For the guys that pre-bore as much of the chamber as possible....
- Thread starter LVLAaron
- Start date
The easiest way to find the angle is set the reamer on centers and set the compound using the angle of the reamer with an indicator.
tac284
Gold $$ Contributor
By case wall, you mean body taper? If so I have set my compound to DMS using the Joe Pie method (you tube) based on the reamer print and then pre-bored the angle with the compound. In the end, I have decided to leave such extravagant exercises to large cases like the Cheytac. Everything else I just straight bore.
I feel the time spent getting the compound angle as perfect as can be just to get the reamer a pinch further in is a wash over just straight boring and getting to reaming.
I feel the time spent getting the compound angle as perfect as can be just to get the reamer a pinch further in is a wash over just straight boring and getting to reaming.
jackieschmidt
Gold $$ Contributor
You need to determine the approx taper of a fired case. Just mic it at the shoulder and base.
Put a straight piece of stock in the lathe sticking out about 4 inches. Set your compound straight with carriage. Run your compound all the way back. Place an indicator stylus on the piece, making sure it is on centerline.
Set the compound at about 1/2 degree. Then run the compound in the length of the cartridge body. If the taper difference is .030, you want .015 difference in the indicator reading. Adjust the compound to read 1/2 the difference in the actual taper of the case.
One note. On really long cases, a taper attachment might be needed, as most small lathe compounds don’t have enough travel. They are usually fine for cases around 308 length.
Put a straight piece of stock in the lathe sticking out about 4 inches. Set your compound straight with carriage. Run your compound all the way back. Place an indicator stylus on the piece, making sure it is on centerline.
Set the compound at about 1/2 degree. Then run the compound in the length of the cartridge body. If the taper difference is .030, you want .015 difference in the indicator reading. Adjust the compound to read 1/2 the difference in the actual taper of the case.
One note. On really long cases, a taper attachment might be needed, as most small lathe compounds don’t have enough travel. They are usually fine for cases around 308 length.
LVLAaron
Gold $$ Contributor
How much do you pre-bore? Meaning, what part of the reamer is making first contact?
LVLAaron
Gold $$ Contributor
That's the "duh" moment I was looking for.
tac284
Gold $$ Contributor
The body. I’m curious, if you did all that what would be your method of driving the reamer?
DShortt
Gold $$ Contributor
I've been confused about this myself.
I only cut my own chambers so reamer wear isn't a problem. But I'm still curious.
I also use a 'floater'. My old lathe has some wear and it's not worth a rebuild just for my uses. I have never cut an oversized or non-concentric chamber, so I'm doing something right.
WSnyder
Silver $$ Contributor
Just pop it (reamer) into the tailstock chuck. I use an Albrecht. It'll get the angle just as well as centers for this purpose. I prefer to step bore with at least three diameters which gives two initial guide supports for the reamer. Easier starts rather than the full grab the taper bore gives you. Pre-drill then bore the smallest dia to near shoulder depth, back out and bore to the next depth, back out and repeat.
Last edited:
That makes sense, Less setup time than setting up on centers. Quick and Dirty!
I think that's what Bruce from BAT does. 3 step parallel bored.
What are you guys using for boring bars and inserts?
I dial on the side of the chuck, or the tailstock quill. Note that the taper given on the drawing is not actually TPI. It is the taper in 20 inches. TPI is 1/20th of the given figure. I like to make the taper just a little greater than actual; to guarantee the shoulder isn't oversize. WH
WSnyder
Silver $$ Contributor
For most std cartridges a Circle (now Widia) 1/4" carbide bar with triangle inserts. I have 1/4", 3/8" and 1/2" Circle bars. They like many things have become very expensive. Back in the day Circle ran promo's including inserts that were very reasonably priced. Thanks to Mike Bryant for originally finding and recommending them. For smaller cartridges like a PPC the little Micro 100 solid carbide bars work great. I'd have to go look at the part number if interested.
I believe this is the equivalent Widia bar to the Circle:
Jonnyofalltrades
Silver $$ Contributor
That's for sure! Wow!
LVLAaron
Gold $$ Contributor
I have several of these. I use polished inserts. Excellent on stainless barrels for pre-bore work, crowns, etc.
LVLAaron
Gold $$ Contributor
Using a chuck makes sense... it's gonna be hard to get the reamer between centers if a barrel is in the chuck
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.