update: rigid reamer holder

[LVLAaron]

Hundreds of times.

I know YOU have.

 

[Larry Boers]

Are you checking the alignment of the chuck jaws or the alignment of the headstock?

There's a rabbit hole to go down. Since lathe head stocks are aligned with a test bar in the tapper of the spindle there's not even a chuck involved and then add the face plate, chuck and chuck jaws the stack up may not be what you want. Does any of that even matter since you've dialed your barrel to the centerline of your lathe?

 

[DaveTooley]

There's a rabbit hole to go down. Since lathe head stocks are aligned with a test bar in the tapper of the spindle there's not even a chuck involved and then add the face plate, chuck and chuck jaws the stack up may not be what you want. Does any of that even matter since you've dialed your barrel to the centerline of your lathe?

Then if you checked the barrel treads with a thread mic you might find some taper in them. Cause- work piece deflection. And we haven't even seen the bottom of the rabbit hole yet.

 

[Larry Boers]

Then if you checked the barrel treads with a thread mic you might find some taper in them. Cause- work piece deflection. And we haven't even seen the bottom of the rabbit hole yet.

I don't own a thread mic "yet". I do this as a hobby. I have a couple of actions that I do use a tail stock for support when I cut and thread the tenon. Not having a thread mic to check it out I wouldn't know how much taper I have since I don't think there's enough oxygen to waste using wires to check the work in serval places to verify. I simply check the fit with the action.

 

[LVLAaron]

I don't own a thread mic "yet". I do this as a hobby. I have a couple of actions that I do use a tail stock for support when I cut and thread the tenon. Not having a thread mic to check it out I wouldn't know how much taper I have since I don't think there's enough oxygen to waste using wires to check the work in serval places to verify. I simply check the fit with the action.

This isn't as good as using a 10 thou mic, but turn your tenon, and then take the lightest scratch pass you possibly can. If it looks even, alignment is "good enough for the girls I go out with" - If it is uneven, gets deeper or more shallow, etc... you're cuttin a taper.

 

[DaveTooley]

This isn't as good as using a 10 thou mic, but turn your tenon, and then take the lightest scratch pass you possibly can. If it looks even, alignment is "good enough for the girls I go out with" - If it is uneven, gets deeper or more shallow, etc... you're cuttin a taper.

A scratch pass doesn't put a load on the tool like the final pass. But like you said it's good enough. The rabbit hole is deep and wide.

 

[LVLAaron]

A scratch pass doesn't put a load on the tool like the final pass. But like you said it's good enough. The rabbit hole is deep and wide.

For sure. It's definitely not positive confirmation that things are correct, but it can be confirmation that something is bad wrong.

A lathe is the sum of it's parts. They all have to sing the same song at the same time.

 

[Alex Wheeler]

This isn't as good as using a 10 thou mic, but turn your tenon, and then take the lightest scratch pass you possibly can. If it looks even, alignment is "good enough for the girls I go out with" - If it is uneven, gets deeper or more shallow, etc... you're cuttin a taper.

If your cutting a taper, the tenon will be tapered as well so the scratch pass will look even since it's following the same taper. If your cutting a taper just twist the bed until th taper is gone. Or you have the taper you desire.

 

[LVLAaron]

True! The good news is it's a lot easier to measure the tenon vs threads.

 

[DaveTooley]

Just did a 30X2 MM threads. AI large tenon. Deep threads. About 2" outboard of the spider. 1.5" tenon length.
Shoulder side the treads measure 28.544 MM's. Breech side measured 28.567MM ( best guess on the third digit)
A difference of .0009"
No concerns here.

 

[LVLAaron]

Mixing inch and metric, I think you just broke a law.

 

[GenePoole]

I believe AI specifies it with both SAE and metric measurements. Dave probably can't tell us because of NDA.

 

[DaveTooley]

All metric on the drawings.
I just did the conversion to make it simple for everyone.

 

[GenePoole]

All metric on the drawings.
I just did the conversion to make it simple for everyone.

Every one of them I've measured have been 1.5 +- 0.002. That comes out to 38.1 mm which seems odd. I got my info from Josh at PVA through a lot of hinting and wink-wink nudge-nudge. AI is pretty hush-hush about the specs.

 

[DaveTooley]

Every one of them I've measured have been 1.5 +- 0.002. That comes out to 38.1 mm which seems odd. I got my info from Josh at PVA through a lot of hinting and wink-wink nudge-nudge. AI is pretty hush-hush about the specs.

So am I

 

[tobnpr]

There's a rabbit hole to go down. Since lathe head stocks are aligned with a test bar in the tapper of the spindle there's not even a chuck involved and then add the face plate, chuck and chuck jaws the stack up may not be what you want. Does any of that even matter since you've dialed your barrel to the centerline of your lathe?

Nope, unless you're thinking of using a rigid setup.
Tailstock "tilt" is a BFD on older machines where there's been substantial tailstock usage.
Uneven wear (front more) due to sliding pressure and foreign matter on the ways (which is why I wipe down my ways, every day before use and re-oil them). I've shimmed mine and gotten them fairly close to dead nuts at the point on the bed used most often- using an ER collet instead of a chuck so you don't get the inevitable chuck error Dave pointed out.

 

[Ksracer]

Are you checking the alignment of the chuck jaws or the alignment of the headstock?

Spindle= headstock.
I suppose I should have clarified that 2 points on the rod need to be dialed out to "0" and if the rod is straight between them you can travel an indicator down the side and top and bring the headstock into alignment (You also need to account for bar sag on the top and you can cheat the end of the rod towards the tool post if you're worried about deflection). And you need to remove the twist from the bed with a precision level first. Then you can mount a test rod in your tailstock and align the top and side of that with the travel of the carriage. (You should remove the quill and check the test rod/quill assembly for runout.)

Yes, the rabbit hole is deep, but you can do a semi decent job of it in a day. You may find that if your bed is worn, you need to make some compromises. Even if you still need to twist the bed a little to account for wear, at least you're starting from something close instead of twisting the crap out of it.

using an ER collet instead of a chuck so you don't get the inevitable chuck error Dave pointed out

A collet doesn't guarantee anything either. When I said "mount" a test bar in the "chuck" I assumed people would understand that to mean all of the runout was dialed out of the bar, but I guess not.
It doesn't really matter how you get there as long as the bar is true to the spindle axis.

Again, it's a deep rabbit hole and there's many ways to skin a cat.

 

[gunsandgunsmithing]

A 7/16 pin does NOT fit into a 7/16" hole. They are the SAME..NO clearance. Either the pin is small or the hole is big. No ifs ands or buts. Same means just that...SAME. Which means there is no clearance. That's all I'm gonna say on this. It's basic stuff. Granted, any amount of clearance is still clearance and there is NO such thing as perfect, but the claim appears to be that a perfect 7/16'ths pin fits into a perfect 7/16ths hole. This CAN NOT be the case. Everything has tolerances and we can only get as close as humanly possible but the fact remains that two parts of exactly the same size do NOT fit into/over one another.

Otherwise, I can see the benefit of the concept, to some degree. The problem is that the two parts, even perfectly machined, can only be as closely aligned as we can indicate the two to one another. Yes, lathe bed and even temp variances matter when it comes right down to it. IMHO, there is just nothing wrong with using a floating holder as long as a reamer will follow the hole that it's put into. Frankly, this is more accurate than some machines and their operators. Not saying that we can take that to great extremes but if due diligence is given to aligning the actual throat with the axis of the spindle and a floating holder, and a pre-bored hole that is also very true...I'm just not sure that can be practically improved upon.

 

[Greg Y]

I've pre bored and reamed using the dead center to push the reamer and a bald eagle style holder. This is with the tailstock as close as I can muster side to side and allowed the tailstock to sag as it extended.

What I found was that the amount of feedback exhibited by the finished chamber was still under half a thou....did this on my heavy 10 and pm1440.

I'm of the belief that the reamer is more likely to follow the path of the bore than to take a hard right and head south. The amount of feel offered by holding the bald eagle style is worth it. You can feel chatter before it starts.

 

[DaveTooley]

A 7/16 pin does NOT fit into a 7/16" hole. They are the SAME..NO clearance. Either the pin is small or the hole is big. No ifs ands or buts. Same means just that...SAME. Which means there is no clearance. That's all I'm gonna say on this. It's basic stuff. Granted, any amount of clearance is still clearance and there is NO such thing as perfect, but the claim appears to be that a perfect 7/16'ths pin fits into a perfect 7/16ths hole. This CAN NOT be the case. Everything has tolerances and we can only get as close as humanly possible but the fact remains that two parts of exactly the same size do NOT fit into/over one another.

Otherwise, I can see the benefit of the concept, to some degree. The problem is that the two parts, even perfectly machined, can only be as closely aligned as we can indicate the two to one another. Yes, lathe bed and even temp variances matter when it comes right down to it. IMHO, there is just nothing wrong with using a floating holder as long as a reamer will follow the hole that it's put into. Frankly, this is more accurate than some machines and their operators. Not saying that we can take that to great extremes but if due diligence is given to aligning the actual throat with the axis of the spindle and a floating holder, and a pre-bored hole that is also very true...I'm just not sure that can be practically improved upon.

Sometimes the method overcomes/compensates for other issues. Perceived or otherwise.