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All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

Piloted Chamber Reamer Tolerances?

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HappyHunter:
After a lot of research on the topic I’m now in the process of making my very first chamber reamer (piloted) for a .177 pellet-shooter project I’m currently working on & was wondering if you more experienced fellas “in-the-know” could clear up a few details for me that I either missed in my search or info wasn’t provided?

1) Do you turn your reamer to the exact final, finished size needed, or do you make it .0005” (+/-) smaller to allow for bore lapping/polishing after cutting with reamer?

2) Should (solid) pilot be sized to just kiss top of lands (i.e-exact fit with bore minor diameter) or would I also make it slightly smaller (.0005”- .001“) to prevent galling of lands? I ‘may’ be able to make it a live pilot w/brass bushing replacing solid pilot if need be, but .177 reamer is already pretty tiny without drilling/tapping end for pilot sleeve.

3) Now this might be a silly question, but I’m new at this & need/want to learn sometime anyways, soooo - how many flutes/cutting edges? Have read that you generally don’t want all your cutting edges to coincide with rifling lands to prevent “train-tracking” (“bump, bump, bump” while reaming). My barrel has 12 lands/grooves, so should I make the reamer with 5 flutes (1 flute always in contact with land), or could I get away with 3 or 6 flutes? I don’t have a spin index so will be using a hex collet block in vice to index flutes, hence the 3 or 6 flute reference. 5 flutes @ 72* apart might be difficult for me to accomplish without a spin index… :o

My apologies for all the questions :-[, just want to make sure I’m going at this the right way & not fubar a $100 barrel!

Thanks for your time & any insight you can offer… :)

rsterne:
You can make a single flute reamer, they work fine, I am currently using 3, and some guys use 6.... I make the pilot at least 0.001" smaller than the lands so that it doesn't damage them.... and the chamber section about 0.001" larger than the groove diameter, to remove them completely.... I use a 1" taper between the sections, but my reamers are for bullets, not pellets, you can probably use a 30-45* leade for pellets.... Here is the cross section I use.... Dimensions are in calibers....



Plunging the end of the mill past the centerline provides the rake on the cutting edge, it is not necessary to clearance the OD of the reamer.... The further you go past the centerline the faster the reamer cuts, but the rougher the cut.... The blue dotted line would be how you would make a single flute reamer.... If you use 6 flutes, you would leave a larger base circle of course.... Here is the one I made for my .257 Monocoque...



The taper for the 1 degree leade starts smaller than the pilot portion, so the reamer doesn't begin cutting until about 1/3 of the way along the flutes, and most of the cutting is done by the time you reach the parallel chamber, which starts about 1/2 way long the flutes.... I use O1 (oil hardening) drill rod, do all the machining and polishing before hardening, then repolish, hone the cutting edge (where the end of the mill cuts only), and then temper to the colour shown (about 1/2 hour in an oven at 480*F)....

I haven't done it, but I understand the best way for non-chattering reamers is to NOT position the flutes at even angles.... ie for a 5 flute reamer, maybe use 68*, 74*, 70*, 76*, 72*.... but cut all of them the same distance past the centerline to get equal rake angles.... I use a Hex collet block for mine....

HTHs....

Bob

HappyHunter:
Thanks, Bob…that is indeed a big help!

I think with my current skill level I may just go with a 3-flute profile this time around using my hex block to index & see how it goes. May try a 6-flute design on something bigger than .177 cal…still have a .22 & .25 barrel to do after this build.

I guess my original design (pics below) for the chamber reamer I drew up for my Cr MKII  project wasn’t too far off the mark then. Although I am going to use a flo-thru bolt probe on this build, I kept the bolt o-ring in the same location as the factory bolt in case I ever decide to go back to factory bolt (however unlikely, but the option is there).

No dimensions to clutter pic, but the rest is drawn to scale & fairly self-explanatory - reamer in yellow, bolt in green, black where o-ring sits.


Reamer, bolt & barrel configuration:

rsterne:
Looks OK.... you may want more compression on the O-ring than just 0.001".... and/or move the 10* taper for it back a bit....

Bob

HappyHunter:

--- Quote from: rsterne on April 15, 2017, 01:44:05 PM ---Plunging the end of the mill past the centerline provides the rake on the cutting edge, it is not necessary to clearance the OD of the reamer....

--- End quote ---

One last query on the topic (I promise! ;))..... I 100% understand what you're saying regarding rake angles with relation to how far past centerline I plunge, but the last part of your statement I quoted in red - does this mean you (I) don't need to cut/grind a small, secondary relief stopping just shy (+/-.010") from cutting edge?

Would be great if that's the case....one less step to mess it up! ;)

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