Help in making a tiny bushing

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John Hasler
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Re: Help in making a tiny bushing

Post by John Hasler »

Pipescs wrote: Chuck up on the steel shaft and turn your bushing to finish diameter.
Use a collet if concentricity is important.
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GlennW
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Re: Help in making a tiny bushing

Post by GlennW »

Turning a .025" wall thickness bushing of those dimensions from brass rod should be no problem at all if the tool bit is anywhere near sharp.

No mandrels needed.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
Ramv
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Re: Help in making a tiny bushing

Post by Ramv »

Thanks all!
I sharpened/honed some HSS tool bits and will try again this weekend. I expect this attempt will prove much more successful.

Regards
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Pipescs
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Re: Help in making a tiny bushing

Post by Pipescs »

Use a collet if concentricity is important.
Oh, yes. Definitly
Charlie Pipes
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GlennW
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Re: Help in making a tiny bushing

Post by GlennW »

Pipescs wrote:
Use a collet if concentricity is important.
Oh, yes. Definitly
Best concentricity is achieved on a lathe when turning the ID and OD without removing the stock/part from the chuck or collet.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
Ramv
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Re: Help in making a tiny bushing

Post by Ramv »

Steve S wrote:
What is the mount your repairing ?
I'm all into the astronomy thing ....

Steve S
Hi Steve, I missed your post completely. It is a takahashi P2Z mount that looks like this
Image

The good thing about this mount is that part of the drive train is exposed. This photo below shows the mount being driven by a swiss Faulhaber motor via a spur gear. Unfortunately that motor burned out (I obviously shorted something) and replaced it with an American pittman servo.
The faulhaber has a shaft of exactly 6mm as does the spur gear central hole. Unfortunately the Pittman is different: 3/16".

Also those ground spur gears are super expensive (over $150 each!). Not to mention metric, so I could not get one with an imperial measurement(those appear to be a lot cheaper) So I had to make a bushing to fit between the spur gear and shaft.

Image
Ramv
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Re: Help in making a tiny bushing

Post by Ramv »

Steve S wrote: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 ...
Yes, this will be exclusively for astrophotography. Some of my photos (using other mounts) are here:
https://www.flickr.com/photos/ramv/albu ... 7136712042
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Harold_V
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Re: Help in making a tiny bushing

Post by Harold_V »

Ramv wrote: So I had to make a bushing to fit between the spur gear and shaft.
All the more reason for you to pay attention to the admonition to make the piece in one setting. Ignore the suggested idea of using a collet, or for any second operation. Neither is required, nor will they yield the degree of precision you can achieve by making the piece in a single operation. Also, reaming the hole is asking for issues. I would not tempt fate if the project was mine. Bore the hole, to ensure roundness and concentricity. Use the existing components as gauges to ensure proper fits, so, when assembled, the gear runs concentric with the shaft.

Making reference to the needed sleeve should not be addressed as it being a coupling. It is not a coupling, it is an adapter, a sleeve.

Just as some readers have a false impression that a Bridgeport mill is the (high) standard by which all mills are judged, so too is the notion that collets present perfect performance. They do not, although they are very convenient, and often do provide a high degree of precision. It would not be the equal of machining a piece in one operation, however, nor should it be expected to be, no more than soft jaws would be. It is not uncommon for collets to introduce not only eccentricity, but a compromise of perpendicularity as well.

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

Post by johnfreese »

Listen to those people telling you to use a SHARP HSS tool.
John Hasler
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Re: Help in making a tiny bushing

Post by John Hasler »

Harold writes:
> Ignore the suggested idea of using a collet

I said "Use a collet" in response to the suggestion that he glue the reamed part to a mandrel and then "chuck it up". Obviously a single setup is to be preferred if it is possible.
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Harold_V
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Re: Help in making a tiny bushing

Post by Harold_V »

John Hasler wrote:Harold writes:
> Ignore the suggested idea of using a collet

I said "Use a collet" in response to the suggestion that he glue the reamed part to a mandrel and then "chuck it up". Obviously a single setup is to be preferred if it is possible.
There was mention of ground gears, which, to me, implies a high degree of precision. Any deviation from true would manifest itself as irregular movement, which may or may not be an issue for the application. However, I can't help but think it would. For that reason, I suggested that a collet for a second operation be avoided, as it is bound to introduce error to some degree. How much would be the question, as would how it might affect the operation of the adapted gear.

In any case, this piece is so simple to make it doesn't warrant any serious consideration. I specialized in small work, did it for years (for gain). I am painfully aware of the problems that can be introduced by simple things--some as simple as too much jaw pressure when closing a chuck or vise. One learns to approach delicate items in the appropriate manner, so problems are avoided. That's exactly why this piece would be best made in one operation. In the hands of a person who understand tool geometry and how to apply such geometry to turning and boring tools, this simple piece shouldn't tax one's ability, especially in brass, which lends itself well to fine cuts, unlike carbon steel.

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 »

[/quote]Yes, this will be exclusively for astrophotography. Some of my photos (using other mounts) are here:
https://www.flickr.com/photos/ramv/albu ... 7136712042[/quote]


Very nice images Ram , Have you gotten around to any solar imaging yet ?
Steve S
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