Adapting micrometer reamer stop for throaters?

[tobnpr]

In lieu of buying Uni-Throaters, I'm thinking about using the micrometer reamer stop to hold the throating reamer (with an adapter/bushing for the 1/4" throater).

My concern is that there's no alignment for the ass end of the reamer, so this would rely entirely on the properly fit pilot in the bore for alignment. Given that the end of the reamer that's doing the cutting is right against the pilot- and it will be done as part of the original setup in the lathe with the floating holder, should be fine? Or, not...?

 

[ridgeway]

UNI Throater or a throating reamer? Two different tools. UNI throater has a guide the centers the reamer when inserted along with a bushing. The shank is threaded to be used as a depth stop. Now a throat reamer, you will definitely need to devise a stop of some sort...

 

[tobnpr]

I think you misread my post.

I'm aware of the Uni-Throater setup- I was speaking about using a chambering reamer micrometer stop (I use the P.O. Ackley), adapted to fit the smaller shank of throating reamers.

The difference you mentioned- the guide that centers the throater- would be lacking. But I gotta wonder if that would make much difference.
Unlike a chambering reamer cutting along its full length, the throater cuts only at the end right behind the pilot. If I'm using a pilot with just a couple tenths clearance I don't see how the cutter right behind it can be anything other than correctly aligned regardless of whether the back is rigidly centered in the chamber.

Surely, someone's done this before...

 

[Dusty Stevens]

You dont think if the back of that throating reamer, say 2” away from the pilot at best, is just say off center by .002 wouldnt cut too big at the end of the cutting area at the neck? Imagine this: Put it in a vise at the pilot area (which is more rigid than the tightest pilot you could use) then push on it 2” away and see with a dial indicator how far you can bend it

 

[ridgeway]

I use a UNI throater alot and have my way of measuring for depth of cut. I simply hold the reamer in a homemade t handle, lube the reamer and hit the jog while pushing reamer in by hand. Done. 30 second job that is simple. My way works well for me...im sure you can make other methods work just as well.

I thought about making a new sleeve to match my chambers and do away with the universal sleeve on the UNI throater...

 

[tobnpr]

You dont think if the back of that throating reamer, say 2” away from the pilot at best, is just say off center by .002 wouldnt cut too big at the end of the cutting area at the neck? Imagine this: Put it in a vise at the pilot area (which is more rigid than the tightest pilot you could use) then push on it 2” away and see with a dial indicator how far you can bend it

I understand the ass end of the reamer will exaggerate any movement at the pilot.
It's how much the reamer moves directly behind the pilot- that leading edge is the only part that cuts. I could probably machine a cone-shaped bushing to self-center the back end, but I believe that any movement directly behind the pilot will be limited to the "play" in the pilot- which is tenths.

 

[Walt Krafft]

I make collars to fit the chamber to support and and guide the throater. I also made 2 collars that slide on the shank. I place the reamer in the chamber where it is just touching the existing throat. Slide one collar up against the barrel and tighten. I then use feeler gages or gage blocks the thickness I want to cut the throat deeper, to space the second collar behind the first. Tighten the second collar. Slide the first collar back to the second and cut the throat.

 

[tobnpr]

I make collars to fit the chamber to support and and guide the throater.

Do you use a tapered/cone shaped "universal" type- or turn a different ones to fit whatever chamber you're working on?

 

[Dusty Stevens]

I understand the ass end of the reamer will exaggerate any movement at the pilot.
It's how much the reamer moves directly behind the pilot- that leading edge is the only part that cuts. I could probably machine a cone-shaped bushing to self-center the back end, but I believe that any movement directly behind the pilot will be limited to the "play" in the pilot- which is tenths.

Just say the cutting area is .150 long, it may not move much right behind the pilot but at the part back by the neck (which will be cutting because its bigger than the front up by the pilot, right?) its going to cut bigger. This is why there is a uni throater to keep the back centered up.

 

[tobnpr]

In looking at the design of the Uni-Throater, the bushing/"stop" sleeve looks to be designed to seat on the shoulder datum of the chamber, and it also functions as the positive "stop" against which the depth control nut seats.

Given that a 6.5 could be a 6.5 Grendel, or a 6.5 STW- there's differences in shoulder angles as well as datum diameter (.350? .400? .420?) so the bushing provides support/centering at the shoulder and none at the back end of the chamber.

I need to figure out how to bush this area to center the reamer while using the back of the tenon and micrometer stop to control depth.