Help in making a tiny bushing

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GlennW
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Re: Help in making a tiny bushing

Post by GlennW »

Something that I hadn't considered is that you may be running the spindle way too slow.

This combined with cutting tools that are not real sharp and the rod sticking out a bit too far from the chuck could cause all sorts of finish and size issues.

With a bushing of that size in brass I'd most likely be running the lathe at its fastest spindle speed.

I can't think of a manual lathe that could possibly turn too fast for a small part such as this.
Glenn

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Conrad_R_Hoffman
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Re: Help in making a tiny bushing

Post by Conrad_R_Hoffman »

I was just making 7 mm long bushings, 0.08" diameter, 0.067" ID. I start with 3/32" low fuming brass welding rod. Why? Had some! Face. Spot. Drill. Turn OD. Cut off.

No real problem, save for being careful not to let the hole wander- sharp drill with equal flutes and frequent lube. The tool was HSS sharpened to a razor edge as described on my site. IMO, that was about as long as one might dare go without support, and longer than many would feel comfortable with. Did 'em at work on the HLV, but it would have gone the same on my Logan.
Conrad

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earlgo
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Re: Help in making a tiny bushing

Post by earlgo »

No-one has yet mentioned that it is possible to use, say 3/8" or 7/16" rod, drill the center and then do the o.d. in 1 deep and 1 very shallow finish pass. The deep pass can be done because the full diameter rod is supporting the cut. The finish pass may or may not be necessary depending...
Something I learned from an old Serbian toolmaker.

--earlgo
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Harold_V
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Re: Help in making a tiny bushing

Post by Harold_V »

I'm going to assume that the situation at hand does not present any problems with how it's held. Either in a good three jaw, a four jaw, or collets.

There's no real need to use larger material. The length of the bushing is well within the three times the diameter in length for machining.

If diameter is critical, it's real dangerous to take a large cut, hoping to hit size. It often results in parts that are not round (deflection between jaws if the chuck is not good), or taper that would have been removed in the finish pass(es).

It's also risky taking a deep cut, followed by a shallow cut. Because tool loading isn't consistent, the second pass generally results in material being removed that one might have hoped remained. That said, I've always taken finish cuts in three passes. One, which is one third the amount of stock remaining, then a second pass of equal depth. Measure, and take the part to size. By following this procedure (which I acknowledge to be slower than other methods), you can generally produce good parts when tolerance is tight.

Harold
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earlgo
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Re: Help in making a tiny bushing

Post by earlgo »

Well that explains why no-one mentioned it.
I'd ask the fellow who used it frequently, and explained it to the rest of us, but unfortunately he is, and will be, unavailable.
Some suggestions are good, some not so much.

--earlgo
Before you do anything, you must do something else first. - Washington's principle.
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Harold_V
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Re: Help in making a tiny bushing

Post by Harold_V »

earlgo-
That method has its place, and can be quite useful. I've used it myself, but only when there are no other options.
When I was running my shop, a test fixture I made for Litton required a half dozen pieces of 5/8" diameter brass with a projecting piece about a half inch long, but only thirty thou in diameter. I was restricted to the 2,000 rpm offered by my Graziano---but making the parts was a piece of cake. I did as you suggested, turning the desired diameter slightly oversized, and taking the cut in only two passes. First one, short, to remove the majority of stock, the second one to take it to size. Repeat until I had the desired length, then I turned to polishing to establish final size and to blend the cuts. Turned out great!

Harold
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Steve S
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Re: Help in making a tiny bushing

Post by Steve S »

Have any pictures of the coupler ? From what I imagine you should be dealing with something like this :

http://losmandy.com/hi-rez-images/MC.jpg

Image

What is the mount your repairing ?
I'm all into the astronomy thing ....

Steve S
Magicniner
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Re: Help in making a tiny bushing

Post by Magicniner »

Steve S wrote:Have any pictures of the coupler ? From what I imagine you should be dealing with something like this :

http://losmandy.com/hi-rez-images/MC.jpg

Image

What is the mount your repairing ?
I'm all into the astronomy thing ....

Steve S
Steve,
I doubt that a spur gear on the end of a flexible coupling is a good idea -
Ramv wrote:Hi,
I am attempting to make a small bushing that has an internal diameter of 3/16" and outer diameter of 6mm. This bushing connects the shaft of a servo motor to a spur gear that drives a worm/wheel arrangement of a telescope.
The coupling will need to be rigid, not flexible,

- Nick
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Harold_V
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Re: Help in making a tiny bushing

Post by Harold_V »

Magicniner wrote:The coupling will need to be rigid, not flexible,
Depends, doesn't it? If both components run in bearings, and are rigid in and of themselves, then it wouldn't matter how they were coupled, assuming the coupling was self centering. If the coupling is expected to carry either of the components, then I'd agree.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Steve S
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Re: Help in making a tiny bushing

Post by Steve S »

So what mount are you working on ?
Curious , no gearbox between the motor and drive ?

Steve
Steve S
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Re: Help in making a tiny bushing

Post by Steve S »

Oppsss , Sorry Magicniner , though you were Ramv .

Most mounts use a gearbox between the servo motor and spur gear . If the coupler is rigid it can cause the tracking to jump . Not as important if the scope is for visual or video astronomy . But awful for long exposures , compound possible by the focal length of the scope .
Just Saying ...
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Pipescs
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Re: Help in making a tiny bushing

Post by Pipescs »

As these guys all say, ditch the carbide and just simply grind a HSS bit. You may have to experiment for best angles

Start with over sized brass solid rod,

Drill and ream to the inside diameter.

Part off the thick walled bushing at this point.

Using Loctite, glue the bushing onto a steel shaft. (the drill shank if you have nothing else).

Chuck up on the steel shaft and turn your bushing to finish diameter.

Remove bushing form bit or shaft with heat.
Charlie Pipes
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