Gunsmithing Anyone pre-bore with the floating reamer holder?

[Wannashootit]

Manual machine....
Anyone using their floating reamer holder to drill/pre-bore?
Even though a pass with a boring bar cleans up the hole, I'm asking myself why I don't make a few adapters for my most common drill bit sizes and use the floating holder. Just like the reamer, allows the drill bit to follow the hole.

I want to absolutely minimize forces trying to shift the barrel given the somewhat tenuous hold on the barrel. Doesn't take much to shift the workpiece a tenth or two. I'll still make a cleanup pass with the boring bar, but just seems like the logical thing to do as with any second op like this.

Just wondering if anyone's doing this...or even thought about it. Gotta love the minutiae

 

[Hateca]

I don’t do pre drilling and or boring any longer. The technique I use to dial in the barrel I found it didn’t same me any time and I found no major difference in my carbide reamer wear and the chambers were always straight. Depending on how you dial in your barrels the drill bit following the bore even with a floating holder can still be crooked. The only true way is boring bar only.

 

[Wannashootit]

^^^
I agree as to chamber accuracy/TIR.
Only recently started to prebore, and when checking runout on one chamber after cutting it- I had nearly a full thou.

Tailstocks are never dead on, and I think that pre-drilling an existing hole created one that was not precisely round and a light skim cut with the boring bar didn't remove it all- and I failed to check it with an indicator before reaming.

Never had an issue before pre-boring, I only chamber a handful or two of barrels a month and use a flush system which has already substantially reduced time and reamer wear as it is. Reamers are like barrels, are like tires, right? I don't need them to last forever, and the prorated cost per barrel is already negligible.

Thanks for the input, food for thought.

 

[Danny1788]

Look into piloted Core drills, I drill with one in a JGS floating holder the pilot helps follow the bore and then I make a light pass with the boring bar to make sure it cut 100% true. Also once that material is removed I always recheck the throat with my long stem DTI

Piloted Core Drills - Pacific Tool and Gauge

 

[lariat]

I’m going to go with Hateca on this. One of the rules I was taught was to never use a drill to make a hole bigger as it can chatter and blow the hole. I have done it and been successful but I have done it and also failed.

We recently did a large run of 40mm tubes out of billet. Drilled and then bored and then reamed. No way I was running the reamer after the drill. Another shop had tried to drill 0.010 under and then chase with a reamer. This went poorly due to drill walking, misalignment, etc.

Even with the PTD drill if you are out of alignment you will have bad results as the floating reamer will only follow the hole. A boring bar imo is the best solution.

 

[1moaoff]

If predrilled on a light set up it may take more than 1 pass to clean and align a hole. Rigid machinery makes this easier.

 

[Rubicon Precision]

I think if I was worried about a drill op moving my workpiece, I’d be looking at a different way to hold my workpiece.

 

[lariat]

I’m not talking about the workpiece moving. I’m talking about the drill flexing or not cutting true during cutting due to misalignment issues, etc. like was stated above, tail stocks are rarely aligned perfectly.

 

[Wannashootit]

I think if I was worried about a drill op moving my workpiece, I’d be looking at a different way to hold my workpiece.

I'm guessing the smaller bit I'd start with, and then incrementally going larger would help. I don't build BR rifles, so I really could care less if the bore is a fraction of a tenth different at the breech than it is at the throat. It was mainly an exercise in trying to save some time. But like I said- even that isn't a big deal to me. Like most here, I'm always eager to try a different approach, to see if it improves results or cuts time measurably.

As I mentioned, I believe the runout was due to cheap HF TiN drill bit, and failure to check after the boring pass to confirm all the runout from drilling had been removed- not from the workpiece shifting- but I can't be sure.

I'm also thinking about ditching the inboard spider and going back to the Buck with heavy copper wire to allow the tube to gimbal.
It can't be denied, that thread "crush" isn't limited to muzzle devices and barrel tenons in this discipline. Need to move the barrel a few tenths? Just torque the fuck out of the screw a little bit more. Plus, brass tips don't really allow the barrel to gimbal freely, but still miles better than holding it rigidly in chuck jaws. Seems logical to me that movement due to the spider screw threads can easily move a workpiece a tenth-or more. Something I can check, when time permits.

This all said, if you've got a way to hold a barrel- and allow it to fully gimbal (I'm not clamping it in the jaws and bending it), without it being a somewhat tenuous setup needing light cuts to prevent shifting- I'm all ears.

Good discussion.

 

[Danny1788]

All steel ball bearing gimbling feet. This has worked well for me for years now. Never had a barrel slip and the setup is rock solid. Got this method from Alex wheeler.

 

[iceng]

I use a similar setup as @Danny1788 and works a treat.

I also regularly check my tailstock for alignment. It might only me 0.02mm out over 150mm, but spend the time to dial it in, and then check with a centre drill and then live centre to confirm.

 

[Wannashootit]

^^^
I remember now seeing that mod posted before.
Grease holding the "shoes" to the bearings, or something else?
Looks like a ball end mill would be use to cut them- how critical is the diameter of the cut to match the barrel? Obviously if it doesn't exactly match the barrel it's only going to contact at the outer edges. Do you have multiple sets, like for 1.2, 1.250, and a few common muzzle diameters or do you find that doesn't affect rigidity of the workholding?

 

[Rubicon Precision]

I'm thinking the female on those cut with a 90* spot drill and it would be better than trying to match the ball, personally.
Also, on the shoes, I think a vee shape would be better than trying to match the barrel diameters. You'd end up with 8 points of "wedge" contact, vs. potentially only 4 very small contact points if the radius is even slightly larger than the barrel. A vee shape would also be better on tapered sections of barrel.

As far as the previous comment about drilling in increments, I personally feel going straight to the largest drill that will still allow a clean up boring pass would be best. A core drill is technically the proper tool to open up an existing hole, but sometimes we use what we have, or make compromises to allow the use of a single tool for multiple applications. I pre-drill all standard bolt face and larger calibers with a 140* 11mm carbide drill. I can't even remember when I changed it last, but I'm sure it has a couple hundred barrels on it. Non-magnum chambers take a single boring pass, and magnums take two or more. I want the body of the chamber to cut like a reamer, and then when it gets there, let the shoulder forward act as a form tool. This nets a really nice and true chamber, and saves miles of cutting on the leade/FB. Yes, the outer edge of the shoulder will wear on the reamer, but if you lose a couple/few tenths on the shoulder diameter, probably NBD. Lose a couple/few tenths in the freebore due to reamer wear, you're going to start having issues. This is a non-issue for most since the reamers typically last indefinitely for the home user.

My guess is something in your setup probably moved after boring, if you ended up with runout in the finish chamber. I would think you'd notice if a boring bar didn't make a full circumference cut.

 

[mudpig]

I've had great luck with brass tips on outboard spider and "L" shaped thin aluminum stock on the jaws holds everything securely. I normally do very little set-up until after pre-bore. Once I've drilled the majority of material away, then I'll dial the bore in measuring with a long reach dial in the "to be" throat area. Then I will use the boring bar to true the hole. I also periodically reconfirm my tailstock trueness at a set torque, so that I know the reamer is true to the chuck/work piece. Seems to work great at keeping things true and minimizes wear to the reamer.

 

[Wannashootit]

Also, on the shoes, I think a vee shape would be better than trying to match the barrel diameters.

Agreed, thanks. No different than a v-block setup in the mill when I think about it... I've got a small 90 degree end mill that would be perfect for the blocks and the female holes on the back side.
Personally, I struggle a bit with boring operations on small holes due to tool deflection. I use a Micro-100 which is razor sharp compared to the carbide turning inserts I use- but I'm thinking I might be better off using a larger bar (I'd need to set above center, but I don't think that would cause an issue) in HSS instead.

Appreciate all the suggestions.

 

[iceng]

I use thick pieces of brass as my soft jaws. I dont put a radius cut or anything in them, and over the years they have a natural bend in them. Replaced them a few times. They will do 1" up to 1.3" no problem.

 

[Danny1788]

Agreed, thanks. No different than a v-block setup in the mill when I think about it... I've got a small 90 degree end mill that would be perfect for the blocks and the female holes on the back side.
Personally, I struggle a bit with boring operations on small holes due to tool deflection. I use a Micro-100 which is razor sharp compared to the carbide turning inserts I use- but I'm thinking I might be better off using a larger bar (I'd need to set above center, but I don't think that would cause an issue) in HSS instead.

Appreciate all the suggestions.

I did not have a mill at the time i made the shoes or i would have cut them in a V shape. They are .750" Radius and hold the barrel shank with 8 contact points evenly. They dont work for small sporter barrels muzzles. I have a 6 jaw set tru that i mainly use now.