how to enlarge a hole in cast aluminium from 1.08 to 1.312 inches?

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dansawyer

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The project is to replace a nylon sleeve bearing with a needle bearing in an aluminum casting. The current hole is about 1.08 in diameter and about an inch thick. The needle bearing measures 1.312 od (I believe it is is actually 5/16).
I have reasonable drill press and a SB 9 inch lathe that is good operating condition. I also have a milling attachment with T slots for the lathe and could mount the casting on the milling attachment. I have a fly cutter set and have experimented with it on the drill press. I was not comfortable with the operation, there was a lot of vibration. Would the fly cutter work better in lathe?
I am stuck on how to proceed. Is it practical to do with what I have or do I need to look for outside help?
 
If you can get the part mounted on the milling attachment then you should be good to go with the fly cutter in the chuck.
 
Show us some pics of the casting, please.
 
The part is about 24 inches long. I can enlarge the three small holes in the picture and mount the part on the milling attachment. The casting is sufficiently 'square' that the ring extension should align the hole properly.
 

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The fit on a needle roller bearing is critical, the tolerance is usually on the order of .0005. Attaching the part to the milling attachment will work, but you will need a cutter that provides fine adjustment, like a boring head, in order to hit the tolerance. The drill press is not an option for this operation.
 
This is part of a telescope mount, declination axis. The telescope weighs about 30 lbs. The maximum rpm equivalent is 10 rpm, the duty cycle is less than 5 total revolutions per day. There are two forks like the one in the picture. They attach to a base to make a large 'U'.
The current sleeve bearings tend to be somewhat temperature sensitive and to bind. This modification is recommended for this mount.
One post indicated the the use of a fly cutter to first enlarge the hole and then a bearing scraper to fit the bearing to the hole. I have never used a bearing scraper. That does not seem to fit with comment that needle bearings require tight tolerance fit.
 
It looks like you will only get one shot at getting the bore right. Typically, high quality needle bearings require really precise fits, with tiny tolerance ranges from 0.0001" - 0.0002". You will NOT get this with a fly cutter, even if you could figure out how to make it work for this application, nor will you be doing this with a bearing scraper. You need a milling machine, a good boring head and an operator who knows how to use it. Might be a good idea to take this one to a good machine shop.
 
dansawyer said:
The project is to replace a nylon sleeve bearing with a needle bearing in an aluminum casting. The current hole is about 1.08 in diameter
<snip>
I am stuck on how to proceed.
Click to expand...

You could make up a brass/bronze sleeve and press it in.
 
In skilled hands, a bearing scraper can do very close work. That's what they're for.

It sounds like the manufacturer selected the wrong plastic for the application. If it's actually nylon, it's a very poor choice. Nylon absorbs moisture and swells accordingly. As Mitch suggested, a bronze bushing might be a better choice and available to fit the existing hole. What are the existing bore and shaft sizes?
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You can do it on a drill press but the hole will almost certainly run oversize, but you can then epoxy or loctite it in. The fit between the inside needles and the shaft it runs on needs to be fairly precise, and the shaft needs to be hardened to get decent life out of the assembly. Slow speeds like a telescope would be more forgiving as far as wear
Mark
ps why not make a brass or bronze replacement for the original nylon and keep it the same size?
 
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