Johntop
Member
My first post - be gentle and forgive its length.
I see several threads addressing my current pet peeve, eccentric barrels, but none that seem to resolve the problem I experience turning with a mandrel. I guess many folks don't consider it a problem since the pens I see our local "experts" produce are at least as out of round as my earlier attempts, but it still frustrates the heck out of me. I think I share a desire for perfection with a lot of you so I'm hoping for some advice.
I have a workaround that corrects a lot of the problem, but it seems pretty clumsy. The problem I see is that there is quite a bit of slop (say about .003") between the tube ID and the mandrel. I've looked at 4 different "A" mandrels and they are all within less than .001" of .245" Every tube I have put on has at least .002" slop (OK, tolerance). When I mount barrels on the mandrel they naturally seek some stable orientation and it’s obviously not perfectly concentric. Overtightening makes it worse, but there is no way to avoid the issue if the fit isn't perfect.
So when I turn the barrels the resulting product is round, but at least a couple thousandths out of concentric true. Plenty enough to see, much less feel.
So my first workaround (and proof this is an issue) is to reduce the slop by increasing the diameter of my mandrel. This is clumsy, but I simply built up a sheath of CA on a mandrel. I found it necessary to apply multiple thin coats to keep it true, but about 15 applications brought the mandrel diameter up by .0025". Had to then apply a coat of wax to slip the pieces parts on since bushings and tubes are now a tight fit. Tight enough that I also have to ream out the tube ends a little to take the flashing off in order to work them on.
The result is barrels that are almost perfectly concentric. Turning a slimline without a center bushing just for a test, the assembled barrels line up with no visible misalignment and almost not enough to feel as you rotate the mechanism. I'd say true and concentric to within significantly less than .001".
So my questions:
1) Any comments in general? I have not seen anything similar commented on and I'm wondering if I'm really off in the weeds. It sure looks like a lot of people accept a degree of misalignment that I find objectionable however, and I want to get rid of it.
2) Anyone out there who will turn me a set of .248" and .249" mandrels for a reasonable price (my local machine shop wants to take me for a ride for this kind of precision).
3) Is there a better way? I have not tried turning without a mandrel, but I don't want to turn to a bushing in the center for the pens I'm working on now so I don't see how to do without a mandrel in that case anyway.
Thanks in advance for any insight.
I see several threads addressing my current pet peeve, eccentric barrels, but none that seem to resolve the problem I experience turning with a mandrel. I guess many folks don't consider it a problem since the pens I see our local "experts" produce are at least as out of round as my earlier attempts, but it still frustrates the heck out of me. I think I share a desire for perfection with a lot of you so I'm hoping for some advice.
I have a workaround that corrects a lot of the problem, but it seems pretty clumsy. The problem I see is that there is quite a bit of slop (say about .003") between the tube ID and the mandrel. I've looked at 4 different "A" mandrels and they are all within less than .001" of .245" Every tube I have put on has at least .002" slop (OK, tolerance). When I mount barrels on the mandrel they naturally seek some stable orientation and it’s obviously not perfectly concentric. Overtightening makes it worse, but there is no way to avoid the issue if the fit isn't perfect.
So when I turn the barrels the resulting product is round, but at least a couple thousandths out of concentric true. Plenty enough to see, much less feel.
So my first workaround (and proof this is an issue) is to reduce the slop by increasing the diameter of my mandrel. This is clumsy, but I simply built up a sheath of CA on a mandrel. I found it necessary to apply multiple thin coats to keep it true, but about 15 applications brought the mandrel diameter up by .0025". Had to then apply a coat of wax to slip the pieces parts on since bushings and tubes are now a tight fit. Tight enough that I also have to ream out the tube ends a little to take the flashing off in order to work them on.
The result is barrels that are almost perfectly concentric. Turning a slimline without a center bushing just for a test, the assembled barrels line up with no visible misalignment and almost not enough to feel as you rotate the mechanism. I'd say true and concentric to within significantly less than .001".
So my questions:
1) Any comments in general? I have not seen anything similar commented on and I'm wondering if I'm really off in the weeds. It sure looks like a lot of people accept a degree of misalignment that I find objectionable however, and I want to get rid of it.
2) Anyone out there who will turn me a set of .248" and .249" mandrels for a reasonable price (my local machine shop wants to take me for a ride for this kind of precision).
3) Is there a better way? I have not tried turning without a mandrel, but I don't want to turn to a bushing in the center for the pens I'm working on now so I don't see how to do without a mandrel in that case anyway.
Thanks in advance for any insight.