Donation

All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Chamber Reamers

(1/8) > >>

rsterne:
I started on the Chamber Reamers for my new .172 cal and .224 cal TJs barrels today.... The first step was to turn the pilot and chamber sections, and then next was to turn the 1 deg. taper between them, which actually does the cutting.... Here is the .224 reamer, mounted in my lathe, while I was turning the taper....



The taper starts about 0.010" smaller than the pilot, and the taper runs out to the chamber diameter about 1" behind the nose of the reamer.... The actual cutting occurs in the last half of the taper, just before the chamber portion.... After polishing, I milled the flutes, and the turned down the clearance portion between the back of the chamber and the shank.... Here are the two fully machined reamers, ready for heat treating....



Wow, that .172 cal reamer is REALLY tiny, I hope I don't break it when cutting the chamber....  ::)

Bob

Mark Davis:
What type of steel do you prefer to use for reamers?

Motorhead:
Question for you Bob,

How do you ... or justify what damage is happening to the rifling with the pilot spud being spun against it ?

Are you machine spinning the reamer ? ... or is this a hand job

 Honest Q
Scott

rsterne:
Mark, I use O1 drill rod, which machines nicely.... I then harden by coating with ivory bar soap (helps prevent it turning black), heating to cherry red (until it looses the ability to attract a magnet) with an acetylene torch set to a reducing flame (blue, but a little rich on acetylene), and then quenching in oil.... That makes it glass hard, but very brittle.... I then polish it again, and then hone the cutting edge with a very fine diamond file.... I then temper it in an oven at 480*F for 2 hours, or until I get an even brown colour…. This gives a good balance between keeping a nice edge and the toughness you require for a reamer so that it doesn't break (hopefully)....

Scott, the pilot is 0.002" smaller than the land diameter, all it does is guide the reamer straight down the bore.... You will note that the flutes do not extend into the pilot, it is polished smooth, with rounded corners front and back.... I blow all chaff out of the bore with compressed air from the breech each time I pull out the reamer, which is every 0.100" that I advance it, and re-lube the pilot.... If the reaming is not going easily (the barrel getting warm is a good indicator), I pull the reamer out and clean it and the bore every 0.050".... I run my lathe at 28 RPM with the barrel in the headstock and the reamer in the tailstock, and I have one groove between the flutes on the top to hold oil, and I blow that out and refill it with cutting oil each time I pull the reamer out.... If the reamer is sharpened and cutting properly, a very small pile of "dust" from the cutting collects in the grooves in the reamer where the tapered part is cutting, just in front of the parallel chamber section.... I advance the reamer VERY slowly, about 0.008" at a time (1/12th of a turn of the handwheel), and let the barrel rotate for about 30 seconds before advancing again.... so it takes me quite a long time to cut the chamber, at least 5 minutes for each 0.10".... When I am getting close to the correct depth, I check how deep I can load a bullet without forcing it, and keep going until the base is just past where the front of the barrel port will be located....

I have never seen any sign of damage to the rifling where the pilot has been.... After I get the chamber to the correct depth, I then machine and deburr the barrel port and O-ring groove, and then polish the chamber with some 400 grit paper on a dowel.... Then I use JB Bore Paste and lap the bore about 100 strokes, 50 full length from the breech, and then gradually less travel from the breech, so that the breech ends up with about 100 strokes, lapping in a tapered fashion 100 strokes at the breech, but only 50 at the muzzle.... After cleaning out the bore paste, I then lap 20-50 strokes with JB Bore Brite until the barrel gleams.... then clean it thoroughly before shooting of course....

Bob

Mark Davis:
Thanks for the Information Bob, I'm pretty new to machining but have made a few things from O-1 drill rod.  Some guys post about D-2 and A-7 tool steel, but do not show much finished tools. You actually make and show tools, giving your recommendations weight.

The ivory soap as an air seal is new to me, do you just rub the part on the bar, or wet the soap and paint it on?

Navigation

[0] Message Index

[#] Next page