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Drill bit for transfer port

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HI,

I am going to open up the transfer port on my .25 Marauder to 3/16th" and was looking for some advice on the types of drill bits to use. Is a bit for mild steel ok or do I need something special for the barrel, valve and reciever.

Thank you,

Jim

~~~~~~~~~~~~~~

I used a Dremel with a metal bore. Worked well on high speed.
Click to expand...


 
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HI,

I am going to open up the transfer port on my .25 Marauder to 3/16th" and was looking for some advice on the types of drill bits to use. Is a bit for mild steel ok or do I need something special for the barrel, valve and reciever.

Thank you,

Jim
Click to expand...

You might be OK with a high speed steel (HSS) drill for the transfer port. You may want to look into cobalt however, if you need a drill that "retains its strength and hardness while offering more abrasion resistance than HSS" in "applications that generate higher temperatures". 

Also, you might want to start with a Number 13 size bit (.185) before moving up to the the 3/16th inch (.187) bit, if moving up is needed. After all, you can always make the hole a little bigger if needed, rather than trying to make it smaller.

Regardless of whether you use a Dremel tool or other handheld drill motor you might want to look into shorter "screw machine" length drills rather than the typical "jobber" length drills available almost everywhere.

If you're really lucky, someone with real machinist skills will jump in with better advice than mine.

Best wishes.

The other Mark B.


 
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In cuting aluminum you have to use high speed with low feed or the drill bit will hang up in the aluminum. There is a way to sharpen regular drill bits made for steel to cut aluminum or brass without hanging up. You take the sharp edge of the bit and grind it flat 90 degrees to the helix of the bit. I know this sounds crazy but it limits the amount the bit can take off per revolution. The method of drilling a hole gradually bigger is called step drilling. This is done to keep hole in center of the part. As you might of guessed I am a machinist and have been over30 years. Yes I’m old. Kerosine is the preferred lubricant for cutting aluminum.
 
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Thurmond,

Is that the 1/4" O.D. 3/16" I.D. ptfe tubing that amazon sells for like $6 per ft.?

Thanks,

Jim
Click to expand...

I use similar ... yes (some use a rigid nylon) or you can get a pre cut one from any of the tuner / dealers such as Tim Hill, Jefferson State Air Rifles, Dennis Baker etc.

PM me your address and I'll send you a couple of inches of the ptfe.
 
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Addertooth's super duper advice on widening the transfer port on a Marauder .25

Empty your air tube completely. Or put a different way, degas your airgun entirely.

Put one pellet in your magazine, cycle the bolt... this will put a pellet in the bore.

Hold the bolt while pulling the trigger, ride the bolt forward.

Do the steps to remove the barrel (which has a pellet in the bore).

Mark/Note where the skirt of the pellet is at in the bore, this will be the maximum amount you want to round the inside of the bore with a Burr/ball grindstone.

Borrow a buddy's drill press to ensure the hole remains perpendicular to the bore. Align the hole to face straight up, clamp the bore in place. Drill the darn hole slowly. Use the drill-stop feature on the drill press to keep the drill bit from hitting the opposite side of the bore, sometimes a bit will "grab" on the last little bit and yank forward. A drill press stop prevents this. 

Clean up the hole you just made with light use of the burr/ball grindstone.... you want it really smooth.

Radius the hole you just drilled on the inside of the bore with a burr/ball grindstone, make the radius bigger on the side of the port which faces the pellet, if you have the room between the transfer port and the back of the pellet, oval it out a bit (but only on the INSIDE of the bore, not on the outside of the barrel where it meets the transfer port tube which mates it to the output of the valve).

While your barrel is off, do whatever bore maintenance you think you would like to do (JB bore paste, very light lapping, etc). You will have to push the pellet out first, before you polish/clean/lap the bore.

Put your bang bang back together, be sure to get a transfer tube which has the same size hole , as the hole you just drilled. 

If your valve has a tiny port in it (smaller than the drill you just used), consider matching the diameter with your bore transfer port size.

Be prepared to dial back your spring hammer a bit, increasing the port size usually increases power.

Enjoy, or we will all make fun of you for going through all of the effort, and not being happy.




 
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Addertooth's super duper advice on widening the transfer port on a Marauder .25

Empty your air tube completely. Or put a different way, degas your airgun entirely.

Put one pellet in your magazine, cycle the bolt... this will put a pellet in the bore.

Hold the bolt while pulling the trigger, ride the bolt forward.

Do the steps to remove the barrel (which has a pellet in the bore).

Mark/Note where the skirt of the pellet is at in the bore, this will be the maximum amount you want to round the inside of the bore with a Burr/ball grindstone.

Borrow a buddy's drill press to ensure the hole remains perpendicular to the bore. Align the hole to face straight up, clamp the bore in place. Drill the darn hole slowly. Use the drill-stop feature on the drill press to keep the drill bit from hitting the opposite side of the bore, sometimes a bit will "grab" on the last little bit and yank forward. A drill press stop prevents this. 

Clean up the hole you just made with light use of the burr/ball grindstone.... you want it really smooth.

Radius the hole you just drilled on the inside of the bore with a burr/ball grindstone, make the radius bigger on the side of the port which faces the pellet, if you have the room between the transfer port and the back of the pellet, oval it out a bit (but only on the INSIDE of the bore, not on the outside of the barrel where it meets the transfer port tube which mates it to the output of the valve).

While your barrel is off, do whatever bore maintenance you think you would like to do (JB bore paste, very light lapping, etc). You will have to push the pellet out first, before you polish/clean/lap the bore.

Put your bang bang back together, be sure to get a transfer tube which has the same size hole , as the hole you just drilled. 

If your valve has a tiny port in it (smaller than the drill you just used), consider matching the diameter with your bore transfer port size.

Be prepared to dial back your spring hammer a bit, increasing the port size usually increases power.

Enjoy, or we will all make fun of you for going through all of the effort, and not being happy.



Click to expand...

What will this mod do? Sorry new to PCP’s just like to educate myself with all these mods. 
 
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It is possible to drill the port if you have the right tools. But...

It is aluminum, and it does "snatch" badly, so a sharp drill bit is a must. If you can find one, a three-fluted drill bit works best. While you're looking for the drill bit, you might as well order a couple of new transfer ports from Benjamin, because you'll need them. Or, just buy the premade cheap ones from Jefferson State, made out of the "freezer" hose mentioned previously. 
 
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The most critical part of drilling out the holes is protecting the parts that aren't to be drilled (after drill breaks through) and then deburring afterwards. The rest shouldn't be over thought too much. What addertooth stated was pretty spot on advice.



What opening ports does on a PCP is change the amount of air released per shot...as adder stated you'll likely wanna dial hammer spring back some because your valve will breathe a lot more with bigger ports. 

Essentially the closest port size you can SAFELY get to bore is going to be the best for POWER, any porting under that is just a restriction in the system that will eventually open up to your bore size anyhow...Big Ports come at a cost of more finely tuned hammer weight/spring rating combos to get lift+dwell in the region one desires. ES (extreme spread) generally remains tightest when one is within 10% of their peak fps for the valve so bigger ports can and will sacrifice ES at lower powered tunes. So what does that say for port size? Either match it to your power level or take it as far as the dynamics of the system allow and live with a little more ES for efficiency. If you don't know how to figure out what port size is best for what power then, leave that to a tuner or inquire on the forums, as I would happily assist!



Here is an example of what port sizes can do.. All the same rifle, 19.5 barrel, 2950 pressure, .25 cal. You can see the modifier the FPE / solution to the equation requires 1/2 the weight in grains for a pellet, so the 105 FPE would require 52.5 gr and the 59 would require at least 29.5. The last modifier at the end changes between the two results as to it being for pellet/air weight ratio, the more pellet mass the higher this ratio..thus providing more energy to move the pellet itself as opposed to air moving its own self. These are also just approximations..

FULL BORE = 105 FPE

=0.25^2*3.1415/4 * 2950 * 0.25/0.25 * (19.5/24) *0.9



STOCK PORT .14" = 52 FPE 

=0.25^2*3.1415/4 * 2950 * 0.14/0.25 * (19.5/24) *0.8
 
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I plan to put a piece of dowel rod to protect the side of tha barrel away from the hole. If you leave the barrel in the breech and turn it upside down the TP will be in alignment. Also a small round burr will remove most of the metal pushed up by the drill bit. A round bit small enough can go through the hole. Jewellers files can remove the rest. Look at the Lane Regulator video.
 
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