How do you mill transfer port sealing area ?

K.O. · January 15, 2014, 06:30:19 PM

I have the .25 barrel coming and am confident I can drill the port but am very unsure about the seating area...

I have a 17 inch Delta drill press can I just make an end mill out of a drill bit?

if so is there a right way to grind it..

I am pretty good with wood and no Metal experience.

Thanks

Kirby

ped · January 15, 2014, 07:23:24 PM

easier to buy a proper end mill i mount the barrel in a breech then clamp in the drill vice and center it on the tp hole in the breech then swap to a bit the size of the port i want in the barrel drill it swap to a 7mm endmill and drill the seat
practice on some scrap first
ped

K.O. · January 15, 2014, 08:26:21 PM

Thanks Ped

I need to get both the vice and end mill.

I think the barrel are mild steel?

Is the inexpensive Home depot vise sufficient?

http://www.homedepot.com/p/Irwin-4-in-Drill-Press-Vise-226340/100578950#

ped · January 15, 2014, 09:12:22 PM

as long as you can clamp the breech securely in the vice and the vice can be fastened to the table and once fixed it won't move it will do the job
but practice first is my thoughts
ped

K.O. · January 15, 2014, 10:21:20 PM

Quote from: ped on January 15, 2014, 09:12:22 PM
as long as you can clamp the breech securely in the vice and the vice can be fastened to the table and once fixed it won't move it will do the job
but practice first is my thoughts
ped

"but practice first is my thoughts"

sage advise...

One of my other hobbies is building dulcimers and lap slides I have used nitrocellulose laquer, true oil, and shellac etc for finnish...

each time I practiced on scrap first.

So yep I will repeat it one more time...

"practice on some scrap first"

I do have a 6"section of .177 barrel to practice on.

BillK · January 17, 2014, 05:06:06 AM

I too have a transfer port to put into a .177 barrel. I thought about using a 1/8" drill & a 13/64" end mill. Does this sound right. Also going to practice on an old 760 barrel.

K.O. · January 17, 2014, 05:15:46 AM

.125 might be choking flow a bit above 525-550 fps...

depend on what fps you are going for...

if going for 600-700 I would go closer to .14 if over 700 go .140 wide and oval forward and aft.

BillK · January 17, 2014, 05:58:38 AM

So about 9/64 drill bit and do you think the 13/64 end mill is correct? I have not got the end mill yet and really don't want to buy more than one.

K.O. · January 17, 2014, 07:33:22 AM

Hey Bill I may be messing up I assumed it is a pumper and even then to truly understand valve size and barrel length factor into it port size.

About the end mill well this will be my first time also...

Gippeto · January 19, 2014, 08:00:57 PM

A little late perhaps, but...

For .25 I drill the transfer port using a #19 drill bit. I use a 1/4" end mill to make the flat for the poly tube.

I clean up the flat using a piece of 1/4" rod faced off in the lathe with 400grit peel and stick sandpaper. Stick....trim...sand...repeat until "happy happy".

HTH,

Al

K.O. · January 19, 2014, 08:40:55 PM

Quote from: Gippeto on January 19, 2014, 08:00:57 PM
A little late perhaps, but...

For .25 I drill the transfer port using a #19 drill bit. I use a 1/4" end mill to make the flat for the poly tube.

I clean up the flat using a piece of 1/4" rod faced off in the lathe with 400grit peel and stick sandpaper. Stick....trim...sand...repeat until "happy happy".

HTH,

Al

Not late at all and all hints and tricks appreciated!

Since I will be of limited valve volume (.136 as close as I can tell for now)I figured that I would use as big of a port as possible which I read is .170 or

so the #19 is very close is there a problem with going a little closer using # 18 @ 1695 ?

I plan on ovaling the ends hopefully to about .2 to .21 or so.

The transfer port will be delrin and I am thinking from valve side .220 till about 2/3 the way to the barrel then blended to the oval...

My working theory

Parasitic losses of the big port are dwarfed by the .25 bore so hit it with as big/heavy charge to get it moving as possible, the large bore will drop psi

like a stone...

but real experience trumps cockeyed theory every time in my book so believe me I am all ears...

Gippeto · January 20, 2014, 07:08:36 AM

Easy enough to make it bigger later. IMO...it's big enough.

My first pcp....a scratch built "sort of Discovery type", had a .100" transfer port...string peaked @920fps with 15.9gr JSB...4% cutoff yielded 19 shots on a 2700psi fill. You don't need monster transfer ports to make good power.

Al

K.O. · January 20, 2014, 08:17:28 AM

"Easy enough to make it bigger later. IMO...it's big enough."

I think I will take that advise, it is a lot easier to take more material away than put it back...,

and because of the modular nature of the 13xx design it is not a pain to disassemble and reassemble.

Thanks for bringing that back into focus.