I don't prebore, but I think I need to start. Please explain your method of preboring and why you choose this method?
Gunsmithing Preboring ?
- Thread starter Danny1788
- Start date
I prebore because it's faster and I want the bushing to ride in the part of the bore
I aligned to the lathe's center line. I chose this method because it was as simple as I could make it.
1) Tram compound parallel to reamer held between centers.
2) Align 3" of bore beyond what will become throat to lathe center line.
3) Thread barrel and time action.
4) Drill under size.
5) Use carriage to cylinder bore under size.
6) Use compound to taper bore until reamer bushing fully engages bore.
7) Turn on chamber flush and use carriage mounted reamer to chamber.
8) Use gray scotch-brite to hone chamber.
Cheers,
I aligned to the lathe's center line. I chose this method because it was as simple as I could make it.
1) Tram compound parallel to reamer held between centers.
2) Align 3" of bore beyond what will become throat to lathe center line.
3) Thread barrel and time action.
4) Drill under size.
5) Use carriage to cylinder bore under size.
6) Use compound to taper bore until reamer bushing fully engages bore.
7) Turn on chamber flush and use carriage mounted reamer to chamber.
8) Use gray scotch-brite to hone chamber.
Cheers,
Is the taper boring important? Or can a guy drill under size then bore with a boring bar strait out
There's so little body taper for most cartridges, I don't see it making any difference whatsoever. I wouldn't waste my time trying to match the taper on a manual machine. I do taper bore in the CNC because it doesn't take any longer.
Not in my opinion. I have a flood coolant flush system and do the same. I think pre-boring is primarily to save time, and secondarily to save wear and tear on your reamer. Both of these are mitigated quite a bit by using a flush system.
With minor variations, this is what I do.
The primary reason is to let the tooling do what it does best. The single point boring bar cuts a coaxial hole. The reamer follows that hole and fills in the details.
With short action calibers, you can take a big chunk out of the reamer travel with just the cylindrical bore.
Long action chamberings can use the taper to further reduce the reamer travel while still allowing the reamer bushing to start in the bore.
It's pretty near a wash on time for me on my equipment. I'm using a flush system. Decision goes to preboring for a more likely to be coaxial chamber and greatly reduced wear on the throat region of the reamer.
Aren't you loosing the front bearing point of the reamer(the pilot) by preboring? I was under the impression the that the pilot helps keep the reamer aligned on the front side so it doesn't cut at an angle. Also I'm using a floating reamer holder and it seems to me that it could be problematic without another point of contact.
The idea is to set up 2 points that align the reamer as far apart from each other as possible.
The purpose of taper boring isn't to save wear on the body portion of the reamer, that section doesn't remove much material anyway.
The purpose of taper boring is to get the reamer deep enough into the prebore to engage the pilot bushing while reducing the cutting travel of the area just behind the bushing. For the case portion of the reamer, thousandths matter. For the bullet portion, tenth thousandths are a better standard. Similar arguments apply to the surface finish because that section can't be cleaned or roughed up afterwards. The front portion of the reamer cuts for the entire travel of the reamer.
It sets up a situation where the reamer is held in alignment by the bushing, and started in alignment an inch or so back at the shoulder or a little behind it. The back alignment ring gets wide very quickly, and the easiest thing for the reamer to do is stay concentric with it.
I prebore to about 0.1" short of the body length. The prebore for a SnipeTac cartridge is ~2.4". That requires taper boring. Using my DRO it only takes a few passes with the compound to get the reamer to fully engage the pilot bearing.
Cheers,
Cheers,
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I use a flush system already, I just don't prebore. I'm not doing this for a living just for my personal rifles. So I was just trying to start a discussion about if it's a better procedure to make my chambering process better than it already is hahha
I do it to align my chamber with the throat and 2" farther into the bore. This is the only place I use to align the whole chamber end including the tennon threads. I don't want my reamer following the curve in the first couple inches of the bore that will become my chamber. I do the same thing for the crown. I use just inside the end of the barrel and then 2" farther back. I'm looking to get my bullets as straight into the barrel bore as possible and then release it perfectly square from the bore.
Straight shooter this makes perfect sense to me. I do understand what your trying to do.
Know to rattle some feathers does it matter? Because I have used a finish reamer start to finish no preboring, with a through the barrel coolant pump, and have got some great results in terms of chamber dimensions to reamer dimensions and groups on paper! I just want to start a conversation on why you think it's better for only the sole purpose of my knowledge not an argument,
A form tool. That's all a chamber reamer really is. In general machining its considered by many to be the most horrible way to try and accurately define a part feature. The reason is a great deal of cutting surface is in contact with the part which invites all the uglies such as chatter, etc.
The idea of roughing a hole to near finish dimension first is not new. It's been done for years and the primary idea behind it is to mitigate tool wear. A great deal of tool pressure is concentrated at the shoulder of the reamer, which by consequence is the distance furthest away from where you hang onto the thing. Ever watch a tool twist up like a torsion bar on a car? -scary...
One comes to appreciate this a great deal when engaged in production of things like reloading dies made from D2. -Very abrasive and generally not the most forgiving material to poke holes into. Anything you can do to stretch tool life on expensive items such as chambering reamers is worth the effort.
Roughing mitigates a great deal of this challenge.
I went about solving this another way. I have my tools made quite a bit different from most. As a result we can chamber a 308 barrel in about 50 seconds. Using the same kind of tool in a manual machine could very likely result in a killed barrel/tool as it requires a great deal of rigidity that most tail stocks just can't provide.
Just poke your hole under the body shoulder diameter and short of final headspace. Enjoy the longer tool life and shorter overall cycle times. Guns will shoot just fine assuming you follow a few basic fundamentals that have already been etched in stone for decades.
The idea of roughing a hole to near finish dimension first is not new. It's been done for years and the primary idea behind it is to mitigate tool wear. A great deal of tool pressure is concentrated at the shoulder of the reamer, which by consequence is the distance furthest away from where you hang onto the thing. Ever watch a tool twist up like a torsion bar on a car? -scary...
One comes to appreciate this a great deal when engaged in production of things like reloading dies made from D2. -Very abrasive and generally not the most forgiving material to poke holes into. Anything you can do to stretch tool life on expensive items such as chambering reamers is worth the effort.
Roughing mitigates a great deal of this challenge.
I went about solving this another way. I have my tools made quite a bit different from most. As a result we can chamber a 308 barrel in about 50 seconds. Using the same kind of tool in a manual machine could very likely result in a killed barrel/tool as it requires a great deal of rigidity that most tail stocks just can't provide.
Just poke your hole under the body shoulder diameter and short of final headspace. Enjoy the longer tool life and shorter overall cycle times. Guns will shoot just fine assuming you follow a few basic fundamentals that have already been etched in stone for decades.
Chad, I figured you would have figured out fully cnc'd chambers by now. No more reamers. Infinite variations.
Been there, tried it, and all it does is make you hemorrhage a lot of cash on tooling. It's just too much work to try and single point a chamber. If your doing 45's and 9 mils' all day it'd be one thing, but to cut a throat that's worth a turd it's a challenging task the deeper the hole gets. The smaller the caliber, the more expletives you add to the vocabulary.
If I were to really pursue this I'd shitcan the lathe all together. Get a big ass 5 axis and just interpolate both ends. Thread mill the tennon and bore the chamber with an endmill. Then flip 180* and do the other side. Just hard to pencil out almost 7 figures for this kind of job. Then "fat finger" in the upkeep on the machine. It runs about 5-9 percent of the purchase price annually to keep a 5X nice and tight.
I've looked into it. . .lol.
I have not been around very many CNC lathes. The ones i have been around, the smiths are simply using a high pressure flush and then using the reamer to cut the hole chamber. In short order i might add. In real life there isnt anything wrong with using the reamer to cut the entire chamber. Your chamber will probably be a Little fat on the ass end, like most middle age american women. The truth though is that really doesn't hurt anything either. for most people. Brass life might suffer a few reloadings, but there again not a big deal in my opinion. When i first started down this path, i too used the reamer to cut the complete chamber. My barrels shot just fine and even earned a few Hall of fame points in short range Benchrest. I dont use that method anymore as i am a little more picky. These daysI prebore to around .070 short of headspace for most chambers. Works well and no messy high pressure flush system needed. Lee
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