The Home Machinist!

I have a flip up front sight that has a .625 bore. I need to open it up to .700. I have a small boring head I can use, but what is the best way to hold this and align it with my mill spindle? What other ways might I do this?

Thanks X

Exodus wrote:I have a flip up front sight that has a .625 bore. I need to open it up to .700. I have a small boring head I can use, but what is the best way to hold this and align it with my mill spindle? What other ways might I do this?

Thanks X

Have not learned how to edit, add arrows, lines, etc., but.......

First, will enough wall be left after making what is there now thinner by almost 0.040"? Type of material? (not hardened?). Tough part to secure adequately, do you have a spare?

I think I would try clamping a small block of material, maybe 3"X3" similar to the sight's and just thick enough to snugly fit between the two projections through which the barrel passes. Squeeze those 2 projections tightly by clamping them against the block, then hold the assembly in the vise, locate center of the .625" hole visible, center-drill the block, then drill several successively larger holes through the block, stopping with perhaps 39/64" (.609") and finish opening the block and sight out to desired diam. by boring carefully, small cuts, of course.

Just my thoughts. CB&Q

CB&Q,

Not that I have a better way, but why would you not remove the vertical part from the piece that is clamped on the barrel? I agree that based on the pic, it looks like removing 0.075" is going to leave the part awfully thin. Maybe ok in use, but it would make it want to deflect while machining, I would think.

Exodus,

Would it be possible to replicate this instead of modifying it?

I think if it has to be modified, I would consider making a negative of it to clamp it in so that the portion being machined would be supported from the outside. Small passes would still be necessary to keep from grabbing the ever thinning material, but that might work.

Dave

assuming that there is enough material to remove, consider

1> take it apart
2> remove the 'squeeze bolts' and measure the gap
3> make a fixture that puts a piece of material in the gap so that you can SQUEEZE it shut with a bolt to be sure it won't move.
4> clamp down as available - probably through the horizontal bolt hole connecting the two rings.
5> cut carefully and pray.

Need a drawing?

They sell two models. One with .625 bore and one with .750 bore. So there is enough meat to open the .625 version up to .700

Material is supposed to be cast 4140

I already own this so making a new on from scratch seems like a lot more work than necessary.

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I got ya Bill. No drawing needed.

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Thanks guys

are the OD profiles of both models the same?

Bill Shields wrote:are the OD profiles of both models the same?

Yes. The one in the picture is actually the .750 version.

.

see...you didn't tell us that before....

hence all the lecturea about 'too thin'....

go for it

You would be better off to ream it out. To ream it put spacers between the gaps in the slit and tighten the screws and then ream it out.

To hold it and bore it with a mill or lathe would be very hard to keep it from getting loose while machining it.

whateg0 wrote:CB&Q,

Not that I have a better way, but why would you not remove the vertical part from the piece that is clamped on the barrel? I agree that based on the pic, it looks like removing 0.075" is going to leave the part awfully thin. Maybe ok in use, but it would make it want to deflect while machining, I would think.

Dave

Right, Dave, I probably would remove the (sight) part; neglected to mention the fact when picturing some way to hold the rest without causing deflection harmful to it.

CB&Q

OK , Here's my susgestion .
Use a small tin of square shape or make a square from the solid type of cardboard ( not coragated) and tape.
Disassemble the sight , fill all holes and cravases with non-hardening modeling clay . spray pieces with bedding release agent or "Pam" cooking spray . Using bedding compound (I like the gel)Fill the box with the equivalent of no more than 1/3 the depth of the work piece . Insert the desired piece into the box , wait 24 hrs .
The odd shape of the ring will keep it from spinning in the box .
The square box clamps easily in a vise or four jaw chuck . I would opt for the mill over the lathe because of supporting the work piece - it may walk out of the holding block if not properly braced again the direction of the cut if held in a lathe chuck .

Steve S

The part would easily be fixtured off of the slot cut in it for the upper removable part. By bolting the part to the simple fixture with this slot and one additional small clamp, it will align itself in one axis and be easily aligned in the other.

The most difficult part is by far explaining how to do it in print, as it would be a matter of minutes to actually set it up and bore it.

I'd most likely line hone it to final size after boring.