What's a recommended way to hold a cylindrical printed part in a lathe?

PNW_Guy said:
Printed part?

Can you print a set of soft jaws, with less infill than the original part? The "squishier" soft jaws should adapt to the lathe jaws, but not distort the main part.
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Yeah, that would be possible. I've been printing so much lately due to print failures, I'd like to give it a rest though. Machining is a bit more fun for me, though.
 
Do you have a mill and a rotary table ? That may work better than a lathe. I don’t think in metric. Part is too long and thin. Still think a mill would face off the cylinder easier than a lathe would. Mount the cylinder in a couple of v blocks parallel to the table then mill the face of each end with the side of a long end mill. If set up right the faces will be parallel and 90 degrees to the length of the cylinder.
 
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I think you're on the right track with a sleeve with a slit. Might want a bit of texture to the ID of that sleeve, i.e., something less than a perfect surface finish. Since you're not boring, just facing, I don't see any advantage to a multi-slit arrangement. PETG has a bit of flex. Single slit in a three jaw, using an aluminum sleeve at least 1/2 the length of your part, would be what I would try.

Other possibility would be a 6 jaw chuck for better distribution of force, but that's money, time if you need to buy one, and probably not as good a solution.
 
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Nutfarmer said:
Do you have a mill and a rotary table ? That may work better than a lathe. I don’t think in metric. Part is too long and thin. Still think a mill would face off the cylinder easier than a lathe would. Mount the cylinder in a couple of v blocks parallel to the table then mill the face of each end with the side of a long end mill. If set up right the faces will be parallel and 90 degrees to the length of the cylinder.
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Yes, I have both. Dimensions are roughly 1-5/8"OD x 6-1/2" long. If aluminum, I'd have no problems. You'd think it would center well enough in a lathe chuck, but at least yesterday it wasn't doing it for me. Ordinarily the run out of my 3 jaw chuck is minimal, around 0.003". For some reason the part is slightly tilted in the chuck.

I could hold the part vertical using v blocks in the mill and fly cut the end?
 
rabler said:
I think you're on the right track with a sleeve with a slit. Might want a bit of texture to the ID of that sleeve, i.e., something less than a perfect surface finish. Since you're not boring, just facing, I don't see any advantage to a multi-slit arrangement. PETG has a bit of flex. Single slit in a three jaw, using an aluminum sleeve at least 1/2 the length of your part, would be what I would try.

Other possibility would be a 6 jaw chuck for better distribution of force, but that's money, time if you need to buy one, and probably not as good a solution.
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Don't think I'll buy a 6 jaw just for this, but then again, I'm always looking.

I have a piece of aluminum I could use, guess it was waiting for me to recognize it's purpose. It's been sitting quietly in my aluminum cabinet.

PETG has a bit of give to it and flows under high forces like under narrow part of a chuck jaw. I'll try the split ring. I don't need this perfectly coaxial to the spindle axis, but it should be parallel to the spindle axis (Z).
 
Went down to the shop - new day. This is a job for the 4 jaw. Not because I can't hold the part in the 3 jaw, but because the bore of the 4 jaw chuck is ~ 54mm ID, and the part can be held with the part inside the chuck bore. The bore of the 3 jaw is smaller than the OD of the cylinder. Using the 4 jaw will lessen the amount of stick out. I'm still going to make a split ring though, that will give more contact area. Using the 4 jaw will also allow me to bore straight through the aluminum without worry about chuck contact. At least there's a plan. There's probably an easier way, but for the moment, that's what I'm going to do.
 
I have 3 messed up parts, two of which were basket cases, so I tried again on the 3 jaw on one of the basket cases. I was able to sort of kinda get it with minimal run out. Not going to lie, I didn't measure it, but it was good enough for the experiment. I turned down the blob of PETG on the cylinder wall, and was able to face the end. There still is a large gouge, where the print head jammed into the part as it was falling over. This particular print had enough meat on the end (and 100% infill) so I tried drilling it for a 1/2-20 tap. (29/64") I was able to tap the hole and try out the design. Despite the truncated design (about 1/2" shorter) due to print failure, it worked. Not as well as the longer one, but it did function. I basically saved this basket case part. Kind of messed it up a little, but it was good enough for my test.
PXL_20231120_221310985.jpgPXL_20231120_221240037.jpg
These are printed plastic moderator prototypes for airguns, and I am told are exempt from tax stamps and forms, since they are not to be used on firearms.

I'm doing this from an engineering perspective, trying to understand the acoustics. So I have been trying my hand at designing acoustic filters. Been trying to drag in my former microwave filter theory into the design, as there are remarkable similarities, and it's been interesting journey. Honestly, at this point, haven't found something that wows me. They are much quieter, but not "oh my goodness, that's really quiet". They do take off the edge though, and sound more like pops than reports. I'll play around with some filter concepts, just for the heck of it.

For the good print, (the longer one) I will make a split ring and use the 4 jaw. I'll probably true up all the ends of all my parts once I get a good method going. The threads should not be the reference surface, the back of the part should be flat and parallel with the mating flange. For my system, the mating flange is the reference. The longer part, by the way, has a modified internal design and has a lower pitch. So far it is the best performer, but there's more work that can be done. Once I find what works, I need to shrink it a bit, it's a bit big for my taste. That's when it gets harder.
 
Al seamed tube and plastic baffles seem to work just fine, and keep the AFT away........
 
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