Accurate location of two concentric cylinders
Accurate location of two concentric cylinders
(OP)
I'm in the process of designing a small bar end grinder. The device has two casings: one which holds a gearbox and another which holds the bar to be ground. These could not be machined from one piece of material and so I need a way to fix them together so that they do not move relative to one another (i.e. thread is inappropriate)
I've uploaded pictures of the parts. The outer housing has an outer diameter of 150mm, and an inner diameter of 140mm. These are not fixed but I'd prefer them not to be too much larger for weight saving purposes.
Any suggestions appreciated
I've uploaded pictures of the parts. The outer housing has an outer diameter of 150mm, and an inner diameter of 140mm. These are not fixed but I'd prefer them not to be too much larger for weight saving purposes.
Any suggestions appreciated





RE: Accurate location of two concentric cylinders
RE: Accurate location of two concentric cylinders
How accurate must they be?
How heavy can they be?
RE: Accurate location of two concentric cylinders
RE: Accurate location of two concentric cylinders
The reason for this is that this machine is to be used to grind the surface of a Hopkinson Bar test rig which relies on stress waves to produce data. So if the surface finish is not accurately perpendicular, then the stress waves go crazy and the data becomes unreliable.
And by the way, thanks for the feedback! I really do appreciate it.
RE: Accurate location of two concentric cylinders
RE: Accurate location of two concentric cylinders
RE: Accurate location of two concentric cylinders
I can't picture what that means. I'm picturing concentric cylinders, the centerline (axis) has no angle orientation?
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RE: Accurate location of two concentric cylinders
It might be possible to weld the cylinders and have them fit with a free running fit or a very small press fit that you can tap in with a hammer. You would then place a deep chamfer on the back edges where the two cylinders meet. You could finish it off in a lathe, like I mentioned before, to keep the ID's concentric. I would worry about warping during welding but if it doesn't need to be balanced then you would just need to keep enough on the roughing passes to allow you to finish it on a finishing pass. Is this a one off part or part of a production setup?
RE: Accurate location of two concentric cylinders
Mike Halloran
Pembroke Pines, FL, USA
RE: Accurate location of two concentric cylinders
With either process, you could put sunken reliefs in the thick parts (think egg crate), reduce the weight, and make the machining go faster.
Low volume? Have the investments made direct by SLA, and just burn 'em up.
Mike Halloran
Pembroke Pines, FL, USA
RE: Accurate location of two concentric cylinders
If you think education is expensive, try Ignorance.
- Andy McIntyre
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RE: Accurate location of two concentric cylinders
I am planning to have a press fit but i need some way to ensure that it stays aligned during use. A suggestion I've been given is to taper the two surfaces and then bolt via external flanges. That way they will stay aligned and firmly held in place. However I think my turners may hate me.
What do you think? Any other suggestions welcome and appreciated!
RE: Accurate location of two concentric cylinders
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: Accurate location of two concentric cylinders
RE: Accurate location of two concentric cylinders
I'm still keen for other suggestions though.
RE: Accurate location of two concentric cylinders
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RE: Accurate location of two concentric cylinders
I'm also not seeing the detail that makes it so essential that the part be made in two pieces and then permanently joined. You might ask your 'turners' if they can conjecture a way to make it in one piece.
Mike Halloran
Pembroke Pines, FL, USA
RE: Accurate location of two concentric cylinders
0.5° is not a very precise angle. Based on your picture and assuming the length is around 200mm, your centreing allowance is almost 2mm.
Investing casting from a rapid prototype is very feasible. Welded, heavy gauge sheet metal could work too.
RE: Accurate location of two concentric cylinders
As for why I need to get inside, An offset epicyclic gear is installed in the widest cylinder. The ring gear has a diameter of 120mm, where the overall diameter is 150mm. Installing this ring gear is the problem. Additionally The grinding tool will need to be replaced at some stage so it needs to be disassemblable.
Yes its going to be made of huge chunks of material, but unfortunately little can be done about that and the turners are willing to provide the time (they're just nice people!)
As for locktite: I presume that you use locktite together with a thread. As far as I understand locktite, it increases the friction between the two surfaces preventing the connection from coming loose. I'll do more research on this.
Thanks again guys and keep the ideas flooding!
RE: Accurate location of two concentric cylinders
James Spisich
Design Engineer, CSWP
RE: Accurate location of two concentric cylinders
See info here: http
Ted
RE: Accurate location of two concentric cylinders
I _really_ don't like the idea of disassembling the gearbox housing for a change of abrasives... which guarantees proximity of, and probably contamination with, abrasive grains.
Mike Halloran
Pembroke Pines, FL, USA
RE: Accurate location of two concentric cylinders
The gears are separated from the grinder by a plate. The grey cylinder (in my first image) holds the gearing and is sealed on both sides by a plate. The grinder protrudes from a hole in this plate. The blue cylinder is used to hold the bar stationary and act as a guide during the grinding process, so separating the two cylinders will not cause the gearbox to be exposed.
hydtools: I had a look at that website and, as MikeHalloran mentioned, separating the cylinders after bonding will be tricky.
Jspisich: I like the idea of shear pins! My only concern is that after disassembly it may be tricky to line up the holes again. But that is a minor concern. Thanks!
Keep the ideas coming guys. I really appreciate it!
RE: Accurate location of two concentric cylinders
I'm designing a hopkinson bar and I'd appreciate to share some information about it. Hence, I can't understand the usage of the gearbox you say in hopkinson bar experiment. Could you clear up my mind?
thanks
lfmarini
ITA - Instituto Tecnologico de Aeronautica
SP, Brasil
RE: Accurate location of two concentric cylinders
I can understand why you're confused. I was designing a machine to grind the surfaces of the bars themselves. A hopkinson bar test rig wouldn't require any sort of gearbox.
Sorry to confuse you
RE: Accurate location of two concentric cylinders
http:
What is your material and sizes?
There are numerous companies that can provide you with very precision ground bar stock
http://www.bostoncenterless.com/AccuRod.htm
http://www.dowelspinsshafts.com/catalog2.html
RE: Accurate location of two concentric cylinders
B-Loc high-torque couplings:
h
Trans-Torque
http:
Also have a look at these CMT Maxi-Torque split bushings. These can be used over a key, I believe. We use a keyless one and it works great.
Keep in mind that all the taper-locking couplers have a hard time repeating axial location since they move axially when you clamp them.
If that doesn't work, how about just a cylindrical alignment boss to hold concentricity, then a bolt flange around it? The bolts will hole rotational alignment pretty good.
Beat to fit, paint to match.
RE: Accurate location of two concentric cylinders
http://www.cmtco.com/maxitorque.html
Beat to fit, paint to match.