

Here is a photo of the tip of my dovetail raising chisel.   It is ground to slightly raise the side of the dovetails from 45 degrees.    The long flat sits in the bottom of the dovetail slot. 

Thanks for sharing Mr. Elliot.

Coryjoe

[David Rase]

Here is a photo of the tip of my dovetail raising chisel.   It is ground to slightly raise the side of the dovetails from 45 degrees.    The long flat sits in the bottom of the dovetail slot. 

Good picture of a cape chisel ground for upsetting dovetail slots.  Mine looks surprisingly similar.  I was just too lazy to post a picture!
David

[L. Akers]

I get this rise in the angles even with a file with a safe edge. I just watch my progress and when I see the rise appearing I flip the file so that the safe edge is against the upper surface of the angle and carefully file the bottom of the angle until it's back where it belongs, flip the file so the safe edge is on the bottom and continue.  I have also used only a chisel to raise the angles.

[rich pierce]

By the way do we mean.30 degrees not 45?

I think 60 degrees.  An equilateral triangle has 60 degree angles.

[smallpatch]

Something that is very helpful. 
Brownells sells a dovetail file which has 2 safe sides and only 1 cutting side.  The sides are straight, not tapered, and the edges are VERY sharp.  Keeps those corners a little sharper and straighter.

[Acer Saccharum]

A sixty deg would be matching a triangular file. Mark's chisel appears more than 60 deg, but so what? 

The chisel opens up the dovetails, pushes up the metal on either side of the cut. So just tap the metal BACK DOWN after you've fitted the sight.

Metal moves around at your command, not like wood, which is a more delicate material.

[Mark Elliott]

Just for the record,  I should have said 60 degrees.  My chisel is more than that.  I just eyeball these things.