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I have a Pre-64 M70 without a front sight. Working on a project to mount one. What is the easiest way to mark/scribe TDC on a barrel so that the sight is indexed to the action ?

As always, if there is an existing thread, just point me to the link... smile

Thank you !


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Do you have a drill press by chance? If so, if the table is relatively level and rigid, open your drill vise to cradle the barrel or use a vee block if you have one. True your action to dead horizontal on the bottom flat where the guard screw goes in with a good quality level (prove your level by checking the bubble position and swapping the level 180 deg, the bubble should be in exactly the same spot in the sight glass). Take any true flat object, a machined and ground steel rule is ideal, maybe a very thick feeler gauge leaf, place it in a teeter totter position. Chuck a pointy tool, spotting drill or even a small center drill, lower the quill firmly onto the rule, adjusting the barrel and vee block/vise until the rule wants to be level under quill pressure...remove the rule, lower the quill firmly enough to dimple a witness mark, repeat for hole #2. The teeter totter is just as good as dials and DRO's if care is taken.


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Very good advice and instructions. GD

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Originally Posted by flintlocke
Do you have a drill press by chance? If so, if the table is relatively level and rigid, open your drill vise to cradle the barrel or use a vee block if you have one. True your action to dead horizontal on the bottom flat where the guard screw goes in with a good quality level (prove your level by checking the bubble position and swapping the level 180 deg, the bubble should be in exactly the same spot in the sight glass). Take any true flat object, a machined and ground steel rule is ideal, maybe a very thick feeler gauge leaf, place it in a teeter totter position. Chuck a pointy tool, spotting drill or even a small center drill, lower the quill firmly onto the rule, adjusting the barrel and vee block/vise until the rule wants to be level under quill pressure...remove the rule, lower the quill firmly enough to dimple a witness mark, repeat for hole #2. The teeter totter is just as good as dials and DRO's if care is taken.
No drill press. But I get the gist of what you are after. Thank you.


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Originally Posted by Orion2000
No drill press. But I get the gist of what you are after. Thank you.

I'd find myself hard pressed to drill (and tap) a barrel for sights without a drill press or vertical mill. Maybe it's just me. The few barrels that I've dripped and tapped for sights, have been done on a vertical mill with the aid of a Forstner (sp) jig, specifically designed for the purpose.


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The Pre 64s without the machined front ramp have a sweated on ramp. Is that what you are planning on using or a later, screwed on ramp?


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I started tinkering with 3D printers about 18 months ago. Finally picked up one for the house earlier this year. Also picked up a shooter grade Pre-64 300H&H earlier this year that was sans front sight. So, the tinkerer in me kicked in. And I started prototyping a 3D printed full band front sight ramp. Started off with PLA resin. Easy to work with. But not so durable. Bottom picture below is my first cut with ABS resin which is higher temp, UV resistant, more durable. TruGlo 0.078" green bead is fixed on with LocTite 406 adhesive. Once I have the "final" sight ramp, I will use LocTite 406 to mount it to the barrel as well.

No holes will be drilled. If I screw up, the end of the barrel will soak in Acetone for a couple hours until the ABS and adhesive dissolve. Using an NECG Weaver rear peep mounted to the Weaver base that came with the rifle. I still need to: (a) sight in to determine how much to increase or decrease the height of the front sight blade, and (b) start fine tuning my ABS print parameters. I had a nice smooth part with PLA resin with minimal post processing. I still have a ways to go to get the ABS part looking slick like the PLA part. Will see how durable it is this fall... smile

FWIW, I also have the digital inlet created for the barreled action and bottom metal. Goal is to create 3D printed Featherweight stock. However, need to step up my game on 3D design programs. Currently using Tinker CAD. I need to find something more robust to do smooth compound curves. Think action to wrist to butt stock transition. Without breaking the bank...

Meanwhile, I continue to tinker...


[Linked Image]

[Linked Image]


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Originally Posted by Orion2000
I started tinkering with 3D printers about 18 months ago. Finally picked up one for the house earlier this year. Also picked up a shooter grade Pre-64 300H&H earlier this year that was sans front sight. So, the tinkerer in me kicked in. And I started prototyping a 3D printed full band front sight ramp. Started off with PLA resin. Easy to work with. But not so durable. Bottom picture below is my first cut with ABS resin which is higher temp, UV resistant, more durable. TruGlo 0.078" green bead is fixed on with LocTite 406 adhesive. Once I have the "final" sight ramp, I will use LocTite 406 to mount it to the barrel as well.

No holes will be drilled. If I screw up, the end of the barrel will soak in Acetone for a couple hours until the ABS and adhesive dissolve. Using an NECG Weaver rear peep mounted to the Weaver base that came with the rifle. I still need to: (a) sight in to determine how much to increase or decrease the height of the front sight blade, and (b) start fine tuning my ABS print parameters. I had a nice smooth part with PLA resin with minimal post processing. I still have a ways to go to get the ABS part looking slick like the PLA part. Will see how durable it is this fall... smile

FWIW, I also have the digital inlet created for the barreled action and bottom metal. Goal is to create 3D printed Featherweight stock. However, need to step up my game on 3D design programs. Currently using Tinker CAD. I need to find something more robust to do smooth compound curves. Think action to wrist to butt stock transition. Without breaking the bank...

Meanwhile, I continue to tinker...


[Linked Image]

[Linked Image]

That ramp appears to have a poor fit in the tang



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Originally Posted by Jkob
Originally Posted by Orion2000
...
[Linked Image]

That ramp appears to have a poor fit in the tang

Indeed. The part prints vertically. There is a certain amount of warpage as the part gets taller and thinner. I need to figure that out along with smoothing the outside of the part when using ABS.


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Brownells sells or used to sell a simple fixture for finding TDC on a barrel or any round stock.

[Linked Image from imagizer.imageshack.com]
[Linked Image from imagizer.imageshack.com]

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Was going to respond but thought better of it, pay a good smith to do it for you

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Originally Posted by hangunnr
Brownells sells or used to sell a simple fixture for finding TDC on a barrel or any round stock.

[Linked Image from imagizer.imageshack.com]
[Linked Image from imagizer.imageshack.com]

THAT would be exactly the ticket... Unfortunately, I can not find that part number or description on Brownell's website.


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Was kinda surprised to see that they weren’t available any longer.

With your prowess with the 3D printing I would speculate you could make your own with little trouble.

If you want or need any other pictures let me know.

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Last edited by Cabriolet; 09/22/22.

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